Tool for electromagnetic logging while drilling

Abstract

FIELD: well logging.SUBSTANCE: invention is intended for electromagnetic logging of specific electrical resistance during the drilling of oil and gas wells. The device is made in the form of a powerful metal body, which is a drill pipe with a central longitudinal channel for the flow of drilling fluid and threaded connecting elements at the ends. The body comprises at least two receiving and at least three transmitting antennas mounted in circular recesses, as well as electronic boards located in recesses made on the outer surface of the body. To connect antennas, electronic boards and transfer elements, transit channels for laying wires are made in the body. Each transit channel is designed in the form of two opposing longitudinal openings, made on the side of opposite ends of the body and communicating through a connecting recess. The body of the device is made of one piece, without welding or joints along the length. The design of the transfer elements ensures the sealing of the transit channels from the ends of the body.EFFECT: increase in the fatigue strength of the device body, an increase in the time between workovers and the total service life, as well as an increase in the device availability factor due to simplified access to the electronic boards.8 cl, 2 dwg

Description

[0001] Technical field

[0002] The invention relates to well logging and is designed for electromagnetic logging of electrical resistivity (ER) during oil and gas well drilling. The device is designed for use as part of a bottomhole assembly (BHA) in conjunction with a downhole telemetry system. The device is a resistivity logging device based on the excitation of induced currents in the environment and the measurement of the resulting electromagnetic field's phase and amplitude parameters.

[0003] Technology Level

[0004] Logging methods are widely used to obtain information about the subsurface during oil and gas well construction. One of the primary methods is electromagnetic resistivity logging (ERL), which is a development of induction logging. The first devices of this type were proposed in 1966 in application FR 1527757 A, which resulted in patent US 3551797 A. The patent, among other things, describes a device comprising at least one transmitting antenna and two receiving antennas located along the elongated body of the device. It also describes a method in which the transmitting antenna emits an electromagnetic field into the rocks surrounding the device, and the receiving antennas measure the change in the electromagnetic field parameters between the near and far receiving antennas. The phase and amplitude of the electromagnetic field are used as parameters.

[0005] Subsequently, the described method was widely adopted and developed in electromagnetic logging while drilling (EMWD) instruments. The most successful implementations of such instruments are disclosed in US Patents 4,899,112 A and 5,594,343 A, where the described devices comprise two adjacent receiving antennas, with transmitting antennas located on either side of the receiving antennas, along the elongated body of the instrument. US Patent 4,899,112 A describes a symmetrical implementation of the instrument, in which transmitting antennas are symmetrically located on either side of the receiving antennas, relative to the central point between them, while US Patent 5,594,343 A describes an asymmetrical implementation, in which a different number of transmitting antennas can be located on either side of the receiving antennas, at different distances from them.The method for measuring the resistivity in such devices includes a combination of measurements carried out while transmitting antennas are located on different sides in such a way as to eliminate the interfering factor in the form of the presence of drilling fluid between the device body and the rocks being studied.

[0006] In addition to the technical result of reducing the influence of drilling mud, as described in US patents 4899112 A and 5594343 A, this measurement method is also less susceptible to measurement errors associated with imperfections in the devices' transmit-receive paths. Specifically, this method significantly reduces the error in resistivity measurement associated with temperature changes in the transmit-receive path and even with limited mechanical damage to the antennas that occurs during device operation. Devices implementing this method are called symmetrical or asymmetrical compensated devices. Asymmetrical compensated devices are often referred to as pseudo-compensated (US 6538447 B2) to more clearly distinguish between the two methods.

[0007] The ability of compensated and pseudo-compensated instruments to eliminate errors associated with imperfections in the receiving and transmitting paths, as well as the compensation mechanism, are described in US Patent 6,538,447 B2. This patent is an example of a patent that discloses more complex instruments and methods for electromagnetic resistivity logging. However, in the current state of the art, the vast majority of electromagnetic resistivity logging while drilling instruments implement the principles described in US Patent 4,899,112 A and US Patent 5,594,343 A, due to their simplicity and reliability.

