Hybrid in-situ shimoiwa drilling

Abstract

To provide suitable hybrid excavation Shimoiwa.SOLUTION: A method for utilizing a millimeter wave drilling apparatus (300) is provided. The method can include monitoring a permeability of a first portion of a borehole of a well while forming the borehole using a drilling apparatus including a drill bit for mechanically removing material from within the borehole. The method can also include determining to utilize a millimeter wave drilling apparatus including a waveguide (430) configured for insertion into the borehole based at least on the permeability of the borehole being below a permeability threshold. The method can further include, in response to the determining, forming a second portion of the borehole utilizing the millimeter wave drilling apparatus. A method for controlling downhole pressure of a well is also provided. An associated system for performing the method is also provided.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority under 35 U.S.C. § 119 to U.S. Patent Application No. 17 / 090,410, filed November 5, 2020, now U.S. Patent No. 11,028,648, issued June 8, 2021, entitled "Basement Rock Hybrid Drilling," the entire contents of which are expressly incorporated herein by reference in their entirety.

[0002] The subject matter described herein relates to drilling of subsurface formations, including conventional drilling and other techniques such as millimeter wave drilling and thermal drilling. [Background technology]

[0003] Conventional drilling, such as rotary drilling, can be used to form well boreholes so that natural resources, such as oil and gas, can be accessed within subsurface formations. Conventional drilling can be limited to accessing formations at shallow subsurface depths and can be less effective at penetrating deeper formations, which can include harder, less permeable rocks. Dense rock formations at greater depths, which are often under higher temperatures and pressures than rocks present at shallower depths, can be more efficiently accessed utilizing unconventional drilling techniques, such as thermal drilling and / or millimeter wave drilling. Summary of the Invention [Means for solving the problem]

[0004] In one aspect, a method for utilizing a millimeter wave drilling rig is provided. In one embodiment, the method can include monitoring the permeability of a first portion of a borehole of a wellbore while forming the borehole using a drilling rig including a drill bit for mechanically removing material from within the borehole. The method can also include determining, based on at least the permeability of the borehole being below a permeability threshold, to utilize a millimeter wave drilling rig including a waveguide configured for insertion into the borehole. The method can further include, in response to the determination, forming a second portion of the borehole using the millimeter wave drilling rig.

[0005] In another embodiment, monitoring the permeability of the first portion of the borehole may include determining the permeability of the first portion of the borehole based on rock porosity and / or fluid saturations measured within the borehole.

[0006] In another embodiment, the drilling rig may be configured to perform a drilling method selected from rotary drilling, percussion drilling, agitation drilling, or diamond drilling.

[0007] In another embodiment, the method may further include monitoring a temperature within the first portion of the borehole and performing a determination further based on the temperature of the borehole exceeding a temperature threshold.

[0008] In another embodiment, the method may further include monitoring a penetration rate of a drill bit of the drilling rig and performing a determination further based on the penetration rate of the drill bit of the drilling rig being below a penetration threshold.

[0009] In another embodiment, the method may further include monitoring a hardness of material present within the first portion of the borehole and performing a determination further based on the hardness of the material exceeding a hardness threshold.

[0010] In another embodiment, the method may further include monitoring a temperature within the first portion of the borehole, a penetration rate of the drill bit of the drilling rig, and a hardness of the material present within the first portion of the borehole, and performing a determination further based on two or more of the temperature within the first portion of the borehole, the penetration rate of the drill bit of the drilling rig, and the hardness of the material present within the first portion of the borehole exceeding a temperature threshold, falling below a penetration threshold valve rate, and / or exceeding a hardness value threshold, respectively.

[0011] In another embodiment, the millimeter wave drilling rig and waveguide are operated to form the second portion of the borehole to a depth greater than the depth limit of the drilling rig. The depth may be between 5,001 meters and 35,000 meters. The depth limit may be between 4,000 meters and 5,000 meters.

[0012] In another embodiment, the monitoring may be performed using a first data processor, and the determining may be performed using the first data processor, a second data processor, or a combination of the first data processor and the second data processor.

[0013] In another aspect, a method for controlling downhole pressure in a wellbore is provided. In one embodiment, the method can include monitoring downhole pressure in the wellbore during formation of a borehole in the wellbore using a millimeter-wave drilling rig including a waveguide configured for insertion into the borehole. The monitoring can include determining the downhole pressure. The downhole pressure can include an amount of pressure present at the bottom of the wellbore. The method can also include determining a lithostatic pressure of rock surrounding the wellbore at the bottom of the wellbore. The method can further include controlling the downhole pressure relative to the lithostatic pressure of rock surrounding the wellbore at the bottom of the wellbore.

[0014] In another embodiment, the method for controlling downhole pressure can include measuring a pressure of fluid delivered into and / or extracted from the borehole. The method can also include determining the downhole pressure of the wellbore using one or more of the pressure of the fluid delivered into the borehole, the pressure of the fluid extracted from the borehole, the downhole pressure determined when a drilling rig including the drill bit is used to form a portion of the wellbore, a measure of the energy input delivered to the millimeter wave drilling rig, and / or a depth of the bottom of the wellbore. Determining the downhole pressure of the wellbore can further include using at least one physical model related to one or more of the downhole pressure determined when a drilling rig including the drill bit is used to form a portion of the wellbore, the measure of the energy input delivered to the millimeter wave drilling rig, and the depth of the bottom of the wellbore.

[0015] In another embodiment, a method for controlling downhole pressure can include controlling one or more of an operation of a gas compressor disposed at a surface and configured to supply gas into a borehole of a well, an input valve position of the gas compressor, an output valve position of the gas compressor, and / or a flow rate of gas supplied by the gas compressor. The flow rate of the gas can be between 0.5 m / s and 50 m / s.

[0016] In another aspect, a millimeter wave drilling rig system is provided. In one embodiment, the system can include a drilling rig including a drill bit for mechanically removing material while forming a first portion of a borehole of a well. The first portion of the borehole can be formed while monitoring the permeability of the first portion of the borehole. The system can also include a millimeter wave drilling rig including a gyrotron configured to inject millimeter wave radiant energy into a second portion of the borehole of the well via a waveguide. The second portion of the borehole can be formed via the millimeter wave drilling rig in response to determining that the permeability of the first portion of the borehole is below a permeability threshold.

[0017] In another embodiment, the drilling rig may be configured to perform a drilling method selected from rotary drilling, percussion drilling, agitation drilling, or diamond drilling.

[0018] In another embodiment, a first portion of the borehole may be formed while monitoring the temperature within the first portion of the borehole, and a second portion of the borehole may be formed via the millimeter wave drilling rig in response to determining that the temperature within the first portion of the borehole exceeds a temperature threshold.

[0019] In another embodiment, a first portion of the borehole can be formed while monitoring the penetration rate of the drill bit of the drilling rig, and a second portion of the borehole can be formed via the millimeter wave drilling rig in response to determining that the penetration rate of the drill bit of the drilling rig is below a penetration rate threshold.

[0020] In another embodiment, a first portion of the borehole may be formed while monitoring the hardness of the material present in the first portion of the borehole, and a second portion of the borehole may be formed via the millimeter wave drilling rig in response to determining that the hardness of the material exceeds a hardness threshold.

[0021] In another embodiment, the first portion of the borehole may be formed while monitoring the temperature within the first portion of the borehole, the penetration rate of the drill bit of the drilling rig, and the hardness of the material present within the first portion of the borehole, and the second portion of the borehole may be formed via the millimeter wave drilling rig in response to determining two or more of the temperature within the first portion of the borehole, the penetration rate of the drill bit of the drilling rig, and the hardness of the material present within the first portion of the borehole exceed a temperature threshold, fall below a penetration rate threshold, and / or exceed a hardness threshold, respectively.

[0022] In another embodiment, the millimeter wave drilling rig and waveguide are operated to form the second portion of the borehole to a depth greater than the depth limit of the drilling rig. The depth may be between 5,001 meters and 35,000 meters. The depth limit may be between 4,000 meters and 5,000 meters.

[0023] In another embodiment, the system can include a data processor coupled to the drilling rig and the millimeter wave drilling rig. The data processor can be configured to perform the monitoring and the determination.

