Approximate equivalent compensation coil structure, resistivity measurement method and stratum property analysis method

Abstract

The invention belongs to the technical field of oil-gas exploration and development, and relates to an approximate equivalent compensation coil structure, a resistivity measurement method and a stratum property analysis method, and the coil structure comprises at least one compensation transmitting coil system and at least one receiving coil; the compensation transmitting coil system comprises a main transmitting coil and at least two secondary transmitting coils, the secondary transmitting coils are arranged on the two sides of the main transmitting coil, the number of the secondary coils on the two sides of the main transmitting coil is the same, the secondary transmitting coils are compensation transmitting coils, and the winding direction of the main transmitting coil is opposite to that of the adjacent secondary transmitting coils. The winding directions of two adjacent secondary transmitting coils are the same or opposite; and the winding directions of the receiving coil and the main transmitting coil are the same or opposite. The method adopts the approximate equivalent compensation coil structure. According to the method, a strong casing background signal can be suppressed, the signal-to-noise ratio of a stratum signal is improved, the transient electromagnetic wave through casing logging response precision is improved, and stratum resistivity extraction under the influence of a high-conductivity casing is achieved.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas exploration and development technology, and relates to electrical logging technology. Specifically, it relates to an approximately equivalent compensation coil structure, a resistivity measurement method, and a formation property analysis method. Background Technology

[0002] In oil and gas field exploration and development, through-casing resistivity measurement technology has significant application value, especially in casing drilling. Through-casing resistivity measurement is one of the important means for evaluating reservoir oil-bearing capacity, monitoring reservoir dynamics, and analyzing remaining oil distribution. It is of great significance for reservoir evaluation in casing drilling, optimizing production well development plans, and improving oil recovery. As a new drilling method in oil and gas exploration and development, casing drilling presents challenges because conventional resistivity logging cannot be directly applied due to the presence of the casing. Therefore, achieving accurate and efficient through-casing resistivity measurement has become a key issue in the industry.

[0003] Currently, the electrode method is commonly used for through-casing resistivity logging. Its basic principle is to infer formation resistivity by measuring the weak current leaking inside and outside the casing. However, the electrode method has the following limitations: (1) It is greatly affected by the quality of the casing: corrosion, thinning or deformation of the casing will significantly affect the contact quality between the electrode and the casing, resulting in inaccurate measurement data. (2) It is affected by the downhole environment: scale, wax, rust and other deposits on the inner wall of the casing will interfere with the stability of the electrode method measurement, requiring time for well cleaning (such as descaling, deoiling, etc.) and other preparatory work, which increases the complexity of logging. (3) The logging efficiency is low: the electrode method usually adopts a point measurement mode, which requires a long time to establish stable measurement conditions, and cannot meet the real-time response requirements for rapid changes in the downhole environment, resulting in low overall logging efficiency.

[0004] Transient electromagnetic wave technology provides a new solution for casing resistivity measurement. Its working principle is to arrange transmitting and receiving coils in the well. Transmitting current pulses are sent to the formation through the transmitting coil. The transient current pulses generate electromagnetic fields that change with time, which excite the formation to generate induced eddy currents that decay with time and spread at different speeds in different media. After the current is turned off, the decay characteristics of the secondary induced electromagnetic field generated by the eddy currents over time are measured to extract formation resistivity information. Transient electromagnetic wave technology has the following advantages: (1) Strong penetration: Low frequency signals can penetrate casing shielding and can effectively collect formation resistivity information. (2) Continuous measurement: Transient electromagnetic waves have wide frequency domain characteristics and can work simultaneously in multiple frequency bands to obtain rich formation information and realize continuous logging. However, transient electromagnetic wave logging also faces the following problems in practical applications: (1) Strong shielding effect of metal casing: The high conductivity of steel casing (10 7 - 10 10The high relative permeability (50μ0-100μ0) of the casing leads to a strong shielding effect on electromagnetic wave signals. The signal measured by the receiving antenna mainly comes from the casing contribution, making it particularly difficult to extract the weak signal of the stratum. (2) The casing background can be suppressed to a certain extent by using the receiving coil compensation method, but due to the propagation characteristics of transient electromagnetic waves, the transient electromagnetic waves cannot reach multiple receiving coils synchronously, making it difficult to suppress the synchronous arrival of the multi-coil signal background. (3) The engineering difficulty is high: the relevant instruments are still in the theoretical research and experimental development stage, lacking mature engineering equipment, and there is still a large gap between them and practical applications.

