TEMPERATURE CONTROL FOR DEEP HOLE DRILLING

Abstract

A defined thermal resistance variation of a drill string along its length is selected such that, when drilling the borehole through the drill string in an underground zone towards and then reaching a target measurement depth, the temperature of the drilling fluid at a wellhead assembly, to which the drilling fluid is delivered by the drill string, neither substantially exceeds nor falls below a target operating temperature range. The borehole is drilled with a drill string that is assembled during drilling to have a specific thermal resistance variation along its length.

Description

CROSS-REFERENCES TO RELATED REGISTRATIONS

[0001] The present application claims the filing date advantage pursuant to 35 USC § 119 of preliminary US patent application No. 63 / 500,835, filed on May 8, 2023, entitled "Temperature Control for Well Drilling." The entire contents of that application are hereby incorporated by reference into the present application. TECHNICAL AREA

[0002] This disclosure relates to drilling in hot underground zones, as required when drilling a geothermal well or any other borehole in a hot zone. BACKGROUND

[0003] The high temperatures of hot underground zones make drilling in these zones difficult. Drill bits and other components of a drill string's drill bit assembly can be sensitive to the temperature encountered downstream. Temperatures above or below certain ranges can adversely affect the desired operation and efficiency of such components. SUMMARY

[0004] This disclosure relates to drilling in hot underground zones, as required when drilling a geothermal well or other borehole in a hot zone.

[0005] From one perspective, a method for drilling a borehole in an underground zone to a target measurement depth comprises drilling towards that target depth with a drill string and, during the drilling process, extending the drill string by attaching predetermined pipe segments to an upstream end of the drill string in a predetermined sequence. The predetermined sequence includes a second subset of predetermined pipe segments that are attached to the drill string after a first subset of predetermined pipe segments.Each pipe segment of at least the second subset includes an insulating coating layer, such that when the borehole reaches the target measurement depth, the total linear thermal resistance of an uphole-bound portion of the drill string comprising the second subset is at least 0.002 meter Kelvin per watt and is greater than the total linear thermal resistance of a downhole-bound portion of the drill string comprising the first subset.

[0006] In one respect, the procedure for drilling a borehole in an underground zone to a target measurement depth involves selecting a predetermined variation in the thermal resistance of a drill string along its length, such that, as the borehole is drilled through the drill string in the underground zone towards and then reaching the target measurement depth, the temperature of the drilling fluid at a wellhead assembly to which the drilling fluid is delivered by the drill string neither substantially exceeds nor substantially falls below a target operating temperature range. The borehole is drilled with a drill string that is assembled during the drilling process to have the predetermined variation in thermal resistance along its length.

[0007] From one perspective, a system for drilling a borehole in an underground zone to a target measurement depth comprises a drill string and a borehole assembly (BHA) connected to a down-hole end of the drill string. The drill string is configured to carry drilling fluid to the BHA and is assembled by attaching predetermined pipe segments to an up-hole end of the drill string in a predetermined sequence as the borehole is drilled, with a second subset of pipe segments being attached to the drill string after a first subset of predetermined pipe segments.Each pipe segment of at least the second subset includes an insulating coating layer, so that when the borehole reaches the target measurement depth, the total linear thermal resistance of an up-hole section of the drill string having the second subset is at least 0.002 meter Kelvin per watt and is greater than the total linear thermal resistance of a down-hole section of the drill string having the first subset.

[0008] The considerations described above may include one, several, or none of the following. In certain cases, the drill string is configured to deliver drilling fluid to the wellhead assembly (BHA), and a specified sequence is such that, during drilling of the well, the temperature of the drilling fluid at the BHA at a target gauge depth will neither substantially exceed nor substantially fall below the target operating temperature range. In certain cases, the subsurface zone adjacent to the well is 250°C or greater, and a minimum of the target operating temperature range of the BHA is equal to or greater than 100°C. In certain cases, the pipe segments of the first subset of specified pipe segments include non-insulating pipe segments.In certain cases, the borehole is a lateral borehole with a heel and a crest, and when the BHA reaches the target measurement depth, the down-hole portion of the drill string containing the first subset extends substantially down-hole from the heel to the crest. In certain cases, a large proportion of the pipe segments of the down-hole portion of the drill string containing the first subset are not insulated. In certain cases, a casing pipe extends substantially from the borehole head to the heel of the lateral borehole, and when the BHA reaches the target measurement depth, the up-hole portion of the drill string containing the second subset does not extend beyond a down-hole end of the casing pipe. In certain cases, a large proportion of the pipe segments of the up-hole portion of the drill string containing the second subset include an insulating coating.In certain cases, the specified sequence is such that the ratio of pipe segments containing an insulating coating to pipe segments without an insulating coating increases as the borehole is drilled to the target measurement depth. In certain cases, the linear thermal resistance of the upstream portion of the drill string containing the second subset is at least 0.008 Kelvin meters per watt. In certain cases, the linear thermal resistance of the upstream portion of the drill string containing the second subset is at least 0.001 Kelvin meters per watt.

[0009] Further features and aspects are described below. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1A is a schematic side section view of an example of a closed geothermal circuit system according to the concepts described herein. Fig.Figure 1B is a schematic side section view of another example of a closed geothermal circuit system according to the concepts described herein. Fig. Figure 2A is a detailed view of an example of a borehole assembly of a drill string for drilling a geothermal borehole, including those in the systems of Fig. 1A and Fig. 1B, according to the concepts described herein. Fig. Figure 2B is a side view of an example of a geothermal borehole, such as those in the systems of Fig. 1A and Fig. 1B, which is drilled with an attached pipe, according to the concepts described herein. Fig. 2C is a side view of an example of a geothermal borehole, such as those in the systems of Fig. 1A and Fig. 1B, which is drilled using coiled pipes, according to the concepts described herein. Fig.Figure 3A is a half-section view of an example of two connections of insulated pipes, according to the concepts described herein. Fig. Figure 3B is a half-section view of another example of two connections of insulated pipes, according to the concepts described herein. Fig. Figure 3C is a half-section view of another example of two connections of insulated pipes, according to the concepts described herein. Fig. 3D is a half-section view of an example of insulated wound tube, according to the concepts described herein. Fig. Figure 3E is an end section view of an example of an insulated pipe with a supply line passing through an interior portion of the pipe, according to the concepts described herein. Fig.3F is an end-section view of an example of an insulated pipe with a layer of conductors defining a supply line between other layers of the pipe. Fig. Figure 4 is a schematic view of a drill string with a down-hole separator, according to the concepts described herein. Fig. Figure 5 is a schematic view of a down-hole separator as a component of a wellhead assembly, according to the concepts described herein. Fig. Figure 6 is a schematic view of another example of a down-hole separator as a component of a drill string, according to the concepts described herein. Fig. Figure 7 is a schematic view of a surface separator and backmixing system, according to the concepts described herein. Fig. 8A and Fig.Figure 8B shows end-section views of two examples of bundled coiled tube, according to the concepts described herein. Fig. 9A and Fig. Figure 9B are end-section perspective views of a bundled, coiled tube, showing the flow through the bundled tubes according to the concepts described herein. Fig. Figures 10A to 10C are schematic views of a method for drilling a borehole in an underground zone to a target measurement depth using a borehole assembly with a changing thermal resistance along its length, according to the concepts described herein. Fig. 11 is a representative temperature profile of the area in Fig. Drilling operations shown in sections 10A to 10C, according to the concepts described herein. Fig. 12 is a process flow diagram of a procedure that corresponds to the one in the reference to Fig.The system described in sections 10A to 10C can be implemented.

[0010] Identical reference numbers in the drawings represent identical elements. DETAILED DESCRIPTION

[0011] When drilling a borehole in a hot zone, such as a geothermal well or other borehole types, thermal control techniques can be selectively implemented to mitigate heat transfer from the ground to the drilling fluid. These techniques help control the temperature of the drilling fluid used to cool the drill string tools and to shock-cool the rock surface being drilled, thereby improving the penetration rate. The selection and implementation of these techniques may be based, among other factors, on achieving a drilling fluid temperature in the drill string that keeps the drill string tools below their maximum allowable temperature. The selection and implementation of these techniques may also be based on the service life / temperature and performance / temperature ratios of the tools.For example, these techniques can be used to target specific operating temperatures and / or target temperature ranges below the maximum permissible tool temperature to achieve a defined tool life or tool performance target. Furthermore, these techniques can be used to improve penetration rates through shock cooling. More details about both the thermal control techniques and how they are applied are described below.

[0012] With reference to Fig.Figure 1A now shows an example of a closed geothermal loop system 100 in a schematic side-section view according to the present concepts. In certain cases, the closed geothermal loop borehole system may, for example, be a system such as that developed by Eavor Technologies Inc. of Calgary, Alberta, which comprises a network of sealed lateral (e.g., horizontal, inclined, or otherwise divergent) boreholes that exchange heat with the subsurface zone.

[0013] System 100 comprises a geothermal borehole 102 drilled into the ground through a geothermal subsurface target zone 104. In certain cases, the subsurface zone is a dry, impermeable formation (matrix permeability of 0.1 millidarcy or less), a section of formation, or multiple formations containing little or no naturally occurring recoverable fluids. In certain cases, the subsurface zone is located within a crystalline basement formation. In certain cases, the rock of the subsurface zone is located within a granite formation (e.g., granite). In the case shown, borehole 102 includes a surface inlet borehole 120 and a surface outlet borehole 130 in close proximity, each of which extends between the surface zone and the subsurface zone 104.The surface inlet well 120 and the surface outlet well 130 are connected within the underground zone 104 by one or more connecting wells 140. In the case shown, the connecting wells 140 define a multilateral pattern of wells comprising a plurality of pairs of lateral wells 150, a subset of which are deflected from the inlet well 120 and a subset of which are deflected from the outlet well 130. The pairs of lateral wells 150 intersect at a respective junction point 154 at or near their respective tips. Thus, the inlet well 120, the outlet well 130, and the connecting wells 140 define a closed loop.

[0014] Inlet well 120 and outlet well 130 can be drilled from the same drilling platform and / or be located on the same drilling site. In certain cases, wells 120 and 130 are drilled at a distance of 10, 25, 50, or 100 meters from each other. In other cases, surface inlet well 120 and surface outlet well 130 may be separated by a greater distance. For example, [reference to relevant section] Fig. 1B, which is described in more detail below, is a configuration in which the surface boreholes 120, 130, and the connecting boreholes 140 define a U-shape configuration. In certain cases, when the geothermal borehole 102 is configured as a U-shape, the surface inlet borehole 120 and the surface outlet borehole 130 are drilled 3,000 meters or more apart.

[0015] In the case shown, the surface inlet borehole 120 and the surface outlet borehole 130 are vertical boreholes drilled essentially straight (i.e., without the use of directional drilling techniques or equipment). In other cases, one or both of the surface boreholes are other than vertical (e.g., inclined) and / or can be drilled using directional drilling techniques. The connecting boreholes 140 are drilled through the surface boreholes 120 and 130 using directional drilling techniques and include a curve in their path, beginning at a deflection point 148 at the surface boreholes 120 and 130. Although shown inclined downwards, in some cases some or all of the connecting boreholes are horizontal. In some cases, the connecting boreholes 140 follow the geological dip of the formation in the subsurface zone. In some cases, the lateral boreholes 150 are located between 2.000 meters to 10,000 meters or more in length and between 1,000 meters to 8,000 meters or more in depth from the surface.

[0016] Fig. Figure 1A shows each pair of lateral boreholes 150 extending parallel to each other in the same direction (azimuth) from their respective surface boreholes 120, 130. The lateral boreholes 150 extending from the surface inlet borehole 120 are shown above the lateral boreholes 150 extending from the surface outlet borehole 130. In some cases, the upper lateral boreholes 150 are directly above them (and in some cases are directly above one of the respective lower lateral boreholes 150). Fig.1A The upper lateral boreholes 150 each turn to intersect their adjacent pair of lower lateral boreholes 150 at the junction point 154 to connect the surface boreholes 120, 130. In other cases, one or more of the lower lateral boreholes 150 could intersect the upper lateral boreholes 150. Regardless, the configuration of the connecting boreholes 140, one group above the other, defines a stacked borehole pattern, with a partial pattern of boreholes above and a partial pattern of boreholes below. In certain cases, one or more additional groups of stacked patterns can be drilled from the surface boreholes 120, 130 at different depths (i.e., with different junction points 148). Fig.In 1A, the lower lateral boreholes 150 extend beyond and below the junction point 154 to define a collection pit 152. The collection pit 152 provides a location for deposits that accumulate outside the flow path through the boreholes. In other cases, one or more of the upper lateral boreholes 150 could extend beyond the junction point to define the collection pit 152.

[0017] Fig.Figure 1B shows another embodiment of a geothermal borehole system 100', which has lateral boreholes 150 extending to each other from the surface inlet borehole 120 and the surface outlet borehole 130, respectively. The pairs of lateral boreholes 150, once intersected, together with the surface inlet and outlet boreholes 120, 130, define a general U-shape. The configuration of the connecting boreholes 140 defines a pattern of boreholes, in certain cases, in the same plane. In certain cases, one or more additional patterns of connecting boreholes can be drilled between the surface boreholes 120, 130 at different depths (i.e., with different deflection points 148).

[0018] With regard to the Fig. 1A and Fig.1B, considered collectively, the surface boreholes 120, 130 are in some cases (at least partially or completely) lined, and the connecting boreholes 140, including the connection point at the deflection points 148, are open (i.e., without casing, lining, or a connection point coating). In some cases, the connecting boreholes 140 may be at least partially lined (e.g., having a lining or casing in those sections where the subsurface zone 104 is fractured, at risk of collapse, unconsolidated, or otherwise requires a lining). The connecting boreholes 140, including the connection points to the surface inlet boreholes and surface outlet boreholes 120, 130, are sealed (completely or substantially) with a sealant to prevent the exchange of fluids with the surrounding subsurface zone 104.The sealant is designed such that all or substantially all of the working fluids circulated through borehole 102 during operation are recovered to the surface, and no or only minimal naturally occurring fluids are recovered from the subsurface zone 104. In other words, the resulting borehole 102 is a closed loop. In certain cases, the sealant may be applied to the boreholes during the drilling of the connecting boreholes 140, for example, by being contained in the drilling fluid and / or introduced in fluid plugs that are distinct from the drilling fluid. Alternatively or additionally, the sealant is applied after drilling and / or during the operation of the borehole. In certain cases, the sealant may be contained in the heat transfer working fluid and / or introduced in fluid plugs that are distinct from the heat transfer working fluid.

[0019] In the illustrated case, the system 100 further comprises a facility 110, which is arranged between the surface inlet borehole 120 and the surface outlet borehole 130. The borehole 102 can be sealed, and a working fluid is added to the closed loop and circulated within the system, thus absorbing heat from the subsurface zone 104. In certain cases, the facility 110 includes valves and pumps for controlling the flow of the working fluid through the borehole 102, as well as a heat exchanger for extracting heat from the working fluid and transferring it to an associated process, such as a Rankine cycle (e.g., organic Rankine cycle) or another thermal cycle that generates electricity, a steam generation process for industrial, agricultural, or residential use, or another process.In certain cases, the unit 110 utilizes the heated working fluid directly, either as an alternative or in addition to a heat exchanger, for example, by passing it through an expander (e.g., a turbine) that drives an electric generator, or by directly utilizing the heat of the working fluid in an industrial, agricultural, or residential process. In some cases, the unit 110 is located at or near the Earth's surface; in other cases, the unit 110 may be located partially or entirely underground. The unit 110 does not have to be housed in one location and may, for example, be distributed as shown in [reference to relevant document]. Fig. 1B shown to be divided between one or more separate locations (shown as Annex 110a, 110b) which are connected by pipelines.

[0020] In any case of Fig. 1A or Fig.1B The geothermal borehole is constructed by drilling and, if lined, lining the inlet borehole 120 and outlet borehole 130. The connecting boreholes 140 are drilled as intersecting lateral boreholes 150 from the inlet borehole 120 and the outlet borehole 130. Specifically, a connecting borehole 140 is constructed as a lateral borehole 150 that starts at the side wall of the inlet borehole 120, i.e., is deflected from the inlet borehole 120, and a lateral borehole 150 that starts at the side wall of the outlet borehole 130, i.e., is deflected from the outlet borehole. The lateral boreholes 150 are drilled to intersect at a junction point 154 to define a connecting borehole 140.Additional connecting boreholes 140 can be drilled as lateral boreholes 150, which are deflected from the inlet borehole 120, outlet borehole 130, and / or any other connecting borehole 140 (or a lateral borehole 150 that may become a connecting borehole 140). The lateral boreholes 150 are drilled using directional drilling techniques with a drill string extending from the surface through the inlet borehole 120 and outlet borehole 130, respectively. In certain cases, a deflection wedge is used to deflect the lateral boreholes 150 from their respective surface boreholes 120 and 130.