[0024] In another aspect, a system for controlling downhole pressure in a wellbore is provided. In one embodiment, the system can include a millimeter wave drilling rig including a gyrotron configured to inject millimeter wave radiant energy into a borehole of the wellbore via a waveguide configured to be inserted into the borehole. The borehole can be formed via the millimeter wave drilling rig and can have a downhole pressure monitored at the bottom of the wellbore. The system can also include a compressor fluidly coupled to the borehole and configured to control the downhole pressure via gas supplied into and / or received from the borehole. The compressor can be configured to control the downhole pressure relative to a lithostatic pressure determined for rock surrounding the wellbore at the bottom of the wellbore.

[0025] In another embodiment, the downhole pressure can be monitored by measuring the pressure of at least the fluids supplied to and / or extracted from the borehole. The downhole pressure of a well can be determined using one or more of the pressure of the fluids supplied to the borehole, the pressure of the fluids extracted from the borehole, the downhole pressure determined when a drilling rig including a drill bit is used to form a portion of the well, a measure of the energy input supplied to the millimeter wave drilling rig, and / or the depth of the bottom of the well.

[0026] In another embodiment, the downhole pressure of the wellbore can be controlled based on one or more of the pressure of fluid supplied into the borehole, the pressure of fluid received from the borehole, the downhole pressure determined when a drilling rig including the drill bit is used to form a portion of the wellbore, a measure of the energy input supplied to the millimeter wave drilling rig, and / or the depth of the bottom of the wellbore. In another embodiment, the downhole pressure can be further controlled based on a physical model related to one or more of the downhole pressure determined when a drilling rig including the drill bit is used to form a portion of the wellbore, the measure of the energy input supplied to the millimeter wave drilling rig, and the depth of the bottom of the wellbore. In another embodiment, the downhole pressure of the wellbore can be further controlled based on controlling one or more of the operation of a compressor, the output valve position of the compressor, and / or the flow rate of gas supplied by the compressor. The flow rate of the gas can be between 0.5 m / s and 50 m / s. The present specification also provides, for example: (Item 1) monitoring the permeability of a first portion of the borehole of a wellbore while forming the borehole using a drilling rig including a drill bit for mechanically removing material from within the borehole; determining, based at least on the permeability of the borehole being below a permeability threshold, to utilize a millimeter wave drilling rig including a waveguide configured for insertion into the borehole; responsive to said determining, utilizing said millimeter wave drilling tool to form a second portion of said borehole; and A method comprising: (Item 2) 2. The method of claim 1, wherein monitoring the permeability of the first portion of the borehole comprises determining the permeability of the first portion of the borehole based at least on rock porosity and / or fluid saturation measured within the borehole. (Item 3) 3. The method of claim 1 or 2, wherein the drilling rig is configured to perform a drilling method selected from rotary drilling, percussion drilling, agitation drilling, or diamond drilling. (Item 4) monitoring a temperature within the first portion of the borehole; and making the determination further based on the temperature of the borehole exceeding a temperature threshold; 4. The method of any one of items 1 to 3, further comprising: (Item 5) monitoring the penetration rate of the drill bit of the drilling rig; performing the determination further based on the penetration rate of the drill bit of the drilling rig being below a penetration rate threshold; 5. The method of any one of items 1 to 4, further comprising: (Item 6) monitoring the hardness of material present within the first portion of the borehole; 6. The method of any one of items 1 to 5, further comprising: performing the determination further based on the hardness of the material exceeding a hardness threshold. (Item 7) monitoring the temperature within the first portion of the borehole, the penetration rate of the drill bit of the drilling rig, and the hardness of material present within the first portion of the borehole; performing said determining further based on two or more of the temperature within said first portion of said borehole, the penetration rate of said drill bit of said drilling rig, and the hardness of said material present within said first portion of said borehole exceeding a temperature threshold, being below a penetration rate threshold, and / or exceeding a hardness threshold, respectively; 4. The method of any one of items 1 to 3, further comprising: (Item 8) 8. The method of any one of items 1 to 7, wherein the millimeter wave drilling rig and the waveguide are operated to form the second portion of the borehole to a depth greater than a depth limit of the drilling rig. (Item 9) 9. The method according to claim 8, wherein the depth is from 5,001 meters to 35,000 meters. (Item 10) 9. The method according to claim 8, wherein the depth limit is between 4,000 meters and 5,000 meters. (Item 11) 11. The method of any one of items 1 to 10, wherein the monitoring is performed using a first data processor and the determining is performed using the first data processor, a second data processor, or a combination of the first data processor and the second data processor. (Item 12) monitoring downhole pressure in a wellbore during formation of the borehole in the wellbore using a millimeter wave drilling rig including a waveguide configured for insertion into a borehole, the monitoring including determining the downhole pressure, the downhole pressure including an amount of pressure present at a bottom of the wellbore; determining a lithostatic pressure of rock surrounding the wellbore at the bottom of the wellbore; controlling the downhole pressure relative to the lithostatic pressure of the rock surrounding the wellbore at the bottom of the wellbore; A method comprising: (Item 13) monitoring the downhole pressure of the well; measuring the pressure of fluid supplied to and / or extracted from said borehole; determining the downhole pressure of the wellbore using one or more of the pressure of the fluid delivered into the borehole, the pressure of the fluid extracted from the borehole, a downhole pressure determined when a drilling rig including a drill bit is used to form a portion of the wellbore, a measure of energy input delivered to the millimeter wave drilling rig, and / or a depth of the bottom of the wellbore; Item 13. The method of item 12, further comprising: (Item 14) 14. The method of claim 12 or 13, wherein determining the downhole pressure of the wellbore further comprises using at least one physical model related to one or more of the downhole pressure determined when forming a portion of the wellbore using a drilling rig including a drill bit, the measure of energy input supplied to the millimeter wave drilling rig, and the depth of the bottom of the wellbore. (Item 15) 15. The method of any one of items 12 to 14, wherein controlling the downhole pressure further comprises controlling one or more of operation of a gas compressor disposed at a surface of the wellbore and configured to supply gas into the borehole of the wellbore, an input valve position of the gas compressor, an output valve position of the gas compressor, and / or a flow rate of the gas supplied by the gas compressor. (Item 16) 16. The method according to any one of items 12 to 15, wherein the flow rate of the gas is between 0.5 m / s and 50 m / s. (Item 17) a drilling rig including a drill bit for mechanically removing material while forming a first portion of a borehole of a well, the first portion of the borehole being formed based on a permeability of the first portion of the borehole; a millimeter wave drilling rig including a gyrotron configured to inject millimeter wave radiant energy into a second portion of the borehole of the wellbore via a waveguide, the second portion of the borehole being formed via the millimeter wave drilling rig in response to determining that the permeability of the first portion of the borehole is less than a permeability threshold; A system comprising: (Item 18) Item 18. The system of item 17, wherein the drilling rig is configured to perform a drilling method selected from rotary drilling, percussion drilling, agitation drilling, or diamond drilling. (Item 19) 19. The system of claim 17 or 18, wherein the first portion of the borehole is formed while monitoring a temperature within the first portion of the borehole, and the second portion of the borehole is formed via the millimeter wave drilling rig in response to determining that the temperature within the first portion of the borehole exceeds a temperature threshold. (Item 20) 20. The system of any one of claims 17 to 19, wherein the first portion of the borehole is formed while monitoring a penetration rate of the drill bit of the drilling rig, and the second portion of the borehole is formed via the millimeter wave drilling rig in response to determining that the penetration rate of the drill bit of the drilling rig is below a penetration rate threshold. (Item 21) 21. The system of any one of claims 17 to 20, wherein the first portion of the borehole is formed while monitoring a hardness of material present in the first portion of the borehole, and wherein the second portion of the borehole is formed via the millimeter wave drilling rig in response to determining that the hardness of the material exceeds a hardness threshold. (Item 22) 22. The system of any one of claims 17 to 21, wherein the first portion of the borehole is formed while monitoring a temperature within the first portion of the borehole, a penetration rate of the drill bit of the drilling rig, and a hardness of material present in the first portion of the borehole, and wherein the second portion of the borehole is formed via the millimeter wave drilling rig in response to determining two or more of the temperature within the first portion of the borehole, the penetration rate of the drill bit of the drilling rig, and the hardness of the material present in the first portion of the borehole exceed a temperature threshold, fall below a penetration rate threshold, and / or exceed a hardness threshold, respectively. (Item 23) 23. The system of any one of items 17 to 22, wherein the millimeter wave drilling rig and the waveguide are operated to form the second portion of the borehole to a depth greater than a depth limit of the drilling rig. (Item 24) 24. The system of claim 23, wherein the depth is between 5,001 meters and 35,000 meters. (Item 25) 24. The system of claim 23, wherein the depth limit is between 4,000 meters and 5,000 meters. (Item 26) 26. The system of any one of items 17 to 25, further comprising a data processor coupled to the drilling rig and the millimeter wave drilling rig, the data processor configured to perform the monitoring and the determining. (Item 27) a millimeter wave drilling rig including a gyrotron configured to inject millimeter wave radiant energy into a borehole of a well via a waveguide configured to be inserted into the borehole, the borehole being formed via the millimeter wave drilling rig and having a downhole pressure monitored at a bottom of the well; a compressor fluidly coupled to the borehole and configured to control the downhole pressure via gas supplied into and / or received from the borehole, the compressor configured to control the downhole pressure relative to a lithostatic pressure determined for rock surrounding the wellbore at the bottom of the wellbore; A system comprising: (Item 28) 28. The system of claim 27, wherein the downhole pressure is monitored by measuring the pressure of at least fluids supplied into and / or extracted from the borehole and determining the downhole pressure in the well using one or more of the pressure of the fluids supplied into the borehole, the pressure of the fluids extracted from the borehole, a downhole pressure determined when a drilling rig including a drill bit is used to form a portion of the well, a measure of energy input supplied to the millimeter wave drilling rig, and / or a depth of the bottom of the well. (Item 29) 29. The system of claim 27 or 28, wherein the downhole pressure of the well is controlled based on one or more of the pressure of the fluid supplied into the borehole, the pressure of the fluid received from the borehole, the downhole pressure determined when a drilling rig including a drill bit is used to form a portion of the well, a measure of energy input supplied to the millimeter wave drilling rig, and / or a depth of the bottom of the well. (Item 30) 30. The system of any one of items 27 to 29, wherein the downhole pressure of the wellbore is further controlled based on a physical model related to one or more of the downhole pressure determined when a drilling rig including a drill bit is used to form a portion of the wellbore, a measure of energy input supplied to the millimeter wave drilling rig, and a depth of the bottom of the wellbore. (Item 31) The devices, systems, methods, and articles described and / or illustrated herein.