[0005] Therefore, based on the concept of controllable emission, designing a reasonable instrument structure and suppressing the influence of the sleeve background are of great theoretical and practical significance for promoting the practical application of transient electromagnetic wave technology in sleeve resistivity measurement. Summary of the Invention

[0006] This invention addresses the problems existing in the prior art by providing an approximate equivalent compensation coil structure, resistivity measurement method, and formation analysis method. These methods can suppress strong casing background signals, improve the signal-to-noise ratio of formation signals, enhance the accuracy of transient electromagnetic wave logging response through casing, and enable formation resistivity extraction and formation property analysis under the influence of high-conductivity casing.

[0007] In a first aspect, the present invention provides an approximately equivalent compensation coil structure, comprising: It includes at least one compensating transmitting coil system and at least one receiving coil; the compensating transmitting coil system includes a main transmitting coil and at least two secondary transmitting coils, the secondary transmitting coils being compensating transmitting coils, the main transmitting coil and its adjacent secondary transmitting coils having opposite winding directions, and the winding directions of two adjacent secondary transmitting coils being the same or opposite; the receiving coil and the main transmitting coil having the same or opposite winding directions.

[0008] In some embodiments, the receiving coil is provided, and the compensating transmitting coil is provided, with the compensating transmitting coil located on one side of the receiving coil; the compensating transmitting coil includes at least a main transmitting coil and a first transmitting coil and a second transmitting coil located on both sides of the main transmitting coil, with the first transmitting coil and the second transmitting coil serving as compensating coils.

[0009] In some embodiments, there are N receiving coils, where N ≥ 2, and the N receiving coils are arranged sequentially to form a measurement array. The winding directions of the N receiving coils are the same. There is one compensation transmitting coil, which is located on one side of the measurement array. The compensation transmitting coil includes at least a main transmitting coil and a first transmitting coil and a second transmitting coil located on both sides of the main transmitting coil. The first transmitting coil and the second transmitting coil serve as compensation coils.

[0010] In some embodiments, there are two receiving coils arranged sequentially to form a measurement array, and the two receiving coils are wound in the same direction; there are two compensation transmitting coil systems, which are respectively located on both sides of the measurement array and symmetrically arranged with respect to the measurement array, with the first compensation transmitting coil system adjacent to the first receiving coil and the second compensation transmitting coil system adjacent to the second receiving coil; the compensation transmitting coil system includes at least a main transmitting coil and a first transmitting coil and a second transmitting coil located on both sides of the main transmitting coil, with the first transmitting coil and the second transmitting coil serving as compensation coils.

[0011] In some embodiments, the compensation transmitting coil system includes a main transmitting coil and two secondary transmitting coils, with one secondary transmitting coil located on one side of the main transmitting coil and the other secondary transmitting coil located on the other side of the main transmitting coil.

[0012] In some embodiments, the compensation transmitting coil is provided with a main transmitting coil and 2M secondary transmitting coils, where M≥2. The M secondary transmitting coils are arranged sequentially to form a first group of secondary transmitting coils, located on one side of the main transmitting coil, and the M secondary transmitting coils are arranged sequentially to form a second group of secondary transmitting coils, located on the other side of the main transmitting coil.

