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

Abstract

The invention provides an array induction instrument coil system direct coupling balance implementation method and device, and relates to the technical field of geophysical logging. The method comprises the following steps: determining theoretical process parameters of each coil system through direct coupling balance design; a direct coupling tuning process is performed for the sub-array. In the method, the direct coupling balance plug gauge and the source spacing compensation plug gauge are used for direct coupling adjustment, and when the nonlinear equation rooting algorithm converges at the target balance position, the plug gauge corresponding to the target balance position can be used for adjusting theoretical process parameters of each coil system determined by direct coupling balance design. The difference between an actually produced instrument and a theoretical design caused by a plurality of factors such as actual coil system base body machining errors, a coil winding process, winding tension and assembly is calibrated, so that the array induction instrument manufactured or improved based on the coil system process parameters eliminates direct coupling signals to the greatest extent; and direct coupling balance and a reasonable signal-to-noise ratio of the instrument are ensured.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of geophysical well logging, especially to the field of exploration and development of coal, oil and other mines, and particularly relates to a method for achieving straight coupling balance of a coil system of an array induction instrument, a device for achieving straight coupling balance of a coil system of an array induction instrument, a computer device and a machine-readable storage medium. BACKGROUND

[0002] In oil well logging and oil and gas evaluation, formation resistivity is an important parameter for estimating oil and gas reserves. Lateral well logging using electrodes to emit direct current to establish an electric field and induction logging using a transmitting coil to excite alternating current in the formation to induce eddy current field are two commonly used resistivity logging methods. In particular, under the condition of air drilling and oil-based mud and other non-conductive drilling medium, the direct current logging method is no longer suitable for use, but the induction logging is still applicable.

[0003] As shown in Figure 1 , induction logging is a method of logging using the mutual inductance principle of alternating current. The working principle of the instrument is that the transmitting coil generates alternating current, which induces eddy current in the formation. This eddy current induces an electromotive force in the receiving coil. Since the transmitting coil and the receiving coil are both in the well, the strength of the eddy current induced in the formation around the well by the alternating current of the transmitting coil is related to the formation resistivity, and therefore the induced electromotive force of the receiving coil is a function of the formation resistivity around it. The coil system is located in a uniform, isotropic, time-invariant formation, where the magnetic permeability μ, the electrical conductivity σ and the dielectric constant ε are all constants. The formation is rotationally symmetric around the well axis, T and R are the transmitting coil and the receiving coil respectively, the number of turns are N T and N R , the coil radius is r', L is the distance between the transmitting coil and the receiving coil, called the source distance, and the coil operates at a certain frequency ω. There is an equal amplitude and stable frequency alternating current I T on the transmitting coil, represented as I T = I0e -iωt . The alternating current in the transmitting coil excites an electromagnetic field in the surrounding formation, thereby generating induced current in the countless formation element rings with the well axis as the axis. The size of the induced current is proportional to the electrical conductivity of the formation element ring. These induced currents, similar to current coils, also generate alternating electromagnetic fields, which are commonly referred to as secondary fields. The secondary field generates an induced electromotive force in the receiving coil, which is called the secondary field induced electromotive force. In a uniform infinite medium, ignoring the interaction between eddy currents, the secondary field induced electromotive force is proportional to the electrical conductivity of the medium. As shown in Figure 2As shown, the secondary induced electromotive force in the receiving coil carries the formation conductivity information, which is called useful signal, and the phase difference between the useful signal and the alternating current of the transmitting coil is 180 degrees. The induced electromotive force directly coupled from the transmitting coil to the receiving coil does not carry the formation information, which is called direct coupling electromotive force or useless signal, and the phase difference between the direct coupling electromotive force and the alternating current of the transmitting coil is 90 degrees. The secondary field induced electromotive force can be detected from the total signal by using the phase-sensitive detection technology, so as to achieve the purpose of measuring the surrounding formation resistivity. The direct coupling signal is often tens to thousands of times of the secondary induction signal, which can drown the secondary induction signal, thereby resulting in extremely low signal-to-noise ratio of the measurement. In order to accurately measure the secondary field induced electromotive force, the induction logging instrument is designed to increase the shielded receiving coil to offset or balance the direct coupling signal. In the actual induction logging instrument, a three-coil subarray structure as shown in Figure 3 The two receiving coils are connected together to form a receiving coil Rx, and the transmitting coil Tx and the receiving coil Rx are combined together and called a subarray.

[0004] According to the induction logging principle, the longer the source distance, the larger the instrument detection range, and the deeper (farther) the detection range in the direction perpendicular to the borehole (radial direction), but the poorer (lower) the resolution ability of the thin layer along the borehole (longitudinal direction). Conversely, the shorter the source distance, the shallower the radial detection depth of the instrument, and the stronger the longitudinal resolution ability of the thin layer. In order to be able to detect the formation conductivity of different depths and different regions around the borehole, and at the same time improve the resolution ability of the thin layer, a composite coil system is designed, especially an array induction logging instrument in which multiple coil systems are optimally combined together. The instrument uses borehole correction and other processing to eliminate the influence of the borehole environment, uses software focusing and other processing to eliminate the influence of the surrounding rock environment, uses radial inversion and other processing to obtain the invasion parameter and the original formation resistivity, and has the advantages of high longitudinal resolution, deep radial detection depth, obvious invasion indication, etc. The array induction instrument provides multiple detection depths and multiple resolution formation resistivity information, which becomes a sharp weapon for oil and gas evaluation and is widely welcomed.

[0005] As shown in Figure 4As shown, the array induction instrument probe is composed of a common transmitting coil Tx and multiple (such as 7) receiving coil systems Rx, each receiving coil system and the transmitting coil constitute a sub-array of a measuring unit. The multiple sub-arrays of the array induction are installed on the same instrument mandrel structure, after the direct coupling balance theoretical design of the array induction instrument, each three-coil system sub-array is independent and directly coupled balanced, but due to the actual coil system substrate machining error, coil winding process and assembly and many other factors, there is a big difference between the actual produced instrument and the theoretical design, that is, there is often a large residual direct coupling signal. At present, in order to eliminate the residual direct coupling signal, the source distance of each three-coil system sub-array is usually adjusted by the "plug gauge" method to highlight the useful signal, improve the signal-to-noise ratio of the instrument, and ensure the direct coupling balance and consistency of the instrument. However, in the "plug gauge" process, different thickness "plug gauge" pieces need to be repeatedly tested to adjust the source distance of the receiving coil. This process of replacing the plug gauge piece needs to be repeatedly loosened and tightened the coil system. For the array induction instrument with multiple sub-arrays, it is quite cumbersome to adjust the process to make each three-coil system reach the best balanced state.

[0006] China Petroleum Group Great Wall Drilling Engineering Co., Ltd. discloses a method for eliminating direct coupling signals in a three-dimensional array induction instrument, wherein the Z component eliminates the direct coupling signals by changing the source distance of the shielding coil. The patent does not disclose specific plug gauge fine-tuning methods, steps, and calibration end criteria. At the same time, since the coils of X, Y, and Z components adopt a common center design, the direct coupling signals in three directions cannot be eliminated by fine-tuning the source distance, and the patent proposes a method of changing the number of turns and area of the shielding coil to eliminate the direct coupling signals in X and Y directions. The fine-tuning of the area of the shielding coil in X and Y directions is achieved by opening holes on the coil surface and fixing conductive bodies in the holes. The patent mainly focuses on the method for eliminating direct coupling signals in X and Y directions. See CN104343443A for details.