[0008] The needs of the modern oil and gas industry place demands on the information content and quality of measurements taken by such instruments. As a result, the following minimum design requirements can be formulated:

[0009] - measurement of phase and amplitude of electromagnetic field;

[0010] - measurement at least at two frequencies, in the range from 300 kHz to 3 MHz (the most common values ​​are 400 kHz and 2 MHz);

[0011] - the presence of at least two compensated measurements with different distances from the transmitting antenna to the center between the receiving antennas, and the maximum value of this distance must be at least 0.9 m.

[0012] The last requirement ensures sufficient depth of investigation for such measurements, which is directly related to the specified distance. As a result, the possible length of the measuring section of such devices is limited from below to approximately 1.8 meters, and even more given the finite dimensions of the antennas and other structural elements necessary for the device's operation.

[0013] Thus, the current state of the art includes compensated symmetrical and asymmetrical electromagnetic resistivity logging instruments and methods for measuring resistivity with such instruments. The metrological characteristics of such instruments generally meet the requirements of the oil production industry.

[0014] In addition to metrological characteristics, important requirements for logging-while-drilling tools include high reliability, long service life between repairs, and high availability. This is due to harsh operating conditions: high mechanical loads (compression, tension, torsion, vibration), abrasive wear on borehole walls, hydroabrasive action of drilling fluid, as well as high temperatures and chemical aggressiveness of the environment. This necessitates continuous improvement in the design of such tools and their manufacturing methods.

[0015] Various designs of such tools are known, but all must meet the basic requirements associated with their operation in conjunction with a downhole telemetry system (BTS) as part of a bottomhole assembly (BHA). Therefore, the tool body is typically designed as a drill pipe with an internal channel for drilling fluid flow and threaded connections at the ends for insertion into the BHA. Adapters located at the ends of the tool are used to connect to other BTS components. The body must transfer significant drilling loads and is therefore typically manufactured from high-strength non-magnetic stainless alloys. However, designs proposed in patents RU 2231091 C1 and RU 2828231 C1 suggest manufacturing individual body parts from radio-transparent composite materials.

[0016] In the design proposed in patent RU 2231091 C1, the power section of the housing consists of a series-connected upper connecting element, an external composite power tube, and a lower connecting element. The material of the connecting elements is not explicitly specified in the patent. However, based on the functional purpose of these elements (torque transmission and connection to the metal parts of the BHA via threads), as well as well-known requirements for drilling tools, it follows that these connectors must be made of metal. A significant drawback of this solution is the presence of two connections of materials with different physical properties, which will operate under conditions of high variable loads and temperature fluctuations. Such connections are known to be susceptible to failure due to high stresses arising in the contact layer due to the different thermal expansion coefficients of the materials.This may lead to a reduction in service life due to a breach in the integrity and tightness of the connections, and consequently to an increased accident rate, low time between repairs and a low overall service life of the proposed design.

[0017] Patent RU 2828231 C1 proposes a design in which the outer load-bearing casing is made of a metal pipe with through-slots sealed with radio-transparent inserts. The internal radio-transparent casing protects these slots and the internal volume of the tool from drilling fluid pressure. A significant drawback of this design is the presence of through-slots in the load-bearing pipe, at the boundaries of which stresses are concentrated, reducing the strength of the casing, increasing the risk of accidents, and shortening its service life. One way to increase strength is to increase the pipe wall thickness. However, the outer diameter of the casing is limited by the diameter of the BHA, so this is only possible by reducing the internal diameter. This reduces the cross-sectional area of ​​the drilling fluid flow channel, leading to increased hydroabrasive wear of the internal radio-transparent casing and a shorter service life of the tool.