[0013] In some embodiments, the compensation transmitting coil is provided with a main transmitting coil and 2M secondary transmitting coils, where M≥2. The M secondary transmitting coils are arranged sequentially to form a first group of secondary transmitting coils, located on one side of the main transmitting coil, and the M secondary transmitting coils are arranged sequentially to form a second group of secondary transmitting coils, located on the other side of the main transmitting coil.

[0014] In some embodiments, the main transmitting coil and the receiving coil are wound in the forward direction, and the first transmitting coil and the second transmitting coil are wound in the reverse direction; or the main transmitting coil is wound in the forward direction, and the receiving coil, the first transmitting coil, and the second transmitting coil are wound in the reverse direction; or the main transmitting coil and the receiving coil are wound in the reverse direction, and the first transmitting coil and the second transmitting coil are wound in the forward direction; or the main transmitting coil is wound in the reverse direction, and the receiving coil, the first transmitting coil, and the second transmitting coil are wound in the forward direction.

[0015] In a second aspect, the present invention provides a method for measuring the resistivity of a controllable emission transient electromagnetic wave through a bushing, employing the approximately equivalent compensation coil structure described in the first aspect of the present invention, the steps of which are as follows: Coil parameter adjustment steps: Under the set bushing background environment, adjust the transmitting coil parameters and excitation time of the approximate equivalent compensation coil structure so that the bushing background signal in the electromagnetic wave emitted by the transmitting coil reaches the receiving coil synchronously. Background signal measurement steps: A transient electromagnetic wave signal is generated by the main transmitting coil as the background signal, and a transient electromagnetic wave signal opposite to that of the main transmitting coil is generated by the secondary transmitting coil as the anti-background signal. Under the sleeve background condition, the background signal and the anti-background signal work together to minimize the total received signal received by the receiving coil. At this time, the total received signal is the suppressed background signal. Actual response signal measurement steps: Under the same casing background environment, change the formation conditions and raise the approximate equivalent compensation coil structure along the wellbore. At this time, the total received signal received by the receiving coil is the actual response signal. Calculation steps: The formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal; Resistivity determination steps: Convert formation anomaly signals into formation resistivity.

[0016] In a third aspect, the present invention provides a method for measuring the resistivity of a controllable emission transient electromagnetic wave through a bushing, employing the approximately equivalent compensation coil structure described in the first aspect of the present invention, the steps of which are as follows: Coil parameter adjustment steps: Under the set bushing background environment, adjust the transmitting coil parameters and excitation time of the approximately equivalent compensation coil structure so that the bushing background signal in the electromagnetic wave emitted by the transmitting coil in the first compensation transmitting coil system reaches the second receiving coil synchronously, and so that the bushing background signal in the electromagnetic wave emitted by the transmitting coil in the second compensation transmitting coil system reaches the first receiving coil synchronously. Background signal measurement steps: A transient electromagnetic wave signal is generated by the main transmitting coil in the first compensated transmitting coil system as the first background signal. Simultaneously, a transient electromagnetic wave signal in the opposite direction to the main transmitting coil is generated by the secondary transmitting coil as the first anti-background signal. The combined effect of the first background signal and the first anti-background signal minimizes the total received signal received by the second receiving coil, which is the first suppressed background signal. A transient electromagnetic wave signal is generated by the main transmitting coil in the second compensated transmitting coil system as the second background signal. Simultaneously, a transient electromagnetic wave signal in the opposite direction to the main transmitting coil is generated by the secondary transmitting coil as the second anti-background signal. The combined effect of the second background signal and the second anti-background signal minimizes the total received signal received by the first receiving coil, which is the second suppressed background signal. The average of the first suppressed background signal and the second suppressed background signal is the suppressed background signal. Actual response signal measurement steps: Under the same casing background environment, change the formation conditions, and the average of the total received signal received by the first receiving coil and the total received signal received by the second receiving coil in the approximate equivalent compensation coil structure is the actual response signal; Calculation steps: The formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal; Resistivity determination steps: Convert formation anomaly signals into formation resistivity.