[0021] The drilling of the inlet and outlet boreholes 120, 130, and the connecting boreholes 140 can be carried out sequentially with one drill rig and one drill string, or simultaneously, and in some cases concurrently, with the two drill strings each drilling their respective lateral boreholes 150 at the same time. In some cases, the inlet borehole 120, the outlet borehole 130, and the connecting boreholes 140 are drilled with two drill rigs, one on the inlet borehole 120 and one on the outlet borehole 130. In other cases, the boreholes are drilled with a single drill rig configured to drill two boreholes simultaneously (e.g., with two masts, two drives, and / or two turntables, etc.). In certain cases, such as when coiled pipe is used, the drill rig may be a coiled pipe drill rig.In certain cases, such as when the drill string consists of both spliced ​​and wound pipe, the drilling rig can be a hybrid spliced / wound pipe drilling rig. For example, such a rig can have spliced ​​pipe handling capability and a drive (e.g., a surface drive, rotary table drive, and / or another pipe drive), as well as handling capability for a casing spool and a continuous injector system, and can switch between the two when different types of pipe, spliced ​​or wound, are installed in the drill string.

[0022] The Fig. Figures 2A to 2C show an exemplary drill string 200, which can be used at least for directional drilling, i.e., for drilling the connecting boreholes 140 and the lateral boreholes 150 that form them. The drill string 200 of Fig.2B is shown suspended from a drilling rig 232 as several connected segments of pipe 202 (individually designated 202i, 202ii, ... 202n), which may be drill string and / or another type of connected pipe, with a borehole fitting (BHA) 210. In other cases, the drill string 200 may be partially or completely constructed of continuous coiled pipe 202. Fig. Figure 2C shows a drill string 200, which is constructed from several connected lengths of coiled pipe 202 in an upper section and connected pipe 202 with a BHA 210 in a lower, further down-hole section. Furthermore, if Fig.2C shows multiple pipes; in certain cases, the drill string 200 may be a single, continuous length of coiled pipe dependent on a coiled pipe drilling rig 234 (or a hybrid drilling rig) and having a wellhead assembly 210 or other components connected at its down-hole end. Furthermore, in certain cases, the drill string 200 may consist of multiple pipes lying side by side, as shown in and in conjunction with the Fig. 8 and Fig. 9 discussed in more detail.

[0023] The BHA 210 includes, among other things, a drill bit 208, a mud motor 212, a direction tool 214, one or more measuring elements 216, a surveying tool 218, and a communication tool 220 (e.g., a mud pulse telemetry, electrical signaling, acoustic, and / or other tool type for transmitting communications to the Earth's surface). The drill string 200 may include other components, shown as component 238 ( Fig.2C), such as fluid separators (discussed below), tractors (for pulling the string through the borehole), agitator / vibrator tools (for reducing the string's static friction in the borehole), mud turbine electric generators, battery systems, capacitors, and / or other components, positioned within the BHA 210 or separate from the BHA 210. Although only one component 238 is shown, one or more could be included in the configurations of the Fig.2A to 2C may be provided. Some or all of the tubes 202 may be insulated, with insulating features such as insulating coatings or linings and / or multiple walls. In certain cases, some or all of the tubes exhibit a linear, volumetric, radial thermal resistance for heat transfer through a side wall of the tube of at least 0.008 m K / W, at least 0.05 m K / W, or higher. In certain cases, the drill string 200 may include one or more actuated fluid diverters and / or separators 204 (i.e., bypasses) above the BHA 210, each of which may be actuated separately to divert at least a portion of the fluid flowing through the interior of the drill string 200 into the annular space around the drill string 200.

[0024] The directional tool 214 is configured to selectively deflect the drill bit 208 towards the side wall of the borehole, thus enabling control over the drilling path. Fig.Figure 2A shows the directional tool 214 as a rotating, controllable tool with actuated blades 222 that can be selectively extended into the side wall of the borehole to push the drill bit 208 in the direction of a defined drilling path. In other cases, the directional tool 214 can be a chamfering element and / or another type of tool to control the path of the drill bit 208. In certain cases, the directional tool 214 can be omitted and the defined drilling path can be achieved by other means.

[0025] One or more measuring elements 216 may be provided (one shown). An exemplary measuring element 216 is a measure-while-drilling (MWD) tool that, among other things, measures the borehole trajectory using one or more sensors (collectively, sensor 240), such as a magnetometer sensor that detects the orientation of the tool (and thus the BHA 210) relative to the Earth's magnetic field, and an accelerometer that detects the orientation of the tool relative to gravity. Another exemplary measuring element 216 is a log-while-drilling (LWD) tool that, among other things, measures formation and lining properties using one or more sensors 240, such as a pressure sensor, an acoustic sensor, a gamma emitter / sensor, and / or other sensors. Other types of measuring elements are contained in the concepts described herein.In certain cases, a measuring element 216 comprises one or more processors (collectively, processor 242) with one or more memories (collectively, memory 244), the memory 244 storing instructions to instruct the processor 242, while the measuring element 216 is down-hole, to generate values ​​from raw sensor data. The calculated values ​​determined by the processor 242, such as inclination, azimuth, density, porosity, and / or other values, can be transmitted to the Earth's surface for use in controlling directional drilling and / or for other purposes. Alternatively, if the measuring element 216 is unable to generate values ​​from the raw data, the raw data itself can be sent to the surface. In either case, communication can be effected by the communication tool 220. The information transmitted by the measuring element 216 can be sent via a cable (e.g.,a wire, an electrical or fiber optic cable embedded in or attached to the drill string 200 and / or wired in other ways) and / or communicated via mud pulse telemetry.

[0026] When drilling a lateral borehole 150, the surveying tool 218 is used to determine the position of the drilled borehole relative to other boreholes, including the lateral boreholes 150 (and connecting boreholes 140) that are being drilled or have already been drilled. In certain cases, the surveying tool 218 is a magnetic surveying tool comprising a highly sensitive magnetometer sensor 240 that operates to detect the magnetic field signal from a source in another borehole, where the source may be a permanent or electromagnetic beacon, magnetically attractive materials (e.g., lining, drill strings, pipes, or other objects made of steel or other magnetically attractive materials), and / or other sources. The surveying tool 218 may additionally or alternatively be an acoustic surveying tool comprising a highly sensitive acoustic sensor 240 (e.g.,a geophone or a fiber optic sensor) that operates to detect an acoustic signal from a source in another borehole, wherein the acoustic signal is sound generated during the drilling of the other borehole, sound generated in a BHA in the other borehole, or another acoustic source. In certain cases, the survey tool 218 may additionally or alternatively be a resistivity survey tool. From the sensor information and other information (e.g., from additional sensors in the survey tool 218 and / or the MWD / LWD tool), the relative direction of the source from the survey tool 218 and the relative distance of the source from the survey tool 218 can be determined.

[0027] In certain cases, the surveying tool 218 comprises one or more processors (collectively, processor 242) with one or more memories (collectively, memory 244), where memory 244 stores instructions to instruct processor 242, while the surveying tool 218 is downhole, to generate the relative direction and distance values ​​from raw sensor data, such as the sensor output 240 (e.g., the magnitude of the signal from the source) and other data (e.g., inclination, azimuth, and / or other raw data). The relative direction and distance values ​​determined by the downhole processor 242 can be communicated to the Earth's surface and / or sent directly to the direction tool 214 for use in controlling directional drilling. Alternatively, if the tool 218 lacks the capability to generate direction and distance values, the raw data can be sent to the surface.In any case, communication to the surface can be made via the Communication Tool 220. Information transmitted by the Survey Tool 218 can be communicated via cable (e.g., a wire, an electrical or fiber optic cable embedded in or coupled to the drill string 200, and / or wired in some other way) and / or via mud pulse telemetry. Mud pulse telemetry is a more commonly used, less expensive means of communicating data from downhole to the surface than cable. However, mud pulse telemetry inherently has a very low bandwidth. Because the generated relative direction and distance values ​​represent a smaller amount of data than the raw data required to generate them, the relative direction and distance values ​​can be more easily transmitted via mud pulse telemetry within a usable, practical timeframe than the larger amount of raw data.In comparison, transmitting raw sensor data via mud pulse telemetry can take so long and delay drilling that using the bearing data becomes impractical or cost-effective. Therefore, the survey tool 218 does not require a cable to generate relative direction and distance to the down-hole source (e.g., no cable in or on the drill string 200, or the survey tool 218 is not mounted on a wire), and mud pulse telemetry can be used. In certain cases, the direction tool 214 can include a processor and memory configured to receive and use the relative direction and distance data generated by the survey tool 218 to autonomously and / or semi-autonomously control the drilling process.

[0028] When drilling a lateral borehole 150, the survey tool 218 is operated as needed to determine the position of the survey tool 218, and thus of the BHA 210 and the current drilling position, relative to one or more sources in another lateral borehole or multiple boreholes 150 or connecting boreholes 140. Such positional information can be measured at defined regular or irregular intervals and used to ensure that the drilled lateral borehole 150 is positioned relative to the other borehole in a defined manner, e.g., in a defined bore trajectory (such as converging, diverging, or parallel (exactly or substantially)) and at a defined distance or distances.As the lateral borehole 150 approaches another lateral borehole 150, intersecting it (and creating a connecting borehole 140), the surveying tool 218 is operated at shorter intervals to determine its position relative to the other lateral borehole 150 more precisely. The power / temperature ratio of the surveying tool 218 can correlate the accuracy of the relative distance and / or relative direction values ​​that can be determined from the raw sensor data 240, or the raw sensor 240 itself, with different temperatures of the surveying tool 218.

[0029] In certain cases, the drill bit 208 is a contact-type drill bit, such as a polycrystalline diamond densification (PDC) drill bit, a rotary drill bit, and / or another type of drill bit that relies on the drill bit touching the rock and mechanically transmitting force to stress the rock face 228 (i.e., the end wall of the borehole 150 where rock is being removed), fracturing the rock and thus drilling. In other cases, the drill bit 208 may be a non-contact drill bit configured to fract the rock at the drilled rock face 228 without requiring mechanical stress from contact between the bit 208 and the rock face 228. Examples of non-contact drill bits include drill bits for plasma drilling (such as the plasma drilling system developed by GA Drilling, AS), laser drilling (such as the laser drilling system developed by Foro Energy), microwave drilling (such as that by Quaise, Inc.Microwave drilling systems (developed), thermal gap drilling (which includes supercritical water jets or flame jets), electro-pulse drilling (such as the electro-pulse drilling systems developed by Tetra Corporation), and particle drilling (e.g., impacting the rock with particles carried in fluid, such as the system developed by Particle Drilling Technologies, Inc.). Although described as "non-contact," this designation is not intended to exclude systems in which parts of a drill bit may touch, scrape, or otherwise come into contact with the formation during the drilling process.For example, an electric pulse drill bit can still be considered a non-contact drill bit if the bit is configured to touch the rock to allow electrical conduction through the rock, as it does not rely on the bit touching the rock and mechanically transmitting force to stress it. In certain cases, the 208 drill bit is a hybrid contact / non-contact drill bit configured for both non-contact and contact drilling. An example of a hybrid drill bit includes a drill body with the cutting components of a non-contact drill bit (e.g., electric pulse drill bit, plasma drill bit, water or flame jet, and / or another type of non-contact drilling) arranged to perform the pre-drilling or main drilling, and the cutting components of a mechanically contact drill bit, such as an array of cutting tools (e.g.,PDC cutting tools and / or another type of cutting tool are arranged around the circumference of the drill bit to clean and / or widen (rebroaden) the borehole drilled by the non-contact portion of the drill bit. Further examples of hybrid drill inserts are included in the concepts presented herein.

[0030] In electro-pulse drilling systems, an electro-crushing drill bit is used, which has multiple electrodes that generate high-energy sparks to fracture formation material, thereby enabling its removal from the path of the drill assembly. The bit can generate multiple sparks per second using a defined excitation current profile that causes a transient spark to form and arc through the most conductive section of the rock surface at the down-hole end of the borehole. The arc causes the section of rock surface penetrated by the arc to disintegrate or fragment and be flushed away by the flow of drilling fluid. Furthermore, in certain cases, the direction and characteristics of the arc can be modulated to control the defined drilling path, as described in U.S. Patent Application Publication No.US20230144083A1 describes this. In certain cases, a highly electrically resistant drilling fluid is used for such electro-pulse drilling. In other cases, an electrically resistant drilling fluid is not required for electro-pulse drilling, and the drilling fluid may include aqueous fluids. Descriptions of some electro-pulse drilling inserts, drilling fluids and related systems and processes that can be used herein can be found, for example, in US patent application no. 4,741,405, US patent application no. 9,027,669, US patent application no. 9,279,322, US patent application no. 10,060,195, US patent application publication no. 12000299562A1 and PCT patent applications WO 2008 / 003092, WO 2010 / 027866, WO 2014 / 008483, WO 2018 / 136033 and WO 1200 / 236189.Since electro-pulse drilling and other forms of non-contact drilling cause rock to fail under tension (as opposed to compression or shear), there may be a further synergistic effect with the cooling effects, which will be discussed in more detail below.

[0031] During the drilling of a lateral borehole 150, drilling fluid 226 is pumped downwards through the internal borehole of the drill string 200 and pumped out through the drill bit 208 to the rock surface 228 being drilled. The drilling fluid stream exits the drill bit 208, and a portion of the stream strikes the rock surface 228 being drilled (which then forms the face wall of the incomplete lateral borehole 150). The drilling fluid then flows upwards in the annular space between the drill string 200 and the side wall of the lateral borehole 150 being drilled, and then upwards to the surface in the annular space between the drill string 200 and the surface borehole 120, 130. One purpose of the drilling fluid is to carry drill cuttings from the rock surface 228 and to transport the drill cuttings to the Earth's surface for removal from the borehole.In certain cases, the drilling fluid can serve other purposes, such as driving mud turbines to generate electricity and / or providing at least partial buoyancy to the drill string 200, for example in non-contact drilling where significant overburden pressure on the drill bit is not necessary for the drill bit 208 to operate. Furthermore, as discussed in more detail below, the drilling fluid 226 also cools the tools in the BHA 210 and cools the pipe 202 as the fluid flows through the bore of the drill string 200 within the tools, and cools the rock surface 228.

[0032] Each of the tools 212-220 and, in certain cases, the pipe 202, in the drill string 200 may have a minimum and / or maximum allowable operating temperature that the component is designed to withstand while operating, typically specified by the manufacturer. For example, many high-temperature tools have a maximum allowable operating temperature of 150°C, 175°C, or 200°C. Certain constructions of pipe 202, such as polymer pipe (either all polymer or polymer reinforced with carbon, aramid, glass fiber, E-glass, and / or other structural fiber), composite pipe (carbon fiber, aramid fiber, glass fiber, E-glass, and / or other structural fiber), pipe with polymer insulation, and / or other constructions, may have maximum allowable operating temperatures in the same range. Drilling operations must keep the tools and pipe below these maximum allowable operating temperatures or risk failure.Some high-temperature tools optimized for operation in high-temperature environments may have a minimum allowable operating temperature below which the tool will not operate effectively or may fail. Some of the tools 208-220 and the tube 202 may also each have a service life / temperature ratio, where the service life of the tool or tube (e.g., reliability against failure) varies under different operating temperatures. Alternatively, some of the tools 208-220 may also have a performance / temperature ratio, where the operating performance of the tool, e.g., efficiency, effectiveness, and / or accuracy, may vary under different operating temperatures.In other words, some of the tools 208-220 may exhibit an efficiency / temperature ratio, effectiveness / temperature ratio, and / or accuracy / temperature ratio, with the relevant parameter varying for different temperatures. Similarly, certain designs of tube 202 may also exhibit performance / temperature ratios, with the tube's properties, such as tensile strength, modulus of elasticity, fatigue strength, and / or other characteristics, varying under different operating temperatures.