[0018] Designs with a housing constructed within a metal tube are the primary designs currently used for electromagnetic logging tools. Such designs are disclosed in patents RU 2392644 C1, RU 2506611 C2, and RU 2829287 C1. In all designs proposed in these patents, the power housing is constructed within a metal tube on which the antennas are mounted, while the electronic boards and connecting wires are located on a chassis inserted into the housing. The advantage of such designs is the ease of routing the wires connecting the antennas and electronic boards, as well as the transit wires used to connect the logging system components located above and below the tool to each other and to the tool itself. However, such designs have several disadvantages.

[0019] The design disclosed in patent RU 2392644 C1 includes a chassis mounted in an internal drilling fluid flow channel. This increases the contact area of ​​the tool with the drilling fluid flow, increases hydroabrasive wear, and reduces the tool's service life. The designs disclosed in RU 2506611 C2 and RU 2829287 C1 are more optimal in terms of service life and failure rate, but are not optimal in terms of availability. Accessing the electronic boards for maintenance or repair requires removing the chassis, which requires dismantling at least one adapter, disconnecting the chassis from another adapter, and disconnecting the chassis from the antennas mounted on the body. After this, the tool becomes inoperable, and testing the boards and antennas is difficult, as they are disconnected from each other and from the standard power supply.As a result, servicing and repairing such devices typically requires specialized test benches and sophisticated laboratory equipment, which increases repair time and reduces device availability.

[0020] An alternative to the above designs is to place the electronic boards in recesses cut into the power case's outer surface. These recesses are covered with protective covers with sealing elements. If necessary, removing the appropriate cover provides access to the desired electronic board without disassembling the device, allowing for removal of the board or testing it in operating mode.

[0021] The difficulty of implementing such a design stems from the need to create a transit channel in the power enclosure for routing wires connecting antennas, electronic boards, and transfer elements. The channel must be located in the enclosure wall and have a small cross-section to avoid unduly reducing its strength. At the same time, to ensure communication between the ZTS components located above and below the device, the channel must extend almost the entire length of the enclosure. According to the above requirements, the length of such a channel must exceed 1.8 m with a characteristic cross-sectional dimension of 6-10 mm (a length-to-cross-sectional ratio greater than 180).

[0022] In practice, considering deep directional drilling as the primary method for forming deep channels, the maximum achievable hole depth-to-diameter ratio is in most cases limited to 100 due to technological limitations arising during the drilling process. This maximum value is typical for deep drilling under the condition of simultaneous rotation of the drill and workpiece, which is a technically challenging task for peripheral drilling in the wall of a housing, far from its axis.

[0023] As a result, the creation of such channels in the wall of the drill pipe body with the specified ratios of length and transverse size is an extremely complex technological task and, in most cases, cannot be implemented using standard deep drilling methods in the conditions of most metalworking industries.

[0024] From the above, it is clear that in order to manufacture a body in the form of a drill pipe with a transit channel of sufficient length, a design is required that allows for a reduction in the maximum drilling depth.

[0025] US Patent 20190048716 A1 discloses a general design applicable to logging-while-drilling tools with a housing shaped like a drill pipe and containing a transit channel, without specifying a logging method. It also provides an overview of the prior art. The described design is also suitable for the manufacture of electromagnetic resistivity logging tools. An electromagnetic resistivity logging tool with a housing constructed according to US Patent 20190048716 A1 is the closest analogue to the proposed invention.

[0026] The patent discloses a design and manufacturing method for logging-while-drilling tools, enabling the tool body to be constructed with a channel for routing wires within a drill pipe of any specified length. For this purpose, the body is welded, consisting of at least two drill pipe segments sequentially welded together. Blind channels for routing wires are formed in the walls of the outer segments, with an open cross-section at the end intended for welding to the other segment, while the segments located between the outer segments have through-channels in the walls for routing wires. Recesses are provided in the welded body for accessing the blind ends of the channel and for connecting channels in different sections, which are then closed with protective covers with sealing elements.