[0007] In order to eliminate the direct coupling balance signals of the array induction instrument as much as possible, the proposal of an efficient and intelligent direct coupling balance adjustment method is a technical difficulty to be overcome in the field. The plug gauge position design and plug gauge series design are optimized based on the analysis of the plug gauge sensitivity of two plug gauge positions, which saves the manufacturing cost of precision plug gauges; at the same time, the intelligent balance adjustment and full sub-array synchronous balance adjustment process based on the plug gauge sensitivity are established, the termination adjustment criterion is proposed, and the related software modules are formed. SUMMARY

[0008] The embodiment of the present application aims to provide a coil system direct coupling balance implementation method for array induction instrument, a coil system direct coupling balance implementation device for array induction instrument, a computer device and a machine readable storage medium, so as to overcome the poor direct coupling balance of the coil system array induction instrument in the prior art.

[0009] In order to achieve the above-mentioned purpose, the first aspect of the embodiment of the present application provides a coil system direct coupling balance implementation method for array induction instrument, comprising:

[0010] determining the theoretical process parameters of each coil system through direct coupling balance design;

[0011] performing a direct coupling adjustment process for each sub-array, wherein the direct coupling adjustment process comprises:

[0012] adding a direct coupling balance plug gauge between the transmitting coil and the shielded receiving coil to change the source distance of the shielded receiving coil, and adding a source distance compensation plug gauge complementary to the direct coupling balance plug gauge between the main receiving coil and the shielded receiving coil according to the principle that the source distance of the main receiving coil of the long sub-array is unchanged, and when the sub-array is a short sub-array, no source distance compensation plug gauge is added between the main receiving coil and the shielded receiving coil, then measuring the current residual direct coupling signal of the sub-array and determining the source distance of the shielded receiving coil of the sub-array according to the thickness of the currently added direct coupling balance plug gauge;

[0013] determining the initial value of the plug gauge sensitivity, and determining the current balance position according to the initial value of the plug gauge sensitivity, wherein the current balance position is the source distance of the shielded receiving coil that makes the residual direct coupling signal 0, and the plug gauge sensitivity represents the rate of change of the residual direct coupling signal with the thickness of the direct coupling balance plug gauge;

[0014] determining the thickness of the direct coupling balance plug gauge corresponding to the current balance position, and when the sub-array is a long sub-array, further determining the thickness of the source distance compensation plug gauge according to the thickness of the direct coupling balance plug gauge;

[0015] using a nonlinear equation root algorithm to iteratively change the thickness of the direct coupling balance plug gauge, and when the sub-array is a long sub-array, further iteratively changing the thickness of the source distance compensation plug gauge, then measuring the current residual direct coupling signal of the sub-array, and the direct coupling adjustment ends after reaching the maximum number of iterations or the nonlinear equation root algorithm converges to the target balance position.

[0016] Optionally, the method for determining the theoretical process parameters of each coil system through direct coupling balance design comprises:

[0017] determining the number of turns of the transmitting coil;

[0018] selecting the source distance and the number of turns of the main receiving coil of each sub-array, wherein the source distance and the number of turns of the main receiving coil are both within a reasonable range determined according to the detection performance index and the induction signal index of the instrument;

[0019] The turns of the shielding receiving coil are an integer or an even number as a constraint condition, and the source distance and the turns of the shielding receiving coil are calculated by using the direct coupling balance formula;

[0020] The coil system structure based on the current main receiving coil source distance and turns, the shielding receiving coil source distance and turns is judged as reasonable or not by taking whether the coil base body accommodating space constraint is met as a reasonableness discrimination standard, if yes, the current main receiving coil source distance and turns, the shielding receiving coil source distance and turns are taken as theoretical process parameters to manufacture or improve the instrument, otherwise the main receiving coil source distance and turns are iteratively updated until the coil system structure is reasonable;

[0021] The direct coupling balance formula is a constraint relationship formula between the main receiving coil source distance and turns, the shielding receiving coil source distance and turns determined according to the principle that the strength of the direct coupling signal is proportional to the inverse of the cube of the coil source distance and the turns for receiving.

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

[0023]

[0024] Wherein, N Rm is the turns of the main receiving coil, -N Rb is the turns of the shielding receiving coil, the negative sign indicates that the winding direction of the shielding receiving coil is opposite to that of the main receiving coil, L m is the source distance of the main receiving coil, L b is the source distance of the shielding receiving coil.

[0025] Optionally, the shielding receiving coil source distance and turns are calculated by using the direct coupling balance formula with the turns of the shielding receiving coil as an integer or an even number as a constraint condition, including:

[0026] The source distance initial value of each subarray shielding receiving coil is calculated according to the source distance ratio initial value, and the turns initial value of the shielding receiving coil is calculated by using the direct coupling balance formula;

[0027] The turns of the shielding receiving coil are adjusted to be an integer or an even number, the source distance ratio update value of the shielding receiving coil and the main receiving coil is calculated by using the direct coupling balance formula, then the source distance update value of the shielding receiving coil is calculated according to the source distance ratio update value, the turns of the shielding receiving coil adjusted to be an integer or an even number are taken as the turns of the shielding receiving coil, and the source distance update value of the shielding receiving coil is taken as the source distance of the shielding receiving coil.

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

[0029] Optionally, the inductive signal indicators include inductive signal strength indicators of the sub-arrays and signal-to-noise ratio indicators of the original collected signals.

[0030] Optionally, the target balance position is a balance position corresponding to a straight-coupling balance plug rule added to a shielded receiving coil source distance when a cross-zero plug rule occurs, or a shielded receiving coil source distance after a current straight-coupling balance plug rule is added so that the residual straight-coupling signal is 0, or a shielded receiving coil source distance after a current straight-coupling balance plug rule is added so that the absolute value of the residual straight-coupling signal is less than a first preset value; the cross-zero plug rule is two straight-coupling balance plug rules corresponding to the minimum thickness difference of one positive and one negative residual straight-coupling signals.

[0031] Optionally, if the nonlinear equation root-finding algorithm converges to the target balance position, the source distance of the shielded receiving coil is further corrected by a straight-coupling balance plug rule corresponding to a balance position when a cross-zero plug rule occurs, and the source distance of the main receiving coil is compensated by a source distance compensation plug rule complementary to the straight-coupling balance plug rule when the sub-array is a long sub-array, or the source distance of the shielded receiving coil is corrected by a current straight-coupling balance plug rule so that the residual straight-coupling signal is 0, and the source distance of the main receiving coil is compensated by a source distance compensation plug rule complementary to the straight-coupling balance plug rule when the sub-array is a long sub-array, or the source distance of the shielded receiving coil is corrected by a current straight-coupling balance plug rule so that the absolute value of the residual straight-coupling signal is less than a first preset value, and the source distance of the main receiving coil is compensated by a source distance compensation plug rule complementary to the straight-coupling balance plug rule when the sub-array is a long sub-array.

[0032] Optionally, the thickness of the straight-coupling balance plug rule corresponding to the current balance position is determined according to the nearest minimum principle.

[0033] The nearest minimum principle is that if a certain straight-coupling balance plug rule is added between the transmitting coil and the shielded receiving coil, the source distance of the shielded receiving coil is closest to the current balance position at this time, the straight-coupling balance plug rule is determined as the target plug rule, and the thickness of the target plug rule is determined as the thickness of the straight-coupling balance plug rule corresponding to the current balance position; if there are two target plug rules, the smallest target plug rule thickness is determined as the thickness of the straight-coupling balance plug rule corresponding to the current balance position.

[0034] Optionally, the plug rule sensitivity initial value is an empirical value or is determined according to the corrected theoretical plug rule sensitivity.

[0035] Optionally, the straight-coupling balance plug rule and the source distance compensation plug rule are selected from the distance-increasing plug rule and the distance-decreasing plug rule, the thickness of the distance-increasing plug rule is the sum of the standard plug rule thickness and the plug rule offset, the thickness of the distance-decreasing plug rule is the difference between the standard plug rule thickness and the plug rule offset, and the plug rule offset is a multiple of the unit plug rule offset.

