Method and device for realizing direct coupling balance of array induction instrument coil system

Abstract

This invention provides a method and apparatus for achieving direct coupling balance of coil systems in an array induction instrument, relating to the field of geophysical logging technology. The method includes: determining the theoretical process parameters of each coil system through direct coupling balance design; and performing a direct coupling calibration process for the sub-array. In this method, direct coupling calibration is performed using a direct coupling balance gauge and a source distance compensation gauge. When the nonlinear equation root-finding algorithm converges to the target equilibrium position, the gauge corresponding to the target equilibrium position can be used to adjust the theoretical process parameters of each coil system determined by the direct coupling balance design. This calibrates the differences between the actually manufactured instrument and the theoretical design caused by various factors such as machining errors of the actual coil system substrate, coil winding process, winding tension, and assembly. This allows the array induction instrument manufactured or improved based on the aforementioned coil system process parameters to eliminate direct coupling signals to the greatest extent possible, ensuring the instrument's direct coupling balance and a reasonable signal-to-noise ratio.

Description

Technical Field

[0001] This invention belongs to the field of geophysical logging technology, particularly for the exploration and development of coal, oil and other mineral fields. Specifically, it relates to a method for achieving direct coupling balance of an array induction instrument coil system, a device for achieving direct coupling balance of an array induction instrument coil system, a computer device, and a machine-readable storage medium. Background Technology

[0002] In oil and gas logging for evaluation, formation resistivity is a crucial parameter for estimating oil and gas reserves. Lateral logging, which uses electrodes to emit direct current into the formation to establish an electric field, and induction logging, which uses alternating current induced in a transmitting coil to generate an eddy current field in the formation, are two commonly used resistivity logging methods. Especially in air drilling and under non-conductive drilling media conditions such as oil-based drilling mud, direct current logging methods are no longer suitable, but induction logging remains applicable.

[0003] like Figure 1 As shown, induction logging is a method of logging that utilizes the mutual inductance principle of alternating current. The instrument works by transmitting an alternating current through a transmitting coil, inducing eddy currents in the formation. These eddy currents then induce an electromotive force (EMF) in the receiving coil. Since both the transmitting and receiving coils are located inside the well, the intensity of the eddy currents induced in the formation around the well by the alternating current of the transmitting coil is related to the formation conductivity. Therefore, the induced EMF in the receiving coil is a function of the surrounding formation conductivity. The coil system is located in a homogeneous, isotropic, and time-invariant formation with constant permeability μ, conductivity σ, and dielectric constant ε. The formation is rotationally symmetrical about the well axis. T and R are the transmitting and receiving coils, respectively, with N turns. T and N R The coil radii are all r′, and L is the distance between the transmitting and receiving coils, called the source distance. The coils operate at a certain frequency ω. A constant-amplitude, frequency-stable alternating current I flows through the transmitting coil. T , represented as I T =I0e -iωt Because the alternating current in the transmitting coil generates an electromagnetic field in the surrounding formation, it induces currents in numerous formation unit loops centered on the well axis. The magnitude of these induced currents is proportional to the conductivity of the formation unit loop. Similar to the current coil, these induced currents also generate alternating electromagnetic fields, commonly referred to as secondary fields. These secondary fields induce an electromotive force (EMF) in the receiving coil, called the secondary field induced EMF. In a homogeneous, infinitely large medium, neglecting the interaction between eddy currents, the secondary field induced EMF is proportional to the conductivity of the medium. For example... Figure 2As shown, the secondary induced electromotive force (EMF) induced in the receiving coil carries formation conductivity information and is called the useful signal. The useful signal has a 180-degree phase difference with the alternating current of the transmitting coil. The induced EMF directly coupled from the transmitting coil to the receiving coil does not carry formation information and is called the direct-coupled EMF or useless signal. The direct-coupled EMF has a 90-degree phase difference with the alternating current of the transmitting coil. Phase-sensitive detection technology can be used to detect the secondary field induced EMF from the total signal, thereby achieving the purpose of measuring the resistivity of the surrounding formation. The direct-coupled signal is often tens to thousands of times stronger than the secondary induced signal, which can overwhelm the secondary induced signal, resulting in an extremely low signal-to-noise ratio. To accurately measure the secondary field induced EMF, induction logging instruments are designed to cancel or balance the direct-coupled signal by adding a shielded receiving coil. In practical induction logging instruments, the following methods are commonly used: Figure 3 The three-coil subarray structure shown consists of a transmitting coil Tx and a pair of receiving coils Rm and Rb. Rm and Rb are respectively called the main receiving coil and the shielded receiving coil. The shielded receiving coil is also called the compensating receiving coil, the secondary receiving coil, or the direct-coupled balanced coil. These two receiving coils are wound in opposite directions and connected together to form the receiving coil Rx. The combination of the transmitting coil Tx and the receiving coil Rx is called the subarray.

[0004] According to the principle of induction logging, the longer the source distance, the larger the instrument's detection range, and the deeper (farther) the detection range in the direction perpendicular to the wellbore (radial), but the worse (lower) the resolution of thin layers along the wellbore (vertical). Conversely, the shorter the source distance, the shallower the radial detection depth of the instrument, and the stronger the vertical resolution of thin layers. In order to detect the formation conductivity at different depths and in different areas around the wellbore, and at the same time improve the resolution of thin layers, composite coil systems, especially array induction logging instruments with optimized combinations of multiple coil systems, have been designed. These instruments utilize wellbore correction and other processing to eliminate the influence of the wellbore environment, software focusing and other processing to eliminate the influence of the surrounding rock environment, and radial inversion and other processing to obtain invasion parameters and original formation resistivity, etc. They have the advantages of high vertical resolution, deep radial detection depth, and clear invasion indication. Array induction logging instruments provide formation resistivity information at multiple detection depths and resolutions, making them a powerful tool for oil and gas evaluation and widely popular.

[0005] like Figure 4As shown, the array induction instrument probe consists of a shared transmitting coil Tx and multiple (e.g., 7) receiving coil systems Rx. Each receiving coil system and the transmitting coil form a subarray, which is a measurement unit. Multiple subarrays of the array induction are mounted on the same instrument spindle structure. After the array induction instrument is designed using direct-coupling balance theory, each three-coil system subarray is independent and directly coupled and balanced. However, due to various factors such as machining errors of the actual coil system substrate, coil winding processes, and assembly, there is often a significant difference between the actual manufactured instrument and the theoretical design, meaning there is often a large residual direct-coupling signal. Currently, to eliminate the residual direct-coupling signal, the source distance of each three-coil system subarray is often adjusted using a "gauge adjustment" method to highlight the useful signal, improve the instrument's signal-to-noise ratio, and ensure the instrument's direct-coupling balance and consistency. However, in the process of "adjusting the plug gauge", it is usually necessary to repeatedly test "plug gauge pieces" of different thicknesses to adjust the source distance of the receiving coil. This process of changing the plug gauge piece requires repeatedly loosening and tightening the coil system. For array sensing instruments with multiple sub-arrays, the adjustment process is quite cumbersome in order to make each three-coil system reach the best balance.

[0006] China National Petroleum Corporation Great Wall Drilling Engineering Co., Ltd. disclosed a method for eliminating direct coupling signals in a three-dimensional array sensing instrument, in which the Z component eliminates direct coupling signals by changing the source distance of the shielding coil. This patent does not disclose details such as the specific plug gauge fine-tuning method, steps, and calibration completion criteria. Furthermore, because the X, Y, and Z coils adopt a common-center design, it is not possible to simultaneously eliminate direct coupling signals in all three directions by fine-tuning the source distance. Therefore, the patent proposes a method of changing the number of turns and area of ​​the shielding coil to achieve the elimination of direct coupling signals in the X and Y directions. The fine-tuning of the shielding coil area in the X and Y directions is achieved by making holes in the coil surface and then fixing a conductor in the holes. This patent mainly focuses on methods for eliminating direct coupling signals in the X and Y directions. See CN104343443A for details.

[0007] To eliminate direct-coupled balance signals in array sensing instruments as much as possible, a highly efficient and intelligent direct-coupled balance calibration method is a key technical challenge that urgently needs to be overcome in this field. Based on the analysis of the sensitivity of two types of plug gauge positions, the design of plug gauge positions and plug gauge series is optimized to save on the manufacturing cost of precision plug gauges. Simultaneously, an intelligent balance calibration and full sub-array synchronous balance calibration process based on plug gauge sensitivity is established, a termination calibration rule is proposed, and related software modules are developed. Summary of the Invention

[0008] The purpose of this invention is to provide a method for achieving direct coupling balance in an array induction instrument coil system, a device for achieving direct coupling balance in an array induction instrument coil system, a computer device, and a machine-readable storage medium, in order to overcome the technical problem of poor direct coupling balance in existing coil system array induction instruments.

[0009] To achieve the above objectives, a first aspect of the present invention provides a method for achieving direct coupling balance in an array induction instrument coil system, comprising:

[0010] The theoretical process parameters of each coil system are determined through direct-coupled balanced design;

[0011] A direct-coupled calibration process is performed on the subarray, the direct-coupled calibration process including:

[0012] A direct-coupled balance plug gauge is added between the transmitting coil and the shielded receiving coil to change the source distance of the shielded receiving coil. In accordance with the principle that the source distance of the main receiving coil of the long subarray remains unchanged, a source distance compensation plug gauge complementary to the direct-coupled balance plug gauge is added between the main receiving coil and the shielded receiving coil. When the subarray is a short subarray, no source distance compensation plug gauge is added between the main receiving coil and the shielded receiving coil. Then, the current residual direct-coupled signal of the subarray is measured and the source distance of the shielded receiving coil of the subarray is determined according to the thickness of the currently added direct-coupled balance plug gauge.

[0013] Given an initial value for the plug gauge sensitivity, and determine the current equilibrium position based on the initial value for the plug gauge sensitivity, the current equilibrium position is the source distance of the shielded receiving coil that makes the residual direct coupling signal zero. The plug gauge sensitivity characterizes the rate of change of the residual direct coupling signal with the thickness of the direct coupling equilibrium plug gauge.

[0014] Determine the thickness of the direct-coupled balance plug gauge corresponding to the current balance position. When the subarray is a long subarray, the thickness of the source distance compensation plug gauge is also determined based on the thickness of the direct-coupled balance plug gauge.

[0015] Using a nonlinear equation root-finding algorithm, the thickness of the direct-coupled balance plug gauge is iteratively changed. When the subarray is a long subarray, the thickness of the source distance compensation plug gauge is also iteratively changed. Then, the current residual direct-coupled signal of the subarray is measured until the maximum number of iterations is reached or the nonlinear equation root-finding algorithm converges to the target equilibrium position, at which point the direct-coupled calibration ends.