[0033] In certain cases, the tool and / or pipe has a service life / temperature ratio with an increasing potential for operational failure with increasing temperature and / or with time at temperature, despite operating below the maximum permissible operating temperature. In other words, the tool or pipe may exhibit an even lower operational failure rate when operated at or below certain temperatures below its maximum permissible operating temperature and / or at or above certain lower temperatures. There may be certain minimum and / or maximum limit temperatures (or time at temperatures) in this ratio, with the potential failure rate increasing significantly when the limit is exceeded and / or for a certain duration.When the service life / temperature (or potential failure rate) is plotted graphically, and temperature and service life are correlated, the limit values ​​can represent inflection points on the curve. In certain cases, the performance / temperature ratio is such that the tool and / or tube exhibit decreasing efficiency, effectiveness, accuracy, and / or other properties (e.g., tensile strength or modulus of elasticity of the tube) with increasing temperature, even while remaining below the maximum permissible operating temperature. Furthermore, the performance / temperature ratio may include certain minimum and maximum limit temperatures within the ratio, where performance changes noticeably (e.g., deteriorates) when the limit is exceeded and / or for a certain duration.When the power / temperature ratio is plotted graphically, and temperature and power correlate, the limiting values ​​can be inflection points on the curve. The tool or pipe may be optimized to deliver a specified performance within a defined minimum and / or maximum temperature range, e.g., an allowable operating temperature or temperature range, typically specified by the manufacturer and below the maximum allowable operating temperature. Thus, defined maximum target and / or minimum temperatures or temperature ranges can be established based on the service life / temperature and / or power / temperature ratios, and drilling operations can be configured to maintain the tools and pipe at the defined target operating temperature or within the specified temperature range.For example, specified maximum and / or minimum target temperatures or temperature ranges can be selected to achieve specified drilling objectives, including objectives such as achieving a specified length and / or duration of the drilling phase without moving the drill string 200 in / out of the borehole, exhibiting specified efficiency, effectiveness, accuracy, and / or other characteristics of tools in the BHA 210, the pipe 202, drilling costs, average time between replacement / failure of components in the drill string 200, and / or other aspects. In certain cases, the specified maximum and / or minimum target temperatures or temperature ranges can be selected based on the limits / inflection points noted above, for example, to be at or near the limit / inflection point on a favorable side of the limit / inflection point for the specified drilling objective.

[0034] In one example, the mud motor 212 is a positive displacement motor driven hydraulically by a flow of drilling fluid through a rotor and stator. The stator is typically made of an elastomer, and the rotor is made of steel or another metal alloy. The different materials cause different rates of thermal expansion between the stator and rotor, which greatly affects their fit. If the fit is too loose, motor efficiency decreases because drilling fluid leaks between lobes of the stator / rotor, the motor's power output drops, and the motor delivers insufficient torque to the drill bit. If the fit is too tight, the motor can "split," with the rotating rotor shearing off pieces of the stator and thus failing. Either situation can necessitate a costly and time-consuming drive of the drill string out of the borehole to replace the motor 212.Thus, the sludge motor 212 has a defined minimum and maximum permissible operating temperature, i.e., a range, and this range is typically specified by the manufacturer. A motor configured for operation at 125°C, for example, may use different components, different materials, and / or a different configuration (e.g., rotor / stator clearances) than a motor configured for operation at 175°C. Furthermore, based on the temperature / lifetime ratio and power / temperature ratio of the motor, a sub-range within the minimum and maximum permissible operating temperatures can be defined where the "fit" produces a defined efficiency (e.g., the highest efficiency or efficiency above a defined limit), has a defined lifespan (e.g.,the longest service life, service life beyond a specified duration, sufficient service life to complete a specified drilling target, such as drilling a specific measured depth or drilling one or more lateral boreholes in a single pass), or efficiency and service life balanced to a specified degree.

[0035] In addition to a maximum permissible operating temperature, many sensor-based tools, such as the MWD and LWD measuring elements 216 and the surveying tool 218, have sensors that, even when operated below their maximum permissible operating temperature, are more or less accurate as a function of temperature. This performance / temperature relationship can be expressed as a temperature / accuracy relationship. Magnetometers used in MWD and surveying tools to measure magnetic fields are sensitive to temperature. In surveying tools, the magnetometers must be highly accurate when drilling borehole intersections. The accuracy of magnetometers decreases with increasing temperature, both in terms of signal-to-noise ratio and temperature deviation. The same is true for acoustic sensors used for acoustic surveying and the sensors used in LWD tools.Accuracy is improved by not only keeping the sensors below the maximum permissible operating temperature of the tool within a temperature / accuracy ratio range with accuracy above a specified accuracy limit (e.g., above a target or required accuracy), but also by maintaining the temperature within a minimum target and maximum temperature (i.e., within a target operating temperature range) on the temperature / accuracy ratio from measurement to measurement taken by the tool, in order to minimize the effect of temperature deviation.Therefore, beyond keeping the tools (and thus the sensors) below the maximum permissible operating temperature, based on the temperature / lifetime ratio and performance / temperature (accuracy) ratio of the tool (or sensor), one can define a sub-range within the minimum and maximum permissible operating temperatures where the sensor has a defined measurement accuracy (e.g., the highest accuracy or accuracy above a defined limit), a defined lifetime (e.g., the longest lifetime, lifetime beyond a defined duration, lifetime enough to survive drilling to a certain point or drilling one or more lateral boreholes in a single pass), or accuracy and lifetime are balanced to a defined degree.

[0036] In another example, batteries (and tools that use batteries) may have performance characteristics, such as electrochemistry, that are inefficient outside a certain temperature range or optimized to operate at a specific efficiency, e.g., a specific discharge efficiency, within a certain temperature range. In certain cases, batteries may experience varying lifetimes; for instance, the number of charge / discharge cycles a battery can withstand before failure may decrease when operating outside a specific temperature range. Similarly, capacitor banks for non-contact drilling may have a design that is less efficient outside a certain temperature range, optimized for a specific temperature range, or exhibits varying lifetimes (e.g., charge / discharge cycles) outside a specific temperature range.Manufacturers therefore supply batteries and capacitor banks with minimum and maximum permissible operating temperatures. In certain cases, some batteries may be usable from room temperature down to -150°C, but high-temperature batteries may only be usable between 100°C and 185°C. Thus, above or below the end temperatures of the permissible range, the battery may not function and / or its efficiency may drop significantly, as will its lifespan. Capacitors in capacitor banks can have similar operating characteristics. In certain cases, the performance may vary for different temperatures within the permissible operating range, exhibiting different efficiencies at different operating temperatures.Based on the temperature / operating life ratio and power / temperature ratio of the battery or capacitor, a sub-range can be defined within the minimum and maximum permissible operating temperatures where the battery / capacitor has a specified discharge efficiency (e.g., the highest efficiency or efficiency above a specified limit), a specified lifetime (e.g., the longest lifetime, lifetime beyond a specified duration, enough lifetime to complete drilling to a specific point, or drilling one or more lateral boreholes in a single pass), or where efficiency and lifetime are balanced to a specified degree.

[0037] In another example, permanent magnets used in surveying and other operations can lose magnetic strength when exposed to high temperatures, and the magnet's strength can be temperature-dependent. Therefore, manufacturers can specify maximum permissible operating temperatures for the magnets, above which the magnet's magnetic strength drops below a predetermined value. Furthermore, the magnets can have a power / temperature ratio, where the magnetic strength decreases with increasing temperature above a specified temperature, while still remaining below the magnet's maximum permissible operating temperature. Thus, in certain cases, the performance can vary for different temperatures within the maximum permissible operating temperature range, exhibiting different magnetic strengths at different operating temperatures.Based on the power / temperature ratio of the magnet, a temperature below the maximum permissible operating temperature can be defined at which the magnet has a defined strength (e.g., the highest efficiency or efficiency above a defined limit) that can affect the range and / or accuracy of the tool using the magnet (e.g., the range and / or accuracy of a surveying tool 218 when determining the position of another borehole).

[0038] In addition to maintaining the temperature of tools in the BHA 210 and / or pipe, in certain cases the rock face (i.e., the face of the borehole being drilled) in front of the drill bit can be rapidly cooled to improve the drilling rate (i.e., penetration rate or ROP). This cooling, referred to herein as shock cooling, is achieved when the difference between the inherent temperature of the rock (i.e., the temperature, apart from the cooling effects of the drilling fluid, of the rock in front of the drill bit that will be immediately penetrated) adjacent to the rock face being drilled (i.e., the face) and the temperature of the drilling fluid at the rock face is at least 100°C. The temperature of the fluid at the rock face is the volumetric fluid temperature, with convective cooling of the rock face occurring, for example, within approximately 1 cm of the rock face being drilled.In certain cases, such a temperature difference can occur in geothermal environments, where the inherent temperature of the rock at and inward from the rock surface is at least 250°C. In some cases, the temperature difference may be greater or lesser. For example, if the inherent temperature of the rock at and adjacent to the rock surface is at least approximately 500°C, the difference between the inherent temperature of the rock adjacent to the rock surface and the temperature of the drilling fluid at the rock surface may be at least approximately 350°C. Such large temperature differences can increase ROP due to the shock cooling effect, which causes the rock surface to thermally contract. This thermal contraction places the rock under tensile stress and reduces the effective confinement pressure at the rock surface. It can also generate tensile microfractures within the rock matrix.

[0039] The increase in ROP (Reference Outcome Probability) due to shock cooling results from two mechanisms: surface embrittlement of the rock and thermally induced microstructural failure, such as microcracks, fractures, and displacement beneath and between rock grains due to varying degrees of thermal contraction. The drilling mud can be cooled to achieve one or both of these mechanisms. Regarding embrittlement, ductile rock transitions to a more brittle state when the temperature or pressure is reduced. When rapid thermal cooling is applied to hot, brittle rock, the internal temperature of the rock is lowered, and the rock transitions to a more brittle state relative to the untreated rock. This zone shift of ductile, semi-brittle, and any combination thereof within the zone, caused by temperature manipulation, results in the embrittlement of the treated rock relative to its initial untreated state.Rock strength (the stress required to cause irreversible deformation) does not necessarily change with an increase in brittleness. However, the deformation mode of a brittle rock is sudden failure and fracturing, whereas for more ductile rock, the failure mode is more about undergoing plastic deformation before failure. ROP generally increases with rock brittleness, regardless of the drilling method. Note that internal damage is a separate and additional effect beyond the embrittlement mechanism discussed earlier. A greater cooling temperature differential is required to cause irreversible damage within the rock, as opposed to simple embrittlement. Irreversible damage manifests as microcracks, fractures, and displacement under and between rock grains due to differential thermal contraction.Sufficient thermal cooling can induce both embrittlement and subsequent irreversible damage in the rock being drilled.

[0040] In certain cases, the temperature difference between the inherent temperature of the rock adjacent to the rock surface and the temperature of the drilling fluid at the rock surface is sufficient to reduce the tensile strength of the rock and / or damage the rock microstructure (which can reduce rock strength due to small microfractures and weaknesses within the rock matrix) and / or induce spalling at the rock surface due to thermal contraction of the rock. In some cases, the temperature difference is sufficient to reduce the confinement pressure at the rock surface (through thermal contraction of the rock and inducing fractures). When thermal contraction occurs to the point where fractures are created in the rock surface, it will lose confinement pressure and become more prone to fracturing.

[0041] Briefly referring back to Fig. 1A and Fig.1B, the temperature of the rock increases with depth in subsurface zone 104 as a function of the thermal gradient of zone 104 (i.e., the temperature increase per unit depth). The connecting boreholes 140 are the deepest boreholes of geothermal borehole 102, drilled in the hottest rock of zone 104 targeted by the borehole. Because the connecting boreholes 140 extend horizontally or dip-down through this hottest part of zone 104, and the connecting boreholes 140 (and the lateral boreholes 150 that form them) are long, often 1–5 km, 10 km or longer, the BHA 210 ( Fig. 2A-2C) to withstand this hottest part of zone 104 for long periods of time while drilling the connecting boreholes 140.

[0042] With reference to Fig.In 2A, heat 224, represented by arrows, is transferred from the rock of zone 104 to the upflowing drilling fluid 226 in the annular space, through the wall of the drill string 200, and then to the downflowing drilling fluid 226 in the borehole of the drill string 200. This heat transfer through the counterflow is the primary heating influence on the fluid flowing down the borehole in the drill string 200.

[0043] The highest rate of heat transfer between the annular space fluid and the fluid in drill string 200 occurs closer to the Earth's surface than to the bottom of the borehole because the temperature difference between the fluid in the annular space and in drill string 200 is greatest near the surface. This high temperature difference is due to the relatively cooler fluid being constantly fed in at the top of drill string 200, and the fluid in the annular space closer to the Earth's surface having a long residence time adjacent to the heat of the surrounding rock to warm up as it traverses from the bottom of the borehole to the surface. Conversely, the rate of heat transfer between the annular space fluid and the fluid in drill string 200 is lowest near the bottom of drill string 200 (near BHA 210) because the fluids have a smaller temperature difference.This lower temperature difference is partly due to the fact that the fluid in the annular space in this region was recently the fluid in drill string 200.

[0044] As described in more detail below, thermal control techniques can be selectively implemented, as needed, to provide a cool flow of drilling fluid to cool the tools in the drill string 200, keeping them below their maximum permissible operating temperature. These techniques can also be selectively implemented to cool the tools to specified temperature setpoints or setpoint ranges (minimum / maximum temperatures) based on temperature-dependent characteristics such as the tool life / temperature ratio and the tool performance / temperature ratio. Furthermore, these techniques can also be selectively implemented to generate drilling fluid to shock-cool the rock surface 228 drilled in front of the drill bit 208 to improve the ROP (Research Outflow Probability).In certain cases, these thermal control techniques can cool the BHA 210 to at least 50°C cooler than the rock temperature, and in certain cases to at least 150°C cooler than the rock temperature. During shock cooling, in certain cases, these thermal control techniques can generate drilling fluid that is released through the drill bit 208 onto the rock surface 228, which is at least 100°C cooler than the rock surface 228 being drilled, and in certain cases 350°C or cooler.

[0045] Thermal control techniques can include the use of insulated tubing to control the volumetric radial thermal resistance to heat transfer (hereinafter referred to as "thermal resistance") through the tubing into the drilling fluid flowing through the drill string 200. Reducing heat transfer with insulated tubing results in a reduction in the temperature of the fluid at the BHA 210 and in the temperature of the fluid being fed into the borehole through the drill bit 208 to the rock surface 228. The string 200, whether spliced ​​or coiled, can be entirely insulated tubing, or a portion of the tubing 202 can be insulated while other parts of the tubing 202 are not.Various pipes 202 with different thermal resistances to heat transfer through the pipe wall (due to different insulation, construction, and / or pipe materials) can be arranged in different ways within the drill string 200 to create a drill string 200 with intervals of varying thermal properties. Furthermore, as drilling progresses, the thermal resistance of the drill string 200 can be modified by changing the quantities (and proportions) of pipes with different thermal resistances, e.g., uninsulated pipe, insulated pipe, and pipes with different insulation properties.The use of insulated pipe and the arrangement of insulated pipe in the drill string 200 may be based on the maximum and / or minimum permissible temperature of the BHA 210 tools and, in certain cases, specified target operating temperatures determined based on the service life / temperature ratio and power / temperature ratio of the tools, as well as temperatures for shock cooling.

[0046] When drilling a borehole, a maximum and / or minimum drilling fluid temperature, both inside and outside the drill string 200, can be specified based on the temperature characteristics of the BHA 210 or the pipe 202 and / or temperature requirements for shock cooling of the rock surface 228. For example, the maximum drilling fluid temperature can be specified based on a fluid temperature required to cool the pipe 202 and / or the BHA 210 to keep the pipe and / or the BHA 210 tools at or below their maximum permissible temperatures and / or a specified maximum target operating temperature for one or more tools and / or the pipe, as well as, in certain cases, based on the temperature of the fluid exiting the drill bit 208, which is required to achieve the desired degree of shock cooling effect.The minimum drilling fluid temperature can be set based on a minimum fluid temperature that will not cool the BHA 210 below a minimum permissible temperature and / or a specified minimum target operating temperature for one or more of its tools.

[0047] A drill string 200 may not require insulated pipe to drill in shallow, cooler depths to keep the fluid below the specified maximum drilling fluid temperature. Thus, a string 200 constructed entirely of insulated pipe 202, assembled to have drilling fluid temperatures below a specified maximum fluid temperature at the end of the run (e.g., at the end of a lateral borehole 150), may result in drilling fluid temperatures that are too cool, e.g., below a specified minimum fluid temperature, in shallower, cooler rock near the start of the run (e.g., when the lateral boreholes 150 are drilled near the deflection point 148). As drilling progresses to hotter, deeper rock (e.g.,Since the majority of the lateral boreholes 150 are located near their end, and pipes with higher thermal resistance are required, a drill string 200, assembled to maintain drilling fluid temperatures above a specified minimum drilling fluid temperature when drilling at shallow, cooler depths, may not have the necessary thermal resistance to keep the drilling fluid temperatures below the specified maximum fluid temperature. The arrangement in the drill string 200, consisting of insulated pipe and / or insulated pipe amid other uninsulated pipes within the drill string 200, can be configured to achieve and maintain drilling fluid temperatures at or below a specified maximum fluid temperature throughout a drilling phase (alone or in conjunction with other techniques described below), while also maintaining at least a specified minimum temperature throughout the drilling phase.In other words, the arrangement of insulated pipe in the drill string 200 can be configured to provide a degree of temperature uniformity over the course of a drilling phase.