[0036] Optionally, when the direct coupling calibration process is performed for multiple or all sub-arrays, the direct coupling calibration process is performed in order of the distance between the shielded receiving coil and the transmitting coil in the sub-arrays.

[0037] Optionally, when the direct coupling calibration process is performed for multiple or all sub-arrays, the direct coupling calibration processes of the multiple or all sub-arrays are performed synchronously, and in the synchronous direct coupling calibration, if the distance between the shielded receiving coil and the transmitting coil in a first sub-array of two sub-arrays is less than the distance between the shielded receiving coil and the transmitting coil in a second sub-array, the source distance offset of the shielded receiving coil caused by the direct coupling balance plug of the first sub-array is added to the second sub-array.

[0038] The second aspect of the embodiment of the present application provides a device for implementing direct coupling balance of coil systems of array induction instruments, and the device comprises:

[0039] a direct coupling balance theoretical design module, configured to determine the theoretical process parameters of each coil system through direct coupling balance design;

[0040] an initial plug adding module, configured to, after the current coil system structure is used for instrument manufacturing or improvement, add a direct coupling balance plug between the transmitting coil and the shielded receiving coil to change the source distance of the shielded receiving coil for a sub-array, and add a source distance compensation plug complementary to the direct coupling balance plug between the main receiving coil and the shielded receiving coil according to the principle that the source distance of the main receiving coil of a long sub-array is unchanged, no source distance compensation plug is added between the main receiving coil and the shielded receiving coil when the sub-array is a short sub-array, then the current residual direct coupling signal of the sub-array is measured, and the source distance of the shielded receiving coil of the sub-array is determined according to the thickness of the current added direct coupling balance plug;

[0041] a first determining module, configured to determine a plug sensitivity initial value, and determine a current balance position according to the plug sensitivity initial value, the current balance position being the source distance of the shielded receiving coil at which the residual direct coupling signal is 0;

[0042] a second determining module, configured to determine the thickness of the direct coupling balance plug corresponding to the current balance position, and determine the thickness of the source distance compensation plug according to the thickness of the direct coupling balance plug when the sub-array is a long sub-array;

[0043] an iteration module, configured to change the thickness of the direct coupling balance plug by using a nonlinear equation root-finding algorithm, and change the thickness of the source distance compensation plug by using the nonlinear equation root-finding algorithm when the sub-array is a long sub-array, then the current residual direct coupling signal of the sub-array is measured, and the direct coupling calibration is ended after the maximum iteration number is reached or the nonlinear equation root-finding algorithm converges to a target balance position;

[0044] wherein the plug sensitivity represents the rate of change of the residual direct coupling signal with the thickness of the direct coupling balance plug.

[0045] Optionally, the direct coupling balance theory design module comprises:

[0046] a third determination module configured to determine the number of turns of the given transmitting coil;

[0047] a first selection module configured to select the source distance and the number of turns of the main receiving coil of each sub-array, the source distance and the number of turns of the main receiving coil being within a reasonable range determined according to the detection performance index and the induced signal index of the instrument;

[0048] a first calculation module configured to calculate the source distance and the number of turns of the shielded receiving coil by using the direct coupling balance formula with the number of turns of the shielded receiving coil as an integer or an even number as a constraint condition;

[0049] a first judgment module configured to determine whether the coil system structure based on the current source distance and the number of turns of the main receiving coil and the source distance and the number of turns of the shielded receiving coil is reasonable by taking whether the coil base space constraint is met as a reasonableness discrimination standard, if yes, the current coil system structure is used for instrument manufacturing or improvement, otherwise, the source distance and the 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 formula between the source distance and the number of turns of the main receiving coil and the source distance and the number of turns of the shielded receiving coil determined according to the principle that the strength of the direct coupling signal is proportional to the inverse of the cube of the source distance and the number of turns of the coil used for receiving.

[0051] Optionally, the target balance position is the source distance of the shielded receiving coil after the addition of the balance position corresponding to the cross-zero plug gauge, or the source distance of the shielded receiving coil after the addition of the current direct coupling balance 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 balance plug gauge that makes the absolute value of the residual direct coupling signal less than a first preset value; the cross-zero plug gauge is the two direct coupling balance plug gauges corresponding to the minimum thickness difference of one positive and one negative of the residual direct coupling signal.

[0052] A third aspect of the embodiment of the present application provides a computer device, comprising a memory, a processor and a computer program stored on the memory and executable on the processor, and the processor implements the array induction instrument coil system direct coupling balance implementation method of the first aspect of the embodiment of the present application when executing the program.

[0053] A fourth aspect of the embodiment of the present application provides a machine readable storage medium having a computer program stored thereon, and the computer program is executed by a processor to implement the array induction instrument coil system direct coupling balance implementation method of the first aspect of the embodiment of the present application.

[0054] In the technical solution, for the short sub-array, the direct coupling balance plug gauge is used for direct coupling adjustment, and when the nonlinear equation root-finding algorithm converges to the target balance position, the direct coupling balance plug gauge corresponding to the target balance position is used to correct the theoretical process parameters of each coil system determined by the direct coupling balance design, for the long sub-array, the direct coupling balance plug gauge and the source distance compensation plug gauge are used for direct coupling adjustment, and when the nonlinear equation root-finding algorithm converges to the target balance position, the direct coupling balance plug gauge and the source distance compensation plug gauge corresponding to the target balance position are used to correct the theoretical process parameters of each coil system determined by the direct coupling balance design, thereby avoiding the large difference between the actual production instrument and the theoretical design caused by various simplification factors of the direct coupling balance theoretical design, actual coil geometric size error, actual coil system base mechanical processing error, coil winding process, winding tension and assembly and other factors, so that the array induction instrument manufactured or improved based on the finally determined process parameters of each coil system can eliminate the direct coupling signal to the greatest extent, highlight the useful signal, ensure the direct coupling balance, and improve the signal-to-noise ratio of the array induction instrument.

[0055] Other features and advantages of the embodiments of the present application will be described in detail in the following specific implementation part. BRIEF DESCRIPTION OF DRAWINGS

[0056] The accompanying drawings are included to provide a further understanding of the embodiments of the present application, and constitute a part of the specification, and are used together with the following specific implementation to explain the embodiments of the present application, but do not constitute a limitation on the embodiments of the present application. In the drawings:

[0057] Figure 1 The principle diagram of the induction logging proposed in the background art is schematically shown;

[0058] Figure 2 The phase relationship of the transmitting coil, the formation element ring and the receiving coil current proposed in the background art is schematically shown;

[0059] Figure 3 The structure schematic diagram of the coil system induction probe proposed in the background art is schematically shown;

[0060] Figure 4 The structure schematic diagram of the array induction instrument probe proposed in the background art is schematically shown;

[0061] Figure 5 The flow chart of the array induction instrument coil system direct coupling balance implementation method according to the embodiments of the present application is schematically shown;

[0062] Figure 6 A flow chart of the direct coupling adjustment process in the specific application example is schematically shown;

[0063] Figure 7The flow chart of the direct coupling balance theoretical design process according to the embodiment of the present application is schematically shown;

[0064] Figure 8 The flow chart of the direct coupling balance theoretical design process in the specific application example is schematically shown;

[0065] Figure 9 The side view of the assembled plug gauge and the half plug gauge is schematically shown;

[0066] Figure 10 The top view of the assembled plug gauge and the two half plug gauges is schematically shown;

[0067] Figure 11 The position diagram of the direct coupling balance plug gauge and the source distance compensation plug gauge is schematically shown;

[0068] Figure 12 The plug gauge diagram of the array induction instrument containing 7 sub-arrays in the specific application example is schematically shown;

[0069] Figure 13 The diagram of the non-linear equation root-finding algorithm for finding the target balance position in the specific application example is schematically shown. DETAILED DESCRIPTION

[0070] The specific embodiments of the embodiments of the present application are described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the embodiments of the present application, and are not intended to limit the embodiments of the present application.