[0016] Optionally, determining the theoretical process parameters of each coil system through direct-coupled balanced design includes:

[0017] Given the number of turns in the transmitting coil;

[0018] The source distance and number of turns of the main receiving coils of each subarray are selected, and both the source distance and number of turns of the main receiving coils are within a reasonable range determined according to the detection performance index and the sensing signal index of the instrument.

[0019] Using the constraint that the number of turns of the shielded receiving coil is an integer or even number, the source distance and number of turns of the shielded receiving coil are calculated using the direct coupling balance formula;

[0020] The rationality criterion is whether the coil substrate space constraint is met. The rationality of the coil system structure based on the current source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil is judged. If it is, the current source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil are used as theoretical process parameters for instrument manufacturing or improvement. Otherwise, the source distance and number of turns of the main receiving coil are iteratively updated until the coil system structure is reasonable.

[0021] The direct coupling balance formula is a constraint relationship between the source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil, determined based on the principle that the strength of the direct coupling signal is proportional to the reciprocal of the cube of the source distance of the receiving coil and the number of coil turns.

[0022] Optionally, the direct coupling balance formula is expressed by the following equation:

[0023]

[0024] Where, N Rm Number of turns of the main receiving coil, -N Rb The number of turns for the shielded receiving coil; the negative sign indicates that the shielded receiving coil is wound in the opposite direction to the main receiving coil. L m Main receiving coil source distance, L b To shield the source distance of the receiving coil.

[0025] Optionally, the step of using the number of turns of the shielded receiving coil as an integer or even number as a constraint condition, and calculating the source distance and number of turns of the shielded receiving coil using the direct coupling balance formula, includes:

[0026] Given an initial value for the source distance ratio between the shielded receiving coil and the main receiving coil, calculate the initial source distance value of each subarray shielded receiving coil based on the initial source distance ratio, and use the direct coupling balance formula to calculate the initial value of the number of turns of the shielded receiving coil.

[0027] Adjust the number of turns of the shielded receiving coil to an integer or even number, calculate the updated value of the source distance ratio between the shielded receiving coil and the main receiving coil using the direct coupling balance formula, and then calculate the updated value of the source distance of the shielded receiving coil based on the updated value of the source distance ratio. Use the adjusted number of turns of the shielded receiving coil (into an integer or even number) as the number of turns of the shielded receiving coil, and use the updated value of the source distance of the shielded receiving coil as the source distance of the shielded receiving coil.

[0028] Optionally, the detection performance indicators include radial detection depth and longitudinal resolution indicators.

[0029] Optionally, the sensing signal indicators include the sensing signal strength indicators of each subarray and the signal-to-noise ratio indicators of the original acquired signals.

[0030] Optionally, the target equilibrium position is the source distance of the shielded receiving coil after the addition of the direct-coupled equilibrium plug gauge corresponding to the equilibrium position when the zero-crossing plug gauge appears, or the source distance of the shielded receiving coil after the addition of the current direct-coupled equilibrium plug gauge that makes the residual direct-coupled signal 0, or the source distance of the shielded receiving coil after the addition of the current direct-coupled equilibrium plug gauge that makes the absolute value of the residual direct-coupled signal less than the first preset value; the zero-crossing plug gauges are the two direct-coupled equilibrium plug gauges with the smallest thickness difference corresponding to the one positive and one negative residual direct-coupled signals.

[0031] Optionally, if the nonlinear equation root-finding algorithm converges to the target equilibrium position, the source distance of the shielded receiving coil is corrected using the direct-coupled balance plug corresponding to the equilibrium position when the zero-crossing plug appears, and the source distance of the main receiving coil is compensated using a source distance compensation plug complementary to the direct-coupled balance plug when the subarray is a long subarray. Alternatively, the source distance of the shielded receiving coil is corrected using the current direct-coupled balance plug that makes the residual direct-coupled signal 0, and the source distance of the main receiving coil is compensated using a source distance compensation plug complementary to the direct-coupled balance plug when the subarray is a long subarray. Alternatively, the source distance of the shielded receiving coil is corrected using the current direct-coupled balance plug that makes the absolute value of the residual direct-coupled signal less than a first preset value, and the source distance of the main receiving coil is compensated using a source distance compensation plug complementary to the direct-coupled balance plug when the subarray is a long subarray.

[0032] Optionally, the thickness of the direct-coupled balance plug gauge corresponding to the current balance position can be determined based on the principle of nearest minimum.

[0033] The principle of nearest minimum is as follows: if a direct-coupled balanced plug gauge is added between the transmitting coil and the shielded receiving coil, and the source distance of the shielded receiving coil is closest to the current equilibrium position, then the direct-coupled balanced plug gauge is determined as the target plug gauge, and the thickness of the target plug gauge is determined as the thickness of the direct-coupled balanced plug gauge corresponding to the current equilibrium position; if there are two target plug gauges, then the thickness of the smallest target plug gauge is determined as the thickness of the direct-coupled balanced plug gauge corresponding to the current equilibrium position.

[0034] Optionally, the initial value of the plug gauge sensitivity can be an empirical value or determined based on the corrected theoretical plug gauge sensitivity.

[0035] Optionally, both the direct-coupled balance plug gauge and the source distance compensation plug gauge are selected from the increasing-distance plug gauge and the decreasing-distance plug gauge. The thickness of the increasing-distance plug gauge is the sum of the standard plug gauge thickness and the plug gauge offset. The thickness of the decreasing-distance plug gauge is the difference between the standard plug gauge thickness and the plug gauge offset. The plug gauge offset is a multiple of the unit plug gauge offset.

[0036] Optionally, when performing direct-coupled calibration for multiple or all subarrays, the direct-coupled calibration process is performed sequentially from closest to farthest from the shielded receiving coil and transmitting coil in the subarray.

[0037] Optionally, when performing direct coupling calibration for multiple or all subarrays, the direct coupling calibration process for these multiple or all subarrays is performed synchronously. In synchronous direct coupling calibration, if the distance between the shielded receiving coil and the transmitting coil in the first subarray is less than the distance between the shielded receiving coil and the transmitting coil in the second subarray, the source distance offset of the shielded receiving coil caused by the direct coupling balance plug gauge of the first subarray is added to the second subarray.

[0038] A second aspect of the present invention provides a device for achieving direct coupling balance of an array induction instrument coil system, the device comprising:

[0039] The direct-coupled balance theory design module is used to determine the theoretical process parameters of each coil system through direct-coupled balance design.

[0040] The initial plug gauge addition module is used to add a direct-coupled balanced plug gauge between the transmitting coil and the shielded receiving coil to change the source distance of the shielded receiving coil after the current coil system structure is used for instrument manufacturing or improvement. In addition, according to the principle that the source distance of the main receiving coil of the long subarray remains unchanged, a source distance compensation plug gauge complementary to the direct-coupled balanced plug gauge is added between the main receiving coil and the shielded receiving coil. When the subarray is a short subarray, no source distance compensation plug gauge is added between the main receiving coil and the shielded receiving coil. Then, the current residual direct-coupled signal of the subarray is measured and the source distance of the shielded receiving coil of the subarray is determined according to the thickness of the currently added direct-coupled balanced plug gauge.

[0041] The first determining module is used to give an initial value of the plug gauge sensitivity and determine the current equilibrium position based on the initial value of the plug gauge sensitivity. The current equilibrium position is the source distance of the shielded receiving coil that makes the residual direct coupling signal zero.

[0042] The second determining module is used to determine the thickness of the direct-coupled balance plug gauge corresponding to the current balance position. When the subarray is a long subarray, the thickness of the source distance compensation plug gauge is also determined based on the thickness of the direct-coupled balance plug gauge.

[0043] The iterative module is used to iteratively change the thickness of the direct-coupled balance plug gauge using a nonlinear equation root-finding algorithm. When the subarray is a long subarray, it also iteratively changes the thickness of the source distance compensation plug gauge. Then, it measures the current residual direct-coupled signal of the subarray until the maximum number of iterations is reached or the nonlinear equation root-finding algorithm converges to the target equilibrium position, at which point the direct-coupled calibration ends.

[0044] Among them, the plug gauge sensitivity characterizes the rate of change of the residual direct coupling signal with the thickness of the direct coupling balanced plug gauge.

[0045] Optionally, the direct-coupled balance theory design module includes:

[0046] The third determining module is used to specify the number of turns of the transmitting coil;

[0047] The first selection module is used to select the source distance and number of turns of the main receiving coil of each subarray. The source distance and number of turns of the main receiving coil are within a reasonable range determined according to the detection performance index and the sensing signal index of the instrument.

[0048] The first calculation module is used to calculate the source distance and number of turns of the shielded receiving coil using the direct coupling balance formula, with the number of turns of the shielded receiving coil being an integer or even number as a constraint.

[0049] The first judgment module is used to judge whether the coil system structure based on the current source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil is reasonable, based on whether the coil substrate space constraint is met as the rationality criterion. If it is reasonable, the current coil system structure is used for instrument manufacturing or improvement; otherwise, the source distance and number of turns of the main receiving coil are iteratively updated until the coil system structure is reasonable.

[0050] The direct coupling balance formula is a constraint relationship between the source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil, determined based on the principle that the strength of the direct coupling signal is proportional to the reciprocal of the cube of the source distance of the receiving coil and the number of coil turns.

[0051] Optionally, the target equilibrium position is the source distance of the shielded receiving coil after the addition of the direct-coupled equilibrium plug gauge corresponding to the equilibrium position when the zero-crossing plug gauge appears, or the source distance of the shielded receiving coil after the addition of the current direct-coupled equilibrium plug gauge that makes the residual direct-coupled signal 0, or the source distance of the shielded receiving coil after the addition of the current direct-coupled equilibrium plug gauge that makes the absolute value of the residual direct-coupled signal less than the first preset value; the zero-crossing plug gauges are the two direct-coupled equilibrium plug gauges with the smallest thickness difference corresponding to the one positive and one negative residual direct-coupled signals.

[0052] A third aspect of the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the direct coupling balance method for the array induction instrument coil system described in the first aspect of the present invention.

[0053] A fourth aspect of the present invention provides a machine-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the direct-coupled balance implementation method for the array induction instrument coil system described in the first aspect of the present invention.