[0027] These and other features will be more readily understood from the following detailed description taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a flowchart illustrating one exemplary embodiment of a method for forming a portion of a borehole using millimeter wave drilling equipment and systems described herein.

[0029] [Figure 2] 1 is a flow chart illustrating one exemplary embodiment of a method for controlling downhole pressure in a well formed using the millimeter wave drilling rigs and systems described herein.

[0030] [Figure 3] FIG. 3 illustrates an exemplary embodiment of a millimeter wave drilling system configured to perform the methods of FIGS. 1 and 2 described herein.

[0031] [Figure 4] FIG. 1 shows a cross-sectional view of a borehole containing a metallic waveguide for low-loss transmission of millimeter-wave radiation.

[0032] [Figure 5] FIG. 1 illustrates an exemplary embodiment of a hybrid drilling approach using a millimeter wave drilling system as described herein.

[0033] [Figure 6] FIG. 10 shows a plot of penetration rates achievable using the millimeter wave drilling system described herein.

[0034] [Figure 7] FIG. 1 illustrates a hybrid drilling approach using an operating millimeter wave drilling system as described herein. [Figure 8] FIG. 1 illustrates a hybrid drilling approach using an operating millimeter wave drilling system as described herein. [Figure 9] FIG. 1 illustrates a hybrid drilling approach using an operating millimeter wave drilling system as described herein. [Figure 10] FIG. 1 illustrates a hybrid drilling approach using an operating millimeter wave drilling system as described herein. [Figure 11] FIG. 1 illustrates a hybrid drilling approach using an operating millimeter wave drilling system as described herein. [Figure 12] FIG. 1 illustrates a hybrid drilling approach using an operating millimeter wave drilling system as described herein.

[0035] [Figure 13]FIG. 1 shows plots of penetration rates achievable using conventional drilling systems and methods and the millimeter wave drilling system described herein. [Figure 14] FIG. 1 illustrates a hybrid drilling approach using an operating millimeter wave drilling system as described herein.

[0036] It should be noted that the drawings are not necessarily to scale. The drawings are intended to depict only typical aspects of the subject matter disclosed herein, and therefore should not be considered as limiting the scope of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0037] Conventional drilling can be used to form a borehole for a well to access natural resources that may exist within subsurface formations surrounding or near the borehole. Conventional drilling can include rotary drilling, hammer drilling, and / or a combination of rotary and hammer drilling. Conventional drilling can use liquids, such as mud or water, and / or gases, such as air or foam, for cleaning and cooling during drilling. Conventional drilling can be used to form boreholes in soft, porous rock and can include the use of rotary drill bits, such as polycrystalline diamond bits, roller cones, and high-pressure liquid jets. Conventional drilling can utilize rotary drilling rigs to cut or grind the rock during borehole formation. The cut or ground rock can be removed via a fluid delivered into the borehole, lifting the cut or ground material out of the borehole. Conventional drilling can achieve lower penetration rates, limited at greater borehole depths, due to the increased temperature and hardness of the rock present at greater borehole depths. The ability to transmit power from the surface to the bottom of the borehole can also limit the penetration rates that can be achieved using conventional drilling in deep boreholes.

[0038] Thermal drilling, such as millimeter wave drilling (MMWD), can achieve greater penetration rates by delivering large amounts of radiant energy into the borehole in combination with pressure to melt or vaporize rock. MMWD can be advantageous compared to conventional drilling because it reduces or eliminates the need to physically remove cut, crushed, or ground rock. Instead, the rock vaporizes into very small particles or melts. Higher penetration rates can be achieved using MMWD compared to conventional drilling because the abundance of applied thermal energy is more effective at penetrating rock compared to the rotary mechanical action of conventional drilling. Therefore, MMWD can be beneficial for creating deeper wells to access natural resources or hot, dry rock that may reside at greater depths below the surface.

[0039] Determining when to switch from conventional drilling to thermal drilling, such as millimeter wave drilling, can be difficult to determine, and errors in this decision can be costly and dangerous. Accurately identifying when to transition from conventional drilling to millimeter wave drilling can be important for maintaining cost-effective penetration rates during borehole formation. For example, conventional drilling can be used to form the first portion of a borehole down to a depth where the penetration rate of conventional drilling equipment slows due to the hardness of the rock and / or the presence of high temperatures. Performing conventional drilling at greater depths can require additional time, personnel, and equipment to monitor and perform the conventional drilling, which can increase the costs and risks associated with forming a borehole at greater depths compared to non-conventional drilling, such as MMWD.

[0040] Thus, some implementations of the present subject matter can provide a technique for determining when to switch from conventional drilling to utilize a millimeter wave drilling device. Because millimeter wave drilling elongates the borehole by using thermal heating (e.g., millimeter waves heat the rock), if the material is permeable, it can allow liquid (e.g., water) to penetrate the porous material and seep into the borehole. Additional liquid in the borehole can interfere with the millimeter wave drilling system by cooling the borehole. In other words, the millimeter waves vaporize the liquid (e.g., water) rather than the borehole rock. This can also increase the risk of a blowout. Thus, some implementations of the present subject matter include monitoring or estimating the permeability of the borehole while utilizing a rotary drilling technique and determining to use a millimeter wave device when the permeability of the rock at the bottom of the borehole falls below a permeability threshold. The monitoring can be direct or indirect; for example, it can be difficult to directly monitor (e.g., measure) permeability in low-permeability zones. As a result, in some implementations, permeability can be inferred from other measurements, such as rock porosity, which can be more easily determined using several existing tools.

[0041] In some implementations, the temperature and / or hardness of the rock at the bottom of the borehole can be monitored during conventional drilling, and the decision to switch to MMWD can be further based on the temperature and / or hardness of the rock. By making the decision to switch to MMWD based on the permeability, temperature, and / or hardness of the rock rather than the costs associated with drilling, some implementations of the present subject matter can provide a decision to switch to thermal drilling, such as MMWD, in that the overall operation of the MMWD is improved, thus resulting in an improved approach to drilling.