[0048] In certain cases, the 200-meter drill string is initially assembled with a first interval adjacent to BHA 210, consisting of either uninsulated pipe or insulated pipe with a first (low) thermal resistance, while being used to drill shallower, cooler portions of Zone 104. Subsequently, insulated pipe, or insulated pipe with a second (higher than the first) thermal resistance, is added to the 200-meter drill string in a second interval at the top of the first pipe interval as drilling progresses into deeper, hotter portions of Zone 104. The addition of higher-thermal-resistance pipe to the 200-meter drill string in the second interval progressively increases the overall thermal resistance to heat transfer of the 200-meter drill string, while the ratio of uninsulated to insulated (or low-thermal-resistance to higher-thermal-resistance) pipe increases.Furthermore, the increase in thermal resistance occurs where it is most needed, near the surface where counterflow heat transfer is greatest. In certain cases, at the end of a run (e.g., at the end of a drilled lateral borehole 150), approximately 30%–15% of the length of the drill string 200 is uninsulated, or has a first, low thermal resistance and approximately 70%–85% of the second, higher thermal resistance. However, other ratios are feasible and fall within the concepts presented here.

[0049] As an example, a drill string 200 can initially be assembled with 50 joints of uninsulated pipe. As 50 more joints of insulated pipe are added and drilling progresses to deeper, hotter rock, drill string 200 (ignoring the BHA) achieves 50% insulation. Drill string 200 achieves 80% insulation with the addition of another 150 joints of insulated pipe as drilling progresses to even deeper, hotter rock. In other words, as drilling progresses to deeper, hotter rock and both the need for and the required degree of thermal resistance increase, the volumetric thermal resistance of drill string 200 also increases. Furthermore, this added thermal resistance is most effective at the top of drill string 200, where counterflow heat transfer is greatest.The same effect can be achieved with a drill string 200 constructed from wound tube, for example by using a different coil of wound tube 202 that has a different thermal resistance for each interval.

[0050] Drill string 200 can also be configured by including three or more intervals of varying thermal resistance. For example, string 200 can begin as uninsulated pipe or insulated pipe with a first thermal resistance in a first interval adjacent to BHA 210. As drilling progresses into deeper, hotter parts of Zone 104, insulated pipe with a higher second thermal resistance than that in the first interval is added at the top of the first interval. Then, as drilling progresses into even deeper, hotter parts of Zone 104, insulated pipe with an even higher third thermal resistance than that in the second and first intervals is added at the top of the second interval.The result, when the drilling reaches its end, is a drill string with three intervals of varying thermal resistance, with the highest thermal resistance near the Earth's surface where the greatest counterflow heat transfer occurs. In other cases, four or more intervals of varying thermal resistance can be incorporated into the drill string.

[0051] Furthermore, the arrangement of insulated pipe 202 in the drill string 200 can be configured with the mechanical characteristics of the pipe and drill string in mind. For example, the insulation material of the insulated pipe 202 may be fragile and may be subject to greater wear and tear than pipe without such an insulation layer (or with a thinner insulation layer). Such wear and tear may be worse in deviated (inclined or horizontal), open (as opposed to lined) sections of the borehole, and especially in those sections of the drill string 200 near BHA 210.This is because torsional vibrations due to drilling near BHA 210 can be greater, abrasion forces can be higher when the pipe lies on its side in inclined or horizontal sections of the borehole (compared to vertical sections), and the rock surface of the open hole in the lateral being drilled can be more abrasive (compared to the lining). Therefore, uninsulated pipe or pipe with robust insulation can be positioned near BHA 210, where wear and tear on the pipe are highest. In certain cases, the potential for wear or damage may necessitate a larger interval of uninsulated pipe near BHA 210 than would be ideal for temperature considerations. This larger interval of uninsulated pipe can be compensated for by even higher thermal resistance in the second, or second and subsequent, intervals.In certain cases, the drill string 200 can be assembled such that, over the course of a drilling phase, the insulated pipe 202 is completely or mostly within the inlet or outlet borehole 120, 130 and upstream of the lateral borehole 150 being drilled. Since the inlet or outlet boreholes 120, 130 are vertical or at a shallower inclination than the lateral boreholes 150, the drill string 200 has easier contact with the borehole wall and thus generates less contact wear on the insulated pipe 202. Furthermore, the inlet and outlet boreholes 120, 130 are typically lined, which results in even less contact wear on the insulated pipe 202.

[0052] Thermal control techniques can also include controlling the drilling fluid flow rate, distribution, and properties to influence heat transfer and thus the fluid temperature. In certain cases, for example with water-based fluids, increasing the flow rate can reduce the drilling fluid temperature, partly because cooler fluid displaces hotter fluid more quickly in the drill string 200, in the borehole around the drill bit 208, and in the annular space near the bottom of the borehole (i.e., near and around the BHA 210). Selecting lower viscosity drilling fluids allows for higher flow rates without excessive heat generation from friction (hydraulic friction losses) that would otherwise occur at these higher flow rates.For example, in a primarily oil-based drilling fluid (whether hydrocarbon or synthetic) containing 90% oil, and with a low-thermal-resistance or uninsulated drill string, the frictional effect means that a lower flow rate is typically better suited for cooling the BHA 210. Furthermore, under these conditions, higher-viscosity fluids, such as the 90% oil-based fluids, are typically better at cooling the BHA 210 than low-viscosity fluids. However, when using insulated or high-thermal-resistance pipe 202, a low-viscosity fluid can be selected to allow the fluid to flow at a higher rate to improve cooling. This is the opposite of uninsulated pipe, where higher-viscosity fluids are selected for their typically lower convective heat transfer coefficient, which is needed to counteract heat transfer into the fluid in the drill string.Thus, the drilling fluid flow rates can be selected based on the specified maximum and / or minimum drilling fluid temperatures discussed above, which in turn are determined based on the maximum permissible temperatures of the tools in the BHA 210, specified maximum target and / or minimum temperatures, which are determined based on the service life / temperature ratio and performance / temperature ratio of the tools, and / or temperatures for shock cooling.

[0053] Controlling the distribution of flow between the annular space and the drill string 200 can also influence heat transfer and can be adjusted by releasing flow from within the drill string 200 into the annular space via one or more fluid diversion tools 204. Three such diversion tools are provided in Fig.Figure 2B shows that in some cases, a smaller or larger number of diversion tools (for example, only one diversion tool or five diversion tools) may be used as part of the drill string 200. For example, a diversion tool 204 above and close to the BHA 210 diverts flow to the annular space, thereby reducing the amount of fluid flowing to the BHA 210 and through the drill bit 208. The flow diversion tools 204 may allow higher flow rates in the upper portion of the drill string 200 where the BHA 210 or the overall well design would otherwise limit the flow rate. In some cases, the greater fluid flow through the drill string 200 above the diversion tool 204 results in a lower fluid temperature at the BHA 210 and exiting through the drill bit 208.The various flow diverters 204 and / or multiple flow diverters 204 can be configured to be actuated to divert different quantities of fluid into the annular space at one or more locations in order to change (e.g., increase) the thermal mass of the fluid flowing through the string 200, in order to influence (e.g., decrease) the fluid temperature through the BHA 210, exiting from the drill bit 208, and in the upstream annular space of the BHA 210. The various flow diverters 204 and / or multiple flow diverters 204 can be configured to be actuated to divert different quantities of fluid into the annular space at one or more locations in order to influence the temperature of the fluid in the annular space, for example, to cool the exterior of the pipe of the drill string 200.In one example, the flow diversion tool 204 can be actuated to divert 70% of the flow to the annular space and direct the remaining flow through the BHA 210. The use of flow diversion tools 204 can also allow circulation of the drilling fluid when drilling is not in progress, to continuously maintain a constant fluid temperature by diverting enough fluid into the annular space so that the fluid reaching the mud motor (if provided) is insufficient to rotate the drill bit 208, or insufficient to rotate the drill bit 208 with enough torque to bore the rock.Thus, the number and configuration of diversion tools 204 in the drill string 200 and when the diversion tools 204 are actuated to divert fluid can be selected based on the specified maximum and / or minimum drilling fluid temperatures discussed above, which in turn are determined based on the maximum allowable temperatures of the tools in the BHA 210 and, in certain cases, the pipe 202 itself, the specified maximum target and / or minimum target temperatures, which are determined based on the lifetime / temperature ratio and performance / temperature ratio of the tools and / or the pipe, and / or temperatures for shock cooling.

[0054] In certain cases, tool 204 can be used instead of or in addition to the flow diversion tools 204, as a separator ( Fig.2C) which is configured to separate drilling fluid 226 into a water-rich stream and an oil-rich (hydrocarbon and / or synthetic oil) stream and to divert the water-rich stream into the annular space above BHA 210.One or more separators may be used, and the number, configuration of the separator tools in the drill string 200 and, if operable, when and to what extent the separator tools are operated to separate and divert fluid, may be selected based on the specified maximum and / or minimum drilling fluid temperatures discussed above, which in turn are based on the maximum allowable temperatures of the tools in the BHA 210 and, in certain cases, of the pipe 202 itself, specified maximum target temperatures and / or minimum target temperatures determined based on the lifetime / temperature ratio and performance / temperature ratio of the tools and / or the pipe, and / or temperatures for shock cooling.Furthermore, by diverting a water-rich (and therefore high heat capacity) flow into the annular space, the flow cools the outside of the pipe 202 (and / or other components with which the annular fluid flow may be in contact) more effectively, while a relatively oil-rich remaining flow reaches the drill bit for lubrication (to reduce torque and drag of the bit at the borehole and / or to lubricate rotating components of tools in the drill string), chemical stability, and dielectric properties (such as those required in pulsed power drilling operations). Thus, the presence of separators with defined properties and / or actuated separators allows for greater control over the oil / water ratio of the drilling fluid and where these ratios are applied than simply supplying fluids of a specific oil / water ratio from the surface.Further details regarding such separator components in specific cases are given below with reference to . Fig. 4-6 described.

[0055] The distribution of flow between the annular space and the drill string 200 can be controlled by releasing flow from the interior of the drill string 200 into the annular space of one or more pipes in the drill string 200 that open to the annular space above the BHA 210. As with reference to Fig.As described in more detail in Figures 8-9, the drill string 200 can have multiple pipes. One or more of the pipes are coupled to the drill bit 208 to supply drilling fluid to the BHA 210, and one or more of the pipes can be open to the annular space and configured to release the fluid into the annular space at one or more locations along the length of the drill string 200, similar to the flow diversion tools 204 discussed above. Because this one or more pipes configured to release fluid into the annular space are separate from the pipe or pipes that supply drilling fluid to the drill bit 208, they can introduce the drilling fluid and / or one or more other fluids, e.g., cooling fluids, into the annular space. If multiple pipes are provided to introduce fluid into the annular space, different fluids can be released into the annular space at different locations along the drill string 200.Thus, the number and configuration of multiple pipes in drill string 200, the fluids in each of the pipes, and where along drill string 200 the pipes introduce flow into the annular space can be selected based on the specified maximum and / or minimum fluid temperatures discussed above, which in turn are based on the maximum permissible temperatures of the tools in BHA 210 and, in certain cases, of the pipe 202 itself, the specified maximum target temperatures and / or minimum target temperatures determined based on the service life / temperature ratio and performance / temperature ratio of the tools and / or the pipe, and / or temperatures for shock cooling.

[0056] Thermal control techniques can include selecting drilling fluid based on its thermal properties. Different drilling fluids can have different thermal properties, such as volumetric heat capacity and thermal conductivity. These different thermal properties thus affect the temperatures of the drilling fluid at BHA 210, of drill string components above BHA 210 (including pipe 202), and in the borehole, as well as the degree to which the drilling fluid cools the tools of BHA 210 and the rock surface 228 (the relevance of cooling the rock surface is discussed in more detail below). For example, heat transfer through the drilling fluid decreases with decreasing thermal conductivity. Thus, the heat transfer from the rock of Zone 104 to the drilling fluid inside drill string 200 can be controlled to some extent by the drilling fluid selection (e.g.,Reducing heat transfer through the fluid by selecting a fluid with lower thermal conductivity (and vice versa). The temperature rise of the drilling fluid for a given amount of heat transfer is lower for higher heat capacities. Thus, the cooling effect of the drilling fluid on the BHA 210, other drill string components, including pipe 202, and the rock surface 228 can be controlled to some extent by the drilling fluid selection (e.g., increasing cooling at the BHA 210 by selecting a fluid with higher heat capacity and vice versa). As a component of drilling fluid, oil has certain advantages over water, including greater lubricity, greater efficiency in removing drill cuttings and retaining slurries, and lower reactivity with geological formations. Furthermore, as a component of the drilling fluid, oil can act as a dielectric fluid, which is necessary for certain non-contact drilling applications.In contrast, water has a higher heat capacity and can therefore be advantageous for cooling downstream pipe and tools. Water can also be more fluidly stable than oil at high temperatures. Oil- and water-based fluids can be mixed in various ratios to achieve different thermal conductivity and heat capacity than purely water-based or oil-based drilling fluids. For example, in certain cases, the fluid may contain between 90% and 60% oil-based fluid and the remainder water-based fluid. Other components can be included in the drilling fluid to increase or decrease its heat capacity and / or thermal conductivity. By selecting oil-based or water-based drilling fluids, or different ratios of each, and / or by selecting specific components of the drilling fluids, the thermal properties of the drilling fluid can be tailored.

[0057] In another example, a phase change material such as water ice or dry ice can be added to the drilling fluid. These phase change materials can absorb thermal energy as they undergo a phase change (e.g., melting). In some cases, the phase change materials can be configured to undergo a phase change close to the drill bit 208, centralizing the cooling effect in the BHA 210 and the fluid exiting the drill bit 208. For example, the properties of the phase change material and / or the flow rate of the drilling fluid can be controlled to direct the phase change.

[0058] Thus, the drilling fluid itself can be selected based on the specified maximum and / or minimum drilling fluid temperatures discussed above, which in turn are determined based on the maximum permissible temperatures of the tools in the BHA 210 and / or the pipe, specified maximum target temperatures and / or minimum temperatures determined based on the service life / temperature ratio and performance / temperature ratio of the tools and / or the pipe, and / or temperatures for shock cooling.

[0059] Furthermore, different drilling fluids can be used for different intervals within a drilling phase. For example, the drilling fluid for a first interval, closer to the surface, can be different from the drilling fluid for a second interval, closer to the target depth of a lateral borehole 150. In certain cases, the drilling fluid for the second interval can be selected based on the fluid's thermal properties to control the temperature of the BHA 210 and the temperature of the fluid exiting the drill bit 208, while in the first interval, other aspects such as drilling performance, cost, and / or other factors can be prioritized. Three, four, or additional intervals, each with different fluids, can be implemented.

[0060] Another thermal control technique can involve cooling the drilling fluid at the surface after it exits the annular space and before reinjection into the drill string 200. This cooling reduces the temperature of the fluid entering the drill string 200, which in turn reduces the temperature of the fluid at the BHA 210 and the temperature of the fluid being fed into the borehole at the drill bit 208. Cooling can be achieved using a cooler 230 ( Fig. 2B and Fig.2C) is carried out, utilizing air or water cooling, refrigeration circuits, evaporative cooling, or any other type of cooling, and typically involves circulating the fluid through a heat exchanger in the cooler. However, a key advantage of using insulated pipe in the 200-meter well string is that the fluid inlet temperature is not as critical as in a 200-meter well string without insulated pipe. Thus, expensive and energy-intensive refrigeration circuit cooling can be avoided or used sparingly with minimal impact on the BHA 210 circulation temperature.

[0061] For example, in certain cases it is possible to cool the drilling fluid at the surface to 38°C and (along with other thermal control techniques) achieve the specified maximum target temperatures without using a chiller. Furthermore, different cooling can be applied during different intervals of the drilling process (during the same or some of the same intervals, as discussed in connection with the drilling fluid, or different intervals). For example, a first interval, closer to the surface, may utilize no cooling or a first degree of cooling, while a second interval, closer to the target depth of the lateral borehole 150, may utilize cooling or a second, different degree of cooling (e.g.,...The first interval can use one type of cooling and the second a different type, and / or the first interval can use a certain number and / or cooling capacity, and the second a different number and / or cooling capacity (e.g., a higher number and / or capacity). In the example above, if needed, a chiller can be temporarily used to temporarily lower the temperature of the drilling fluid at the surface, for example, to 32°C. Although described only with reference to two intervals, three, four, or additional intervals, one or more of which may have different cooling methods, can be implemented.Thus, the use of surface cooling and the type of surface cooling can be selected based on the specified maximum and / or minimum drilling fluid temperatures discussed above, which in turn are determined based on the maximum permissible temperatures of the tools in the BHA 210 and, in certain cases, of the pipe 202 itself, specified maximum target temperatures and / or minimum temperatures determined based on the service life / temperature ratio and performance / temperature ratio of the tools, and / or temperatures for shock cooling.