[0054] In the above technical solution, for short subarrays, direct coupling calibration is performed using a direct coupling balance gauge. When the nonlinear equation root-finding algorithm converges to the target equilibrium position, the theoretical process parameters of each coil system determined by the direct coupling balance design can be corrected using the direct coupling balance gauge corresponding to the target equilibrium position. For long subarrays, direct coupling calibration is performed using a direct coupling balance gauge and a source distance compensation gauge. When the nonlinear equation root-finding algorithm converges to the target equilibrium position, the theoretical process parameters of each coil system determined by the direct coupling balance design can be corrected using the direct coupling balance gauge and the source distance compensation gauge corresponding to the target equilibrium position. This avoids the significant differences between the actual manufactured instrument and the theoretical design caused by various simplification factors in the direct coupling balance theoretical design, actual coil geometric dimension errors, actual coil system substrate machining errors, coil winding process, winding tension, and assembly, etc. This allows the array sensing instrument manufactured or improved based on the finally determined process parameters of each coil system to eliminate direct coupling signals to the greatest extent, highlight useful signals, ensure direct coupling balance, and improve the signal-to-noise ratio of the array sensing instrument.

[0055] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0056] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings:

[0057] Figure 1 The schematic diagram illustrates the principle of induction logging as presented in the background art;

[0058] Figure 2 The schematic diagram illustrates the phase relationship between the currents in the transmitting coil, the ground unit loop, and the receiving coil as presented in the background art;

[0059] Figure 3 A schematic diagram of the coil-based induction probe structure proposed in the background art is shown.

[0060] Figure 4 A schematic diagram of the array sensing instrument probe structure proposed in the background art is shown.

[0061] Figure 5 A flowchart illustrating a method for achieving direct coupling balance of an array induction instrument coil system according to an embodiment of the present invention is shown.

[0062] Figure 6 This schematically illustrates a flowchart of a direct-coupled calibration process in a specific application example;

[0063] Figure 7A flowchart illustrating the design process of the direct-coupled equilibrium theory according to an embodiment of the present invention is shown schematically.

[0064] Figure 8 The flowchart illustrates the design process of direct-coupled equilibrium theory in a specific application example.

[0065] Figure 9 The schematic diagram shows the side view of the assembled and half-piece plug gauge;

[0066] Figure 10 The diagram schematically shows the top view of the assembled plug gauge and the two halves;

[0067] Figure 11 The schematic diagram shows the positions of the direct-coupled balance plug gauge and the source distance compensation plug gauge;

[0068] Figure 12 The diagram illustrates a plug gauge for an array sensing instrument containing seven subarrays in a specific application example.

[0069] Figure 13 The illustration shows a schematic diagram of a nonlinear equation root-finding algorithm for finding the target equilibrium position in a specific application example. Detailed Implementation

[0070] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0071] Example 1

[0072] See Figure 5 This invention provides a method for achieving direct coupling balance in an array induction instrument coil system, comprising the following implementation steps:

[0073] Step S100: Determine the theoretical process parameters of each coil system through direct coupling balance design, so as to use the theoretical process parameters to manufacture or improve the array induction instrument.

[0074] Step S200: Perform direct coupling calibration for the subarray.

[0075] The direct coupling calibration process includes the following sub-steps:

[0076] Step S210: Add a direct-coupled balance plug gauge between the transmitting coil and the shielded receiving coil to change the source distance of the shielded receiving coil. In accordance with the principle that the source distance of the main receiving coil of the long subarray remains unchanged, add a source distance compensation plug gauge that is complementary to the direct-coupled balance plug gauge between the main receiving coil and the shielded receiving coil. When the subarray is a short subarray, no source distance compensation plug gauge is added between the main receiving coil and the shielded receiving coil. Then measure the current residual direct-coupled signal of the subarray and determine the source distance of the shielded receiving coil of the subarray based on the thickness of the currently added direct-coupled balance plug gauge.

[0077] Step S220: Given an initial value for the plug gauge sensitivity, determine the current equilibrium position based on the initial value for the plug gauge sensitivity. The current equilibrium position is the source distance of the shielded receiving coil that makes the residual direct coupling signal zero. The plug gauge sensitivity characterizes the rate of change of the residual direct coupling signal with the thickness of the direct coupling equilibrium plug gauge.

[0078] Step S230: Determine the thickness of the direct-coupled balance plug gauge corresponding to the current balance position, and record it as the thickness of the direct-coupled balance plug gauge before the change. When the subarray is a long subarray, the thickness of the source distance compensation plug gauge is also determined based on the thickness of the direct-coupled balance plug gauge.

[0079] Step S240: Using a nonlinear equation root-finding algorithm, the thickness of the direct coupling balance plug gauge is iteratively changed. When the subarray is a long subarray, the thickness of the source distance compensation plug gauge is also iteratively changed. Then, the current residual direct coupling signal of the subarray is measured until the maximum number of iterations is reached or the nonlinear equation root-finding algorithm converges to the target equilibrium position, and the direct coupling calibration ends.

[0080] Among them, the sensitivity of the plug gauge characterizes the rate of change of the residual direct coupling signal with the thickness of the direct coupling balanced plug gauge; the target balance position is the source distance of the shielded receiving coil after the addition of the direct coupling balanced plug gauge when the zero-crossing plug gauge appears, or the source distance of the shielded receiving coil after the addition of the current direct coupling balanced plug gauge that makes the residual direct coupling signal 0, or the source distance of the shielded receiving coil after the addition of the current direct coupling balanced plug gauge that makes the absolute value of the residual direct coupling signal less than the first preset value; the zero-crossing plug gauge is the two direct coupling balanced plug gauges with the smallest thickness difference corresponding to the positive and negative residual direct coupling signals.

[0081] For example, combined Figure 7 As shown, in a specific embodiment, the theoretical process parameters of each coil system are determined through direct-coupled balanced design. The direct-coupled balanced theoretical design process is as follows:

[0082] Step S110: Given the number of turns of the transmitting coil;

[0083] Step S120: Select the source distance and number of turns of the main receiving coil of each subarray. The source distance and number of turns of the main receiving coil are within a reasonable range determined according to the detection performance index and sensing signal index of the instrument.

[0084] Step S130: Using the number of turns of the shielded receiving coil as an integer or even number as a constraint, the source distance and number of turns of the shielded receiving coil are calculated using the direct coupling balance formula.

[0085] Step S140: Using whether the coil substrate space constraint is met as the rationality criterion, determine whether the coil system structure based on the current source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil is reasonable. If so, the current source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil are used as theoretical process parameters for instrument manufacturing or improvement. Otherwise, iteratively update the source distance and number of turns of the main receiving coil until the coil system structure is reasonable.

[0086] The direct coupling balance formula is a constraint relationship between the source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil, determined based on the principle that the strength of the direct coupling signal is proportional to the reciprocal of the cube of the source distance of the receiving coil and the number of coil turns.

[0087] In the above embodiments, the process parameters of the coil system structure are determined by the direct coupling balance formula based on electromagnetic field theory. The process parameters include the source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil. This enables the array induction instrument made or improved based on the core parameters of the determined coil system structure to have theoretical direct coupling balance, and can achieve partial elimination of direct coupling signals.

[0088] For example, in one specific embodiment, the direct coupling balance formula is expressed by the following equation:

[0089]

[0090] Where, N Rm Number of turns of the main receiving coil, -N Rb The number of turns for the shielded receiving coil; the negative sign indicates that the shielded receiving coil is wound in the opposite direction to the main receiving coil. L m Main receiving coil source distance, L b To shield the source distance of the receiving coil.

[0091] In one specific embodiment, the source distance and number of turns of the shielded receiving coil are calculated using the direct coupling balance formula, with the number of turns being an integer or even number as a constraint. This includes:

[0092] Given an initial value for the source distance ratio between the shielded receiving coil and the main receiving coil, calculate the initial source distance value of each subarray shielded receiving coil based on the initial source distance ratio, and use the direct coupling balance formula to calculate the initial value of the number of turns of the shielded receiving coil.

[0093] Adjust the number of turns of the shielded receiving coil to an integer or even number, calculate the updated value of the source distance ratio between the shielded receiving coil and the main receiving coil using the direct coupling balance formula, and then calculate the updated value of the source distance of the shielded receiving coil based on the updated value of the source distance ratio. Use the adjusted number of turns of the shielded receiving coil (into an integer or even number) as the number of turns of the shielded receiving coil, and use the updated value of the source distance of the shielded receiving coil as the source distance of the shielded receiving coil.

[0094] Based on the above embodiments, such as Figure 8 As shown, in a specific application, a concrete implementation process of the direct-coupled balance theory design includes:

[0095] Step SS100: Determine the number of turns of the shared transmitting coil.

[0096] Step SS200 involves selecting the source distance of the main receiving coils for each subarray. The source distance of the main receiving coils must be within a reasonable range determined based on the detection performance indicators. It is known that, to ensure the detection performance of the array sensing instrument meets the requirements, the configurable detection performance indicators include radial detection depth and longitudinal resolution.

[0097] Step SS300 involves selecting the number of turns of the main receiving coil for each subarray. The number of turns of the main receiving coil is within a reasonable range determined based on the induction signal specifications. It is known that, to ensure the induction signal of the array sensing instrument meets the requirements, the induction signal specifications that can be set include the induction signal strength of each subarray and the signal-to-noise ratio of the original acquired signal.

[0098] Step SS400: Given an initial value β for the source-to-source distance ratio of the shielded receiving coil to the main receiving coil, calculate the initial source-to-source distance L for each subarray shielded receiving coil based on the initial source-to-source distance ratio β. b =βL m The initial number of turns of the shielded receiving coil was obtained using the direct coupling balance formula.

[0099] Step SS500: Adjust the number of turns of the shielded receiving coil to an integer N'. Nb =int(β) 3 N Rm The source distance L of the shielded receiving coil is either even or zero, and the updated value β' of the source distance ratio between the shielded receiving coil and the main receiving coil is obtained using the direct coupling balance formula. Then, the source distance L of the shielded receiving coil is recalculated based on the updated value β'. b =β'L m That is, to calculate the source distance update value of the shielded receiving coil;

[0100] Step SS600, Structural Compatibility Check: Based on whether the coil substrate accommodates the space constraints, determine whether the coil system structure based on the current source distance of the main receiving coil, the number of turns of the main receiving coil, the source distance of the shielded receiving coil, and the number of turns of the shielded receiving coil after adjustment to an integer or even number is reasonable. If reasonable, proceed to step SS700; otherwise, jump to step SS200.