[0042] In some implementations, during millimeter wave drilling, control of the wellbore must be maintained to prevent collapse of the wellbore. For example, conventional drilling techniques can use fluids (e.g., mud) to lubricate and control downhole pressure, and can use metal casing and cement to support the borehole (e.g., to prevent collapse). Mud weight and a filter cake formed by the mud around the wellbore wall can prevent collapse. Metal casing can be inserted after drilling and cemented in place to maintain wellbore stability. However, fluids (e.g., mud) may not be transparent to millimeter waves. As temperatures in the borehole increase, installing the casing and cementing can become increasingly difficult. While millimeter wave drilling can utilize gas, low pressure can cause the wellbore to collapse. Thus, some implementations of the present subject matter include using a millimeter wave drilling rig to monitor downhole pressure in a wellbore during borehole formation in the wellbore, determining the lithostatic pressure of the rock surrounding the wellbore at the bottom of the wellbore, and controlling the downhole pressure relative to the lithostatic pressure of the rock surrounding the wellbore at the bottom of the wellbore. By controlling the downhole pressure using the managed pressure drilling techniques described herein, the downhole pressure can be controlled relative to the lithostatic pressure of the rock so that wellbore control can be maintained and wellbore collapse can be prevented or suppressed. In addition to controlling the pressure to prevent wellbore collapse, the pressure can be controlled to reach lithostatic pressure or fracturing pressure. Controlling the pressure to reach or exceed lithostatic pressure can enable equilibrium or over-equilibrium conditions. Also, controlling the pressure to reach fracturing pressure can enable the melt produced by the MMWD process to be forced into the formation instead of returning condensed rock particles to the surface.

[0043] The managed pressure drilling techniques described herein may be advantageous compared to other pressure drilling techniques that can create over-balanced pressure conditions within a closed volume of the wellbore. The managed pressure drilling techniques described herein can be used in an open volume system. The open volume system can be configured to actively circulate fluid and / or gas from the surface down the wellbore to the cutting front and back to the surface. Actively circulating the fluid and / or gas helps cool and lubricate drilling components and can transport cuttings to the surface. The direction of active circulation can be normal or reverse. In normal circulation, the fluid and / or gas is supplied to the wellbore through a waveguide and back through the wellbore annulus. In reverse circulation, the fluid and / or gas is supplied to the wellbore through the wellbore annulus and back from the wellbore through a waveguide. In contrast, a closed volume system creates a flow restriction along the circulation path. For example, a complete or partial blockage of flow can be used to manage downhole pressure. A closed volume system can be used to implement the managed pressure drilling techniques described herein. In a closed volume system, the pressure within the closed loop of the closed volume system can be higher at each point in the circulation path compared to an open volume system.

[0044] Improved systems and methods for performing hybrid MMWD to form a well borehole are described herein. The hybrid MMWD systems and methods can provide advantages that may be difficult to achieve using only conventional drilling or MMWD to form the entire borehole. For example, conventional drilling can be efficiently performed in shallow subsurface rock formations at depths of 0 km to 3 km, where the rock is softer, shallower, and / or has lower mechanical specific energy. For example, the mechanical specific energy of conventionally drilled rock is approximately 100 Joules / cm. 3 whereas the specific mechanical energy to melt rock is about 5000 Joules / cm 3 The specific mechanical energy required to vaporize the rock is approximately 12,000 Joules / cm3 The rock may be at or beyond 5 km depth. At depths greater than 5 km, conditions may favor the use of MMWD. Drilling a well deeper than 5 km using conventional drilling techniques may take longer than if the well were drilled using the hybrid MMWD systems and methods described herein.

[0045] As rock hardness, permeability, and borehole temperature increase at greater depths, penetration rates can slow, potentially increasing the cost of continuing conventional drilling operations. The mechanical efficiency of conventional drilling at greater depths and in less permeable rock can decrease due to increased wear on the drill bit and increased friction and torque transmission required to penetrate the rock. Rotary drill bits can wear out more quickly under these conditions. The costs and workflow associated with maintaining a borehole can also increase at depth using conventional drilling. For example, larger, more expensive, and shallower borehole casings may be required to accommodate the larger-sized drill bits required to form boreholes at greater depths.

[0046] Borehole temperatures can also affect when to switch from conventional drilling to MMWD. For example, depths where borehole temperatures can exceed 260°C can be problematic for electronic components used in conventional drilling. Additionally, at depths where these temperature conditions may exist, high-temperature fluid breakdown can reduce the mud's rising and cooling characteristics. Conventional drilling at these depths and temperatures can utilize drill bits rated to 300°C, which can require operators to circulate the mud at high speeds in a constant manner.

[0047] While MMWD is more efficient at forming boreholes in less permeable and / or harder rocks at higher temperatures and greater depths, it may be less advantageous for forming the initial portion of a borehole near the surface due to the low specific mechanical energy required for shallow rock formation, at least in shallow rock formations. For example, MMWD delivers a large amount of radiant energy into the borehole to melt or vaporize the rock. MMWD systems include a millimeter-wave generator called a gyrotron and utilize a waveguide to form and direct the energy into the borehole. Deploying such systems to form the entire borehole to significant depths is not always cost-effective or mechanically efficient for adequately removing certain types of rock present in the initial portion of the borehole. For example, in shallow subsurface formations where the initial portion of a borehole can be formed, the rock may contain limestone, which cannot be effectively vaporized or melted using MMWD. The hybrid MMWD systems and methods described herein can utilize conventional drilling and subsequent MMWD to form boreholes to greater depths than conventional drilling alone and can provide greater penetration rates when rock permeability and / or rock hardness decreases and / or borehole temperatures or pressures increase, such as those present in deeper subsurface formations of rock.

[0048] FIG. 1 is a flowchart illustrating one exemplary embodiment of a method 100 for forming a portion of a borehole using the millimeter wave drilling rig and systems described herein. In operation 105, the permeability of a first portion of the borehole is monitored while forming the borehole using a drilling rig including a drill bit for mechanically removing material from within the borehole. In some embodiments, monitoring the permeability of the first portion of the borehole may include estimating (e.g., determining) the permeability based on rock porosity and fluid saturation measured within the borehole. A model determined based on core measurements (e.g., measurements of rock porosity and fluid saturation measured within the borehole) may be used to determine the permeability of the first portion of the borehole. In some embodiments, the porosity and saturation of the borehole may be monitored instead of the permeability of the borehole. The drilling rig may be configured to perform conventional drilling, percussion drilling, agitation drilling, diamond drilling, etc. In some embodiments, the monitoring may include monitoring the temperature of the borehole, the penetration rate of a drill bit of the drilling rig, and / or the hardness of the material present within the first portion of the borehole. In some embodiments, the monitoring can be performed using a data processor, such as using a computing device configured to receive data corresponding to the permeability rate. In some embodiments, the data processor can also be configured to monitor the temperature of the borehole, the penetration rate of the drill bit, the hardness of the material, and any combination thereof.

[0049] The permeability of the first portion of the borehole can be monitored based on data related to fluids applied within and received from the borehole. For example, fluids can be supplied to and received from the borehole to remove cuttings or ground material. Fluid velocity or fluid pressure can be used to estimate the permeability of the rock surrounding the first portion of the borehole. In some embodiments, the permeability can be estimated from logging data collected during the formation of the first portion of the borehole or the borehole at different locations. The logging data can include, for example, logs from logging-while-drilling (LWD) records, which can be created by conventional drilling techniques. In some embodiments, the permeability can be monitored based on core samples sent to a laboratory for direct measurement. For example, by flowing a single-phase fluid through a core of known diameter and length, the pressure drop across the rock sample can be measured. The permeability of the core sample can be calculated using Darcy's law. In some embodiments, the permeability can be monitored by measurements using a wireline logging tool. In some embodiments, the permeability can be monitored by measurements using downhole pressure and sampling tools. In some embodiments, permeability can be monitored using drillstem testing (DST). DST can be used to determine average in-situ permeability based on transient analysis of downhole pressure. In some embodiments, permeability can be determined based on historical data derived from offset wells drilled near the well being monitored. In some embodiments, permeability can be estimated based on monitoring porosity and fluid saturations to estimate the allowable amount of ingress fluid in the borehole. In some embodiments, permeability can be monitored or determined using measurement while drilling (MWD), which can include the use of formation evaluation tools that provide reservoir information in real time or near real time.

[0050] Borehole temperatures can be monitored using one or more downhole sensors. Downhole sensors can be utilized up to approximately 300°C. Currently, "ultra-high temperature" drilling fluids are rated at 260°C or approximately 500°F, and "ultra-high temperature" motors are also rated at 260°C or approximately 500°F. Ultra-high temperature motors can operate in higher temperature zones than rotary steerable motors because they do not contain downhole electrical components. Rotary steerable systems (RSSs) and motors are typically limited to a maximum downhole temperature of 200°C due to temperature limitations associated with downhole electrical components. "High" temperature drilling fluids and motors can be rated to approximately 200°C or approximately 400°F. "Normal" temperature drilling fluids and motors can be rated to approximately 150°C or approximately 300°F. Conventional drilling can drill into high reservoir temperature zones, but may require circulating large amounts of drilling fluid to cool the borehole to stay within any temperature limits of the drilling rig.