[0017] In a fourth aspect, the present invention provides a method for analyzing formation properties, employing the approximate equivalent compensation coil structure described in the first aspect of the present invention, the steps of which are as follows: Coil parameter adjustment steps: Under the set bushing background environment, adjust the transmitting coil parameters and excitation time of the approximate equivalent compensation coil structure so that the bushing background signal in the electromagnetic wave emitted by the transmitting coil reaches the receiving coil synchronously. Background signal measurement steps: A transient electromagnetic wave signal is generated by the main transmitting coil as the background signal, and a transient electromagnetic wave signal opposite to that of the main transmitting coil is generated by the secondary transmitting coil as the anti-background signal. The background signal and the anti-background signal work together to minimize the total received signal received by the receiving coil. At this time, the total received signal is the suppressed background signal. Actual response signal measurement steps: Under the same casing background environment, change the formation conditions, and the total received signal received by the receiving coil in the approximate equivalent compensation coil structure is the actual response signal; Calculation steps: The formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal; Resistivity determination steps: Convert formation anomaly signals into formation resistivity; Steps for analyzing formation properties: Analyze formation properties based on changes in formation resistivity.

[0018] Compared with the prior art, the advantages and positive effects of the present invention are as follows: (1) The approximate equivalent compensation coil structure provided by the present invention suppresses the mid-term background signal through the approximate equivalent compensation transmission method, highlights the useful signal (i.e. the induced electromotive force related to formation resistivity), improves the response accuracy of transient electromagnetic waves through casing logging, realizes formation resistivity extraction under the influence of high-conductivity casing, and has high accuracy in formation resistivity measurement.

[0019] (2) The approximate equivalent compensation coil structure provided by the present invention uses an array design for the receiving coil, which can reduce noise and improve the signal-to-noise ratio of formation signals. On the other hand, it can realize near-far well and near-middle-far well formation resistivity measurement, thereby improving the efficiency of transient electromagnetic wave logging through casing.

[0020] (3) The approximate equivalent compensation coil structure provided by the present invention, through the design of dual receiving coils and symmetrical compensation transmitting coil system, can realize the correction of the influence of casing deformation and improve the effectiveness of transient electromagnetic wave logging through casing.

[0021] (4) The controllable emission transient electromagnetic wave resistivity measurement method provided by the present invention is designed for situations where the formation signal of transient electromagnetic wave logging is small in magnitude and it is difficult to achieve synchronous extraction of the casing background signal by multiple receiver combination methods. The method adopts a controllable emission approximate equivalent compensation coil structure. By adjusting the coil parameters (including the number of coil turns, coil spacing, etc.) and excitation time, the synchronous arrival and compensation suppression of the casing background signal are achieved, thereby improving the signal-to-noise ratio of the formation signal and improving the measurement accuracy of the formation resistivity through the casing.

[0022] (5) The transient electromagnetic wave resistivity measurement method through the casing provided by the present invention can correct the influence of casing deformation and improve the effectiveness of transient electromagnetic wave logging through the casing by using a dual receiving coil and a symmetrical compensation transmitting coil system with an approximately equivalent compensation coil structure.