[0101] It should be understood that the transmitting coil, the main receiving coil, and the shielded receiving coil are all wound in the slots of the coil base according to the preset turn spacing. Therefore, the space constraint of the coil base means that after calculating the coil length based on the number of coil turns and the turn spacing, and considering the reserved positions of structural components such as terminals, the total length occupied by the coil system as a whole does not exceed the total length of the coil base.

[0102] Step SS700 involves calculating the signal magnitude of each subarray, evaluating the signal-to-noise ratio, analyzing and assessing the instrument's accuracy and measurement dynamic range, and examining the detection performance and direct coupling balance of each subarray. The latest source distance of the main receiving coil, the number of turns of the main receiving coil, the source distance of the shielded receiving coil, and the number of turns of the shielded receiving coil adjusted to an integer or even number are used for the manufacture or improvement of the array sensing instrument.

[0103] For induction logging in homogeneous media, the induced electromotive force in the receiving coil can be derived from electromagnetic field theory as follows:

[0104]

[0105] In Equation 1, i is the imaginary unit, ω is the angular frequency, μ is the permeability (in H / m), and I... T =I0e -iωt I T I0 is the emission current, and I0 is the amplitude of the emission current, A. T A is the area of ​​the transmitting coil. R N is the area of ​​the receiving coil. T and N R Here, represents the number of turns of the transmitting and receiving coils, respectively, and k is the wavenumber of the formation medium. 2 =iωμσ, where σ is the conductivity of the space medium. In Equation 1, when σ = 0, i.e., k = 0, the direct-coupled electromotive force is obtained as:

[0106]

[0107] In such Figure 3In the coil array induction instrument structure shown, since the magnitude of the useful secondary induction signal is inversely proportional to the source distance, while the magnitude of the useless direct-coupled signal is inversely proportional to the cube of the source distance, theoretically, the direct-coupled signal can be completely canceled by optimizing the design of the number of turns and position of the shielded receiving coil, sacrificing some of the useful signal, thus achieving the purpose of shielding the direct-coupled signal. Assume the distances from the center of the transmitting coil Tx to the centers of the main receiving coil and the shielded receiving coils Rm and Rb are L... m and L b The number of turns of the main receiving coil and the shielded receiving coil are N respectively. Rm and -N Rb The negative sign indicates that the shielded receiving coil and the main receiving coil are wound in opposite directions. This is because the magnitude of the direct-coupled signal is the reciprocal of the cube of the source distance. and the number of turns N of the receiving coil R If they are directly proportional, then the main receiving coil and the shielded receiving coil are wound in opposite directions and connected in series, and the number of turns satisfies the following relationship with the source distance:

[0108]

[0109] Theoretically, this can cancel out the direct-coupled signal and partially retain the secondary signal generated by the formation vortex, thereby improving the signal-to-noise ratio of the instrument.

[0110] For each subarray of a coil array induction instrument, since the transmitting and receiving coils have the same area, theoretically, as long as the design of the number of turns and source distance of the main receiving coil and the shielded receiving coil satisfies the relationship shown in Equation 3, the array induction instrument can achieve direct coupling balance. However, there are multiple ways to satisfy Equation 3, even under the condition that the main receiving coil Rm is given, i.e., for a given number of turns N... Rm and source distance L m For any main receiving coil Rm, there are multiple possibilities for the shielded receiving coil Rb that satisfies Formula 3, namely, the number of turns of the shielded receiving coil - N. Rb and source distance L b There are multiple possible combinations. In an extreme case, take -N. Rb =-1, meaning that a single-turn reverse-wound coil can be designed as a shielded receiving coil. In this case, the source distance L of the shielded receiving coil Rb is... b Satisfies Formula 3, that is Theoretically, this can completely cancel out direct-coupled signals, at which point the source distance between the shielded receiving coil and the main receiving coil differs the greatest. At the other extreme, the shielded receiving coil and the main receiving coil can be made as close as possible, provided the number of turns of the shielded receiving coil Rb is -N. Rb As long as formula 3 is satisfied, that is Theoretically, it is possible to completely cancel out the direct-coupled signal, at which point the number of turns of the shielded receiving coil and the main receiving coil are closest.

[0111] The detailed derivation of Formula 3 is as follows:

[0112] According to the principles of electromagnetic fields, the electromotive force induced in the receiving coil of a unit magnetic pole at a point in space is:

[0113] V=iωμ0N R A R H(Formula 4);

[0114] In Equation 4, i is the imaginary unit, ω is the angular frequency, μ0 is the free space permeability (in H / m), and A R N is the area of ​​the receiving coil. R Let H be the number of turns of the receiving coil, and H be the magnetic field strength at the receiving coil, which can be expressed by the following formula:

[0115]

[0116] In Formula 5, (r,z) represents the spatial cylindrical coordinates of the field point, and k represents the wavenumber of the formation medium. 2 =iωμσ, where σ is the conductivity of the space medium;

[0117] From Equation 4, it can be seen that the phase difference between the induced electromotive force V in the receiving coil and the magnetic field strength H at the receiving coil is 90 degrees. Therefore, the magnetic field strength H at the receiving coil can be expressed as two parts: a real part and an imaginary part, i.e.:

[0118] H = H' + iH (Formula 6);

[0119] Substituting formula 6 into formula 4, we get:

[0120] V=-ωμ0N R A R H”+iωμ0N R A R H'(Formula 7);

[0121] As shown in Formula 7, the magnetic field signal in the receiving coil is the sum of two magnetic field signals: the primary magnetic field and the secondary magnetic field. The primary field H' is the directly coupled magnetic field induced by the transmitting coil at the position of the receiving coil, and it is independent of the surrounding strata information. The secondary magnetic field H” is the magnetic field signal related to the strata, which is the information that the array sensing instrument needs to measure.

[0122] Under low-frequency electromagnetic field conditions, e ikr The first three terms of the Taylor expansion Substitute into public

[0123] Equation 5, through mathematical derivation, yields an approximate expression for the magnetic field strength H at the receiving coil:

[0124]

[0125] Equation 8 is derived based on the magnetic dipole. Considering the number of turns and area of ​​the transmitting coil, the secondary magnetic field or useful signal received by the receiving coil, i.e., the real part of Equation 7, is:

[0126]

[0127] When the conductivity of the space medium σ = 0, i.e., k = 0, the direct-coupled electromotive force is obtained as:

[0128]

[0129] In Formula 10, I T =I0e -iωt I T I0 is the emission current, and I0 is the amplitude of the emission current, A. T It is the area of ​​the transmitting coil, A R N is the area of ​​the receiving coil. T N represents the number of turns in the transmitting coil. R This refers to the number of turns of the receiving coil.

[0130] As shown in Formulas 9 and 10, the magnitude of the useful secondary induction signal is inversely proportional to the source distance, while the useless direct coupling signal is inversely proportional to the cube of the source distance. Thus, theoretically, the direct coupling signal can be completely canceled by optimizing the design of the number of turns of the shielded receiving coil and the source distance, at the cost of sacrificing some of the useful signal. However, in addition to eliminating the direct coupling signal by winding the two receiving coils in opposite directions and satisfying Formula (3) for the source distance and number of turns, it is also necessary to consider the magnitude and degree of sacrifice of the useful signal while eliminating the direct coupling signal, as well as the consistency of the detection range between the shielded coil and the main receiving coil.

[0131] Let the ratio of the source distance of the shielded receiving coil to the main receiving coil be... Then, according to the above direct-coupled balance formula, the number of turns of the shielded receiving coil can be expressed as:

[0132]

[0133] Since the number of turns must be an integer or even number, the number of turns of the shielded receiving coil is N'. Nb =int(β) 3 N Rm () or even number;

[0134] After adjusting the number of turns of the shielded receiving coil to an integer or even number, we can obtain the following from Formula 12:

[0135]

[0136] Where β' is the updated value of the ratio of the source distance between the shielded receiving coil and the main receiving coil;

[0137] Then, recalculate the source distance L of the shielded receiving coil using Formula 11. b =β'L m .

[0138] Therefore, the key to the design of the shielded receiving coil lies in determining β'. Thus, by connecting a reverse-wound shielded receiving coil in series with the main receiving coil, the direct-coupled signals of the main and shielded receiving coils are equal in magnitude but opposite in direction, and when connected in series, they cancel each other out. The ratio of the magnitude of the secondary induced signals in the shielded and main receiving coils—that is, the useful signals related to the formation—is:

[0139]

[0140] As can be seen from Formula 14, by sacrificing the useful signal β' of the main receiving coil 2 This completely eliminates direct coupling signals. Clearly, β' 2 This characterizes the degree to which the shielded receiving coil cancels out the useful signal. β' 2 If β' is too large, it will lead to excessive loss of useful signal while eliminating direct coupling signal, resulting in a low signal-to-noise ratio for the array sensing instrument. Conversely, if β' is too small... 2 If β' is too small, on the one hand, the source distance difference between the shielded receiving coil and the main receiving coil will be too large, resulting in a significant difference in the detection range between the shielded receiving coil and the main receiving coil of the subarray, thus degrading the detection performance of the subarray. On the other hand, an excessively small β' 2 This will make the shielded receiving coil overly sensitive to changes in source distance, which is not conducive to the calibration of direct coupling balance in actual production and manufacturing.

[0141] In practice, the design makes β' 2 ≈0.5 is appropriate; generally, 0.5 ≤ β' is taken. 2 ≤0.618. Considering the shallower detection area of ​​the short subarray, and the more drastic changes in the conductivity of the surrounding medium near the wellbore due to the presence of drilling fluid and intrusion, the source distance between the shielded receiving coil and the main receiving coil of the short subarray should be relatively close to ensure that they detect the same area as much as possible. At the same time, the relatively large signal magnitude of the short subarray also allows it to tolerate a larger β'. 2 value.

[0142] For example, in one specific embodiment, the initial value of the plug gauge sensitivity is an empirical value or determined based on the corrected theoretical plug gauge sensitivity.

[0143] For example, in one specific embodiment, when performing a direct-coupled calibration process for multiple or all subarrays, the direct-coupled calibration process is performed sequentially from closest to furthest from the shielded receiving coil and transmitting coil in the subarray. Although the balance position of each subarray and the direct-coupled calibration process of the balance position are independent of each other, the position of the longer subarray is affected by the direct-coupled calibration results of the preceding shorter subarrays and the replacement of the gauge plug. By adding the source distance offset of the shielded receiving coil caused by the direct-coupled balance gauge of the preceding shorter subarray to the gauge plug of the subsequent longer subarray according to the positional relationship of the subarrays, the balance position and the current adjustment position of each subarray remain unchanged, thereby achieving direct-coupled balance calibration of multiple or all subarrays. Compared with calibration not based on the positional relationship of the subarrays, this reduces the frequent loosening and tightening of coil systems when changing gauge plugs, thus improving the efficiency of direct-coupled calibration.