[0071] Embodiment One

[0072] Referring to Figure 5 The present application provides a coil system direct coupling balance implementation method for array induction instruments, which comprises the following implementation steps:

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

[0074] Step S200, performing a direct coupling adjustment process for the sub-arrays.

[0075] The direct coupling adjustment process comprises the following sub-steps:

[0076] Step S210, a direct coupling balance plug is added between the transmitting coil and the shielded receiving coil to change the source distance of the shielded receiving coil, and a source distance compensation plug complementary to the direct coupling balance plug is added between the main receiving coil and the shielded receiving coil according to the principle that the source distance of the main receiving coil is unchanged, the sub-array is a short sub-array, and then the current residual direct coupling signal of the sub-array is measured, and the source distance of the shielded receiving coil of the sub-array is determined according to the thickness of the current added direct coupling balance plug;

[0077] Step S220, a plug sensitivity initial value is given, and a current balance position is determined according to the plug sensitivity initial value, the current balance position being a source distance of the shielded receiving coil at which the residual direct coupling signal is 0, wherein the plug sensitivity represents a rate of change of the residual direct coupling signal with the thickness of the direct coupling balance plug;

[0078] Step S230, a thickness of the direct coupling balance plug corresponding to the current balance position is determined, and is recorded as a thickness of the direct coupling balance plug before the change, and when the sub-array is a long sub-array, a thickness of the source distance compensation plug is also determined according to the thickness of the direct coupling balance plug;

[0079] Step S240, a non-linear equation root-finding algorithm is used to iteratively change the thickness of the direct coupling balance plug, and when the sub-array is a long sub-array, the thickness of the source distance compensation plug is also iteratively changed, and then the current residual direct coupling signal of the sub-array is measured, and the direct coupling adjustment ends after reaching a maximum iteration number or the non-linear equation root-finding algorithm converges to a target balance position.

[0080] The plug sensitivity represents a rate of change of the residual direct coupling signal with the thickness of the direct coupling balance plug; the target balance position is a source distance of the shielded receiving coil after the direct coupling balance plug corresponding to the balance position at which the cross-zero plug appears is added, or a source distance of the shielded receiving coil after the current direct coupling balance plug is added at which the residual direct coupling signal is 0, or a source distance of the shielded receiving coil after the current direct coupling balance plug is added at which the absolute value of the residual direct coupling signal is less than a first preset value; and the cross-zero plug is two direct coupling balance plugs corresponding to the minimum thickness difference of one positive and one negative residual direct coupling signal.

[0081] Exemplarily, in combination with FIG. 1, in one specific embodiment, the theoretical process parameters of each coil system are determined through the direct coupling balance design, that is, the direct coupling balance theoretical design process is as follows: Figure 7

[0082] Step S110, the number of turns of the transmitting coil is given;

[0083] Step S120, the source distance and the number of turns of the main receiving coil of each sub-array are selected, and the source distance and the number of turns of the main receiving coil are both within a reasonable range determined according to the detection performance index and the induced signal index of the instrument;

[0084] ​Step S130, the turns of the shielded receiving coil are calculated by the direct coupling balance formula as an integer or even number as a constraint condition.

[0085] Step S140, whether the coil system structure is reasonable based on the current main receiving coil source distance and turns, shielded receiving coil source distance and turns is judged as a reasonable discrimination standard, if yes, the current main receiving coil source distance and turns, shielded receiving coil source distance and turns are taken as the theoretical process parameters to manufacture or improve the instrument, otherwise, the main receiving coil source distance and turns are iteratively updated until the coil system structure is reasonable.

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

[0087] In the above embodiment, the process parameters of the coil system structure are determined by the direct coupling balance formula based on the electromagnetic field theory, including the main receiving coil source distance and turns, shielded receiving coil source distance and turns, so that the array induction instrument made or improved based on the determined core parameters of the coil system structure has the theoretical direct coupling balance, and the elimination of part of the direct coupling signal can be realized.

[0088] Exemplarily, in one specific embodiment, the direct coupling balance formula is represented by the following formula:

[0089]

[0090] Wherein, N Rm is the turns of the main receiving coil, -N Rb is the turns of the shielded receiving coil, the negative sign indicates that the winding direction of the shielded receiving coil is opposite to that of the main receiving coil, L m is the source distance of the main receiving coil, L b is the source distance of the shielded receiving coil.

[0091] In one specific embodiment, the turns of the shielded receiving coil are calculated by the direct coupling balance formula as an integer or even number as a constraint condition, including:

[0092] Given the initial value of the source distance ratio of the shielded receiving coil to the main receiving coil, the initial value of the source distance of each subarray shielded receiving coil is calculated according to the initial value of the source distance ratio, and the initial value of the turns of the shielded receiving coil is calculated by the direct coupling balance formula;

[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, structure accommodation check: whether the coil system structure based on the current main receiving coil source distance, main receiving coil turns, shield receiving coil source distance and shield receiving coil turns adjusted to an integer or an even number is reasonable is judged as a rationality judgment standard of whether the coil base accommodation space constraint is met, if reasonable, step SS700 is executed, otherwise jump to step SS200.

[0101] It should be understood that the transmitting coil, the main receiving coil and the shield receiving coil are all wound in the wire slot of the coil base according to the preset turn spacing, therefore the coil base accommodation space constraint refers to that the total length occupied by the coil system as a whole does not exceed the total length of the coil base after calculating the coil length according to the coil turns and the turn spacing and considering the reserved position of structural members such as terminal posts.

[0102] Step SS700, the signal magnitude of each subarray is calculated, the signal-to-noise ratio is evaluated, the instrument accuracy and measurement dynamic range are analyzed and evaluated, and the detection performance and direct coupling balance of each subarray are investigated, and the latest main receiving coil source distance, main receiving coil turns, shield receiving coil source distance and shield receiving coil turns adjusted to an integer or an even number are used for array induction instrument manufacturing or improvement.

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

[0104]

[0105] In formula 1, i is an imaginary unit, ω is an angular frequency, μ is a magnetic permeability (unit: H / m), I T =I0e -iωt , I T is a transmitting current, I0 is a transmitting current amplitude, A T is a transmitting coil area, A R is a receiving coil area, N T and N R are the turns of the transmitting coil and the receiving coil respectively, k is the wave number of the medium, k 2 =iωμσ, σ is the electrical conductivity of the space medium. In formula 1, when σ = 0, i.e. k = 0, the direct coupling electromotive force is obtained as:

[0106]

[0107] In the formula 1, when σ = 0, i.e. k = 0, the direct coupling electromotive force is obtained as: 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 receiving line is shielded.

[0109] The winding direction of the coil is opposite to that of the main receiving coil. Since 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:

[0110]

[0111] 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.

[0112] 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.

[0113] The detailed derivation of Formula 3 is as follows:

[0114] 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:

[0115] V=iωμ0N R A R H(Formula 4);

[0116] 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:

[0117]

[0118] In Formula 5, (r,z) are the spatial cylindrical coordinates of the field point, and k is the wavenumber of the formation medium. 2 =iωμσ, where σ is the conductivity of the space medium;

[0119] 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.:

[0120] H = H' + iH (Formula 6);

[0121] Substituting formula 6 into formula 4, we get:

[0122] V=-ωμ0N R A R H”+iωμ0N R A R H'(Formula 7);

[0123] 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.