[0023] (6) The formation property analysis method provided by the present invention uses an array design for the receiving coil of the approximately equivalent compensation coil structure, which can measure the formation resistivity at the corresponding position of different receiving coils. Based on the difference between the formation resistivity at the corresponding position of different coils, the formation properties in the radial direction near the well can be effectively determined. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the approximate equivalent compensation coil structure described in the first aspect embodiment of the present invention; Figure 2 This is a schematic flowchart of the controllable emission transient electromagnetic wave resistivity measurement method through a bushing according to the second aspect of the present invention. Figure 3 This is a schematic diagram illustrating the working principle of the approximate equivalent compensation coil structure described in the second aspect embodiment of the present invention. Figure 4 This is a schematic diagram illustrating the principle of background signal suppression using an approximately equivalent compensation sleeve according to a second aspect embodiment of the present invention; Figure 5 This is a schematic diagram of the approximately equivalent compensation coil structure described in the third aspect embodiment of the present invention; Figure 6 This is a schematic flowchart of the transient electromagnetic wave resistivity measurement method through a bushing according to the fifth aspect embodiment of the present invention; Figure 7 This is a structural diagram of the approximate equivalent compensation coil structure described in the sixth aspect embodiment of the present invention; Figure 8 This is a structural diagram of the approximate equivalent compensation coil structure described in the eighth aspect embodiment of the present invention; Figure 9 This is a schematic diagram of an approximate equivalent compensation coil structure comprising three receiving coils according to an eighth aspect embodiment of the present invention; Figure 10This is a schematic diagram of the structure of an approximate equivalent compensation coil according to a tenth aspect embodiment of the present invention; Figure 11 This is a schematic diagram of the structure of the approximate equivalent compensation coil structure according to the eleventh aspect of the present invention; Figure 12 This is a schematic flowchart of a method for measuring the resistivity of a controllable emission type transient electromagnetic wave through a bushing, according to the twelfth aspect of the present invention. Figure 13 This is a schematic diagram illustrating the working principle of the controllable emission transient electromagnetic wave resistivity measurement method through a bushing according to the twelfth aspect embodiment of the present invention. Figure 14 This is a schematic diagram illustrating the principle of how the heterogeneity of the sleeve affects the upper and lower measurement signals in this invention. Figure 15 This is a schematic diagram illustrating the principle of the present invention of reducing and correcting sleeve heterogeneity by taking the average value; Figure 16 This is a schematic diagram of the structure of an approximate equivalent compensation coil according to the thirteenth aspect embodiment of the present invention; Figure 17 This is a schematic flowchart of a stratigraphic property analysis method according to the fourteenth aspect of the present invention. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings through exemplary embodiments. However, it should be understood that, without further description, elements, structures, and features in one embodiment may be advantageously incorporated into other embodiments.

[0026] Transient electromagnetic wave signals are time-domain decaying signals. The early, middle, and late periods reflect the properties of the near and far media. The early period mainly reflects casing information, the late period mainly reflects formation information, and the middle period contains both casing and formation information. The relative contribution of the formation signal increases as time progresses, resulting in greater detection depth but decreased vertical resolution. For the middle period, this invention provides an approximate equivalent compensation coil structure, resistivity measurement method, and formation analysis method. By using an approximate equivalent compensation emission method to suppress the mid-term background signal and highlight the useful signal (i.e., the induced electromotive force related to formation resistivity), it can improve the accuracy of transient electromagnetic wave logging response through casing, achieve formation resistivity extraction under the influence of high-conductivity casing, ensure formation identification capability, and provide high accuracy in formation resistivity measurement.

[0027] See Figure 1According to a first aspect of the present invention, an approximately equivalent compensation coil structure is provided, including a compensation transmitting coil system and a receiving coil R, wherein the compensation transmitting coil system is disposed on one side of the receiving coil R. The compensation transmitting coil system includes a first transmitting coil T1, a main transmitting coil T0, and a second secondary transmitting coil T2 arranged in sequence, wherein the first transmitting coil T1 and the second transmitting coil T2 are compensation transmitting coils.

[0028] It should be noted that in the compensated transmitting coil system, the first transmitting coil T1 and the second transmitting coil T2 work together. Under casing background conditions, a virtual transmitting coil is approximately equivalent to being set at the location of the main transmitting coil, with the virtual transmitting coil having the same number of turns in the opposite direction to the main transmitting coil. The virtual transmitting coil effectively compensates for the main transmitting coil, suppressing the background signal. This compensated transmitting coil system structure utilizes the difference between the response signal of the transient electromagnetic wave signal and the suppressed background signal to suppress strong background and improve the signal-to-noise ratio of weak formation signals.