[0144] As an improvement to the above embodiment, when performing direct-coupled calibration for multiple or all subarrays, the direct-coupled calibration process for these subarrays is performed synchronously. In synchronous direct-coupled calibration, based on the positional relationship between any two subarrays, if the distance between the shielded receiving coil and the transmitting coil in the first subarray is less than the distance between the shielded receiving coil and the transmitting coil in the second subarray, then the source-pitch offset of the shielded receiving coil caused by the direct-coupled balancing gauge in the first subarray is added to the second subarray. By synchronously performing direct-coupled calibration on each subarray and accumulating the source-pitch offset of the shielded receiving coil according to the positional relationship of the subarrays, the efficiency of direct-coupled calibration is improved.

[0145] For example, in one specific embodiment, the algorithm for finding the root of nonlinear equations employs methods such as the bisection method, the secant method, the general trial-and-error method, the Ridders method, and the Brent method.

[0146] For example, in one specific embodiment, a nonlinear equation root-finding algorithm is used to iteratively change the thickness of the direct-coupled balance plug gauge. When the subarray is a long subarray, the source distance compensation plug gauge thickness is also iteratively changed. Then, the current residual direct-coupled signal of the subarray is measured until the maximum number of iterations is reached or the nonlinear equation root-finding algorithm converges to the target equilibrium position, at which point the direct-coupled calibration ends. This includes:

[0147] Step S2410: Change the thickness of the direct coupling balance plug gauge. When the subarray is a long subarray, also change the thickness of the source distance compensation plug gauge and measure the current residual direct coupling signal of the subarray.

[0148] Step S2420: Determine whether the maximum number of iterations has been reached or whether the nonlinear equation root-finding algorithm has converged to the target equilibrium position; if so, the direct coupling calibration ends; otherwise, determine the new gauge sensitivity and equilibrium position based on the residual direct coupling signal before and after the change in the thickness of the direct coupling balance gauge and the source distance of the shielded receiving coil, and jump to step S230.

[0149] It is evident that the termination condition for direct-coupled tuning is reaching the maximum number of iterations or the nonlinear equation root-finding algorithm converging to the target equilibrium position. The nonlinear equation root-finding algorithm converging to the target equilibrium position occurs when one of the following three conditions is met:

[0150] 1) A zero-crossing plug gauge appears;

[0151] 2) The addition of the current direct-coupled balanced plug gauge makes the residual direct-coupled signal zero;

[0152] 3) The addition of the current direct-coupled balanced plug gauge makes the absolute value of the residual direct-coupled signal less than the first preset value.

[0153] For example, in one specific embodiment, the thickness of the direct-coupled balance plug gauge corresponding to the current equilibrium position is determined according to the principle of nearest minimum. The principle of nearest minimum is as follows: if a direct-coupled balance plug gauge is added between the transmitting coil and the shielded receiving coil, and the source distance of the shielded receiving coil is closest to the current equilibrium position, then the direct-coupled balance plug gauge is determined as the target plug gauge, and the thickness of the target plug gauge is determined as the thickness of the direct-coupled balance plug gauge corresponding to the current equilibrium position; if there are two target plug gauges, then the thickness of the smaller target plug gauge is determined as the thickness of the direct-coupled balance plug gauge corresponding to the current equilibrium position.

[0154] For example, in one specific embodiment, if the nonlinear equation root-finding algorithm converges to the target equilibrium position, the source distance of the shielded receiving coil is corrected using the direct-coupled balance plug corresponding to the equilibrium position when the zero-crossing plug appears, and the source distance of the main receiving coil is compensated using a source distance compensation plug complementary to the direct-coupled balance plug when the subarray is a long subarray. Alternatively, the source distance of the shielded receiving coil is corrected using the current direct-coupled balance plug that makes the residual direct-coupled signal 0, and the source distance of the main receiving coil is compensated using a source distance compensation plug complementary to the direct-coupled balance plug when the subarray is a long subarray. Alternatively, the source distance of the shielded receiving coil is corrected using the current direct-coupled balance plug that makes the absolute value of the residual direct-coupled signal less than a first preset value, and the source distance of the main receiving coil is compensated using a source distance compensation plug complementary to the direct-coupled balance plug when the subarray is a long subarray.

[0155] It is important to understand that, traditionally, a plug gauge refers to a precision measuring tool, also known as a caliper, primarily used to measure the diameter or gap dimensions of round and cylindrical holes. In this embodiment of the invention, the plug gauge is a series of precision-polished structural components of varying thicknesses, used to be inserted between the coil substrates; hence, it is defined as a plug gauge. Its function is to: achieve fine-tuning of the position of the shielded receiving coil through the addition of the plug gauge, thereby achieving fine-tuning of the source distance of the shielded receiving coil, and to compensate for changes in the position of the main receiving coil in the long subarray caused by the fine-tuning of the shielded receiving coil position. The series of structural components can be a series of annular plates, which can be ceramic plates, etc.

[0156] In one specific embodiment, the structure of the plug gauge is as follows: Figure 9 and Figure 10 As shown, the position of the plug gauge on the array sensing instrument is as follows: Figure 11 and Figure 12 As shown. Figure 10 In this device, the plug gauge is made of two semi-ring-shaped ceramic discs that have been precision-ground. A pair of semi-ring plug gauges of the same thickness are inserted into the gap of the loosened coil base, and then the coil system is tightened. In this way, the source distance of the coil can be changed by changing the thickness of the plug gauge. The plug gauge has binding grooves, which can be used to easily bind and fix the two semi-ring plug gauges with fine cotton thread to prevent the plug gauge from falling off before and after the coil system is tightened when changing the plug gauge. Figure 12 The array sensing instrument includes four short subarrays R0, R1, R2, and R3, and three long subarrays R4, R5, and R6. The short subarray R0 contains the main receiving coil R... 0m and shielded receiving coil R 0b The short subarray R1 contains the main receiving coil R. 1m and shielded receiving coil R 1b The short subarray R2 contains the main receiving coil R. 2m and shielded receiving coil R 2b The short subarray R3 contains the main receiving coil R. 3m and shielded receiving coil R 3b The array sensing instrument incorporates seven direct-coupled balance plug gauges: S0, S1, S2, S3, and S... 4b S 5b S 6b In addition, three source distance compensation plug gauges S were added. 4m S 5m S 6m .

[0157] For example, in one specific embodiment, both the direct-coupled balancing plug gauge and the source-pitch compensation plug gauge are selected from the increasing-pitch plug gauge and the decreasing-pitch plug gauge. The thickness of the increasing-pitch plug gauge is the sum of the standard plug gauge thickness and the plug gauge offset, and the thickness of the decreasing-pitch plug gauge is the difference between the standard plug gauge thickness and the plug gauge offset. The plug gauge offset is a multiple of the unit plug gauge offset. Based on the above embodiment, by setting the standard plug gauge, the decreasing-pitch plug gauge with stepped thickness reduction, and the increasing-pitch plug gauge with stepped thickness increase, the selection of the direct-coupled balancing plug gauge and the source-pitch compensation plug gauge becomes more flexible, thereby improving the efficiency of direct-coupled calibration.

[0158] For example, in a specific application, the plug gauge series consisting of increasing-distance plug gauges, decreasing-distance plug gauges, and standard plug gauges is shown in Table 1. The standard plug gauge is designated BZ, and for easy identification, the name "BZ" is marked on the plug gauge surface with a black pen. J1, J2, J3, ..., J26 are decreasing-distance plug gauges with thicknesses of 9.95mm, 9.90mm, 9.85mm, ..., 7.00mm, respectively, and offsets of -0.05mm, -0.10mm, -0.15mm, ..., -3.00mm, respectively. A J26 plug gauge can reduce the source distance by 3.00mm compared to the initial standard plug gauge BZ. The name of the decreasing-distance plug gauge is marked on the plug gauge surface with a green pen. Z1, Z2, Z3, ..., Z26 are offset plug gauges with thicknesses of 10.05mm, 10.10mm, 10.15mm, ..., 13.00mm respectively, and offsets of 0.05mm, 0.10mm, 0.15mm, ..., 3.00mm respectively. One Z26 plug gauge increases the source distance by 3.00mm relative to the initial standard plug gauge BZ. The name of the offset plug gauge is marked in red on the gauge surface. Meanwhile, Z1 and J1 are mutually compensating plug gauges because their offsets are opposites. Similarly, Z2 and J2, Z3 and J3, ..., Z26 and J26 are also mutually compensating plug gauges. Source distance compensating plug gauges can be placed... Figure 11The source distance compensation plug gauge positions shown in Table 1 compensate for the offset of the direct coupling balance plug gauge in the long subarray coil system to ensure that the source distance of the main receiving coil of the long subarray remains unchanged. The plug gauge sequence J26, J25, ..., J1, BZ, Z1, Z2, ..., Z26 in Table 1 are arranged from thinnest to thickest, with the plug gauge thickness increasing from 7mm to 13mm and the plug gauge offset increasing from -3mm to +3mm. In the plug gauge sequence, two adjacent plug gauges are called adjacent plug gauges, and the minimum range between adjacent plug gauges is only 0.05mm. Preferably, each plug gauge position can be designed to accommodate two plug gauges. This two-plug-gauge design, on the one hand, changes the maximum source distance increase or decrease of 3.00mm relative to one standard plug gauge to 6.0mm, expanding the source distance adjustment range without increasing the plug gauge series. On the other hand, it provides more combinations of plug gauges, improving the reuse rate of plug gauges and significantly saving costs. At the same time, it should be emphasized that the final direct coupling calibration result allows for only one plug gauge position, or three or more plug gauges, but in practice, two plug gauge positions are sufficient to calibrate to the balanced position.