[0027] This design eliminates the drawbacks inherent in chassis-based designs and allows for the manufacture of electromagnetic logging tools with electronic boards housed in special recesses within the power housing, sealed with covers with sealing elements. However, a significant drawback of this design is the presence of welded joints, which act as stress concentrators. Residual stresses arise in the welds due to structural changes in the material during heating during welding. Under cyclic loads and vibrations, this leads to a reduced service life of the tool due to fatigue cracks or failure of the housing, leading to a downhole accident.

[0028] Thus, there is still a need for more advanced design solutions and manufacturing methods for electromagnetic logging tools for resistivity while drilling.

[0029] Disclosure of the essence of the invention

[0030] The technical objective of the present invention is to create a design for an electromagnetic logging device for resistivity during drilling, which has an increased fatigue strength of the housing, an increased overhaul and full service life compared to the closest analogue, as well as a better availability factor compared to devices containing in their design a chassis intended for placing electronic boards.

[0031] The technical task is achieved by a special design of the device, which contains:

[0032] - a power metal housing made in the form of a solid metal pipe with a central longitudinal channel for the flow of drilling fluid, and the housing is made without the use of welding and connections along the length of the housing, and at its ends there are threaded connecting elements designed to include the device in the BHA, as well as internal end surfaces, the diameter of which is smaller than the diameter of the threaded elements;

[0033] - upper and lower transfer elements designed to connect the device with other ZTS devices;

[0034] - circular recesses made in the body and intended for installing the receiving and transmitting antennas of the device;

[0035] - at least one transit channel made in the housing and intended for laying wires, wherein each transit channel is made in the form of two opposing longitudinal openings with a total length of at least 1.8 m, having the largest linear dimension of the cross-section of no more than 10 mm, made coaxially from the side of the opposite ends of the housing, with an acceptable technological misalignment, wherein each of the openings has a beginning on one of the said internal end surfaces and an end in a unifying recess, the transverse dimensions of which exceed the transverse dimension of the said openings by at least the value of their possible technological misalignment,

[0036] - recesses intended for various purposes: placement of electronic boards, insertion of antenna contacts into transit channels and transfer of wires from transit channels to transfer elements, all recesses are made on the outer surface of the housing;

[0037] - protective covers with sealing elements that ensure hermetic closure of the specified recesses, with the exception of circular recesses intended for antennas;

[0038] - sealing elements designed to seal transit channels from the upper and lower ends of the housing, which in one embodiment can be made in the form of separate structural elements, and in another embodiment - as part of the design of the transition elements;

[0039] - antennas, electronic boards and connecting wires that ensure the operation of the device.

[0040] To perform compensated measurements of the phase and amplitude of the electromagnetic field, the device contains at least two receiving antennas located adjacent to each other, and at least three transmitting antennas located on either side of the receiving antennas. The antennas are mounted in the specified circular recesses and are inductive loops with at least one turn. The magnetic moment of the antennas is approximately aligned with the housing axis.

[0041] The proposed design of transit channels, formed by two opposing holes communicating through a connecting recess, reduces the required hole depth by approximately half, allowing the device housing to be manufactured to the required length without the use of welding or joints. Furthermore, the design allows for the placement of electronic boards in recesses cut into the outer surface of the housing, which is achieved through the presence of transit channels of this design.

[0042] The absence of welds and joints in the housing design increases the fatigue strength of the housing, extending the device's lifespan between repairs and overall service life compared to its closest analogue. The design of the recesses for the electronic boards facilitates access, increasing repair speed and, consequently, increasing device availability compared to designs containing a chassis designed to house electronic boards and wires.

[0043] Brief description of drawings

[0044] Fig. 1 - Schematic representation of the resistivity logging tool during drilling.

[0045] Fig. 2 - Schematic representation of the connection unit of the transfer elements with the housing.