[0124] Under low-frequency electromagnetic field conditions, e ikr The first three terms of the Taylor expansion Substitute into public

[0125] Formula 5, through mathematical derivation, an approximate expression of the magnetic field strength H at the receiving coil is obtained:

[0126]

[0127] Formula 8 is derived based on the magnetic dipole, considering the number of turns and the area of the transmitting coil, then the secondary magnetic field or useful signal received by the receiving coil, i.e. the real part of formula 7, is:

[0128]

[0129] When the space medium conductivity σ = 0, i.e. k = 0, the direct coupling electromotive force is obtained:

[0130]

[0131] In formula 10, I T = I0e -iωt , I T is the transmitting current, I0 is the transmitting current amplitude, A T is the transmitting coil area, A R is the receiving coil area, N T is the number of turns of the transmitting coil, and N R is the number of turns of the receiving coil.

[0132] As can be seen from formula 9 and formula 10, the useful secondary induction signal is inversely proportional to the source distance, and the useless direct coupling signal is inversely proportional to the cube of the source distance, so theoretically, by optimizing the number of turns of the shielding receiving coil and the source distance, the direct coupling signal can be completely offset at the cost of sacrificing part of the useful signal. However, in addition to counter-winding the two receiving coils and satisfying formula (3) in terms of source distance and number of turns to eliminate the direct coupling signal, the magnitude of the useful signal and the degree of sacrifice need to be considered when eliminating the direct coupling signal, and the consistency of the detection range of the shielding coil and the main receiving coil needs to be considered.

[0133] After the ratio of the source distance of the shielding receiving coil to the main receiving coil is denoted as , according to the above direct coupling balance formula, the number of turns of the shielding receiving coil can be represented as:

[0134]

[0135] Since the number of turns must be an integer or an even number, the number of turns of the shielding receiving coil is taken as N' Nb = int(β 3 N Rm ) or an even number.

[0136] After adjusting the number of turns of the shielding receiving coil to be an integer or an even number, according to formula 12, we have:

[0137]

[0138] Where β' is the updated value of the ratio of the source distance between the shielded receiving coil and the main receiving coil;

[0139] Then, recalculate the source distance L of the shielded receiving coil using Formula 11. b =β'L m .

[0140] 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:

[0141]

[0142] 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.

[0143] 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.

[0144] 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.

[0145] For example, in a specific embodiment, when performing the direct coupling adjustment process for multiple or all sub-arrays, the direct coupling adjustment process is performed in order of the distance from the shielded receiving coil to the transmitting coil in the sub-arrays. Although the balance position of each sub-array and the direct coupling adjustment process of the balance position are independent of each other, the position of the long sub-array is affected by the direct coupling adjustment result of the front short sub-array and the plug gauge replacement. By adding the source distance offset of the direct coupling balance plug gauge of the front short sub-array to the plug gauge of the rear long sub-array according to the position relationship of the sub-arrays, the balance position of each sub-array and the current adjustment position are ensured to be unchanged, thereby realizing the direct coupling balance adjustment of multiple or all sub-arrays. Compared with the adjustment without considering the position relationship of the sub-arrays, the frequency of loosening and tightening the coil system during the replacement of the plug gauge is reduced, and the efficiency of the direct coupling adjustment is improved.

[0146] As an improvement of the above embodiment, when performing the direct coupling adjustment process for multiple or all sub-arrays, the direct coupling adjustment processes of the multiple or all sub-arrays are performed synchronously. In the synchronous direct coupling adjustment, according to the position relationship of any two sub-arrays, if the distance from the shielded receiving coil in the first sub-array to the transmitting coil is less than the distance from the shielded receiving coil in the second sub-array to the transmitting coil, the source distance offset of the direct coupling balance plug gauge of the first sub-array is added to the second sub-array. By synchronously performing the direct coupling adjustment of each sub-array and adding the source distance offset of the shielded receiving coil according to the position relationship of the sub-arrays, the efficiency of the direct coupling adjustment is improved.

[0147] For example, in a specific embodiment, the nonlinear equation root-finding algorithm adopts the dichotomy method, the secant method, the general trial method, the Ridders method, and the Brent method, etc.

[0148] For example, in a specific embodiment, the nonlinear equation root-finding algorithm is used to iteratively change the thickness of the direct coupling balance plug gauge, and when the sub-array is a long sub-array, the thickness of the source distance compensation plug gauge is also iteratively changed. Then, the current residual direct coupling signal of the sub-array is measured until the maximum iteration number is reached or the nonlinear equation root-finding algorithm converges to the target balance position, and the direct coupling adjustment is ended, including:

[0149] Step S2410, changing the thickness of the direct coupling balance plug gauge, and when the sub-array is a long sub-array, changing the thickness of the source distance compensation plug gauge, and measuring the current residual direct coupling signal of the sub-array;

[0150] Step S2420, determining whether the maximum iteration number is reached or the nonlinear equation root-finding algorithm converges to the target balance position; if yes, the direct coupling adjustment is ended, otherwise, determining the new plug gauge sensitivity and balance position according to the residual direct coupling signals before and after the change of the thickness of the direct coupling balance plug gauge and the source distance of the shielded receiving coil, and jumping to step S230.

[0151] It can be seen that the direct coupling adjustment end condition is that the maximum iteration number is reached or the nonlinear equation root-finding algorithm converges to the target balance position. The nonlinear equation root-finding algorithm converging to the target balance position means that one of the following three situations occurs:

[0152] 1) a cross-zero choke appears;

[0153] 2) the current direct coupling balance choke added makes the residual direct coupling signal 0;

[0154] 3) the current direct coupling balance choke added makes the absolute value of the residual direct coupling signal less than a first preset value.

[0155] Exemplarily, in one specific embodiment, the thickness of the direct coupling balance choke corresponding to the current balance position is determined according to the nearest minimum principle, wherein the nearest minimum principle is that if a certain direct coupling balance choke is added between the transmitting coil and the shielded receiving coil, at this time the source distance of the shielded receiving coil is closest to the current balance position, then the direct coupling balance choke is determined as the target choke, and the thickness of the target choke is determined as the thickness of the direct coupling balance choke corresponding to the current balance position; if there are two target chokes, the smallest target choke thickness is determined as the thickness of the direct coupling balance choke corresponding to the current balance position.

[0156] Exemplarily, in one specific embodiment, if the nonlinear equation root-finding algorithm converges to the target balance position, then the source distance of the shielded receiving coil is also corrected by the direct coupling balance choke corresponding to the balance position when the cross-zero choke appears, and the source distance of the main receiving coil is compensated by the source distance compensation choke complementary to the direct coupling balance choke when the subarray is a long subarray, or the source distance of the shielded receiving coil is corrected by the current direct coupling balance choke that makes the residual direct coupling signal 0, and the source distance of the main receiving coil is compensated by the source distance compensation choke complementary to the direct coupling balance choke when the subarray is a long subarray, or the source distance of the shielded receiving coil is corrected by the current direct coupling balance choke that makes the absolute value of the residual direct coupling signal less than the first preset value, and the source distance of the main receiving coil is compensated by the source distance compensation choke complementary to the direct coupling balance choke when the subarray is a long subarray.

[0157] It needs to be understood that the plug gauge in the traditional sense refers to a precision measuring tool, also known as a plug gauge, which is mainly used for measuring the diameter or gap size of round holes and cylindrical holes. In the embodiment of the present application, the plug gauge is a series of structural parts with different thicknesses that are precisely polished and used to be inserted between the coil bases, so it is defined as a plug gauge, which functions as follows: through the addition of the plug gauge, the position of the shielded receiving coil is fine-tuned, and then the source distance of the shielded receiving coil is fine-tuned, and the change in the position of the main receiving coil caused by the fine-tuning of the position of the shielded receiving coil in the long sub-array is compensated. The series of structural parts can be a series of ring-shaped pieces, and the series of ring-shaped pieces can be ceramic pieces, etc.