[0159] Table 1

[0160]

[0161]

[0162] pass Figure 7 and Figure 8 The subarrays of the coil array induction instrument implemented by the illustrated process are theoretically directly coupled and balanced. However, the array induction instrument is very sensitive to direct-coupled signals. Due to various factors such as the introduction of simplification factors like magnetic dipoles in formulas 1 to 14, the influence of actual coil geometry, and the existence of structural and manufacturing errors, the direct-coupled signals of the actually manufactured and assembled array induction instrument are not completely canceled out and require fine-tuning and calibration. Figure 11 As can be seen, the coil in the coil system is wound on a rigid substrate. The material of the rigid substrate generally requires easy precision machining and small temperature expansion effects, while mechanical strength and material processing costs must also be considered. Ceramic is generally chosen as the coil substrate, and metal wire (usually copper or lithium wire) is wound in a pre-machined groove in the coil substrate to form the induction coil. The coil substrate of the induction coil has a pre-machined hole in the middle. The instrument spindle is a beryllium copper tube, with a fiberglass bushing on the outside of the tube. During instrument assembly, a rubber O-ring is placed between the fiberglass bushing and the ceramic substrate of the induction coil. In this way, the position of the coil wound in the groove in the coil substrate is fixed relative to the coil substrate, and the length of the coil substrate is also fixed. This allows for fine adjustment of the coil position by changing plug gauges of different thicknesses between the coil substrates. It is evident that achieving direct coupling balance by adjusting plug gauges is feasible.

[0163] Furthermore, to adapt to various detection needs, array sensing instruments typically include short subarrays and long subarrays. Here, the distinction between long and short subarrays is determined by their source distance and a preset threshold. If the source distance of a subarray does not exceed the preset threshold, it can be identified as a short subarray; otherwise, it is a long subarray. For short subarrays, the direct-coupled signal is extremely sensitive to fine-tuning of the shielded receiving coil's position, and the source distance adjustment is relatively small. Simultaneously, within each short subarray, the space between the shielded receiving coil and the main receiving coil is limited. To improve the accuracy of the array sensing instrument, the shielded receiving coil and the main receiving coil are usually wound on the same coil base. Therefore, when adjusting the gauge, the gauge position can only be designed between the transmitting coil and the shielded receiving coil. By changing the thickness of the direct-coupled balanced gauge, the source distance between the shielded receiving coil and the main receiving coil increases or decreases synchronously. For the long subarray, the position sensitivity of its shielded receiving coil is relatively small. At the same time, the space between the shielded receiving coil and the main receiving coil in each long subarray is relatively ample. To ensure that the source distance of the main receiving coil does not change due to the direct coupling adjustment process, for a certain long subarray, in addition to designing a plug gauge position between its transmitting coil and shielded receiving coil to insert a direct coupling balance plug gauge to adjust the position of the shielded receiving coil, a plug gauge position is also designed between its main receiving coil and shielded receiving coil to insert a source distance compensation plug gauge. The thickness increase or decrease of the source distance compensation plug gauge inserted at this plug gauge position is opposite to the thickness increase or decrease of the direct coupling balance plug gauge inserted in the long subarray. This is to compensate for the change in the source distance of the main receiving coil caused by the replacement of the direct coupling balance plug gauge, thereby ensuring that the relative position of the main receiving coil with respect to the transmitting coil does not change, that is, ensuring that the source distance of the main receiving coil remains unchanged.

[0164] In the above embodiments, the direct coupling signal of the main receiving coil can be obtained from formula 10 as follows:

[0165]

[0166] The direct coupling signal of the shielded receiving coil is:

[0167]

[0168] Let the plug gauge offset be l mb For a short subarray with a direct-coupled balancing plug placed only between the transmitting coil and the shielded receiving coil, the total direct-coupled electromotive force of the main receiving coil and the shielded receiving coil connected in series, i.e., the residual direct-coupled signal, is:

[0169]

[0170] Furthermore, the plug sensitivity of the short subarray is defined as:

[0171]

[0172] Similarly, for the long-spin array, the total direct-coupled electromotive force of the main receiving coil and the shielded receiving coil connected in series, i.e., the residual direct-coupled signal, is:

[0173]

[0174] Furthermore, the plug sensitivity of the long subarray is defined as:

[0175]

[0176] L b =βL m and Substituting into formula (18), considering 0.5≤β 2 ≤0.618 and plug gauge offset l mb If it is very small, the plug sensitivity of the short subarray can be further expressed as:

[0177]

[0178] From Equations 20 and 21, it can be seen that the residual direct coupling signal varies with the gauge offset l mb The sensitivity decreases monotonically. Furthermore, as shown by the direct-coupled balance formula, a balance position exists, which is the theoretical basis for the aforementioned direct-coupled calibration process. Comparing Formulas 18 and 20, it can be seen that for short subarrays, setting only one direct-coupled balance gauge to simultaneously change the source distance of the shielded receiving coil and the source distance of the main receiving coil reduces the gauge sensitivity of the short subarray compared to setting two gauges: a direct-coupled balance gauge and a source distance compensation gauge. This is beneficial for the direct-coupled calibration of the short subarray. It should be noted that the gauge sensitivity expressed in Formulas 20 and 21 is the theoretical gauge sensitivity.

[0179] Based on the above embodiments, such as Figure 6 and Figure 13 As shown, in a specific application, the direct-coupled calibration process for the subarray based on the chord cleavage method includes the following implementation steps:

[0180] Step A1: Add an initial direct-coupled balancing plug gauge between the transmitting coil and the shielded receiving coil to change the source distance of the shielded receiving coil. Also, according to the principle of keeping the source distance of the main receiving coil constant in the long subarray, add an initial source distance compensation plug gauge between the main receiving coil and the shielded receiving coil. Do not add an initial source distance compensation plug gauge between the main receiving coil and the shielded receiving coil in the short subarray. Then measure the current residual direct-coupled signal of the subarray. Refer to Table 1 to find the total plug gauge offset S of the direct-coupled balanced plug gauge. ini Based on this, the source distance of the shielded receiving coil of the subarray is calculated. Use the calibrated theoretical plug gauge sensitivity or empirical value As the initial value for the sensitivity of the plug gauge, use the formula (Formula 22) Calculate the equilibrium position;

[0181] Step A2, based on the calculated equilibrium position L' balance Based on the principle of nearest minimum, the direct coupling balance gauge corresponding to the balance position is determined. At the same time, the source distance compensation gauge of the subarray is determined according to the principle of unchanged source distance of the main receiving coil of the long subarray. Then, a new direct coupling balance gauge is replaced. When the subarray is a long subarray, a new source distance compensation gauge is also replaced. Then, the current residual direct coupling signal of the subarray is measured.

[0182] Step A3: Determine if the plug gauge calibration termination condition is met. If yes, proceed to the next step; otherwise, determine the residual direct coupling signal before replacing the plug gauge in the subarray. Residual direct coupling signal after replacing plug gauge Shielded receiver coil source distance L before replacing plug gauge old And the source distance L of the shielded receiving coil after replacing the plug gauge new and formula The new plug gauge sensitivity is calculated, and based on the formula... Calculate the new equilibrium position, then proceed to step A2;

[0183] Step A4: Plug gauge calibration complete. Furthermore, a conclusion of success or failure can be given after calibration, a detailed report can be issued, the calibration process and results can be stored in a database, the calibration results can be compared with the calibration results in the database, and the residual direct coupling and final plug gauge statistical results can be provided.

[0184] Furthermore, no zero-crossing plug gauge occurred even after reaching the maximum number of iterations. Specifically, it could be one of the following two situations: 1) During iteration, as the source distance of the shielded receiving coil continuously decreases, the residual direct coupling signal continuously increases, but remains negative; 2) During iteration, as the source distance of the shielded receiving coil continuously increases, the residual direct coupling signal continuously decreases, but remains positive.

[0185] The derivation of formula 23 is as follows:

[0186]

[0187] visible, This indicates the sensitivity of the plug gauge;

[0188] Therefore, formula 26 can be rewritten as follows:

[0189] Experiments show that in the above applications, the adjustment can be completed with a maximum of three gauge replacements, resulting in high adjustment efficiency.

[0190] Example 2

[0191] This invention provides a device for achieving direct coupling balance of an array induction instrument coil system. The device includes a direct coupling balance theoretical design module, an initial gauge insertion module, a first determination module, a second determination module, and an iteration module, wherein:

[0192] The direct-coupled balance theory design module is used to determine the theoretical process parameters of each coil system through direct-coupled balance design.

[0193] The initial plug gauge addition module is used to add a direct-coupled balanced plug gauge between the transmitting coil and the shielded receiving coil to change the source distance of the shielded receiving coil after the current coil system structure is used for instrument manufacturing or improvement. In addition, according to the principle that the source distance of the main receiving coil of the long subarray remains unchanged, a source distance compensation plug gauge complementary to the direct-coupled balanced plug gauge is added between the main receiving coil and the shielded receiving coil. When the subarray is a short subarray, no source distance compensation plug gauge is added between the main receiving coil and the shielded receiving coil. Then, the current residual direct-coupled signal of the subarray is measured and the source distance of the shielded receiving coil of the subarray is determined according to the thickness of the currently added direct-coupled balanced plug gauge.

[0194] The first determining module is used to give an initial value of the plug gauge sensitivity and determine the current equilibrium position based on the initial value of the plug gauge sensitivity. The current equilibrium position is the source distance of the shielded receiving coil that makes the residual direct coupling signal zero.

[0195] The second determining module is used to determine the thickness of the direct-coupled balance plug gauge corresponding to the current balance position. When the subarray is a long subarray, the thickness of the source distance compensation plug gauge is also determined based on the thickness of the direct-coupled balance plug gauge.

[0196] The iterative module is used to iteratively change the thickness of the direct-coupled balance plug gauge using a nonlinear equation root-finding algorithm. When the subarray is a long subarray, it also iteratively changes the thickness of the source distance compensation plug gauge. Then, it measures the current residual direct-coupled signal of the subarray until the maximum number of iterations is reached or the nonlinear equation root-finding algorithm converges to the target equilibrium position, at which point the direct-coupled calibration ends.

[0197] Among them, the plug gauge sensitivity characterizes the rate of change of the residual direct coupling signal with the thickness of the direct coupling balanced plug gauge.

[0198] In one specific embodiment, the direct-coupled equilibrium theory design module includes a third determination module, a first selection module, a first calculation module, and a first judgment module, wherein:

[0199] The third determining module is used to specify the number of turns of the transmitting coil;

[0200] The first selection module is used to select the source distance and number of turns of the main receiving coil of each subarray. The source distance and number of turns of the main receiving coil are within a reasonable range determined according to the detection performance index and the sensing signal index of the instrument.

[0201] The first calculation module is used to calculate the source distance and number of turns of the shielded receiving coil using the direct coupling balance formula, with the number of turns of the shielded receiving coil being an integer or even number as a constraint.

[0202] The first judgment module is used to judge whether the coil system structure based on the current source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil is reasonable, based on whether the coil substrate space constraint is met as the rationality criterion. If it is reasonable, the current coil system structure is used for instrument manufacturing or improvement; otherwise, the source distance and number of turns of the main receiving coil are iteratively updated until the coil system structure is reasonable.