[0051] In some embodiments, the borehole temperature can be inferred from fluid received from the borehole. In some embodiments, such as when performing MMWD, the borehole temperature can be determined using pyrometry and / or radiometry. In some embodiments, the borehole temperature can be measured while drilling, for example, using a resistance temperature detector (RTD) or fiber optic sensor. In some embodiments, the borehole temperature can be measured using a wireline logging tool. In some embodiments, the borehole temperature can be determined based on historical data. In some implementations, the temperature can be determined by analyzing LWD records. In some embodiments, the RSS tool can monitor the control unit temperature. In some embodiments, the temperature can be monitored at the drill bit using a memory gauge. In some embodiments, the borehole temperature can be monitored using an RTD while logging while drilling. Other approaches are possible.

[0052] The rate of penetration (ROP) of a drilling rig's drill bit can be monitored using one or more sensors configured on or associated with the drilling rig, including the drill bit. In some implementations, ROP can be determined by analyzing LWD recordings. In some implementations, ROP may not be the only metric used in determining when to switch to using the hybrid MMWD systems and methods described herein. For example, ROP can be reduced due to a variety of issues, all of which can be related to the RSS, motor, and drill bit, and how these components dynamically operate. ROP can also be reduced due to the presence of a hard rock layer in one location, followed by a softer, more permeable rock layer. Key factors affecting ROP include rock depth, rock porosity, rock permeability, downhole temperature, and specific mechanical energy. Because integrating accelerometers into the downhole environment can produce poor results, it is typically necessary to monitor ROP from the surface, such as at a block location. Measurement while drilling (MWD) can utilize accelerometers and magnetometers to provide the spatial orientation of the bottom hole assembly (BHA) from which ROP can be determined.

[0053] Effective ROP (EROP) can be the ROP that accounts for the amount of time not spent deepening the borehole. For example, EROP can include the time required to remove and replace a worn drill bit. Because MMWD does not require replacing worn drill bits or BHA components, MMWD does not require such extra time. As a result, the amount of non-productive time (NPT) spent on forming the borehole can be reduced, and the EROP, i.e., time to target depth, can be significantly shorter than conventional drilling. Furthermore, boreholes formed via MMWD may be vitrified and do not require the application of casing or cement therein. This can further reduce the amount of NPT and increase the EROP. In some embodiments, the hybrid MMWD systems and methods described herein can achieve an EROP of approximately 1 mm / sec. Accordingly, some exemplary implementations of the hybrid MMWD systems and methods described herein can achieve depths of approximately 10 km in 100 days of drilling.

[0054] The hardness of the material present in the first portion of the borehole can be monitored based on the velocity of the fluid exiting the borehole. In some embodiments, the hardness of the material can be inferred or measured from data related to the permeability of the first portion of the borehole. In some embodiments, the hardness of the material can be inferred or measured from analysis of rock cuttings. For example, the rock type can indicate the hardness of the rock. In some embodiments, the hardness of the material can be inferred or measured using a logging tool. Logging tool measurements can be taken while drilling or using a wireline tool, such as a through-bit logging configuration. In some embodiments, the hardness of the material can be inferred or measured from the frequency at which a worn drill bit changes. In some embodiments, the hardness of the material can be inferred or measured from direct measurement of a core sample. In some embodiments, the hardness of the material can be inferred or measured from historical data. In some embodiments, the hardness of the material can be inferred or measured from the amount of surface torque or downhole torque, the weight of the drill bit, the ROP, and / or the revolutions per minute (RPM) of the drill bit. Excessive vibration and low ROP may indicate harder material. In some embodiments, at-bit or in-bit logging tools can provide weight-on-bit (WOB), downhole WOB (DWOB), torque-on-bit (TOB), and / or downhole TOB (DTOB) data from which hardness can be inferred. Additionally, MWD tools can provide formation evaluation data from which rock formation type and corresponding rock hardness can be inferred.

[0055] Based on the foregoing measurements and / or data, a proxy measurement corresponding to the hardness of the material can be calculated. In some embodiments, the proxy measurement can include apparent formed strength. For example, apparent formed strength can be calculated as (DWOB*RPM) / (ROP*Depth). In some embodiments, the proxy measurement can include a measurement of digging specific energy. For example, digging specific energy can be calculated as ((DWOB*RPM) / (Depth)). 2 *ROP)). In some embodiments, the proxy measurement may include a measure of the mechanical work required to break a unit volume of rock.

[0056] In operation 110, a decision may be made to utilize an MMWD device including a waveguide configured for insertion into the borehole. The decision may be made based at least on the borehole's permeability falling below a permeability threshold. For example, the decision to switch to the MMWD device may be made based on determining the permeability of the borehole and determining a decrease in the permeability of the rock surrounding the borehole as the drilling rig drills deeper. In some implementations, the decision may be made by a first data processor of a first computing device associated with the monitoring performed in operation 105, a second data processor associated with a second computing device located remotely from the data processor and computing device from which the monitoring data is received, or a combination of the first and second data processors. In some embodiments, the decision may be made based on an inferred borehole permeability rather than a borehole permeability measured directly in the borehole.

[0057] The permeability threshold can be a value determined from previous borehole formations. In some embodiments, the permeability threshold can be determined based on geological surveys that identify the subsurface formations and rock composition present in the region of the well borehole. The threshold permeability value is used to determine if fluid inflow is too high for the amount of energy available for drilling. 3 / s or equivalent units. For example, since MMWD can heat all material downhole, a ROP of 1 mm / s in an 8 inch diameter borehole is 25,000 Joules / cm 3 Assuming the total energy required to vaporize 0.0000324m of rock, 3 / s(3.24E-5m 3 / s). If fluid were flowing into the borehole at the same rate, the ROP would be zero. In this example, the ROP is canceled because the energy generated via MMWD is transferred to the inflowing fluid rather than the rock formation. Thus, the threshold permeability value can be a function of permeability, the difference between lithostatic pressure and wellbore pressure, and the desired ROP. In some embodiments, the permeability threshold can be a value between 1.0 microdarcy (uD) and 10.0 millidarcy (mD).

[0058] In some embodiments, operation 110 may also include determining to utilize the MMWD device based on the monitored temperature of the borehole exceeding a temperature threshold. In some embodiments, the temperature threshold may be determined as a function of the type of conventional drilling equipment used. For example, the maximum temperature may be related to the temperature rating of the equipment. The temperature rating of equipment including electronics within the drilling rig may be limited to 260°C, and the temperature rating of the drilling rig's motor lining may be limited to 150°C. As a result, the maximum temperature may be determined by the lowest temperature of the two.

[0059] For non-geothermal wells, the well is formed without RSS using geosteering. In this way, the well can be drilled deeper but may not be truly vertical. As a result, the transition to MMWD may be suboptimal. If RSS is used to form the initial portion of the borehole, the RSS should be operated in tilt-holding mode to minimize any vertical deviation of the borehole formation. In some implementations, the borehole formed by rotary drilling is nearly vertical to improve MMWD performance, and the use of RSS or similar technology can enable a more vertical borehole compared to some boreholes formed by rotary drilling, which may appear helical.

[0060] In some embodiments, operation 110 may also include determining to utilize an MMWD device based on an effective penetration rate of the drill bit of the drilling rig being below a penetration rate threshold. In some embodiments, the penetration rate threshold may be determined based on geological surveys identifying the subsurface formations and rock composition present in the region of the well borehole. In some embodiments, the penetration rate threshold may be determined based on historical data. In some embodiments, the penetration rate threshold may be determined based on modeling and simulation data of expected EROP from known formation types for both rotary and MMWD systems and / or methods. In some embodiments, the effective penetration rate threshold may be between 0.5 and 2.0 mm / s.