[0158] In one specific embodiment, the structure of the plug gauge is as shown in Figure 9 and Figure 10 The position of the plug gauge on the array induction instrument is as shown in Figure 11 and Figure 12 . Figure 10 In the embodiment, the plug gauge is made of two half-ring-shaped ceramic pieces that are precisely polished, and a pair of half-ring plug gauges with the same thickness are inserted into the gap of the coil base after being loosened, and then the coil system is tightened, so that the source distance of the coil can be changed by changing the thickness of the plug gauge. A binding wire slot is provided on the plug gauge, through which the two half-ring plug gauges can be fixed with fine cotton thread or the like to prevent the plug gauge from falling off before the coil system is tightened and after being loosened when the plug gauge is replaced. Figure 12 In the embodiment, the array induction instrument includes four short sub-arrays R0, R1, R2, R3 and three long sub-arrays R4, R5, R6. The short sub-array R0 includes a main receiving coil R 0m and a shielded receiving coil R 0b . The short sub-array R1 includes a main receiving coil R 1m and a shielded receiving coil R 1b . The short sub-array R2 includes a main receiving coil R 2m and a shielded receiving coil R 2b . The short sub-array R3 includes a main receiving coil R 3m and a shielded receiving coil R 3b . Seven direct-coupled balanced plug gauges S0, S1, S2, S3, S 4b , S 5b , S 6b are added to the array induction instrument, and three source distance compensation plug gauges S 4m , S 5m , S 6m are added.

[0159] Exemplarily, in one specific embodiment, the directly coupled balance plug gauge and the source distance compensation plug gauge are both selected from the increased distance plug gauge and the decreased distance plug gauge, the thickness of the increased distance plug gauge is the sum of the thickness of the standard plug gauge and the plug gauge offset, the thickness of the decreased distance plug gauge is the difference between the thickness of the standard plug gauge and the plug gauge offset, and 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 decreased distance plug gauge with stepped thickness reduction, and the increased distance plug gauge with stepped thickness increase, the selection of the directly coupled balance plug gauge and the source distance compensation plug gauge is more flexible, and thus the directly coupled adjustment efficiency is improved.

[0160] For example, in one specific application, the plug gauge series composed of the increased distance plug gauge, the decreased distance plug gauge and the standard plug gauge is shown in Table 1. Among them, the name or code of the standard plug gauge is BZ, and the name "BZ" of the standard plug gauge is marked on the surface of the plug gauge with a black pen for easy identification. J1, J2, J3,..., J26 are the decreased distance plug gauges, the thicknesses of which are 9.95 mm, 9.90 mm, 9.85 mm,..., 7.00 mm, and the plug gauge offsets are -0.05 mm, -0.10 mm, -0.15 mm,..., -3.00 mm, respectively. One J26 plug gauge can reduce the source distance by 3.00 mm relative to the initial standard plug gauge BZ, and the name of the decreased distance plug gauge is marked on the surface of the plug gauge with a green pen. Z1, Z2, Z3,..., Z26 are the increased distance plug gauges, the thicknesses of which are 10.05 mm, 10.10 mm, 10.15 mm,..., 13.00 mm, and the plug gauge offsets are 0.05 mm, 0.10 mm, 0.15 mm,..., 3.00 mm, respectively. One Z26 plug gauge can increase the source distance by 3.00 mm relative to the initial standard plug gauge BZ, and the name of the increased distance plug gauge is marked on the surface of the plug gauge with a red pen. At the same time, Z1 and J1 are the compensation plug gauges of each other because the plug gauge offsets are opposite numbers. Similarly, Z2 and J2, Z3 and J3,..., Z26 and J26 are also the compensation plug gauges of each other. The source distance compensation plug gauge can be placed in the source distance compensation plug gauge position of the directly coupled balance plug gauge, and the directly coupled balance plug gauge can be placed in the directly coupled balance plug gauge position of the source distance compensation plug gauge. Figure 11The source distance compensation plug position compensates the direct coupling plug offset of the long sub-array coil system to ensure that the source distance of the main receiving coil of the long sub-array is constant. The plug sequence J26, J25,..., J1, BZ, Z1, Z2,..., Z26 in Table 1 is arranged from thin to thick, and the plug thickness increases from 7 mm to 13 mm. The plug offset increases from -3 mm to +3 mm. In the plug sequence, the two plugs adjacent to each other are called adjacent plugs, and the minimum difference between the adjacent plugs is only 0.05 mm. Preferably, each plug position can be designed to accommodate two plugs. The two plugs are designed to increase or decrease the maximum source distance of 3.00 mm relative to one standard plug to 6.0 mm, thereby expanding the source distance adjustment range without increasing the plug series. Meanwhile, the selection of the plug has more combinations, which can improve the reuse rate of the plug and greatly save the cost. Meanwhile, it is emphasized that the final direct coupling calibration result allows only one plug in the plug position, and also allows three or more plugs, but in practice, two plug positions are sufficient to calibrate to the balance position.

[0161] Table 1

[0162]

[0163]

[0164] Through Figure 7 and Figure 8 The sub-arrays of the coil system array induction instrument realized by the processes shown in the above formulas are theoretically direct coupling balanced, but the array induction instrument is very sensitive to the response of the direct coupling signal. Due to the introduction of the magnetic dipole in the above formulas 1-14, the influence of the actual coil geometry, the existence of structural process errors, and many other factors, the direct coupling signal of the array induction instrument actually manufactured and assembled is not completely canceled out, and needs to be fine-tuned and calibrated. As can be seen from Figure 11 The coil of the coil system is wound on a rigid base. The material of the rigid base is generally required to be easy to precisely process and have small temperature expansion effect, and the mechanical strength and material processing cost also need to be considered. Generally, ceramic is selected as the coil base, and metal wire (generally copper wire or lithium wire) is wound in the pre-processed wire slot of the coil base to form an induction coil. The coil base has a hole processed in the middle. The instrument mandrel is a beryllium copper tube, and a glass steel bushing is laid outside the tube. When the instrument is assembled, the glass steel bushing and the induction coil ceramic base are placed between the rubber O-rings. In this way, the position of the coil wound in the wire slot of the coil base is fixed relative to the coil base, and the length of the coil base is also fixed. Therefore, the fine tuning of the coil position can be realized by replacing the plugs with different thicknesses between the coil bases. It can be seen that it is feasible to realize the direct coupling balance by adjusting the plug.

[0165] In addition, in order to adapt to various detection requirements, the array induction instrument usually comprises a short sub-array and a long sub-array, where the long sub-array and the short sub-array are determined according to whether the source distance of the sub-array exceeds a preset threshold value, if the source distance of the sub-array does not exceed the preset threshold value, the sub-array is determined as the short sub-array, otherwise, the sub-array is determined as the long sub-array. For the short sub-array, the position of the shield receiving coil is extremely sensitive to the direct coupling signal, the source distance adjustment amount is relatively small, and meanwhile, the space between the shield receiving coil and the main receiving coil in each short sub-array is limited, in order to improve the precision of the array induction instrument, the shield receiving coil and the main receiving coil are usually wound on the same coil base, therefore, during the plug gauge adjustment, the plug gauge position can only be designed between the transmitting coil and the shield receiving coil, by changing the thickness of the direct coupling balance plug gauge, the source distance of the shield receiving coil and the main receiving coil is synchronously increased or decreased. For the long sub-array, the position of the shield receiving coil is relatively less sensitive, and meanwhile, the space between the shield receiving coil and the main receiving coil in each long sub-array is relatively sufficient, in order 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 sub-array, in addition to designing a plug gauge position between the transmitting coil and the shield receiving coil to put the direct coupling balance plug gauge to adjust the position of the shield receiving coil, a plug gauge position is also designed between the main receiving coil and the shield receiving coil to put the source distance compensation plug gauge, the thickness increase or decrease amount of the source distance compensation plug gauge put in the plug gauge position is opposite to the thickness increase or decrease amount of the direct coupling balance plug gauge put in the long sub-array, to compensate for the change of the source distance of the main receiving coil caused by the replacement of the direct coupling balance plug gauge, so as to ensure that the relative position of the main receiving coil relative to the transmitting coil does not change, that is, to ensure that the source distance of the main receiving coil is always unchanged.