[0203] The direct coupling balance formula is a constraint relationship between the source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil, determined based on the principle that the strength of the direct coupling signal is proportional to the reciprocal of the cube of the source distance of the receiving coil and the number of coil turns.

[0204] In one specific embodiment, the direct coupling balance formula is expressed by the following equation:

[0205]

[0206] Where, N Rm Number of turns of the main receiving coil, -N Rb The number of turns for the shielded receiving coil; the negative sign indicates that the shielded receiving coil is wound in the opposite direction to the main receiving coil. L m Main receiving coil source distance, L b To shield the source distance of the receiving coil.

[0207] In one specific embodiment, the source distance and number of turns of the shielded receiving coil are calculated using the direct coupling balance formula, with the number of turns being an integer or even number as a constraint. This includes:

[0208] Given an initial value for the source distance ratio between the shielded receiving coil and the main receiving coil, calculate the initial source distance value of each subarray shielded receiving coil based on the initial source distance ratio, and use the direct coupling balance formula to calculate the initial value of the number of turns of the shielded receiving coil.

[0209] Adjust the number of turns of the shielded receiving coil to an integer or even number, calculate the updated value of the source distance ratio between the shielded receiving coil and the main receiving coil using the direct coupling balance formula, and then calculate the updated value of the source distance of the shielded receiving coil based on the updated value of the source distance ratio. Use the adjusted number of turns of the shielded receiving coil (into an integer or even number) as the number of turns of the shielded receiving coil, and use the updated value of the source distance of the shielded receiving coil as the source distance of the shielded receiving coil.

[0210] In one specific embodiment, the detection performance indicators include radial detection depth and longitudinal resolution.

[0211] In one specific embodiment, the sensing signal index includes the sensing signal strength index of each subarray and the signal-to-noise ratio index of the original acquired signal.

[0212] In one specific embodiment, the target equilibrium position is the source distance of the shielded receiving coil after the addition of the direct-coupled equilibrium plug gauge corresponding to the equilibrium position when the zero-crossing plug gauge appears, or the source distance of the shielded receiving coil after the addition of the current direct-coupled equilibrium plug gauge that makes the residual direct-coupled signal 0, or the source distance of the shielded receiving coil after the addition of the current direct-coupled equilibrium plug gauge that makes the absolute value of the residual direct-coupled signal less than a first preset value; the zero-crossing plug gauges are the two direct-coupled equilibrium plug gauges with the smallest thickness difference corresponding to the one positive and one negative residual direct-coupled signals.

[0213] In one specific embodiment, the array sensing instrument coil system direct coupling balance realization device further includes a process parameter correction module. The process parameter correction module is used to correct the source distance of the shielded receiving coil using a direct coupling balance gauge corresponding to the balance position when the nonlinear equation root-finding algorithm converges to the target balance position, and to compensate the source distance of the main receiving coil using a source distance compensation gauge complementary to the direct coupling balance gauge when the subarray is a long subarray, or to correct the source distance of the shielded receiving coil using a current direct coupling balance gauge that makes the residual direct coupling signal 0, and to compensate the source distance of the main receiving coil using a source distance compensation gauge complementary to the direct coupling balance gauge when the subarray is a long subarray, or to correct the source distance of the shielded receiving coil using a current direct coupling balance gauge that makes the absolute value of the residual direct coupling signal less than a first preset value, and to compensate the source distance of the main receiving coil using a source distance compensation gauge complementary to the direct coupling balance gauge when the subarray is a long subarray.

[0214] In one specific embodiment, the thickness of the direct-coupled balance plug gauge corresponding to the current equilibrium position is determined according to the principle of nearest minimum. The principle of nearest minimum is as follows: if a direct-coupled balance plug gauge is added between the transmitting coil and the shielded receiving coil, and the source distance of the shielded receiving coil is closest to the current equilibrium position, then the direct-coupled balance plug gauge is determined as the target plug gauge, and the thickness of the target plug gauge is determined as the thickness of the direct-coupled balance plug gauge corresponding to the current equilibrium position; if there are two target plug gauges, then the thickness of the smaller target plug gauge is determined as the thickness of the direct-coupled balance plug gauge corresponding to the current equilibrium position.

[0215] In one specific embodiment, the initial value of the plug gauge sensitivity is an empirical value or determined based on the corrected theoretical plug gauge sensitivity.

[0216] In one specific embodiment, both the direct-coupled balance plug gauge and the source distance compensation plug gauge are selected from the increasing-distance plug gauge and the decreasing-distance plug gauge. The thickness of the increasing-distance plug gauge is the sum of the standard plug gauge thickness and the plug gauge offset, and the thickness of the decreasing-distance plug gauge is the difference between the standard plug gauge thickness and the plug gauge offset. The plug gauge offset is a multiple of the unit plug gauge offset.

[0217] In one specific embodiment, when performing a direct-coupled calibration process for multiple or all subarrays, the direct-coupled calibration process is performed sequentially from the nearest to the farthest shielded receiving coil to the transmitting coil in the subarray.

[0218] In one specific embodiment, when performing a direct-coupled calibration process for multiple or all subarrays, the direct-coupled calibration process for these multiple or all subarrays is performed synchronously. In synchronous direct-coupled calibration, according to the positional relationship between any two subarrays, if the distance between the shielded receiving coil and the transmitting coil in the first subarray is less than the distance between the shielded receiving coil and the transmitting coil in the second subarray, then the source distance offset of the shielded receiving coil caused by the direct-coupled balancing plug gauge of the first subarray is added to the second subarray.

[0219] On the other hand, embodiments of the present invention also provide a machine-readable storage medium storing a computer program thereon, wherein the computer program, when executed by a processor, implements any of the above-described methods for achieving direct coupling balance of the array induction instrument coil system.

[0220] In another aspect, embodiments of the present invention also provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement any of the above-described methods for achieving direct coupling balance of array induction instrument coil systems.

[0221] Furthermore, embodiments of the present invention also provide a digital twin platform, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements any of the above-described methods for achieving direct coupling balance of the array sensing instrument coil system. The digital twin platform constructed using the above methods enables big data analysis and services for the design, optimization, calibration, scaling, and manufacturing of array sensing instruments, greatly improving the efficiency of array sensing instrument manufacturing or improvement processes and reducing manufacturing costs.

[0222] In another aspect, embodiments of the present invention also provide a computer program product, which, when executed on a data processing device, is suitable for executing a program that initializes the following method steps:

[0223] The theoretical process parameters of each coil system are determined through direct-coupled balanced design;

[0224] A direct-coupled calibration process is performed on the subarray, the direct-coupled calibration process including:

[0225] A direct-coupled balance plug gauge is added between the transmitting coil and the shielded receiving coil to change the source distance of the shielded receiving coil. In accordance with the principle that the source distance of the main receiving coil of the long subarray remains unchanged, a source distance compensation plug gauge complementary to the direct-coupled balance plug gauge is added between the main receiving coil and the shielded receiving coil. When the subarray is a short subarray, no source distance compensation plug gauge is added between the main receiving coil and the shielded receiving coil. Then, the current residual direct-coupled signal of the subarray is measured and the source distance of the shielded receiving coil of the subarray is determined according to the thickness of the currently added direct-coupled balance plug gauge.

[0226] Given an initial value for the plug gauge sensitivity, and determine the current equilibrium position based on the initial value for the plug gauge sensitivity, the current equilibrium position is the source distance of the shielded receiving coil that makes the residual direct coupling signal zero. The plug gauge sensitivity characterizes the rate of change of the residual direct coupling signal with the thickness of the direct coupling equilibrium plug gauge.

[0227] Determine the thickness of the direct-coupled balance plug gauge corresponding to the current balance position. When the subarray is a long subarray, the thickness of the source distance compensation plug gauge is also determined based on the thickness of the direct-coupled balance plug gauge.

[0228] Using a nonlinear equation root-finding algorithm, the thickness of the direct-coupled balance plug gauge is iteratively changed. When the subarray is a long subarray, the thickness of the source distance compensation plug gauge is also iteratively changed. Then, the current residual direct-coupled signal of the subarray is measured until the maximum number of iterations is reached or the nonlinear equation root-finding algorithm converges to the target equilibrium position, at which point the direct-coupled calibration ends.

[0229] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0230] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0231] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0232] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for achieving direct coupling balance in an array induction instrument coil system, characterized in that, The method includes: The theoretical process parameters of each coil system are determined through direct-coupled balanced design; A direct-coupled calibration process is performed on the subarray, the direct-coupled calibration process including: A direct-coupled balance plug gauge is added between the transmitting coil and the shielded receiving coil to change the source distance of the shielded receiving coil. In accordance with the principle that the source distance of the main receiving coil of the long subarray remains unchanged, a source distance compensation plug gauge complementary to the direct-coupled balance plug gauge is added between the main receiving coil and the shielded receiving coil. When the subarray is a short subarray, no source distance compensation plug gauge is added between the main receiving coil and the shielded receiving coil. Then, the current residual direct-coupled signal of the subarray is measured and the source distance of the shielded receiving coil of the subarray is determined according to the thickness of the currently added direct-coupled balance plug gauge. Given an initial value for the plug gauge sensitivity, and determine the current equilibrium position based on the initial value for the plug gauge sensitivity, the current equilibrium position is the source distance of the shielded receiving coil that makes the residual direct coupling signal zero. The plug gauge sensitivity characterizes the rate of change of the residual direct coupling signal with the thickness of the direct coupling equilibrium plug gauge. Determine the thickness of the direct-coupled balance plug gauge corresponding to the current balance position. When the subarray is a long subarray, the thickness of the source distance compensation plug gauge is also determined based on the thickness of the direct-coupled balance plug gauge. Using a nonlinear equation root-finding algorithm, the thickness of the direct-coupled balance plug gauge is iteratively changed. When the subarray is a long subarray, the thickness of the source distance compensation plug gauge is also iteratively changed. Then, the current residual direct-coupled signal of the subarray is measured until the maximum number of iterations is reached or the nonlinear equation root-finding algorithm converges to the target equilibrium position, at which point the direct-coupled calibration ends.