[0029] In one specific embodiment, the coil is wound as follows: the main transmitting coil T0 and the receiving coil R are wound in the forward direction, while the first transmitting coil T1 and the second transmitting coil T2 are wound in the reverse direction.

[0030] Alternatively, the coils can be wound in the following way: the main transmitting coil T0 is wound in the forward direction, while the receiving coil R, the first transmitting coil T1, and the second transmitting coil T2 are wound in the reverse direction.

[0031] In another specific embodiment, the coils are wound in the following manner: the main transmitting coil T0 and the receiving coil R are wound in opposite directions, while the first transmitting coil T1 and the second transmitting coil T2 are wound in the forward direction.

[0032] Alternatively, the coils can be wound in the following way: the main transmitting coil T0 is wound in the reverse direction, while the receiving coil R, the first transmitting coil T1, and the second transmitting coil T2 are wound in the forward direction.

[0033] When using the approximate equivalent compensation coil structure described in this embodiment of the invention to suppress background signals, under a set casing background, the parameters (including the number of turns and coil spacing) and excitation time of the transmitting coil are adjusted so that the casing background signal in the electromagnetic waves emitted by the main transmitting coil and the secondary transmitting coil reaches the receiving coil synchronously. This allows the signal compensation and cancellation of the transmitting coil under the casing background, improving the signal-to-noise ratio of the formation signal. It can improve the accuracy of transient electromagnetic wave logging response through the casing, realize the extraction of formation resistivity under the influence of high-conductivity casing, and achieve high accuracy in formation resistivity measurement.

[0034] See Figure 2 According to a second aspect of the present invention, a method for measuring the resistivity of a controllable emission transient electromagnetic wave through a bushing is provided, employing the approximately equivalent compensation coil structure described in the first aspect of the present invention. The steps are as follows: S1. Coil parameter adjustment steps: Under the set bushing background environment, adjust the transmitting coil parameters and excitation time of the approximate equivalent compensation coil structure so that the bushing background signal in the electromagnetic wave emitted by the transmitting coil reaches the receiving coil synchronously.

[0035] Specifically, such as Figure 3 As shown, the excitation time of the first transmitting coil T1 is t1, the excitation time of the main transmitting coil is t2, and the excitation time of the second transmitting coil T2 is t3. t1 = t2 + Δt1, t2 = t3 + Δt2, where Δt1 is the transmission delay time of the main transmitting coil T0 relative to the first transmitting coil T1 when transmitting a signal, and Δt2 is the transmission delay time of the second transmitting coil T2 relative to the main transmitting coil T0 when transmitting a signal.

[0036] S2. Background signal measurement steps: A transient electromagnetic wave signal is generated by the main transmitting coil as the background signal, and a transient electromagnetic wave signal opposite to that of the main transmitting coil is generated by the secondary transmitting coil as the anti-background signal. Under the sleeve background condition, the background signal and the anti-background signal work together to minimize the total received signal received by the receiving coil. At this time, the total received signal is the suppressed background signal.

[0037] Specifically, see [link to relevant documentation] Figure 3 The main transmitting coil T0 emits a transient electromagnetic wave signal TC, which is the background signal. The first transmitting coil T1 and the second transmitting coil T2 emit transient electromagnetic wave signals TC in the opposite direction to the main transmitting coil T0, which are the anti-background signals. The three transmitted signals work together to minimize the total received signal TIV received by the receiving coil R, where TIV = V1 + V2 + V3, where V1 is the signal received by the receiving coil R from the first transmitting coil T1, V2 is the signal received by the receiving coil R from the main transmitting coil T0, and V3 is the signal received by the receiving coil R from the second transmitting coil T2.

[0038] Specifically, the signal received by the receiving coil from the transmitting coil is an induced electromotive force.