[0046] Implementation of the invention

[0047] The electromagnetic logging tool for resistivity while drilling is shown schematically in Fig. 1. The tool comprises a power metal housing made in the form of a single drill pipe (1) with a central longitudinal channel (2) designed for the flow of drilling fluid. The body of the tool is manufactured without the use of welding or joints along its length. The design of the tool also includes upper (3) and lower (4) adapter elements, ensuring the connection of the tool with the upper and lower parts of the wellbore assembly. At the ends of the body, conical coupling locking threaded elements (5) are made, used for drill pipes and designed to incorporate the tool into the BHA.

[0048] One of the possible device versions features a compensated symmetrical measurement scheme with two receiving antennas (6 and 7) located side by side, and four transmitting antennas (8, 9, 10, and 11) located symmetrically relative to the central point between the receiving antennas. Two transmitting antennas are located on each side. The device performs measurements of the phase and amplitude of the electromagnetic field at two frequencies, for example, at frequencies close to 400 kHz and 2 MHz, which are most common in electromagnetic resistivity logging while drilling (EMLD) tools. The device contains two sets of antennas (8, 6, 7, and 11) and (9, 6, 7, and 10), implementing compensated measurements with greater and lesser survey depths, respectively. The distances from the central point between the receiving antennas to the transmitting antennas are selected based on the requirements of the operating organization, but the longer of the lengths exceeds 0.9 meters.For example, these distances can be: for antennas (8,11) - 0.915 m, for antennas (9, 10) - 0.570 m, for antennas (6,7) - 0.11 m.

[0049] The measured compensated values ​​for phase and amplitude for the two specified frequencies and the two specified sets of antennas are stored in the device memory and, upon request, transmitted to the control module of the ZTS and then transmitted to the wellhead using the telemetry device included in the ZTS.

[0050] The obtained values, using known numerical relationships linking instrument readings to the conductivity of a homogeneous medium, are converted into an equivalent resistivity value, commonly referred to as apparent resistivity. The obtained results are used to make decisions affecting well construction.

[0051] The design of the device in one of the possible versions has the following implementation:

[0052] Circular recesses are made in the housing at the antenna installation locations.

[0053] The antennas are made of wire in the form of an inductive loop with at least one turn, mounted on special dielectric bases located in recesses. The antennas' magnetic moment is approximately aligned with the housing axis.

[0054] The antennas are covered with protective metal covers with slots designed to allow the electromagnetic field to penetrate from the antenna into the rocks and back.

[0055] The free space in the internal volume of the antenna recesses is filled with a suitable dielectric filler, for example, one of the varieties of epoxy resins.

[0056] The internal volume of the recesses where the antennas are located is not hermetically sealed, therefore the electrical terminals of the antennas are fed through the sealed entries into the transition recesses (12).

[0057] Electronic boards are mounted in recesses (13).

[0058] Antennas, electronic boards and connectors (14) intended for connection with the mating connectors of the upper and lower parts of the ZTS are connected using wires laid in transit channels (15).

[0059] For the transition of wires from transit channels to transfer elements (3) and (4), recesses (16) are provided.

[0060] The device housing may contain several transit channels, for example, three, each of which is designed for separate routing: power wires for transmitting antennas, signal wires for receiving antennas, and transit wires connecting the upper and lower transition elements of the device. This separate routing reduces electromagnetic interference from the power wires to the signal wires.

[0061] Each transit channel is designed as two opposing longitudinal holes formed by deep directional drilling on the opposite ends of the housing, made coaxially, with an acceptable technological misalignment. The holes have their origins on the inner end surfaces (17, see Fig. 2) located on the ends of the housing and having a diameter smaller than the diameter of the threaded elements. The holes are connected by means of a connecting recess (18) located between the receiving antennas. The transverse dimensions of the connecting recess exceed the diameter of the said holes by at least the value of their possible technological misalignment, and its longitudinal dimensions provide installation access to the ends of the transit channel holes for laying and connecting wires.