[0062] Another thermal control technique can involve supplying cool fluid through one of several pipes in the drill string to cool the drilling fluid flowing to BHA 210 and drill bit 208. As with reference to Fig. 8 and Fig.As described in more detail and briefly discussed in Section 9, the drill string 200 can have several pipes, with one or more of the pipes being coupled to the drill bit 208 for supplying drilling fluid to the BHA 210 and the drill bit 208. In certain cases, cooling fluid that has been cooled at the surface (e.g., by cooler 230) can flow through one or more of the other pipes that are in close proximity to, and in certain cases in contact with, the pipe(s) through which the drilling fluid flows to cool the drilling fluid. Additionally or alternatively, the cooling fluid can be selected based on its thermal properties to insulate the drilling fluid from the heat in the annular space around the drill string 200. In certain cases, the cooling fluid can be the same fluid that is released into the annular space, as discussed above, or it can be recirculated to the surface through other pipes.Thus, the use of cooling fluids in a multi-tube drill string 200, the number of tubes comprising the cooling fluid, and the types and flow rates of fluids used can be selected based on the specified maximum and / or minimum drill fluid temperatures discussed above, which in turn are determined based on the maximum permissible temperatures of the tools in the BHA 210 and, in certain cases, of the tube 202 itself, specified maximum target temperatures and / or minimum target temperatures determined based on the service life / temperature ratio and performance / temperature ratio of the tools, and / or temperatures for shock cooling.

[0063] When developing a drilling plan for geothermal well 102, the drill string configuration 200 is determined, as well as how the drill string 200 will change over a drilling phase when pipe 202 is added. This analysis includes determining the configuration of BHA 210 (e.g., the tools contained in BHA 210, the drill bit type and characteristics, maximum permissible operating temperatures of the tools in BHA 210, service life / temperature and / or performance / temperature ratios of BHA 210, and / or other aspects) and the arrangement of pipe 202 and other tools (e.g., arrangement of insulated and / or uninsulated pipe, the number of pipe intervals, the number, position / location, and characteristics of insulated pipe in each interval, the number and position of fluid diverters and / or separators, if any, the use of a multi-pipe drill string, and / or other aspects).The configuration of the drill string 200 is selected along with the choice of drilling fluid (composition, thermal properties, flow rate, and / or other aspects) and if and how the drilling fluid is changed during the drilling phase, as well as additional operational aspects such as whether and when cooling fluid is used, whether and when coolers 230 are used, and the configuration of the coolers 230 (cooler type, number, cooling capacity, and / or other aspects). The characteristics of the drilling phases, including the number of phases (drill string 200 entry, drilling, and drill string 200 exit), the target drilling interval for each phase, and / or other aspects, are also determined along with the aspects mentioned above. Each of the lateral boreholes 150 can be drilled in one or more phases, with a preference for drilling each lateral borehole 105 in the fewest (or one) phases.

[0064] The plan is developed iteratively using mathematical and / or numerical analysis models of heat transfer and drilling, with each aspect determined based on the other, as well as based on the properties of borehole 102 and the boreholes (e.g. length, depth, number and / or relative position of lateral boreholes 150 / connecting boreholes 140 and / or other aspects) and the underground zone 104 (e.g. geomechanical and geothermal properties of zone 104, including rock type, modulus of elasticity, strength, geothermal gradient, temperature, temperature gradient and / or other aspects).The plan is developed based on maintaining the BHA 210 and, in certain cases, the pipe 202 itself below the maximum permissible temperatures of the tools and / or the pipe within it over an entire drilling phase. In certain cases, it is also developed based on maintaining minimum target temperatures and / or maximum temperatures over an entire drilling phase or during specific intervals within a drilling phase, based on the service life / temperature and / or performance / temperature ratios of the BHA 210 tools and / or the pipe. The plan can be developed by iterating through various configurations of BHA 210 tools and drill string 200 with different thermal control techniques and wellbore and borehole characteristics.

[0065] In certain cases, the drilling plan can be developed not only based on keeping the temperature of the mud motor 212 below the maximum permissible operating temperature, but also based on a maximum target operating temperature and / or a minimum target operating temperature, which is determined based on the service life / temperature and / or power / temperature ratio of the mud motor 212. The minimum target operating temperature may, in certain cases, be above or below the minimum permissible temperature of the mud motor 212, and / or the maximum target operating temperature may be above the maximum permissible temperature. For example, to achieve a target drilling depth (e.g.,To achieve a specific drilling depth (measured depth) in a single pass, two passes, or the fewest possible passes, the minimum and / or maximum target operating temperature can be selected based on the target drilling depth, a target number of passes to reach the depth, and a temperature range within the lifetime / temperature ratio that will achieve the target drilling depth within the target number of passes. Additionally or alternatively, to maintain a specific performance level of the mud motor 212 (e.g., a specified efficiency at or above a limiting efficiency), the minimum target operating temperature and / or the maximum target operating temperature can be selected based on the target performance characteristic(s) and a temperature and / or temperature range within the power / temperature ratio that will achieve the target performance characteristic(s).

[0066] In certain cases, the drilling plan can be developed based not only on keeping the temperature of the sensor-based tools, comprising the measuring elements 216 and / or the surveying tool 218, below their maximum permissible operating temperature, but also on a maximum target operating temperature and / or a minimum target operating temperature, determined based on the service life / temperature and / or the performance / temperature ratio of one, several, or all of the sensor-based tools. The minimum target operating temperature may, in certain cases, be above or below the minimum permissible temperature of the specific sensor-based tool, and / or the maximum target operating temperature may be above the maximum permissible temperature.For example, the minimum and / or maximum target operating temperature can be selected based on the target measurement accuracy and a temperature and / or temperature range within the power / temperature ratio that will achieve the target measurement accuracy. Different minimum and / or maximum target operating temperatures can be determined for different sensor-based tools based on the desired accuracy and the power / temperature ratio. Additionally or alternatively, the minimum and / or maximum target operating temperature can be selected based on a target tool life (e.g., reliability against failure) and a temperature and / or temperature range within the life / temperature ratio that will achieve the target tool life.Different minimum and / or maximum target operating temperatures can be determined for various sensor-based tools based on the target tool life and the life-to-temperature ratio. Furthermore, different minimum and / or maximum target operating temperatures can be determined for different drilling depths. For example, a different minimum and / or maximum target operating temperature can be selected to achieve higher measurement accuracy (than elsewhere in the borehole) at a specific depth or over a specific depth range where higher accuracy is required or would benefit. Borehole intersections and parallel boreholes in close proximity are two examples where higher measurement accuracy may be needed or advantageous.

[0067] In certain cases, the drilling plan can be developed based not only on keeping the temperature of batteries (and tools containing batteries) below their maximum permissible operating temperature, but also on a maximum target operating temperature and / or a minimum target operating temperature, determined based on the lifespan / temperature and / or performance / temperature ratio of the batteries. The minimum target operating temperature selected for a battery may, in certain cases, be above or below the battery's minimum permissible temperature, and / or the maximum target operating temperature may be above the maximum permissible temperature. For example, to achieve a target drilling diameter (e.g.,To achieve a specific measured depth with a single run, two runs, or the fewest runs, the minimum and / or maximum target operating temperature can be selected based on the target borehole diameter, a target number of runs to that diameter, and a temperature range in the lifetime / temperature ratio that will achieve the target borehole diameter in the target number of runs. Additionally or alternatively, to maintain a specific battery performance (e.g., a specified discharge efficiency at or above a threshold efficiency), the minimum target operating temperature and / or maximum target operating temperature can be selected based on the target performance characteristic(s) and a temperature and / or temperature range in the performance / temperature ratio that will achieve the target performance characteristic(s).

[0068] In certain cases involving temperature-sensitive pipe, the drilling plan can be developed based not only on keeping the pipe temperature below its maximum permissible operating temperature, but also on a maximum target operating temperature, determined based on the lifetime / temperature and / or performance / temperature ratio of the pipe material.

[0069] In each of the above-mentioned cases, by utilizing the thermal control techniques described herein, the BHA 210 tools can have a lower maximum allowable temperature than would be required without these techniques, because the maximum temperature experienced by the tools is lower than what would have occurred without the cooling techniques. Enabling the use of tools with a lower maximum allowable temperature can enable features that would not be possible without them, or that would be more difficult to implement in tools with a higher maximum allowable temperature. For example, processors and memory for hole-down data processing are difficult to make resistant to high temperatures and are therefore omitted in many tools with high maximum allowable temperatures.However, tools with lower maximum permissible temperatures, such as measuring elements 216 and surveying tools 218, can benefit from down-hole data processing. For example, the use of thermal control techniques here enables the use of a surveying tool 218, as discussed above, which can process the sensor raw data down-hole and transmit the less bandwidth-intensive (than the raw data) distance and direction data, which is more practical to transmit via mud-pulse telemetry in a workable timeframe. Enabling the use of tools with lower maximum permissible temperatures can also have other advantages, such as reduced costs (tools with higher maximum permissible temperatures are more expensive than those with lower maximum permissible temperatures) and greater availability (tools with higher maximum permissible temperatures are specialized and more difficult and / or time-consuming to obtain).

[0070] In certain cases, the specified minimum and / or maximum target operating temperatures of a tool can be prioritized over similar temperatures of other tools in the BHA 210. For example, in certain cases, the accuracy of the survey tool 218 can be prioritized over the accuracy of the measuring elements 216 because the accuracy requirement of the survey tool 218 may be greater, especially when drilling a borehole intersection. Thus, if the maximum target operating temperature determined for the accuracy of the survey tool 218 is lower than the maximum target operating temperature determined for the target accuracy desired for other measuring elements 216, then the drilling plan and the implemented thermal control techniques are selected to maintain the maximum target operating temperature determined for the survey tool 218 rather than for the other measuring elements 216.In other words, the implemented drilling plan and thermal control techniques will be selected based on the power / temperature ratio of the survey tool 218. Priority can be given to other tools in the BHA 210 in a similar manner, depending on the drilling targets. Likewise, the specified maximum temperatures required for the shock-cooling effect can be given priority over the specified minimum and / or maximum target operating temperatures of any of the tools in the BHA 210.

[0071] Furthermore, while priority is given to one tool in BHA 210 over others or the shock-cooling effect, the specified minimum and / or maximum target operating temperatures of other tools or the need for shock cooling can also be taken into account. For example, if priority is given to the specified maximum target operating temperature determined for the survey tool 218, as in the example above, and / or the need for shock cooling, the implemented drilling plan and thermal control techniques can be based on a specified minimum target temperature of another tool, such as a measuring element 216 and / or another tool with a battery.

[0072] Furthermore, priorities can differ during various intervals of a drilling run. For example, the specified maximum target temperature, determined for the survey tool 218 based on the power / temperature ratio to achieve a specified accuracy, may only be required at times when the survey tool 218 is operating to determine the relative distance and direction to another borehole (e.g., when boreholes are intersecting and periodically when parallel boreholes are being drilled). Therefore, the implemented drilling plan and thermal control techniques can be selected to prioritize the specified maximum target temperature for the survey tool 218, for example, by operating a chiller 230 (or a different number and / or type of chillers 230) and / or changing drilling fluids, only for intervals when the survey tool 218 is operating.During the remaining intervals, the drilling plan can be selected to target the specified maximum target temperature of another tool and / or the need for shock cooling.

[0073] In certain cases, the same and / or identical types of thermal control techniques described above can be used to control all of the boreholes of the systems shown in Fig. 1A and Fig.1B, to drill. In other cases, the thermal control techniques used to drill the connecting boreholes 140 (and the lateral boreholes 150 that form the connecting boreholes) may differ from those used to drill the inlet and outlet surface boreholes 120, 130. For example, because the highest temperatures are encountered in the formations through which the connecting boreholes 140 are drilled, and lower temperatures are encountered in the formations through which the inlet and outlet boreholes 120 and 130 are drilled, some (e.g., fewer) or none of the thermal control techniques used to drill the connecting boreholes 140 may be used when drilling the inlet and outlet surface boreholes 120 and 130. Similarly, shock cooling may have a greater effect on the ROP if the rock is hot, for example, above 250°C.The ROP advantage may be less in the inlet and outlet surface boreholes 120, 130 and much more significant when drilling a network of connecting boreholes 140 drilled at depth within hot rock, such as the examples shown in . Fig. 1A and Fig. Figure 1B shows that thermal control techniques can be configured to effect shock cooling in boreholes where the majority of drilling takes place within very hot rock.

[0074] According to some embodiments, a method for drilling a borehole, as part of a geothermal borehole or for another borehole in a hot subsurface zone, comprises determining a drilling plan for drilling the borehole to a target measurement depth using a drill string configured to deliver drilling fluid to a BHA. The drilling plan includes constructing the drill string by attaching specified pipe sections of varying thermal resistance in a specified sequence to an upstream end of the drill string while drilling the borehole. The specified sequence is such that (a) a large portion of the pipe of an upstream section of the drill string is insulated or has a specified (e.g.,(a) has a high or increased thermal resistance compared to conventional pipe, (b) the overall thermal resistance of a lower section of the drill string closer to the BHA remains lower than that of the upper section of the drill string, and / or (c) when drilling the well to the target measurement depth, the temperature of the drilling fluid at the BHA does not substantially exceed or fall below a maximum target and / or minimum fluid temperature, as discussed above. Once the drilling plan has been established, the well is drilled and the thermal control techniques are employed according to the plan. In other words, the BHA and drill string are assembled in accordance with the plan, the specified fluids are used, the specified chillers are deployed, and the specified flow rates are implemented.If conditions change or unexpected circumstances arise, the drilling plan can be reassessed and, if necessary, revised, and further drilling can be carried out in accordance with the revised drilling plan.

[0075] Fig. Figure 3A illustrates an example of insulated pipe 302 (e.g. drill string and / or wound pipe) that can be used as pipe 202 of Fig.2A-2C. Two lengths of 302 tube are shown joined to each other at fittings 322, which are typically (but not necessarily) threaded spigot and socket fittings. In the context of drill string, the 302 tube is relatively rigid and is provided in short lengths referred to as "shocks" of tube. In certain cases, the joints are approximately 30 feet long. In the context of coiled tube, the 302 tube is relatively flexible, designed to be wound onto and off a reel (e.g., reel 236). In certain cases, the coiled tube may be provided in lengths from 500 m to 5,000 m or longer, although any length may be provided for and used herein.

[0076] Each tube 202 comprises a main body 350. In some cases, the main body 350 is carbon or chromium-molybdenum steel, aluminum alloy, titanium alloy, fiber composite (e.g., a composite of carbon fiber, aramid fiber, glass fiber, E-glass, and / or other structural fiber in a resin binder), and / or polymer (e.g., entirely polymer or polymer reinforced with fiber such as carbon, aramid, glass fiber, E-glass, or other structural fiber). The tube 302 comprises an insulating inner coating layer 304 that covers (completely or partially) the inner circumferential surface of the tube 302. The insulating inner coating layer 304 is configured with a specified thermal resistance to conductive heat transfer through the coating and thus into the main body 350 of the tube 302.In the illustrated case, the inner coating layer 304 covers the entire inner surface of the tube 302, encompassing the full length of the tube 302 and the inner surface of the connector 322. By covering the inner surface of the connector 322 with the inner coating layer 304, heat transfer through the tube 302 to the connector 322 is reduced.

[0077] The pipe 302 is also shown with an outer coating layer 306 that covers (completely or partially) the outer circumferential surface of the pipe 302. In the illustrated case, the connector 322 has a larger diameter than the main section of the body 350 and can therefore be subject to more contact and, consequently, greater friction against the borehole wall or other components of the borehole system. In the illustrated case, the outer coating layer 306 covers the section of the pipe 302 between the connectors 322, but not the larger-diameter area around the connectors 322. In this way, the outer coating layer 306 is less exposed to the friction occurring at the connectors 322.