[0061] In some embodiments, operation 110 may also include determining to utilize the MMWD device based on the monitored hardness of the material present in the first portion of the borehole exceeding a hardness threshold. In some embodiments, the hardness threshold may be determined based on a geological survey identifying the composition of the subsurface formations and rock present in the region of the well borehole. In some embodiments, the hardness threshold may be determined based on an analysis of cuttings removed from the borehole and an analysis of the drill bit when the drill bit is replaced. In some embodiments, the hardness threshold may be determined based on a correlation between the ROP, the weight of the drill bit, and the torque applied to the drill bit. In some embodiments, the hardness threshold may be a value between 4 and 6 as measured on the Mohs hardness scale. In some embodiments, the hardness threshold may be a value exceeding 100 MPa compressive strength of the rock. In some embodiments, the hardness threshold may correspond to an amount of downhole torque or specific mechanical energy.

[0062] In operation 115, a second portion of the borehole can be formed utilizing the MMWD apparatus in response to the determination. The MMWD apparatus can be configured to form the second portion of the borehole once it is determined that the conventional drilling rig is no longer achieving sufficient progress to form the borehole relative to the various thresholds used in operation 110. Forming the second portion of the borehole using the MMWD apparatus can be advantageous based on a more robust analysis of geophysical variables associated with conventional drilling operations, such as the permeability, temperature, borehole hardness, and penetration rate of the conventional drilling rig, rather than solely based on the monetary cost of operating the conventional drilling rig. In this manner, the decision to change from a conventional drilling rig to an MMWD apparatus can be made in a more accurate manner, which can result in cost savings, higher penetration rates, and safer drilling operations, than a decision to change from a conventional drilling rig to an MMWD apparatus based solely on cost. The decision to change from a conventional drilling rig to an MMWD apparatus can also reduce or eliminate well completion steps that require the installation of casing and cement. Before switching to the MMWD apparatus, the well can be cased and cemented, and the mud can be replaced with gas configured for use in the MMWD.

[0063] FIG. 2 is a flowchart illustrating one exemplary embodiment of a method 200 for controlling downhole pressure in a wellbore formed using the millimeter wave drilling equipment and systems described herein. Controlling downhole pressure during borehole formation can be important to ensure the structural stability of the borehole and manage fluid inflow into the borehole. It may be desirable to maintain a pressure at the bottom of the borehole sufficient to prevent hole collapse. In some cases, the amount of sufficient pressure can be less than the lithostatic pressure of the surrounding rock. In some cases, the amount of sufficient pressure can be greater than the lithostatic pressure of the rock surrounding the borehole. For example, downhole pressure is controlled to be greater than the lithostatic pressure, which can enhance rock fracturing and force particulate matter from molten or vaporized rock into fractures in the surrounding rock. In some embodiments, wellbore pressure can be at least 2*rock density*gravity*depth-rock compressive strength. In some embodiments, wellbore pressure is not required. For example, at lower depths, the rock has sufficient capacity to support itself.

[0064] In operation 205, a MMWD device including a waveguide configured for insertion into the borehole is used to monitor downhole pressure in the well during borehole formation in the well. The monitoring can include determining the downhole pressure in the borehole. The downhole pressure in the borehole can include the amount of pressure present at the bottom of the well or borehole. The downhole pressure in the well or borehole can be determined based on the surface pressure and pressure of the gas delivered into the borehole during MMWD. For example, one or more of the surface injection pressure, flow rate, one or more fluid properties, flow area dimensions, depth, bottomhole temperature, and / or last physical bottomhole pressure measurement from conventional drilling methods may be known. The injection rate, fluid properties, flow area, and depth can be used to calculate the pressure drop. The depth and fluid properties can be used to calculate the hydrostatic pressure. The ideal gas law or another empirical equation can be used to determine the pressure rise due to an appropriate temperature rise, such as (PV=NRT). These calculations can be used to determine the bottomhole pressure.

[0065] In some embodiments, a modified Bernoulli equation, the Darcy-Weisbach equation, the Fanning equation, and / or the Hazen-Williams equation can be used to solve for the pressure at the second point. By comparing the calculated bottomhole pressure to the last measured bottomhole pressure measurement, a determination of the downhole pressure can be made relative to a reference value. The last bottomhole pressure measurement can be linearly extrapolated to successively deeper bottomhole pressure values ​​to determine whether the bottomhole pressure is sufficient to maintain borehole integrity or whether the bottomhole pressure needs to be increased.

[0066] In some embodiments, the model can further correlate the amount of input energy provided to the gyrotron of the MMWD device to downhole pressure. In some embodiments, the model can include downhole pressure data associated with conventional drilling, such as rotary drilling. In some embodiments, the downhole pressure can be determined by modeling wellbore flow based on downhole temperature, depth (e.g., wellbore volume), inflow, and inlet / outlet pressure. In operation 210, the lithostatic pressure of the rock surrounding the wellbore at the bottom of the wellbore can be determined. In some embodiments, the lithostatic pressure can be determined based on historical geological survey data and / or models of geophysical data associated with the wellbore site.

[0067] In operation 215, downhole pressure can be controlled relative to the lithostatic pressure of the rock surrounding the wellbore at the bottom of the wellbore. Controlling downhole pressure can be important to overbalance, unbalance, or balance the downhole pressure relative to the lithostatic pressure to maintain structural stability of the borehole and wellbore. A severe imbalance of downhole pressure relative to the lithostatic pressure of the surrounding rock can cause borehole instability and collapse. In some embodiments, a rotating pressure control head (RCPH) can be used.

[0068] In some embodiments, downhole pressure can be controlled by controlling the operation of a gas compressor located at the surface where the entrance to the borehole is located. The gas compressor can be configured to supply gas into the borehole via one or more valves, such as an input valve and an output valve. The downhole pressure can be controlled by controlling the gas compressor input valve position, the gas compressor output valve position, and / or the flow rate of gas supplied by the gas compressor. In some embodiments, the gas flow rate can be from 0.5 m / s to 50 m / s. In some embodiments, the downhole pressure can be controlled via the compressor inlet mass flow rate and back pressure. In some embodiments, the downhole pressure can be controlled based on calculations of the Mach number of the flow at different locations (e.g., at the orifice plate).

[0069] In operation 220, particulate matter produced by the MMWD device can be removed. The MMWD can produce small particulate matter formed as a result of rock vaporization. For example, the particulate matter can be less than 1 micron in size. The particles can be removed by applying a gas flow to remove the particles. In some embodiments, the downhole pressure can be controlled to remove the particles by forcing them into fractures in the surrounding rock, thus reducing the need to lift the particles out of the borehole.

[0070] FIG. 3 illustrates an exemplary embodiment of a millimeter-wave drilling apparatus 300 configured to perform the methods of FIGS. 1 and 2 described herein. The millimeter-wave drilling apparatus 300 illustrated in FIG. 3 can be configured as described in U.S. Patent No. 8,393,410 to Woskov et al., entitled "Millimeter-wave Drilling System," which is incorporated herein by reference in its entirety. The MMWD apparatus 300 illustrated in FIG. 3 includes a gyrotron 302 connected via a power cable 304 to a power supply 306 that provides power to the gyrotron 302. The high-power millimeter-wave beam output by the gyrotron 302 is guided by a waveguide 308 having a waveguide section 326 with a waveguide bend 318, a window 320, and an opening 328 for off-gassing and pressure control. A portion of the waveguide is below ground level 330 to help seal the borehole.

[0071] As part of the waveguide transmission line 308, there is an isolator 310 to prevent reflected power from returning to the gyrotron 302 and the interface 312 for diagnostic access. The diagnostic access is connected to the diagnostic electronics and data acquisition 316 by a low-power waveguide 314. The window 320 has a pressurized gas supply unit 322 connected to the window by piping 324, which injects a clean gas flow across the window's inner surface to prevent deposition on the window. A second pressurization unit 336 is connected to the waveguide opening 328 by piping 332 and helps control the pressure in the borehole 348 and introduce and remove borehole gas as needed. The window gas injection unit 322 operates at a slightly higher pressure than the borehole pressure unit 336 to maintain gas flow across the window surface. A branch line 334 in the borehole pressurization piping 332 is connected to a gas analysis monitoring unit 340 and then to a pressure relief valve 338 to allow venting of volatilized borehole material and window gases to atmosphere 346 via a gas filter 342 and exhaust duct 344. In another embodiment, exhaust duct 344 returns the gases to the pressurization unit 336 for reuse.

[0072] The pressure within the borehole is increased partially or entirely by partial volatilization and melting of the subsurface material. A thermal melt front 352 at the end of the borehole 348 propagates into the subsurface layer under the combined action of the mmWave power and gas pressure, leaving behind a glass / ceramic borehole wall 350. This wall acts as a dielectric waveguide for transmitting the mmWave beam to the thermal front 352.