[0062] The recesses (12), (13), (16) and (18) are covered with protective covers with sealing elements, which ensure the tightness of the internal volume of the device, and the outer ends of the transit channels are sealed using transfer elements (3) and (4). The mating unit of the housing and transfer element (3) is shown in more detail in Fig. 2. Sealing elements (19) are located on transfer elements (3) and (4) and ensure their tight mating with the housing. As a result, the internal volume of the device is hermetically sealed.

[0063] The described design of the housing, adapters, and transit channels, formed by two holes joined in a connecting recess, allows for drilling to a depth of approximately half the housing's length. This allows for a housing long enough to accommodate the specified antenna sets, with a distance of 1.93 m between the outer antennas, without the use of welding or joints. The absence of welded joints increases the housing's fatigue strength, the time between repairs, and the overall service life of the device compared to its closest analogue.

[0064] The presence of transit channels allows the placement of electronic boards in the recesses of the housing, which simplifies access to them and leads to an increase in the speed of repair and replacement of electronic boards and, ultimately, increases the availability factor compared to devices whose design contains a chassis intended for placing electronic boards.

Claims

1. An electromagnetic logging-while-drilling device intended for use as part of a bottomhole assembly (BHA) together with a downhole telemetry system during the drilling of oil and gas wells, which performs compensated measurements of the specific electrical resistance of rocks in phase and amplitude of the electromagnetic field using at least two frequencies in the range from 300 kHz to 3 MHz, the design of which comprises a power metal housing made in the form of a drill pipe with a central longitudinal channel for the flow of drilling mud, wherein threaded connecting elements are made on the ends of the power metal housing, at least two receiving antennas located nearby, and at least three transmitting antennas located on either side of the receiving antennas, wherein the antennas are mounted in circular recesses made in the power metal housing and are inductive loops with at least one turn,the magnetic moment of which is co-directed with the axis of the power metal housing; electronic boards placed in recesses made in the power metal housing and hermetically sealed with protective covers with sealing elements; at least one transit channel for laying wires connecting antennas, electronic boards and transfer elements, characterized in that the power metal housing is made integral, the recesses for the electronic boards are made on the side of the outer surface of the power metal housing, on the ends of the power metal housing there are internal end surfaces, the diameter of which is smaller than the diameter of the said threaded elements, on the side of the outer surface of the power metal housing there is at least one unifying recess formed, forming part of the transit channel and closed with a protective cover with sealing elements, each transit channel is made in the form of two opposing longitudinal openings with a total length of at least 1.8 m,with the largest linear dimension of the cross-section of no more than 10 mm, made from the side of the opposite ends of the power metal casing coaxially, with an acceptable technological misalignment, wherein each of the openings has a beginning on one of the said internal end surfaces and an end in the said connecting recess, the design of the said transition elements contains surfaces and sealing elements intended for sealing the transit channels from the side of the upper and lower ends of the power metal casing.

2. The device according to paragraph 1, characterized in that the longitudinal holes forming part of the transit channel are made by deep directional drilling from the side of the corresponding ends of the power metal body.

3. The device according to paragraph 1, characterized in that the connecting recess is located between two receiving antennas.

4. The device according to paragraph 1, characterized in that the connecting recess is designed to provide installation access to the ends of the longitudinal openings of the transit channel for laying and connecting wires.

5. The device according to paragraph 1, characterized in that the power metal housing contains at least two transit channels, made separately for laying the power wires of the transmitting antennas and the signal wires of the receiving antennas, respectively.

6. The device according to paragraph 1, characterized in that the recesses intended for placing electronic boards and the corresponding protective covers are designed to allow access to the electronic boards.

7. The device according to paragraph 1, characterized in that the recesses intended for placing electronic boards and the corresponding protective covers are designed with the possibility of dismantling and replacing the electronic boards.

8. The device according to paragraph 1, characterized in that the circular recesses of the antennas are covered with protective metal covers with a slot system.

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