[0078] In certain cases, the inner coating layer 304 comprises one or more of the following materials: epoxy novolac resins and epoxy phenolic resins. In certain cases, the thickness of the inner coating layer 304 comprising the epoxy phenolic resin is in the range of 150 to 250 µm. In certain cases, the thickness of the inner coating layer 304 comprising the epoxy novolac resin is in the range of 400 to 1270 µm. In certain cases, the epoxy phenolic resins have an average thermal conductivity of approximately 0.8 W / m·K (watts per meter and Kelvin). In certain cases, the epoxy novolac resin has an average thermal conductivity of approximately 0.4 W / m·K. Insulating particles may be added to these or other resins to further reduce the thermal conductivity.

[0079] In certain cases, the outer coating layer 306 has a fiber composite coating (such as a carbon fiber composite, an E-glass composite, and / or another fiber composite coating) with a thickness of approximately 2540 µm. In certain cases, E-glass has a thermal conductivity of approximately 0.288 W / m·K. In certain cases, carbon fiber has a thermal conductivity of approximately 0.8 W / m·K.

[0080] In certain cases, the linear, volumetric, radial thermal resistance of the pipe string wall is at least approximately 0.002 K·m / W (Kelvin times meters per watt). In certain cases, the linear, volumetric, radial thermal resistance of the pipe string wall is at least approximately 0.01 K·m / W. Referring to Fig.3A, the thickness 310 of the wall is defined by the inner surface of the inner coating layer 304 and the outer surface of the outer coating layer 306. For these purposes, the "length-specific thermal resistance" is the effective conductive thermal resistance of the strand for radial heat transfer, taking into account the different materials along its length, and is the temperature difference required to transfer 1 watt of energy over an axial material length of 1 meter.

[0081] The following is the linear thermal resistance of the wall of the pipe string in certain cases with a main body 350 made of steel and an inner coating layer 304 with the specified materials and thicknesses (without outer coating layer 306): coating layer Length-related thermal resistance Epoxy phenolic resin 100 µm 0.00062 K·m / W Epoxy phenolic resin 250 µm 0.0010 K·m / W Epoxy-novolac resin 250 µm 0.0017 K·m / W Epoxy-novolac resin 400 µm 0.0024 K·m / W

[0082] The following is the linear thermal resistance of the wall of the pipe string in certain cases with a main body 350 made of steel and an inner coating layer 304 made of the specified materials and thicknesses, and an outer coating layer 306 (“jacket”) made of E-glass with the specified thickness: coating layer Length-related thermal resistance Epoxy phenolic resin 100 µm + 2.5mm jacket 0.0032 K·m / W Epoxy-phenolic resin 100 µm + 5 mm sheath 0.0034 K·m / W Epoxy phenolic resin 250 µm + 2.5mm jacket 0.0048 K·m / W Epoxy-phenolic resin 250 µm + 5 mm sheath 0.0054 K·m / W Epoxy novolak resin 250 µm + 2.5mm coat 0.0070 K·m / W Epoxy-novolac resin 250 µm + 5 mm sheath 0.0082 K·m / W Epoxy novolak resin 400 µm + 2.5mm coat 0.0092 K·m / W Epoxy-novolac resin 400 µm + 5 mm sheath 0.011 K·m / W

[0083] In certain cases, the pipe has 302, as in Fig. Figure 3A shows an inner coating layer 304 made of an epoxy novolac resin with a thickness of approximately 400 micrometers and an outer coating layer 306 made of E-glass with a thickness of approximately 5 millimeters. In such a case, assuming an underground zone with a thermal gradient of approximately 60°C / km and a drill string with a length of approximately 8,000 m and water-based drilling fluid with a circulation rate of approximately 3 m³ / h, the following can be assumed: 3 / min and a temperature at the rock surface of about 490° C, such a drill string 200, which consists entirely or substantially of such pipe 302, leads to a temperature difference between the adjacent rock at the rock surface and the drilling fluid at the rock surface of about 346° C.

[0084] In certain cases, the pipe has 302, as in Fig. Figure 3A shows an inner coating layer 304 made of an epoxy phenolic resin with a thickness of approximately 250 micrometers and an outer coating layer 306 made of E-glass with a thickness of approximately 2.5 millimeters. In such a case, assuming an underground zone with a thermal gradient of 40°C / km and a pipe string with a length of approximately 9,000 m and water-based drilling fluid with a circulation rate of approximately 3.5 m³ / h, 3 / min and a temperature at the rock surface of about 370°C, such a drill string 200, which consists of such pipe 202, leads to a temperature difference between the adjacent rock at the rock surface and the drilling fluid at the rock surface of about 196°C.

[0085] In other cases, the inner coating layer 304 and / or the outer coating layer 306 may have a greater or lesser thickness and / or may consist of or include other types of coatings, for example, ceramic inorganic coatings such as silicate-bonded ceramics.

[0086] Fig. Figure 3B shows another configuration of an insulated 302 tube. The 302 tube from Fig. 3B is the one from Fig.3A similar, except as described below. The inner coating layer 354 covers at least part of an inner circumferential surface of the pipe 302. In the illustrated case, the inner coating layer 354 covers only the inner circumferential surface of the pipe 302 in the region and near the connector 322. By covering the area of ​​the inner circumferential surface of the pipe 302 in the region and near the connector 322 with the inner coating layer 354, the heat transfer at the connector 322 is reduced. In other cases, the inner coating layer 354 covers the entire inner circumferential surface of the pipe 302.

[0087] In certain cases, the inner coating layer 354 can be in Fig. 3B have the same materials and thicknesses as those used in relation to the inner coating layer 304 of Fig.3A are described. In certain cases, the inner coating layer 354 may have other suitable materials or thicknesses. In certain cases, the pipe may be vacuum-insulated pipe (VIT), in which the insulation is provided by a vacuum layer inside the pipe, instead of or in addition to the inner coating layer 304 (or 354) and the outer coating layer 306.

[0088] Fig. 3C shows another configuration of an insulated 302 tube. The 302 tube from Fig. 3C is the one from Fig. 3A similar, except as described below. In particular, the pipe is of Fig.3C comprises a double-walled, insulated tube 302 with an additional outer tube 324 that completely encloses layer 306. The outer tube 324 provides a protective layer to the underlying layers, absorbing the contact and impact occurring during drilling operations and shielding the underlying layers. The outer tube 324 allows the use of more sensitive insulating materials than layer 306, since the underlying layers do not have to withstand the contact and impacts to which the outer layer 306 is exposed. Fig. 3A is exposed. Accordingly, layer 306 may have a different structure (e.g., thicker, made of a material with higher thermal resistance) than the outer coating layer of the pipe 302. Fig. 3A. The inner layer 304 can be placed in the insulated tube 302 of Fig.3C may be omitted or provided only over a section of the inner circumference of the tube 302. In certain cases, the inner layer 304 may cover the inner circumference near the connectors 322, leaving the central section of the tube 302 free. In certain cases, a wire 326, for example, an electrical conductor, an optical fiber, and / or another type of wire, runs through the tube 302. The wire 326 is configured to transmit signals (e.g., data, values, communication, and / or other signals) and / or power through the tube 302 and, in certain cases, is configured to connect to one or more tools in the BHA 210 ( Fig. 2A), including the communication tool 220, to be coupled to transmit signals and / or power to the tools of the BHA 210. While the wire 326 can be provided in each of the embodiments, the wire 326 can be located in the tube 302 of Fig.3C is largely located in the space between the body 350 and the outer tube 324, with only the end sections of the wire 326 extending into the connectors 322. The wire 326 can be positioned in the connectors 322 such that when the lengths of tube 302 are joined together, the connectors 322 are connected to each other, and continuity of the wire 326 is provided to transmit signals and / or energy between each of the lengths of tube 302.

[0089] Fig. 3D represents another configuration of insulated tube, in particular an insulated coiled tube 302. While the coiled tube 302 may include the internal and / or external coatings described herein, it shows Fig.Figure 3D shows an example of a wound polymer tube with a protective sheath 356, wherein the polymer of the wound tube is configured to provide insulation. The sheath 356 is constructed of a material with a relatively higher abrasion resistance than that of the polymer, such as steel, aluminum, titanium, and / or another material, and can be relatively thin so that it does not contribute substantially to the weight of the tube. In certain cases, the sheath 356 is 7 mm or thinner. In certain cases, the length-normalized, volumetric, radial thermal resistance of the wound polymer tube 302 is at least 0.02 m K / W and in certain cases greater than 0.05 m K / W, 0.2 m K / W, or 0.3 m K / W. These values ​​can be achieved by selecting the thermal conductivity of the polymer and its thickness. In certain cases, the thermal conductivity range is approximately 0.15–0.5 W / m K.In certain cases, the coiled pipe 302 has a dry density of less than 2000 kg / m. 3 and in certain cases of less than 1500 kg / m² 3 At this density, the wet weight of the 302 pipe is minimal once it is immersed in the borehole drilling fluid.

[0090] Typical drilling fluids have densities in the range of 1.0–2.0 specific gravity (although they can be higher or lower). Therefore, such an insulated 302 pipe would have excellent thermal resistance, sufficient hydraulic flow capacity, a negligible impact on the wet (floating) weight of the drill string, no problems with external abrasion, and it can be handled in the same way as regular wound pipe during operation. The wound polymer pipe may have several concentric layers of different polymers and other materials bonded together. In certain cases, the pipe has a specific "dry weight" tensile strength of at least 50 kN·m / kg, but when the pipe is immersed in drilling fluid ("wet weight"), the specific tensile strength of the pipe is at least 150 kN·m / kg, as the weight of the pipe floats due to the drilling fluid.

[0091] In certain cases (e.g., for communication with a rotating steerable system, for drilling with a non-contact drill bit, and / or in other cases), the 302 conduit of any of the above configurations may include a supply cable carrying conductors (e.g., electrical, fiber optic, hydraulic, and / or other types) for power and / or communication from an upwell location and / or the earth surface to the BHA 210. In certain cases, the supply cable may be clamped to the outside of the 302 conduit, or the supply cable may be, as shown in Fig. As shown in Figure 3E, the supply cable can be routed through the interior of the tube 302. In certain cases, the supply cable can be routed into a bore through a side wall of the main body 350 and / or otherwise be integral with the main body 350. In certain cases, as shown in Fig. Figure 3F shows that the supply cable is implemented as conductor 352 between layers of the tube 302. The supply cable configurations of the Fig. 3E and Fig. 3F can be implemented in any of the pipe configurations described herein.

[0092] In certain cases, the main body 350 in any of the above embodiments may incorporate a high-strength-to-weight steel drill string, such as UDI 65 steel drill string, available from NOV, Inc. In some cases, such steel drill string may be UD-165 steel drill string, which may have a yield strength of approximately 165,000 psi (1,138 MPa), a tensile strength of approximately 1,000,000 lbf (4.45 MN), a length-normalized joint air weight of 24.76 lbf / ft (361.3 N / m), and a joint strength-to-weight ratio of approximately 900 lbf / lbf (900 N / N) for a drill string with an outside diameter of 5.875 in (14.92 cm).

[0093] In some cases, the main body 350 may incorporate a titanium alloy tube. In some instances, such a titanium alloy tube may be Ti-6Al-4V and may have a yield strength of approximately 120,000 psi (827 MPa), a tensile strength of approximately 750,000 lbf (3.34 MN), a length-normalized joint air weight of 16 lbf / ft (233.8 N / m), and a joint strength-to-weight ratio of approximately 1,000 lbf / lbf (1,000 N / N) for a drill string with an outside diameter of 5.875 inches (14.92 cm).

[0094] In some cases, the main body 350 may contain an aluminum alloy tube. In some cases, such an aluminum alloy tube may be Al-Zn-Mg II aluminum alloy and may have a yield strength of approximately 70,000 psi (483 MPa), a tensile strength of approximately 600,000 lbf (2.67 MN), a length-normalized joint air weight of 15.5 lbf / ft (226 N), and a joint strength-to-weight ratio of approximately 825 lbf / lbf (825 N / N) for a 5.787-inch (14.699 cm) outside diameter drill string. In some cases, such an aluminum alloy tube may be FarReach™ drill string, available from Alcoa Energy Systems. In some cases, such an aluminum alloy drill string may be aluminum drill string, available from Aluminum Drill Pipe, Inc.

[0095] In some cases, the main body 350 can be a carbon fiber composite pipe. In some cases, such a carbon fiber composite pipe can be Advance Composite Drill Pipe, available from Advance Composite Products & Technology, Inc.

[0096] In some cases, the drill string 200 may be made entirely of pipe of the same construction, e.g., the main body 350 made of the same material. In other cases, the drill string 200 may comprise two, three, or more different intervals (i.e., different sections) with one or more lengths within each interval that have the same material as the main body 350 and the other intervals. For example, in some cases, a portion of the pipe, i.e., a first interval, may be made of one main body material, and the remainder of the drill string 200 may be made of a different main body material (such as steel).

[0097] In another case, a large portion of the pipe in a section near drill bit 208 may be made of a material that is lighter than the section further up the hole from drill bit 208 on a length-normalized air-weight basis. For the examples above, titanium drill pipe is approximately 35% lighter than steel, and aluminum drill pipe is approximately 37% lighter than steel. Those pipes 202 in a section further up the hole from drill bit 208 may include main bodies made of a higher-strength material. For the examples above, UD-165 drill pipe has a tensile strength approximately 67% greater than aluminum, and titanium drill pipe has a tensile strength approximately 25% greater than aluminum.The difference in tensile strength and length-normalized weight can also be achieved with a single material, but with varying thicknesses / diameters of pipe in the upstream section compared to the downstream section in a telescopic manner.

[0098] In one instance, the majority of the 202 pipe in the section near the drill bit is approximately 35% lighter than the majority of the 202 pipe in the up-hole section, and a large portion of the 202 pipe in the down-hole section has a tensile strength approximately 25% higher than a large portion of the 202 pipe in the section near the drill bit. Such use of different drill string materials can enable drilling into much hotter rocks existing at greater depths and therefore requires an isolated drill string with sufficient tensile strength to extend to such depths. The materials mentioned above, when appropriately combined, allow drilling to depths greater than 9 km, up to and including 14 km or more. The Earth's geothermal gradient causes rocks to have higher temperatures at greater depths.The shock cooling technology presented here provides a method for increasing penetration rates and drilling performance in high-temperature rock. A synergistic effect results from combining deeper drilling, made possible by combining different weight / strength drill string segments, with the cooling technology described herein. Closed-loop multilateral boreholes can be drilled at a sufficient depth (and therefore rock temperature) to allow the shock cooling effect, thereby significantly reducing the time and cost of drilling these multilateral boreholes.

[0099] In certain cases, the design of the pipe 202, together with the drilling fluid, can be selected to allow the drill string 200 to gain buoyancy, or at least partial buoyancy, from the drilling fluid in the borehole. For example, when drilling with a non-contact drill bit, no significant weight on the bit is required to effect drilling. The bit simply needs to be held in close proximity to the rock surface it is drilling. Selecting main bodies 350 made of composite material and / or polymer allows a pipe and / or drill string volume density to drilling fluid volume density ratio of 2, and in certain cases 1.5 or less, so that the drill string 200 gains at least partial buoyancy from the fluid, and the floating weight of the string is much less than with main bodies 350 made of steel.The target ratio can account for components in the drill string that are not pipe, such as the BHA and the supply cable, and the mixing of different types of pipe 202 (e.g., different main body materials), resulting in an overall ratio of 2.0 or greater. At least partially, the buoyancy of the drill string 200 in this way reduces the forces between the string and the borehole walls, and thus the sliding friction. This makes it easier to move very long drill strings through the boreholes, requiring a smaller, less powerful surface drilling rig (with a smaller hoist). Furthermore, at least partially, the buoyancy of the drill string 200 in this way also reduces the tensile forces on the drill string 200, allowing for longer drill strings and thus longer boreholes, as well as greater freedom in selecting the pipe 202 construction to achieve the specified minimum / maximum temperatures discussed above.

[0100] In one example, a pipe 202 with a composite and / or polymer main body 350 can have a density of approximately 1.3 SG (typical for polymers) to 2 SG (typical fiber composites range from 1.5 to 2 SG), and for the purposes of this example, approximately 1.5 SG. When immersed in a drilling fluid that is mostly water (i.e., approximately 1 SG), the density ratio is 1.5. In comparison, typical steel is 7.8 SG, so a pipe 202 with a steel main body 350 in a water-based drilling fluid will have a density ratio of approximately 7.8. Additionally, the buoyancy of the drill string 200 can be controlled by controlling the drilling fluid density (i.e., composition). For example, a less dense drilling fluid than would be used in an operating buoyancy condition (e.g.,The 2-1.5 ratio discussed above can be introduced into the borehole when the drill string is being lowered to reduce buoyancy and make insertion easier and faster. Conversely, a denser drilling fluid than that used in the operational drilling buoyancy condition can be introduced into the borehole when the drill string is withdrawn to increase buoyancy and make withdrawal easier and faster, reducing stress on the drill string and drilling rig. The drilling fluid density can be adjusted by modifying the inlet temperature, the inlet pressure (when operating with controlled pressure drilling), and by changing the dissolved solids / salts and the solids content in the fluid.Furthermore, in certain cases a drag motor can be used to apply a force to the drill string 200 to pull it through the borehole, and vibratory / shaker tools can be used to reduce the static friction of the drill string 200 in the borehole.