2. The method for achieving direct coupling balance of the array induction instrument coil system according to claim 1, characterized in that, The determination of the theoretical process parameters for each coil system through direct-coupled balanced design includes: Given the number of turns in the transmitting coil; The source distance and number of turns of the main receiving coils of each subarray are selected, and both the source distance and number of turns of the main receiving coils are within a reasonable range determined according to the detection performance index and the sensing signal index of the instrument. Using the constraint that the number of turns of the shielded receiving coil is an integer or even number, the source distance and number of turns of the shielded receiving coil are calculated using the direct coupling balance formula; The rationality criterion is whether the coil substrate space constraint is met. The rationality of the coil system structure based on the current source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil is judged. If it is, the current source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil are used as theoretical process parameters for instrument manufacturing or improvement. Otherwise, the source distance and number of turns of the main receiving coil are iteratively updated until the coil system structure is reasonable. The direct coupling balance formula is a constraint relationship between the source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil, determined based on the principle that the strength of the direct coupling signal is proportional to the reciprocal of the cube of the source distance of the receiving coil and the number of coil turns.

3. The method for achieving direct coupling balance of the array induction instrument coil system according to claim 2, characterized in that, The direct coupling balance formula is expressed by the following equation: Where, N Rm Number of turns of the main receiving coil, -N Rb The number of turns for the shielded receiving coil; the negative sign indicates that the shielded receiving coil is wound in the opposite direction to the main receiving coil. L m Main receiving coil source distance, L b To shield the source distance of the receiving coil.

4. The method for achieving direct coupling balance of the array induction instrument coil system according to claim 2, characterized in that, The calculation of the source distance and number of turns of the shielded receiving coil using the direct coupling balance formula, with the number of turns of the shielded receiving coil being an integer or even number as a constraint, includes: Given an initial value for the source distance ratio between the shielded receiving coil and the main receiving coil, calculate the initial source distance value of each subarray shielded receiving coil based on the initial source distance ratio, and use the direct coupling balance formula to calculate the initial value of the number of turns of the shielded receiving coil. Adjust the number of turns of the shielded receiving coil to an integer or even number, calculate the updated value of the source distance ratio between the shielded receiving coil and the main receiving coil using the direct coupling balance formula, and then calculate the updated value of the source distance of the shielded receiving coil based on the updated value of the source distance ratio. Use the adjusted number of turns of the shielded receiving coil (into an integer or even number) as the number of turns of the shielded receiving coil, and use the updated value of the source distance of the shielded receiving coil as the source distance of the shielded receiving coil.

5. The method for achieving direct coupling balance of the array induction instrument coil system according to claim 2, characterized in that, The detection performance indicators include radial detection depth and longitudinal resolution.

6. The method for achieving direct coupling balance of the array induction instrument coil system according to claim 2, characterized in that, The inductive signal indicators include the inductive signal strength indicators of each subarray and the signal-to-noise ratio indicators of the original acquired signals.

7. The method for achieving direct coupling balance of the array induction instrument coil system according to claim 1, characterized in that, The target equilibrium position is the source distance of the shielded receiving coil after the addition of the direct-coupled equilibrium plug gauge when the zero-crossing plug gauge appears, or the source distance of the shielded receiving coil after the addition of the current direct-coupled equilibrium plug gauge that makes the residual direct-coupled signal 0, or the source distance of the shielded receiving coil after the addition of the current direct-coupled equilibrium plug gauge that makes the absolute value of the residual direct-coupled signal less than the first preset value. The zero-crossing plug gauges are the two direct-coupled equilibrium plug gauges with the smallest thickness difference corresponding to the one positive and one negative residual direct-coupled signals.

8. The method for achieving direct coupling balance of the array induction instrument coil system according to claim 7, characterized in that, If the nonlinear equation root-finding algorithm converges to the target equilibrium position, the source distance of the shielded receiving coil is corrected using the direct-coupled balance plug corresponding to the equilibrium position when the zero-crossing plug appears, and the source distance of the main receiving coil is compensated using a source distance compensation plug complementary to the direct-coupled balance plug when the subarray is a long subarray. Alternatively, the source distance of the shielded receiving coil is corrected using the current direct-coupled balance plug that makes the residual direct-coupled signal 0, and the source distance of the main receiving coil is compensated using a source distance compensation plug complementary to the direct-coupled balance plug when the subarray is a long subarray. Alternatively, the source distance of the shielded receiving coil is corrected using the current direct-coupled balance plug that makes the absolute value of the residual direct-coupled signal less than a first preset value, and the source distance of the main receiving coil is compensated using a source distance compensation plug complementary to the direct-coupled balance plug when the subarray is a long subarray.

9. The method for achieving direct coupling balance of the array induction instrument coil system according to claim 1, characterized in that, The thickness of the direct-coupled balance plug gauge corresponding to the current balance position is determined based on the principle of nearest minimum. The principle of nearest minimum is as follows: if a direct-coupled balanced plug gauge is added between the transmitting coil and the shielded receiving coil, and the source distance of the shielded receiving coil is closest to the current equilibrium position, then the direct-coupled balanced plug gauge is determined as the target plug gauge, and the thickness of the target plug gauge is determined as the thickness of the direct-coupled balanced plug gauge corresponding to the current equilibrium position; if there are two target plug gauges, then the thickness of the smallest target plug gauge is determined as the thickness of the direct-coupled balanced plug gauge corresponding to the current equilibrium position.

10. The method for achieving direct coupling balance of the array induction instrument coil system according to claim 1, characterized in that, The initial value of the plug gauge sensitivity is an empirical value or determined based on the corrected theoretical plug gauge sensitivity.

11. The method for achieving direct coupling balance of the array induction instrument coil system according to claim 1, characterized in that, Both the direct-coupled balanced plug gauge and the source distance compensation plug gauge are selected from the increasing-distance plug gauge and the decreasing-distance plug gauge. The thickness of the increasing-distance plug gauge is the sum of the standard plug gauge thickness and the plug gauge offset. The thickness of the decreasing-distance plug gauge is the difference between the standard plug gauge thickness and the plug gauge offset. The plug gauge offset is a multiple of the unit plug gauge offset.

12. The method for achieving direct coupling balance of the array induction instrument coil system according to claim 1, characterized in that, When performing direct-coupled calibration for multiple or all subarrays, the direct-coupled calibration process is performed sequentially from the nearest to the farthest shielded receiving coil to the transmitting coil in the subarray.

13. The method for achieving direct coupling balance of the array induction instrument coil system according to claim 1, characterized in that, When performing direct coupling calibration for multiple or all subarrays, the direct coupling calibration process for these multiple or all subarrays is carried out synchronously. In synchronous direct coupling calibration, if the distance between the shielded receiving coil and the transmitting coil in the first subarray is less than the distance between the shielded receiving coil and the transmitting coil in the second subarray, the source distance offset of the shielded receiving coil caused by the direct coupling balance plug gauge of the first subarray is added to the second subarray.

14. A device for achieving direct coupling balance of an array induction instrument coil system, characterized in that, The device includes: The direct-coupled balance theory design module is used to determine the theoretical process parameters of each coil system through direct-coupled balance design. The initial plug gauge addition module is used to add a direct-coupled balanced plug gauge between the transmitting coil and the shielded receiving coil to change the source distance of the shielded receiving coil after the current coil system structure is used for instrument manufacturing or improvement. In addition, according to the principle that the source distance of the main receiving coil of the long subarray remains unchanged, a source distance compensation plug gauge complementary to the direct-coupled balanced plug gauge is added between the main receiving coil and the shielded receiving coil. When the subarray is a short subarray, no source distance compensation plug gauge is added between the main receiving coil and the shielded receiving coil. Then, the current residual direct-coupled signal of the subarray is measured and the source distance of the shielded receiving coil of the subarray is determined according to the thickness of the currently added direct-coupled balanced plug gauge. The first determining module is used to give an initial value of the plug gauge sensitivity and determine the current equilibrium position based on the initial value of the plug gauge sensitivity. The current equilibrium position is the source distance of the shielded receiving coil that makes the residual direct coupling signal zero. The second determining module is used to determine the thickness of the direct-coupled balance plug gauge corresponding to the current balance position. When the subarray is a long subarray, the thickness of the source distance compensation plug gauge is also determined based on the thickness of the direct-coupled balance plug gauge. The iterative module is used to iteratively change the thickness of the direct-coupled balance plug gauge using a nonlinear equation root-finding algorithm. When the subarray is a long subarray, it also iteratively changes the thickness of the source distance compensation plug gauge. Then, it measures the current residual direct-coupled signal of the subarray until the maximum number of iterations is reached or the nonlinear equation root-finding algorithm converges to the target equilibrium position, at which point the direct-coupled calibration ends. Among them, the plug gauge sensitivity characterizes the rate of change of the residual direct coupling signal with the thickness of the direct coupling balanced plug gauge.

15. The array induction instrument coil system direct coupling balance realization device according to claim 14, characterized in that, The direct-coupled balance theory design module includes: The third determining module is used to specify the number of turns of the transmitting coil; The first selection module is used to select the source distance and number of turns of the main receiving coil of each subarray. The source distance and number of turns of the main receiving coil are within a reasonable range determined according to the detection performance index and the sensing signal index of the instrument. The first calculation module is used to calculate the source distance and number of turns of the shielded receiving coil using the direct coupling balance formula, with the number of turns of the shielded receiving coil being an integer or even number as a constraint. The first judgment module is used to judge whether the coil system structure based on the current source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil is reasonable, based on whether the coil substrate space constraint is met as the rationality criterion. If it is reasonable, the current coil system structure is used for instrument manufacturing or improvement; otherwise, the source distance and number of turns of the main receiving coil are iteratively updated until the coil system structure is reasonable. The direct coupling balance formula is a constraint relationship between the source distance and number of turns of the main receiving coil and the source distance and number of turns of the shielded receiving coil, determined based on the principle that the strength of the direct coupling signal is proportional to the reciprocal of the cube of the source distance of the receiving coil and the number of coil turns.

16. The array induction instrument coil system direct coupling balance realization device according to claim 14, characterized in that, The target equilibrium position is the source distance of the shielded receiving coil after the addition of the direct-coupled equilibrium plug gauge corresponding to the equilibrium position when the zero-crossing plug gauge appears, or the source distance of the shielded receiving coil after the addition of the current direct-coupled equilibrium plug gauge that makes the residual direct-coupled signal 0, or the source distance of the shielded receiving coil after the addition of the current direct-coupled equilibrium plug gauge that makes the absolute value of the residual direct-coupled signal less than the first preset value. The zero-crossing plug gauges are two directly coupled balanced plug gauges with the smallest thickness difference corresponding to the positive and negative residual direct coupling signals.

17. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the direct-coupled balance implementation method of the array induction instrument coil system as described in any one of claims 1 to 13.

18. A machine-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the direct-coupled balance implementation method of the array induction instrument coil system as described in any one of claims 1 to 13.

Images