[0073] Figure 4 shows a more detailed view of the MMWD system, corresponding to the one described in U.S. Patent No. 8,393,410 to Woskov et al., entitled "Millimeter-wave Drilling System." A borehole 400, having a glass / ceramic wall 410 and a transparent glass 412, has a metal waveguide section 430 inserted to improve the efficiency of gyrotron beam propagation. The diameter of the inserted waveguide is smaller than the diameter of the borehole to form an annular gap 414 for evacuation / extraction. The standoff distance 440 of the leading edge of the metal insert waveguide from the thermal fusion front 420 of the borehole is sufficient to allow the emitted millimeter-wave beam divergence 432 to allow the dielectric borehole 400 to be filled 434 by the guided millimeter-wave beam. The standoff distance 440 is also sufficient to keep the temperature of the metal insert low enough for survivability. The inserted millimeter-wave waveguide also serves as a conduit for a pressurized gas flow 436 from the surface. This gas flow keeps the waveguide clean and contributes to the extraction / displacement of rock material from the borehole. The gas flow from the surface 436 mixes 442 with the volatilized outgassing of the rock material 444 and carries the condensed rock vapor to the surface through the annular space 414. The exhaust gas flow 446 is large enough to limit the size of the volatilized rock particles and carry them to the surface.

[0074] FIG. 5 illustrates an exemplary embodiment of a hybrid drilling system 500 configured to use the millimeter wave drilling system described herein. The hybrid drilling systems and methods described herein use a hybrid drilling method to effectively drill rock, such as subsurface rock. The hybrid drilling systems and methods are advantageous compared to conventional drilling alone because the benefits of conventional drilling and MMWD can provide an optimized solution for drilling in low-permeability or hard rock, such as subsurface rock. The first step of the hybrid drilling systems and methods described herein leverages conventional drilling. The hybrid drilling systems and methods can initially utilize a liquid-based drilling process to ensure wellbore stability and control during initial formation. Casing and cement can be installed during the initial formation of the wellbore to seal the wellbore and prevent wellbore collapse. Once sealed, drilling mud can be circulated from the wellbore, and the wellbore can be cleaned out to ensure all remaining fluids have been forced out before draining the wellbore. Evacuation can include forcing all liquid out of the hole so that the wellbore is filled with a gaseous medium, such as nitrogen, argon, or any gas that is substantially permeable to millimeter waves. The next step using MMWD can be initiated once subsurface rock is reached, or penetration rates have slowed significantly, or high temperatures prevent further progress with conventional drilling equipment. In wellbore holes prepared for MMWD, a second drilling step utilizing MMWD can be initiated. In some cases, it may be necessary to return to conventional drilling and then utilize MMWD again. Such an iterative method can be repeated multiple times depending on geological conditions. In some cases, conventional drilling can proceed with gas rather than liquid to minimize fluid switching operations.

[0075] As shown in Figure 5, the hybrid drilling system includes surface equipment 505, such as a conventional drilling rig configured at the surface 510, that is used to form a first portion of a borehole 515 in subsurface rock 520. A second portion of a borehole 525 can be formed in subsurface rock 530 via an MMWD apparatus to achieve a desired target depth 535.

[0076] FIG. 6 illustrates a plot 600 of penetration rates achievable using the millimeter wave drilling system described herein. As shown in FIG. 6, the vertical axis is the effective rate of penetration (EROP) as a function of depth on the horizontal axis. At a given depth at or near the subsurface rock, the effectiveness of conventional drilling methods is significantly reduced. Region S1 corresponds to step 1, where conventional drilling methods can provide more efficient borehole formation. Region S2 corresponds to step 2, where the use of direct energy methods, such as MMWD, can provide more efficient borehole formation. The point where the two curves intersect may be near the subsurface rock, which is the point where it may be advantageous to switch from conventional drilling methods to MMWD methods.

[0077] Figures 7-12 and 14 illustrate a hybrid drilling approach using the millimeter wave drilling system described herein in operation. Figure 7 is a diagram 700 illustrating the initial configuration of the hybrid drilling system described herein. As shown in Figure 7, a first portion of a borehole 515 can be formed using drill pipe 710, rotary steerable equipment 715, and drill bit 720. A conventional drilling rig 505 can direct the drill bit 720 to the bottom of the borehole 725 and into a transition region 730 between the non-subsurface rock 520 and the subsurface rock 530. The rotary steerable equipment 715 is used to maintain the wellbore formation in a straight, vertical line with little or no deviation. Having a vertically straight borehole can minimize the total distance drilled to the target depth 535 and can reduce wear on the drilling rig by repeatedly feeding equipment in and out of the rotary drilling borehole 515. In an alternative embodiment, the first portion of the borehole may be reused from a previously operated oil and / or gas well, geothermal well, or water well, thus reducing the overall time to reach the final desired target depth 535.

[0078] As further shown in FIG. 7 , distance “Z” is the distance from the bottom of the borehole 725 to the desired target depth 535. Distance Z may be greatest at the beginning of conventional drilling. The initial rate of change of distance Z with time using conventional drilling may be large, indicating a high penetration rate in the non-subsurface rock 520. As conventional drilling progresses to form the first portion of the borehole 515, distance Z may continue to decrease. Depending on the composition and changes in the non-subsurface rock 520, the rate of change of distance Z with depth with time may vary. The general trend of the rate of change of distance Z with time may continue to decrease, indicating that the penetration rate may decrease as the borehole is formed to greater depths.

[0079] 8 is a diagram 800 illustrating the depth of a first portion of a borehole 515 using conventional drilling equipment while maintaining an acceptable penetration rate. At some point, typically in the subsurface rock 530, or in the subsurface rock transition region 730, the penetration rate reaches a level that is mechanically and financially unacceptable. Additionally or alternatively, a threshold temperature limit may be reached, which prevents drilling deeper via conventional drilling equipment.

[0080] FIG. 9 is a diagram 900 illustrating a conventional drilling rig reaching the subsurface rock transition region 730. As shown in FIG. 9, the conventional drilling rig 505 reaches the subsurface rock transition region 730 at a depth Z from the desired target depth 535. The rate of change of distance Z with respect to time, or the penetration rate, is too small to continue with the conventional drilling rig 505 used to form the first portion of the borehole 515. Once permeable rock below the subsurface rock 530 is reached using the conventional drilling rig 505, or the penetration rate slows significantly, a decision can be made to deepen the borehole using an MMWD device. Any fluids need to be removed from the borehole 515 before utilizing the MMWD device. In some embodiments, non-conventional drilling methods other than MMWD (e.g., plasma drilling, laser drilling, projectile drilling, electric impact drilling) can be utilized to continue deepening the borehole.

[0081] FIG. 10 is a diagram 1000 illustrating the completion of a borehole 515 by a conventional drilling rig 505. As shown in FIG. 10, the borehole 515 is formed in a subsurface rock transition zone 730 that separates non-subsurface rock 520 from subsurface rock 530. At this point, casing and cement have been applied within the borehole 515 to ensure borehole stability and to remove any remaining liquid within the borehole 515. In some embodiments, the borehole 515 can be formed beyond the subsurface rock transition zone 730 to extend the borehole 515 beyond the discontinuity in the transition zone 730 and ensure a safe transition point for initiating MMWD.

[0082] FIG. 11 is a diagram 1100 illustrating the initiation of MMWD using an MMWD apparatus 1105. As shown in FIG. 11, a conventional drilling rig 505 has been modified and reconfigured as the MMWD apparatus 1105. Implementing the MMWD apparatus 1105 following use of the conventional drilling rig 505 may include replacing the liquid (e.g., water-based, oil-based, or gas-based) mud system with a gas system compatible with MMWD. A waveguide 1110 has been inserted into the borehole 515. Once the waveguide is positioned at or near the bottom of the borehole 725, MMWD of the subsurface rock 530 can proceed.

[0083] 12 is a diagram 1200 illustrating the formation of a borehole 1205 via a thermal melt front 1210 generated via MMWD. During operation, the gyrotron generates and supplies radiant energy to melt and vaporize subsurface rock 530, forming and advancing the thermal melt front 1210. The distance Z continues to decrease, and the effective penetration rate becomes greater than the effective penetration rate achieved using conventional drilling rig 505.