[0101] In certain cases, a carbon steel pipe with an internal coating of 400µm thickness of epoxy novolak over its entire length (and no external coating) can generate an approximately 91°C greater temperature difference between the internal fluid flow and the rock formation in a 5000-meter drill string compared to the same length of uninsulated carbon steel pipe using a water-based drilling fluid with a viscosity of approximately 3.5 m 3 / min is pumped, and there is a temperature gradient from the Earth's surface to the rock surface of approximately 50°C / km.

[0102] In certain cases, a carbon steel pipe with an internal coating of 400 µm thick epoxy novolak and an external coating of 5 mm E-glass sheathing, both over the entire length, can generate a temperature difference of approximately 346°C between the internal fluid flow and the rock formation in an 8000-meter string compared to the same length of uninsulated carbon steel pipe using a water-based drilling fluid with a viscosity of approximately 3.5 m 3 / min is pumped, and a temperature gradient from the Earth's surface to the rock surface of approximately 60°C / km is assumed.

[0103] As above with reference to Fig. As discussed in 2A-2C, a drill string can be configured with a down-hole separator to separate a water-rich (and therefore high-heat-capacity) flow and divert it into the annular space, while the remaining relatively oil-rich flow continues to the drill bit for lubrication, chemical stability, and (where applicable) dielectric properties. In certain cases, the water-rich flow can be diverted into the annular space for enhanced cooling of the outside of the drill string pipe (and the outside of other components upstream of the separator), while the oil-rich flow continues to the drill bit. Furthermore, the separators can remove heavy contaminants from the drilling fluid that can adversely affect bit / rock interaction and drilling performance. Fig. Figure 4 presents details of an exemplary drill string 400, which in some cases is referred to as drill string 200. Fig. 2A-2C could be used. The drill string 400 comprises pipe 402 with a drill bit 404, which in some cases is pipe 202 or drill bit 208 of the Fig. 2A-2C could be. The drill string 400 further comprises a fluid separator 406 upstream of the drill bit 404, which connects to the separator 204 in Fig. It could be 2A-2C. In some cases, the separator 406 may be a cyclone separator, a driven centrifuge, or another type of separator. In some cases, for example, the separator 406 may be the separator 500 from Fig. 5 or the separator 600 from Fig. 6.

[0104] During drilling with the drill string 400, drilling fluid 408 flows through the interior of the pipe 402 and through the fluid separator 406. The fluid separator 406 separates a relatively water-rich fluid stream 410 from the drilling fluid 408 (that is, stream 410 has a higher water-to-oil ratio than the remaining section 412 of the drilling fluid 408) and diverts stream 410 to the annular space 414 surrounding the pipe 402. From the separator 406, the remaining section 412 (with a lower water-to-oil ratio compared to the diverted stream 410) flows to the drill bit 404. One or more separators 406, alone or in conjunction with diversion tools (such as flow diversion tools 204 of the Fig. 2B-2C) can be positioned and configured based on a specified target temperature or temperatures of the pipe 402 (or sections of pipe 402 and / or other components upstream or downstream of the separator) that are to be cooled by the water-rich stream, and also based on specified parameters of the oil-rich stream for the operation of the drill bit 404 (for example, lubrication, chemical stability, and dielectric properties). The specified target temperature may be an allowable operating temperature or a temperature range, typically specified by the manufacturer and below the maximum allowable operating temperature.Thus, specified temperatures or temperature ranges can be defined based on service life / temperature and / or power / temperature ratios, and drilling operations can be configured to maintain the pipe or other components at the specified target operating temperature or within temperature ranges. The separators 406 can include one or more actuated valves, orifices, and / or passages, actuated from the surface hydraulically, electrically, mechanically, chemically, and / or otherwise to control the flow and pressure in and / or around the separator 406. In certain cases, one or more of the separators 406 can be placed in the down-hole string 400 from any mud turbine electric generator to avoid diverting fluid flow that would otherwise drive the mud turbine electric generator.A supply cable in or coupled to pipe 402 can be used to deliver power from the slurry turbine electric generator to components below it. Alternatively, the separator 406 and its effect on the fluid flow can be taken into account when selecting the characteristics of the slurry turbine electric generator and when determining the fluid flow to ensure that the required power generation is achieved.

[0105] Fig. Figure 5 illustrates a detail of an exemplary fluid separator 500, which in some cases is referred to as fluid separator 406 by Fig. 4 could be used. The separator 500 comprises a cyclone chamber 502 within a housing 504. An inlet 506 of the cyclone chamber 502 is configured to receive drilling fluid 408 from the pipe 402. The drilling fluid enters the cyclone unit tangentially. An external vortex is generated in the cyclone, which imposes a centripetal force that drives the separation between the lower-density oil phase and the higher-density water phase. The heavier water phase exits the outlet 508 as a water-rich stream 410 to flow into the annular space outside the pipe 402. The lighter oil phase migrates to the center of the cyclone to emerge as an oil-rich stream 412, which flows from the outlet 510 to the drill bit 404.

[0106] Fig. Figure 6 shows a detail of another exemplary fluid separator 600, which in some cases is referred to as fluid separator 406 by Fig. 4 could be used. The separator 600 comprises spiral guide vanes 602 above a chamber 604 within a housing 606. When drilling fluid 408 enters the separator, rotation is transmitted through the spiral guide vanes 602. The denser phase (water) is forced to the walls of the separator to exit as a water-rich stream 410. The lighter oil phase remains in the central section of the chamber to exit separately as an oil-rich stream 412. In some cases, the separator 600 can be a driven unit in which the spiral guide vanes 602 are rotated by an electrically or hydraulically driven motor.

[0107] When using a hole-down separator (such as the types found in Fig. 5 and Fig. As shown in Figure 6), the use of a drilling fluid with defined fluid properties (such as the degree of emulsion) can, in some cases, lead to more efficient and effective separation of the water and oil phases. For example, in some cases, a “loose” (only partially emulsified) drilling fluid mixture can result in greater separation efficiency or other preferred separation behavior compared to the “solid” emulsion typical of many drilling fluids. A suitable Drilling System 700 for generating and using a loose-emulsion drilling system in some cases is described in Figure 700. Fig. 7 shown. With reference to Fig. Drilling fluid 702 flows at the surface from the annular space 704. Solids such as drill cuttings and low-temperature material (LCM) can be separated from the drilling fluid at the primary solids separator 706. From the separator 706, drilling fluid 440 flows to the cooling system 708, which in some cases includes one or more coolers 230. Fig. 2A-2C. The cooling system 708, for example, can use air cooling, evaporative cooling, chiller cooling, or a combination of the three and can be positioned as shown, receiving the stream from the separator 706, but it can be positioned elsewhere in the system to cool combined or separate fluid streams. At the oil-water separation system 710, fluid 702 is separated into two separate fluid trains (or streams): an oil-rich stream 712 and a water-rich stream 714. The separation system 710 can be, for example, a gravity separator, a centrifugal separator, and / or a cyclone separator. The oil-rich stream 712 and the water-rich stream 714 can undergo further solids removal or other suitable treatment at treatment systems 716 and 718, respectively, after which they can flow into their respective storage tanks 720 and 722. Pumps 724 and 726 pump the two streams to a common mixing system 728.The mixing system 728 can be configured to provide turbulent mixing of the two streams to produce a loose emulsion fluid mixture (i.e., not fully emulsified), and a pump to return the combined stream 730 to the drill string 732. The drilling fluid can flow down the drill string in highly turbulent flow and pass through the crown at high shear rates. The mechanical mixing action of turbulent flow / high shear rates ensures sufficient mixing of the two fluids without the need for emulsifying chemicals. In some cases, the mixing system 728 can be configured so that the resulting loose emulsion has a desired predetermined target emulsion stability or other target properties of the mixture.The target property or properties of the mixture may in some cases be based on a desired target separation performance (such as separation efficiency or degree of separation) of the fluid separator or other operating parameters of the separator.

[0108] Alternatively or additionally, a drill string with multiple pipes 804, as in Fig. 8A and Fig. 8B demonstrated the elimination of the need for an underground separator. Fig. 8A and Fig. Figure 8B shows in particular cross-sectional views of two exemplary pipes 802, which are made up of several bundled pipes 804 within a protective casing 806, forming a drill string 200 ( Fig. 2A-2C). Such multiple 804 tubes allow different fluids to flow through different 804 tubes while keeping the fluids separate. As discussed in more detail below, the 804 tubes can have different destination locations within the drill string, which makes it possible to direct different fluids to different locations without the need to separate mixed fluids.

[0109] Fig. Figure 8A shows five conduits 804 bundled around a supply cable 808, although fewer or more conduits could be provided, and in certain cases the supply cable 808 could be omitted. The supply cable 808 can be one or more electrical, fiber optic, hydraulic, and / or other types of conduits, and if multiple conduits are provided within the supply cable 808, several different types of conduits may be included. In certain cases, the supply cable 808 provides electrical power and / or communications, such as control signals, data, and / or other communications. Thus, for example, in the context of a contactless drill bit (discussed above), the supply cable 808 may be coupled to the drill bit to supply power to the bit from a power source (e.g., generator, battery, capacitor bank, and / or other power source) at an uphole location and / or on the Earth's surface (e.g., a drill bit).The 808 supply cable may provide power and / or communications to other components in the drill string, including the BHA. The 808 supply cable may additionally or alternatively provide power and / or communications to other components in the drill string, including the BHA. The 808 supply cable may be armored and / or electrically and thermally insulated, but by configuring the 804 tubes to surround the 808 cable, it does not need to be armored to resist abrasion typical of a cable that would contact the borehole wall or be exposed to abrasive drilling fluids.Furthermore, the supply cable 808 does not need to contribute to supporting the BHA, and support for the BHA can be provided by the pipes 804.

[0110] Fig. Figure 8B shows three pipes 804 and a supply cable 808 bundled around a support cable 812. In certain cases, the support cable 812 is configured to bear the full weight and other tensile loads, such as during manipulation and driving the pipe 802 into / out of the borehole, without requiring any contribution from the remaining aspects of the pipe 802. In other cases, the support cable 812 bears only a portion of the tensile loads, and the remainder is borne by the other aspects of the pipe 802. In other cases, the support cable 812 may be periodically anchored to the other aspects of the pipe 802 to support those other aspects. The 812 suspension cable can be multi-stranded (as shown) or solid and metallic (e.g. steel, titanium, aluminum and / or another metallic material) or non-metallic (e.g. carbon fibers, aramid fibers, glass fiber, E-glass, polymer fibers and / or another non-metallic material).The 804 pipes can be bundled at the time of manufacture and transported to the drilling site as bundles, or they can be transported to the drilling site as separate 804 pipes and bundled on-site before and / or during the drilling process. The 804 pipes can be spliced ​​or coiled. In the case of coiled pipe, bundling the 804 pipes at the drilling site allows for the transport of individual 804 pipe coils instead of coils of bundled 804 pipes. Coils of individual 804 pipes will have a smaller diameter for a given length than a coil of bundled 804 pipes. Such smaller-diameter coils are easier and less expensive to transport, especially when transported by road, which has payload width and height restrictions.

[0111] In certain cases, the individual 804 tubes are made of steel, titanium, aluminum, polymer, fiber-reinforced composite (e.g., carbon fiber, aramid fiber, glass fiber), and / or another material. Different individual 804 tubes within a bundle may be made of different materials. Some or all of the individual 804 tubes may be provided with an internal and / or external insulating coating (such as the coatings described above), and different 804 tubes may have different coatings. The bundled 802 tube is shown, including a protective tube, such as a casing 806. The casing 806 not only holds the individual 804 tubes together, but it can also be configured to withstand the wear and tear and impact of the bundled 802 tube passing through the borehole and abrasive drilling fluids.Therefore, the individual 804 pipes need not be made of steel or another material selected to resist wear and impact, or if the 804 pipes are covered in an insulating coating, the coating need not be designed to resist wear and impact. For example, the 806 sheathing allows the use of polymer or fiber composite materials that have properties selected for their thermal resistance rather than for durability against wear and impact. In certain cases, the 806 sheathing is steel or aluminum, polymer (e.g., thermoplastic), composite, or another material. In certain cases, the 806 sheathing is 0.25 inches of steel or aluminum.

[0112] The cavities between the casing 806 and the individual pipes 804 (and the supply cable 808, if present) can be filled with insulation 810. In certain cases, the insulation 810 may be a material selected partly to contribute to the buoyancy of the bundled pipe 802 in the fluids within the borehole. In certain cases, the insulation 810 is selected to have a density lower than that of the expected fluid in the annular space, which may be the drilling fluid or a combination of the drilling fluid and other fluids, e.g., the cooling fluid. In certain cases, the insulation is a polymer as described above with respect to the pipe. Some examples include polyetheretherketone (PEEK), with a thermal conductivity of ~0.25 W / mK at room temperature, polytetrafluoroethylene (PTFE), with a thermal conductivity of ~0.3 W / mK at room temperature, and / or other polymers.In certain cases, the insulation can be omitted, and the cavities sealed and filled with a fluid (gas or liquid) that is partially selected to contribute to the buoyancy of the bundled pipe in the fluid within the borehole. In certain cases, this fluid has a density lower than that of the fluid in the borehole. In certain cases, as in . Fig. 9A and Fig. Figure 9B shows the sheath 806 as a tube configured to handle fluid flow, and the cavities between the sheath 806 and the individual tubes 804 are used for the flow. Fig. 9A and Fig. 9B shows the 804 pipes used for down-hole flow. Fig. 9A shows the cavities used for down-hole flow and Fig. Figure 9B shows the cavities used for upward flow through the hole.

[0113] In other cases, the bundled tubes 804 can be provided without the sheathing 806 and clamped together with ring clamps, joined with adhesive, welded and / or otherwise held together.

[0114] In certain cases, the individual 804 tubes may all be the same size, or one or more may be different sizes, selected based on the relative fluid flow rates through the 804 tubes. Although all sizes of individual 804 tubes are within the concepts described here, in certain cases the individual 804 tubes may be standard, commercially available tube sizes (e.g., 1 in, 1.25 in, 1.5 in, 1.75 in, 2 in, 2.375 in, 2.625 in, 2.875 in outside diameter). In certain examples, the bundled 802 tube, size 2 in outside diameter / 1.8 in inside diameter, comprises individual 804 tubes around a 2-inch supply cable 808. Such a configuration would have a flow range equivalent to a 4.4-inch diameter single tube and provide sufficient hydraulic flow capacity to drill an 8.5-inch borehole.The flow range would be greater than that of a standard 4 inch coiled pipe, while still being easier to transport to the drilling site.

[0115] In certain cases, one or more of the 804 tubes can be coupled to the drill bit (e.g., bit 208) and used to supply drilling fluid from the surface and through the bit into the drilled borehole, while one or more of the remaining 804 tubes can be open to the annular space around the drill string at one or more locations above the BHA (e.g., BHA 210) to allow cooling fluid to flow into the annular space around the drill string above BHA 210. The 804 tubes can be open to the annular space, for example, by stopping just before BHA 210 or by one or more openings through a sidewall of the 804 tube above BHA 210. Different 804 tubes can be open to the annular space at different locations along the drill string to allow the cooling fluid to be discharged at different points, similar to the multiple fluid diverters discussed above.Furthermore, the multiple 804 tubes allow different fluids with different properties (e.g., different thermal properties such as heat capacity and conductivity, different density, different lubrication and / or other properties) to be conveyed to different locations, as well as at different flow rates, by allowing the different fluids to flow through selected 804 tubes.

[0116] Additionally or alternatively, one or more pairs of the remaining 804 tubes can be coupled together so that the fluid can be circulated in a loop (i.e., a closed system), from the Earth's surface to a specific location along the drill string through one 804 tube and back to the Earth's surface through another 804 tube. The 804 tubes configured for a loop allow the use of cooling fluid without introducing it into the annular space or otherwise into the borehole. In certain cases, the closed system is desirable for fluids that are expensive, difficult to extract from the drilling fluid, incompatible with the drilling fluid or surrounding rock, or where there is otherwise a need or desire to avoid introducing the fluid into the borehole. For example, the closed system configuration allows the use of a surface-cooled coolant (e.g.,via cooler 230) and / or other fluids as cooling fluid.