[0166] In the above embodiment, the direct coupling signal of the main receiving coil can be obtained from formula 10:

[0167]

[0168] The direct coupling signal of the shield receiving coil is:

[0169]

[0170] Suppose the plug gauge offset is l mb Therefore, for the short sub-array in which only the direct coupling balance plug gauge is placed between the transmitting coil and the shield receiving coil, the total direct coupling electromotive force of the main receiving coil and the shield receiving coil in series, that is, the residual direct coupling signal is:

[0171]

[0172] Further, the plug gauge sensitivity of the short sub-array is defined as:

[0173]

[0174] 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:

[0175]

[0176] Furthermore, the plug sensitivity of the long subarray is defined as:

[0177]

[0178] 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:

[0179]

[0180] 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.

[0181] 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:

[0182] 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 (22) to calculate the balance position;

[0183] Step A2, according to the calculated balance position L' balance , the balance position corresponding to the direct coupling balance plug gauge is determined according to the nearest minimum principle, and the source distance compensation plug gauge of the subarray is determined according to the principle of constant source distance of the main receiving coil of the long subarray, then the new direct coupling balance plug gauge is replaced, and when the subarray is a long subarray, the new source distance compensation plug gauge is also replaced, then the current residual direct coupling signal of the subarray is measured;

[0184] Step A3, it is judged whether the plug gauge adjustment end condition is met, if yes, the next step is executed, otherwise the residual direct coupling signal of the subarray before the plug gauge is replaced the residual direct coupling signal after the plug gauge is replaced the source distance L of the shield receiving coil before the plug gauge is replaced old and the source distance L of the shield receiving coil after the plug gauge is replaced new and the formula the new plug gauge sensitivity is calculated, and the new balance position is calculated according to the formula , then jump to step A2;

[0185] Step A4, the plug gauge adjustment is completed. In addition, after the plug gauge adjustment is completed, the adjustment success or failure conclusion can be given, a detailed report is issued, the adjustment process and result are stored in the database, and the adjustment result can be compared with the adjustment result in the database to give the statistical result of the residual direct coupling and the final plug gauge.

[0186] In addition, the maximum number of iterations is reached without appearing the cross-zero plug gauge, specifically, one of the following two cases: 1) in the iteration, as the source distance of the shield receiving coil becomes smaller and smaller, the residual direct coupling signal increases continuously, but is always negative; 2) in the iteration, as the source distance of the shield receiving coil becomes larger and larger, the residual direct coupling signal decreases continuously, but is always positive.

[0187] The derivation process of formula 23 is as follows:

[0188]

[0189] It can be seen that represents the plug gauge sensitivity;

[0190] Further, formula 26 can be rewritten as

[0191] Experiments show that in the above application, the adjustment can be completed through at most three plug gauge replacements, and the adjustment efficiency is high.

[0192] Embodiment two

[0193] The embodiment of the present application provides a coil system direct coupling balance realization device of an array induction instrument, the device comprises a direct coupling balance theoretical design module, an initial plug gauge adding module, a first determination module, a second determination module and an iteration module, wherein:

[0194] The direct coupling balance theoretical design module is used for determining the theoretical process parameters of each coil system through direct coupling balance design.

[0195] The initial plug gauge adding module is used for adding a direct coupling balance plug gauge between a transmitting coil and a shield receiving coil to change the source distance of the shield receiving coil, and adding a source distance compensation plug gauge which is complementary to the direct coupling balance plug gauge between the main receiving coil and the shield receiving coil according to the principle that the source distance of the main receiving coil of a long subarray is unchanged, when the current coil system structure is used for instrument manufacturing or improvement.

[0196] The first determination module is used for determining the current balance position according to the initial plug gauge sensitivity, and the current balance position is the source distance of the shield receiving coil which makes the residual direct coupling signal 0.

[0197] The second determination module is used for determining the thickness of the direct coupling balance plug gauge corresponding to the current balance position, and the thickness of the source distance compensation plug gauge is determined according to the thickness of the direct coupling balance plug gauge when the subarray is a long subarray.

[0198] The iteration module is used for changing the thickness of the direct coupling balance plug gauge by using a nonlinear equation root algorithm, and the thickness of the source distance compensation plug gauge is also changed by iteration when the subarray is a long subarray, and then the current residual direct coupling signal of the subarray is measured until the maximum iteration number is reached or the nonlinear equation root algorithm converges to the target balance position, and the direct coupling adjustment is completed.

[0199] The plug gauge sensitivity represents the rate of change of the residual direct coupling signal with the thickness of the direct coupling balance plug gauge.

[0200] In a specific embodiment, the direct coupling balance theoretical design module comprises a third determination module, a first selection module, a first calculation module and a first judgment module, wherein:

[0201] The third determination module is used for giving the number of turns of the transmitting coil.

[0202] The first selection module is used for selecting the source distance and the number of turns of the main receiving coil of each subarray, and the source distance and the number of turns of the main receiving coil are both in a reasonable range determined according to the detection performance index and the induction signal index of the instrument.

[0203] The first calculation module is configured to calculate the source distance and the number of turns of the shielded receiving coil by using the direct coupling balance formula with the number of turns of the shielded receiving coil being an integer or an even number as a constraint condition.

[0204] The first judgment module is configured to judge whether the coil system structure based on the current source distance and the number of turns of the main receiving coil and the source distance and the number of turns of the shielded receiving coil is reasonable with whether the coil base body accommodation space constraint is satisfied as a reasonableness discrimination standard, and if so, the current coil system structure is used for instrument manufacturing or improvement, otherwise, the source distance and the number of turns of the main receiving coil are iteratively updated until the coil system structure is reasonable.

[0205] The direct coupling balance formula is a constraint relationship formula between the source distance and the number of turns of the main receiving coil and the source distance and the number of turns of the shielded receiving coil determined according to the principle that the strength of the direct coupling signal is proportional to the inverse of the cube of the source distance and the number of turns of the coil used for receiving.

[0206] In one specific embodiment, the direct coupling balance formula is represented by the following formula:

[0207]

[0208] Wherein, N Rm is the number of turns of the main receiving coil, -N Rb is the number of turns of the shielded receiving coil, the negative sign indicates that the winding direction of the shielded receiving coil is opposite to that of the main receiving coil, L m is the source distance of the main receiving coil, L b is the source distance of the shielded receiving coil.

[0209] In one specific embodiment, the source distance and the number of turns of the shielded receiving coil are calculated by using the direct coupling balance formula with the number of turns of the shielded receiving coil being an integer or an even number as a constraint condition, including:

[0210] Given the initial value of the source distance ratio of the shielded receiving coil to the main receiving coil, the initial value of the source distance of each subarray shielded receiving coil is calculated according to the initial value of the source distance ratio, and the initial value of the number of turns of the shielded receiving coil is calculated by using the direct coupling balance formula;

[0211] The number of turns of the shielded receiving coil is adjusted to be an integer or an even number, the updated value of the source distance ratio of the shielded receiving coil to the main receiving coil is calculated by using the direct coupling balance formula, then the updated value of the source distance of the shielded receiving coil is calculated according to the updated value of the source distance ratio, the number of turns of the shielded receiving coil adjusted to be an integer or an even number is taken as the number of turns of the shielded receiving coil, and the updated value of the source distance of the shielded receiving coil is taken as the source distance of the shielded receiving coil.