[0084] FIG. 13 illustrates a plot 1300 of penetration rates through subsurface rock 530 achievable using the MMWD apparatus 1105 and method compared to the conventional drilling apparatus 505 and method described herein. As shown in FIG. 13, the penetration rate using direct energy or MMWD apparatus and method can be maintained at a nearly constant rate and does not decrease substantially as a function of depth, as shown for conventional drilling apparatus and methods. Because there is no direct contact between the MMWD apparatus 1105 and the rock, EROP is fairly continuous until the target depth is reached. Continuous EROP is beneficially achieved because the MMWD apparatus 1105 does not require downtime to remove or replace worn components, such as drill bits, and is not significantly affected by rock hardness and / or rock temperature.

[0085] Figure 14 is a diagram 1400 illustrating the completion of MMWD when the thermal fusion front 1210 reaches the target depth 535. Once the target depth 535 is reached, the MMWD apparatus 1105 and waveguide 1110 can be removed from the borehole 1205 and transported to the next well site for hybrid MMWD formation of additional well boreholes.

[0086] In some embodiments, a batch process can be used with the hybrid MMWD systems and methods described herein. For example, multiple well boreholes in a given area can be formed using conventional drilling equipment and methods before changing surface equipment to an MMWD apparatus used to deepen the borehole within the depth of the subsurface rock. As a result, time and resources can be saved by performing conventional drilling and MMWD in batches. In other embodiments, a conventional drilling rig 505 can be easily converted into an MMWD apparatus 1105 for changeover operations without moving the rig structure.

[0087] The improved systems, apparatus, and methods described herein address the technical challenge of determining when to change from conventional drilling techniques, such as conventional drilling equipment and methods, to MMWD techniques, such as MMWD equipment and methods. This determination can be useful for efficiently deploying equipment and resources at a well site and for implementing well site planning based on the geophysical properties of the subsurface formation being accessed rather than operational costs. In this manner, the hybrid MMWD systems and methods described herein can enable deeper boreholes into less permeable and / or harder rocks that occur at higher temperatures below the surface. As a result, deeper deposits of natural and thermal resources can be accessed more efficiently than using conventional drilling equipment and methods.

[0088] Certain exemplary embodiments have been described to provide a general understanding of the principles of the structure, function, manufacture, and use of the systems, devices, and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the systems, devices, and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments, and that the scope of the present invention is defined only by the claims. Features illustrated or described in connection with one exemplary embodiment may be combined with features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention. Furthermore, in this disclosure, like-named components of embodiments generally have similar features, and therefore, within a particular embodiment, every feature of each like-named component is not necessarily described in detail.

[0089] As used herein throughout the specification and claims, approximation language can be applied to modify any quantitative expression that can vary within acceptable limits without resulting in a change in the basic function to which it pertains. Thus, values ​​modified by terms such as "about," "approximately," and "substantially" are not limited to the exact value specified. In at least some instances, approximation language can correspond to the precision of the instrument used to measure the value. Herein and throughout the specification and claims, range limitations are combinable and / or interchangeable, and unless the context or language dictates otherwise, such ranges are identified and include all subranges contained therein.

[0090] Those skilled in the art will appreciate further features and advantages of the present invention based on the above-described embodiments. Accordingly, the present application is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated by reference in their entirety.

Claims

1. Monitoring downhole pressure in a well during formation of the borehole using a millimeter wave drilling device including a waveguide configured for insertion into a borehole in the well, said monitoring including determining said downhole pressure, said downhole pressure including an amount of pressure present at the bottom of the well; determining a lithostatic pressure of rock surrounding the wellbore at the bottom of the wellbore; controlling the downhole pressure relative to the lithostatic pressure of the rock surrounding the wellbore at the bottom of the wellbore; A method comprising:

2. monitoring the downhole pressure of the well; measuring the pressure of fluid supplied to and / or extracted from said borehole; determining the downhole pressure of the wellbore using one or more of the pressure of the fluid delivered into the borehole, the pressure of the fluid extracted from the borehole, a downhole pressure determined when a drilling rig including a drill bit is used to form a portion of the wellbore, a measure of energy input delivered to the millimeter wave drilling rig, and / or a depth of the bottom of the wellbore; The method of claim 1 further comprising:

3. 3. The method of claim 1 or 2, wherein determining the downhole pressure of the wellbore further comprises using at least one physical model related to one or more of the downhole pressure determined when forming a portion of the wellbore using a drilling rig including a drill bit, the measure of energy input supplied to the millimeter wave drilling rig, and the depth of the bottom of the wellbore.

4. 4. The method of claim 1, wherein controlling the downhole pressure further comprises controlling one or more of: operation of a gas compressor disposed at a surface of the wellbore and configured to supply gas into the borehole of the wellbore; an input valve position of the gas compressor; an output valve position of the gas compressor; and / or a flow rate of the gas supplied by the gas compressor.

5. 5. The method of claim 1, wherein the flow rate of the gas is between 0.5 m / s and 50 m / s.

6. A millimeter wave drilling rig including a gyrotron configured to inject millimeter wave radiant energy into a borehole of a borehole via a waveguide configured to be inserted into the borehole, the borehole being formed via the millimeter wave drilling rig and having a downhole pressure monitored at the bottom of the borehole; a compressor fluidly coupled to the borehole and configured to control the downhole pressure via gas supplied into and / or received from the borehole, the compressor configured to control the downhole pressure relative to a lithostatic pressure determined for rock surrounding the wellbore at the bottom of the wellbore; A system comprising:

7. 7. The system of claim 6, wherein the downhole pressure is monitored by measuring the pressure of at least fluids supplied into and / or extracted from the borehole and determining the downhole pressure in the well using one or more of the pressure of the fluids supplied into the borehole, the pressure of the fluids extracted from the borehole, a downhole pressure determined when a drilling rig including a drill bit is used to form a portion of the wellbore, a measure of energy input supplied to the millimeter wave drilling rig, and / or a depth of the bottom of the wellbore.

8. 8. The system of claim 6 or 7, wherein the downhole pressure of the well is controlled based on one or more of the pressure of the fluid supplied into the borehole, the pressure of the fluid received from the borehole, the downhole pressure determined when a drilling rig including a drill bit is used to form a portion of the well, a measure of energy input supplied to the millimeter wave drilling rig, and / or a depth of the bottom of the well.

9. 9. The system of claim 6, wherein the downhole pressure of the wellbore is further controlled based on a physical model related to one or more of the downhole pressure determined when a drilling rig including a drill bit is used to form a portion of the wellbore, a measure of energy input supplied to the millimeter wave drilling rig, and a depth of the bottom of the wellbore.

10. At least one data processor; memory that stores computer-readable instructions; A system comprising: The computer-readable instructions, when executed by the at least one data processor, cause the at least one data processor to perform an operation: The operation is monitoring downhole pressure in a wellbore during formation of a borehole in the wellbore, wherein the monitoring comprises determining the downhole pressure, the downhole pressure comprising an amount of pressure present at a bottom of the wellbore; determining a lithostatic pressure of rock surrounding the wellbore at the bottom of the wellbore; controlling the downhole pressure relative to the lithostatic pressure of the rock surrounding the wellbore at the bottom of the wellbore; Including, the system.

11. Monitoring the downhole pressure of the well, measuring the pressure of fluid supplied to and / or extracted from said borehole; determining the downhole pressure of the wellbore using one or more of the pressure of the fluid supplied into the borehole, the pressure of the fluid extracted from the borehole, a downhole pressure determined when forming a portion of the wellbore using a mechanical drilling rig including a drill bit, a measure of energy input supplied to the millimeter wave drilling rig, and / or a depth of the bottom of the wellbore; The system of claim 10 further comprising:

12. The system of claim 11, wherein determining the downhole pressure of the well bore further comprises using at least one physical model related to one or more of the downhole pressure determined when forming a portion of the well bore using the mechanical drilling equipment including a drill bit, the measure of energy input supplied to the millimeter wave drilling equipment, and the depth of the bottom of the well bore.

13. The system described in claim 10, wherein the lithostatic pressure of the rock surrounding the well at the bottom of the well is determined using historical geological survey data and / or a model of geophysical data related to the well.

14. The system described in claim 10, further comprising a rotary pressure control head operable to control the downhole pressure of the well.

15. The system of claim 10, wherein controlling the downhole pressure further comprises controlling one or more of the operation of a gas compressor positioned on the surface of the well and configured to supply gas into the borehole of the well, an input valve position of the gas compressor, an output valve position of the gas compressor, and / or a flow rate of the gas supplied by the gas compressor.

16. The system of claim 15, wherein the gas flow rate is between 0.5 m / s and 50 m / s.

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