[0117] Circulation temperatures that are too low (below the minimum of the BHA operating temperature range) can lead to the failure of components designed for high bottom temperatures. Specifically, for example, standard batteries may function down to ~150°C, while high-temperature batteries may function up to 185°C. However, the high-temperature batteries may have an effective minimum temperature of, for example, 100°C. Similarly, mud motor efficiency and longevity (operating time) can depend on the fit between the rotor and stator, and this fit can be temperature-dependent (i.e., the motor configured for optimal operating conditions at 125°C may use different components and / or a different configuration than a similar motor optimized for 175°C).Therefore, to reduce equipment failures and thus the number of trips required to repair or replace BHA components, it may be desirable to maintain the drilling fluid at a relatively constant circulation temperature. While insulated pipe can allow for cooler drilling fluid temperatures at the BHA than an upper maximum as the BHA progresses down the borehole, it can also result in BHA temperatures that fall below a minimum operating temperature at certain drilling depths. Furthermore, such insulation material can be brittle and may experience greater wear than a string or string sections without such insulation (or with a thinner layer of it).Such wear can be worse in divergent, open (as opposed to lined) borehole sections, and especially in those sections of the drill string connected to or near the BHA, because torsional vibrations near the BHA may be greater, frictional forces in divergent boreholes may be increased, and the rock surface of the open borehole may be more abrasive than the lining (e.g., steel lining). Therefore, in some cases, it may be desirable to configure the borehole system and develop / determine its operating plan so that, when drilling the borehole to a target gauge depth, the borehole fluid temperature at the BHA neither significantly exceeds nor falls below a target operating temperature range.Such temperatures or ranges can be permissible operating temperatures or temperature ranges, typically specified by the manufacturer, which may be above or below the permissible operating temperatures. Thus, specified temperatures or temperature ranges can be established based on service life / temperature and / or power / temperature ratios, and drilling operations can be configured to keep the BHA within the specified target operating temperature range or temperature ranges.For example, for variable boreholes, by carefully selecting where and how much insulation is used along the drill string and adding more coated drill string segments as drilling progresses, the circulation temperature can be controlled to be relatively the same at the beginning of a horizontal section (e.g., the heel of the borehole) as at the end of the horizontal section (e.g., the tip of the borehole). Modifying the circulation flow rate (of the cooled drilling fluid) and the inlet fluid temperature (with mud coolers) can further refine the underground circulation temperature to keep it within the operating range of BHA components.For divergent boreholes, the operating plan may be such that sections with an insulating coating layer (or otherwise high thermal resistance) remain mostly or entirely within the lining, and sections without an insulating coating layer or otherwise less insulated are used for the divergent / horizontal section. As drilling progresses, more coated drill string segments are added to the top of the string, so the insulated section increases as a percentage of the total string as drilling progresses.In this way, coated sections are located far away from the BHA, thus reducing exposure to severe torsional vibrations and wear, which further reduces the required frequency of trips needed to repair or replace the BHA, its components and / or those sections of the drill string that are connected to or near the BHA.

[0118] In the Fig. The case shown in 10A-10C includes, for example, a drill string 1000 (which, for example, is drill string 200 from Fig. 2A-2C) a hole-downward section 1002, which is a first subset of pipe segments (including segments 1004a and 1004b in Fig. 10A) which are not coated with an insulating coating layer, attached to a hole-upward section 1006 which comprises a second subset of pipe segments (shown as 1004c and 1004d in Fig. 10A) which has an insulating coating layer (as in one or more of the Fig. (described in 3A-3D), such that the hole-upward section 1006 has a greater thermal resistance (for example, at least 0.002 meter Kelvin per watt, or at least 0.008 meter Kelvin per watt, or at least 0.01 meter Kelvin per watt) than the hole-downward section 1002. While sections 1002 and 1006 are shown with only two segments each for illustrative purposes, it will be understood that each subset may be composed of fewer or a greater number of segments (for example, only one segment (a singleton set), or one hundred or more segments in each subset). With reference to Fig. 10B, the drill string 1000 can be used to drill a surface borehole 1008 (which, for example, connects boreholes 120 or 130 from Fig. 1A or Fig. 1B) and a lateral borehole 1010 (which, for example, connects the lateral boreholes 150 from Fig. 1A or Fig. 1B can be) to drill. In the in Fig. 10B and Fig. In the case shown in Figure 10C, surface borehole 1008 is lined with a liner 1012, and lateral borehole 1010 is unlined. In the case shown, the heel 1014 of lateral borehole 1010 (and the shoe (down-hole end) 1014 of the liner 1012) is at a gauge depth of approximately 13,000 feet, and the target gauge depth 1016 is approximately 23,000 feet. Other cases may have different gauge depths. The drill string 1000 is constructed in accordance with an operational plan, such that a subset of less isolated segments (for example, segments 1004a and 1004b) are Fig. 10A) near BHA 1018 to extend the lower subset 1006 of drill string 1000 from heel 1014 to tip 1020. However, some or all of the segments added to construct the upper subset 1006 are more isolated segments (for example, segments 1004c and 1004d from Fig. 10A), thereby forming a length of insulated drill string which, as in Fig. As shown in Figure 10C, the lower subset 1002 remains within the lining 1012 while the BHA 1018 reaches the target measurement depth 1016, thus minimizing wear on the coated segments while keeping the BHA 1018 within both the upper and lower operating temperature ranges. While in the illustrated case the lower subset 1002 is composed entirely of segments with a thinner insulating coating layer than that of the upper section (or without an insulating coating layer and / or with abrasion-resistant layers or coatings), so that they have a lower thermal resistance, in other cases at least part of the lower subset 1002 may be composed of segments that have a higher thermal resistance than some of the segments of the upper subset 1006.Similarly, while in the illustrated case the upper subset 1006 is composed entirely of segments with higher thermal resistance than the lower section, in other cases some or all of the upper subset 1006 may be composed of segments with lower thermal resistance than some of the segments in the lower subset. In some cases, instead of the drill string being composed of segments with varying thermal resistance, all or a section of the drill string may have an insulating coating layer that varies in thickness or has other insulating and / or protective properties while extending over multiple segments, or extending over a continuous drill string (for example, a case where all or part of the drill string is composed of coiled pipe).

[0119] A representative temperature profile of the Fig. 10B and Fig. The drilling operation shown in 10C, from heel 1014 to tip 1020, is in Fig. Figure 11 compares cases where all, some, or no parts of the drill string are insulated. Line 1102 shows the BHA circulation temperatures as a function of depth when the well is drilled using a drill string composed entirely of low-thermal-resistance segments. Line 1102 demonstrates that while temperatures initially remain within the BHA's operating temperature range when using such a drill string, they rapidly increase and exceed the maximum temperature as drilling progresses toward the target depth. In contrast, line 1104 shows the BHA circulation temperatures as a function of depth when the well is drilled using a drill string composed entirely of highly insulated segments.Line 1104 shows that while temperatures do not exceed the maximum operating temperature as the BHA approaches the target depth, temperatures may fall below the minimum of the operating temperature range when lateral circulation is initiated near the heel. Line 1106 shows the BHA circulation temperatures as a function of depth when the borehole is drilled using a drill string as shown in [reference missing]. Fig. 10C and Fig. Figure 10B shows a drill string configuration with a lower section (approximately the length from heel to target depth) composed of segments with lower thermal resistance than the upper section. Line 1106 demonstrates that such a drill string configuration keeps BHA temperatures within operating range 1108 as the well is drilled from heel to target depth. In other words, the temperature profile is "flattened" by using a drill string constructed with such a defined sequence of segments with varying thermal resistance, thus keeping it within the operating range.

[0120] Fig. 12 is a process flow diagram of a procedure 1200, which is related to Fig. 10A-10C and Fig. The system described in section 11 can be implemented. The procedure begins at step 1202, in which a defined deviation of the thermal resistance of a drill string is selected along its length such that, as the borehole is drilled through the drill string in the subsurface zone towards and then reaching the target measurement depth, the temperature of the drilling fluid at a borehole assembly to which the drilling fluid is delivered through the drill string neither substantially exceeds nor falls below the maximum nor the minimum temperature of a target operating temperature range. The selection can be developed using a numerical model (for example, using finite element analysis) to model temperature, fluid flow, and other aspects of the borehole along the length of the borehole and drill string, taking into account different sequences of segments with varying thermal resistance.The deviation of the thermal resistance of the drill string can be achieved, for example, by extending the drill string by attaching defined pipe segments in a defined sequence to the upstream end of the drill string during drilling of the borehole, with a second subset of the defined pipe segments being attached to the drill string after a first subset of the defined pipe segments, as above in relation to . Fig. Described in sections 10A-10C. In some cases, the individual pipe segments of at least the second subset may have an insulating coating layer, so that when the borehole reaches the target measurement depth, the total thermal resistance of an up-hole section of the drill string containing the second subset is greater than the total thermal resistance of a down-hole section of the drill string containing the first subset. As we proceed to step 1204, the string is assembled to have the specified thermal resistance variation. In step 1206, the borehole is drilled using the drill string assembled in step 1204, which has the specified thermal resistance variation along its length.In some cases, at least some of the activities in steps 1204 and 1206 can be carried out simultaneously, with the drill string being at least partially assembled during drilling by attaching the specified pipe segments to the drill head in a specified sequence (where the individual segments have the same or a different thermal resistance than some or all of the other segments), as above in relation to . Fig. 10A-10C described. In some cases, instead of (or in addition to) discrete pipe segments, the variation in thermal resistance can be achieved partially or completely by using a drill string that is, for example, at least partially constructed of wound pipe having a varying thermal resistance along some or all of its length (for example, wound pipe with an insulating coating layer whose width tapers along the length of the wound pipe).

[0121] The term "hole-up" as used herein means in the direction along a borehole from its distal end towards the surface, and "hole-down" as used herein means in the direction along a borehole from the surface towards its distal end. A hole-down location means a location along a borehole downstream of the surface.

[0122] Although this disclosure contains many specific implementation details, these should not be understood as limitations on the subject matter or what can be claimed, but rather as descriptions of features that may be specific to certain implementations. Certain features described in this disclosure in connection with separate implementations may also be implemented in combination or in a single implementation. Conversely, various features described in connection with a single implementation may also be implemented in multiple implementations, separately or in any suitable combination.Furthermore, although previously described features were described as acting in certain combinations and were even initially claimed as such, in some cases one or more features from a claimed combination may be removed from the combination and the claimed combination may be directed towards a partial combination or a variation of a partial combination.

[0123] Specific implementations of the subject matter have been described. Nevertheless, it is understandable that various modifications, substitutions, and deviations may be made. While operations in the drawings or claims are shown in a particular order, this should not be interpreted as meaning that such operations must be carried out in the specified order or in sequential order, or that all the operations shown must be performed (some operations may be considered optional) to achieve desirable results. Accordingly, the exemplary implementation described above does not define or limit this disclosure. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 63 / 500,835

[0001] US 20230144083A1

[0030] US 4,741,405

[0030] US 9,027,669

[0030] US 9,279,322

[0030] US 10,060,195

[0030] US 12000299562A1

[0030] WO 2008 / 003092

[0030] WO 2010 / 027866

[0030] WO 2014 / 008483

[0030] WO 2018 / 136033

[0030] WO 1200 / 236189

[0030]

Claims

[1] Method for drilling a borehole in an underground zone to a target measurement depth, the method comprising: Drilling the borehole towards a target measurement depth using a drill string; and Extending the drill string by attaching specified pipe segments in a specified sequence to an upstream end of the drill string while drilling the borehole, wherein a second subset of specified pipe segments is attached to the drill string after a first subset of specified pipe segments, each pipe segment of at least the second subset having an insulating coating layer, such that when the borehole reaches the target measurement depth, the total linear thermal resistance of an upstream section of the drill string having the second subset is at least 0.002 meter Kelvin per watt and is greater than the total linear thermal resistance of a downstream section of the drill string having the first subset. [2] Method according to claim 1, wherein the drill string is configured to deliver a drilling fluid to a borehole assembly (BHA) and wherein the specified sequence is such that when drilling the borehole to the target measurement depth, the temperature of the drilling fluid at the BHA neither substantially exceeds nor substantially falls below a target operating temperature range. [3] Method according to claim 2, wherein the underground zone adjacent to the borehole is 250°C or greater, and a minimum of the target operating temperature range of the BHA is equal to or greater than 100°C. [4] Method according to claim 1, wherein the pipe segments of the first subset of the specified pipe segments comprise pipe segments that are not coated with insulating material. [5] Method according to claim 1, wherein the borehole is a lateral borehole having a heel and a tip, and wherein, when the BHA reaches the target measurement depth, the down-hole portion of the drill string comprising the first subset extends substantially down-hole from the heel to the tip. [6] Method according to claim 5, wherein a large proportion of the pipe segments of the downstream area of ​​the drill string comprising the first subset is not coated with insulating material. [7] Method according to claim 5, wherein a casing pipe extends substantially from the borehole head to the heel of the lateral borehole and wherein, when the BHA reaches the target measurement depth, the up-hole portion of the drill string comprising the second subset does not extend over a down-hole end of the casing pipe. [8] Method according to claim 7, wherein a large proportion of the pipe segments of the hole-upward region of the drill string comprising the second subset has an insulating coating layer. [9] Method according to claim 1, wherein the sequence is such that the ratio of pipe segments having an insulating coating layer to pipe segments without an insulating coating layer increases when drilling the borehole to the target measurement depth. [10] Method according to claim 1, wherein the length-related thermal resistance of the upstream portion of the drill string comprising the second subset is at least 0.008 meter Kelvin per watt. [11] Method according to claim 1, wherein the length-related thermal resistance of the upstream portion of the drill string comprising the second subset is at least 0.01 meter Kelvin per watt. [12] System for drilling a borehole in an underground zone to a target measurement depth, the system comprising: a drill string; and A borehole assembly (BHA) connected to a downhole end of the drill string, the drill string being configured to carry drilling fluid to the BHA, and the drill string being constructed by attaching specified pipe segments in a specified sequence to an uphole end of the drill string during drilling of the borehole, with a second subset of specified pipe segments being attached to the drill string after a first subset of specified pipe segments, each pipe segment of at least the second subset having an insulating coating layer, such that when the borehole reaches the target measurement depth, the total linear thermal resistance of an uphole portion of the drill string having the second subset is at least 0.002 meter Kelvin per watt and greater than the total linear thermal resistance of a downhole portion of the drill string having the first subset. [13] System according to claim 12, wherein the specified sequence is such that when drilling the borehole to the target measurement depth, the temperature of the drilling fluid at the BHA neither substantially exceeds nor substantially falls below a target operating temperature range. [14] System according to claim 13, wherein the underground zone adjacent to the borehole is 250°C or greater, and a minimum of the target operating temperature range of the BHA is equal to or greater than 100°C. [15] System according to claim 12, wherein the pipe segments of the first subset of the specified pipe segments are pipe segments that are not coated with insulating material. [16] System according to claim 12, wherein the borehole is a lateral borehole having a heel and a tip, and wherein, when the BHA reaches the target measurement depth, the down-hole portion of the drill string comprising the first subset extends substantially down-hole from the heel to the tip. [17] System according to claim 16, wherein a large proportion of the pipe segments of the downstream area of ​​the drill string comprising the first subset is not coated with insulating material. [18] System according to claim 16, wherein a casing pipe extends substantially from the borehole head to the heel of the lateral borehole and wherein, when the BHA reaches the target measurement depth, the up-hole portion of the drill string comprising the second subset does not extend over a down-hole end of the casing pipe. [19] System according to claim 18, wherein a large proportion of the pipe segments of the hole-upward region of the drill string comprising the second subset has an insulating coating layer. [20] System according to claim 12, wherein the specified sequence is such that the ratio of pipe segments having an insulating coating layer to pipe segments without an insulating coating layer increases when drilling the borehole to the target measurement depth. [21] System according to claim 12, wherein the length-related thermal resistance of the upstream portion of the drill string comprising the second subset is at least 0.008 meter Kelvin per watt. [22] System according to claim 12, wherein the length-related thermal resistance of the upstream portion of the drill string comprising the second subset is at least 0.01 meter Kelvin per watt. [23] Method for drilling a borehole in an underground zone to a target measurement depth, the method comprising: Selecting a specified deviation of the thermal resistance of the drill string along its length such that, when drilling the borehole through the drill string in an underground zone towards and then reaching the target measurement depth, the temperature of the drilling fluid at a borehole assembly to which the drilling fluid is conveyed by the drill string neither substantially exceeds nor substantially falls below a target operating temperature range; and Drilling the borehole with a drill string, wherein the drill string is built up during the drilling of the borehole to have the specified variation in thermal resistance along its length.

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