[0212] In one specific embodiment, the detection performance indicators include radial detection depth and longitudinal resolution indicators.

[0213] In one specific embodiment, the inductive signal indicators include inductive signal strength indicators of the sub-arrays and signal-to-noise ratio indicators of the original collected signals.

[0214] In one specific embodiment, the target balance position is a balance position corresponding to a source distance of the shielded receiving coil after adding a straight-coupling balance plug rule when a cross-zero plug rule occurs, or a source distance of the shielded receiving coil after adding a current straight-coupling balance plug rule that makes the residual straight-coupling signal 0, or a source distance of the shielded receiving coil after adding a current straight-coupling balance plug rule that makes the absolute value of the residual straight-coupling signal less than a first preset value; the cross-zero plug rule is two straight-coupling balance plug rules corresponding to the minimum thickness difference of one positive and one negative residual straight-coupling signals.

[0215] In one specific embodiment, the array inductive instrument coil system straight-coupling balance implementation device further includes a process parameter correction module, which is configured to correct the source distance of the shielded receiving coil by using a straight-coupling balance plug rule corresponding to a balance position when a cross-zero plug rule occurs when it is determined that the non-linear equation root-finding algorithm converges to the target balance position, and compensate the source distance of the main receiving coil by using a source distance compensation plug rule complementary to the straight-coupling balance plug rule when the sub-array is a long sub-array, or correct the source distance of the shielded receiving coil by using a current straight-coupling balance plug rule that makes the residual straight-coupling signal 0, and compensate the source distance of the main receiving coil by using a source distance compensation plug rule complementary to the straight-coupling balance plug rule when the sub-array is a long sub-array, or correct the source distance of the shielded receiving coil by using a current straight-coupling balance plug rule that makes the absolute value of the residual straight-coupling signal less than a first preset value, and compensate the source distance of the main receiving coil by using a source distance compensation plug rule complementary to the straight-coupling balance plug rule when the sub-array is a long sub-array.

[0216] In one specific embodiment, the thickness of the straight-coupling balance plug rule corresponding to the current balance position is determined according to the nearest minimum principle; the nearest minimum principle is that if a certain straight-coupling balance plug rule is added between the transmitting coil and the shielded receiving coil, the source distance of the shielded receiving coil at this time is closest to the current balance position, then the straight-coupling balance plug rule is determined as the target plug rule, and the thickness of the target plug rule is determined as the thickness of the straight-coupling balance plug rule corresponding to the current balance position; if there are two target plug rules, the smallest target plug rule thickness is determined as the thickness of the straight-coupling balance plug rule corresponding to the current balance position.

[0217] In one specific embodiment, the plug rule sensitivity initial value is an empirical value or is determined according to the corrected theoretical plug rule sensitivity.

[0218] In one specific embodiment, the straight-coupling balance plug rule and the source distance compensation plug rule are selected from the distance-increasing plug rule and the distance-decreasing plug rule, the thickness of the distance-increasing plug rule is the sum of the standard plug rule thickness and the plug rule offset, the thickness of the distance-decreasing plug rule is the difference between the standard plug rule thickness and the plug rule offset, and the plug rule offset is a multiple of the unit plug rule offset.

[0219] In one embodiment, when the direct coupling calibration process is performed for multiple or all sub-arrays, the direct coupling calibration process is performed in order of the distance from the shielded receiving coil to the transmitting coil in the sub-arrays.

[0220] In one embodiment, when the direct coupling calibration process is performed for multiple or all sub-arrays, the direct coupling calibration processes of the multiple or all sub-arrays are performed synchronously. In synchronous direct coupling calibration, according to the positional relationship of any two sub-arrays, if the distance from the shielded receiving coil in the first sub-array to the transmitting coil is less than the distance from the shielded receiving coil in the second sub-array to the transmitting coil, the source distance offset of the shielded receiving coil caused by the direct coupling balance plug gauge in the first sub-array is accumulated to the second sub-array.

[0221] In another aspect, the embodiments of the present application also provide a machine readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement any of the above-mentioned direct coupling balance implementation methods for coil systems of array inductive instruments.

[0222] In yet another aspect, the embodiments of the present application also provide a computer device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and the processor implements any of the above-mentioned direct coupling balance implementation methods for coil systems of array inductive instruments when executing the program.

[0223] In yet another aspect, the embodiments of the present application 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, and the processor implements any of the above-mentioned direct coupling balance implementation methods for coil systems of array inductive instruments when executing the program. The digital twin platform constructed by the above-mentioned method realizes big data analysis and services for the design, optimization, calibration, scaling, manufacturing, etc. of array inductive instruments, greatly improves the work efficiency of array inductive instruments in the manufacturing or improvement process, and reduces the manufacturing cost.

[0224] In yet another aspect, the embodiments of the present application also provide a computer program product, which, when executed on a data processing device, is adapted to execute a program that initializes the following method steps:

[0225] determining the theoretical process parameters of each coil system through direct coupling balance design;

[0226] performing the direct coupling calibration process for the sub-arrays, and the direct coupling calibration process includes:

[0227] adding a direct coupling balance plug between the transmitting coil and the shielded receiving coil to change the source distance of the shielded receiving coil, and adding a source distance compensation plug complementary to the direct coupling balance plug between the main receiving coil and the shielded receiving coil according to the principle that the source distance of the main receiving coil is unchanged, not adding the source distance compensation plug between the main receiving coil and the shielded receiving coil when the subarray is a short subarray, then measuring the current residual direct coupling signal of the subarray and determining the source distance of the shielded receiving coil according to the thickness of the current added direct coupling balance plug;

[0228] given a plug sensitivity initial value, and determining a current balance position according to the plug sensitivity initial value, the current balance position being the source distance of the shielded receiving coil that makes the residual direct coupling signal 0, the plug sensitivity representing the rate of change of the residual direct coupling signal with the thickness of the direct coupling balance plug;

[0229] determining the thickness of the direct coupling balance plug corresponding to the current balance position, and determining the thickness of the source distance compensation plug according to the thickness of the direct coupling balance plug when the subarray is a long subarray;

[0230] using a nonlinear equation root algorithm to iteratively change the thickness of the direct coupling balance plug, and iteratively changing the thickness of the source distance compensation plug when the subarray is a long subarray, then measuring the current residual direct coupling signal of the subarray, and the direct coupling adjustment ending after reaching a maximum iteration number or the nonlinear equation root algorithm converging to a target balance position.

[0231] The device embodiments described above are merely illustrative, wherein the units shown as separate components can or can not be physically separate, and the components shown as units can or can not be physical units, i.e., can be located in one place or distributed on multiple network units. Part or all of the modules can be selected to achieve the purpose of the embodiment scheme according to actual needs. Those skilled in the art can understand and implement without creative labor.

[0232] Those skilled in the art will appreciate that embodiments of the application can be provided as methods, systems, or computer program products. Accordingly, the application can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the application can take the form of a computer program product on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage media, etc.) having computer-usable program code embodied therein.

[0233] It should also be noted that the terms "comprising", "comprises" or any other variation thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0234] Finally, it should be noted that the above examples are merely used to illustrate the technical solutions of the present application, rather than limiting the same; even though the present application has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacements for some of the technical features; and these modifications or replacements 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 application.

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.

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