[0039] Specifically, the first transmitting coil T1 and the second transmitting coil T2 work together to approximately set a virtual transmitting coil at the position of the main transmitting coil T0 under the background conditions of the bushing. The virtual transmitting coil has the same number of turns as the main transmitting coil T0 in the opposite direction. The virtual transmitting coil is equivalent to the main transmitting coil T0 in compensating for the background signal.

[0040] It should be noted that approximate equivalence does not require the background signal to be entirely zero, but only to minimize the intermediate transient signal over a certain time period. See [link to relevant documentation]. Figure 4 The diagram shown illustrates the principle of background signal suppression in an approximately equivalent compensation bushing. The background signal is significantly suppressed and relatively stable within 0.004s.

[0041] S3. Actual response signal measurement steps: Under the same casing background environment, change the formation conditions, and the total received signal received by the receiving coil in the approximate equivalent compensation coil structure is the actual response signal.

[0042] S4. Calculation steps: The formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal.

[0043] S5. Resistivity determination steps: Convert formation anomaly signals into formation resistivity.

[0044] It should be noted that when the formation properties of the casing well are different from the casing well background, the transient electromagnetic signal generated by the compensation transmitting coil system in the approximate equivalent compensation coil structure deviates from the casing background. The difference reflects the electrical properties of the formation outside the casing. The above-mentioned method in the embodiment of the present invention realizes the casing background suppression and subtraction, and the effective formation signal measurement through the approximate equivalent compensation coil structure, thereby improving the formation signal-to-noise ratio.

[0045] See Figure 5 According to a third aspect of the present invention, an approximately equivalent compensation coil structure is provided, including a compensation transmitting coil system and a receiving coil R, wherein the compensation transmitting coil system is disposed on one side of the receiving coil R. The compensation transmitting coil system includes a first transmitting coil T1, a second transmitting coil T2, a main transmitting coil T0, a third transmitting coil T2', and a fourth transmitting coil T1' arranged in sequence, wherein the four secondary transmitting coils are compensation transmitting coils.

[0046] Unlike the approximate equivalent compensation coil structure described in the first aspect of the present invention, the approximate equivalent compensation coil structure described in the present invention uses four secondary transmitting coils working together to approximately equivalently set a virtual transmitting coil at the position of the main transmitting coil under the background conditions of the bushing. The virtual transmitting coil has an equal number of turns in the opposite direction to the main transmitting coil. The virtual transmitting coil is equivalent to the main transmitting coil in compensating for the background signal.

[0047] A fourth aspect of the present invention provides a method for measuring the resistivity of a controllable emitted transient electromagnetic wave through a bushing, employing the approximately equivalent compensation coil structure described in the third aspect of the present invention. The steps are essentially the same as those in the second aspect of the present invention for measuring the resistivity of a controllable emitted transient electromagnetic wave through a bushing, and will not be repeated here.

[0048] Unlike the controllable emission transient electromagnetic wave resistivity measurement method described in the second aspect embodiment of the present invention, in this embodiment, the excitation time of the first transmitting coil T1 is t1, the excitation time of the second transmitting coil T2 is t2, the excitation time of the main transmitting coil T0 is t3, the excitation time of the third transmitting coil T2' is t4, and the excitation time of the fourth transmitting coil T1' is t5. t1 = t2 + Δt1, t2 = t3 + Δt2, t3 = t4 + Δt3, t4 = t5 + Δt4. Δt1 is the transmission delay time when the second transmitting coil T2 transmits a signal relative to the first transmitting coil T1, Δt2 is the transmission delay time when the main transmitting coil T0 transmits a signal relative to the second transmitting coil T2, Δt3 is the transmission delay time when the third transmitting coil T2' transmits a signal relative to the main transmitting coil T0, and Δt4 is the transmission delay time when the fourth transmitting coil T1' transmits a signal relative to the third transmitting coil T2'. All of the above transmission delay times can also be 0.

[0049] Unlike the controllable emission transient electromagnetic wave resistivity measurement method described in the second aspect of the present invention, in this embodiment of the present invention, the total received signal TIV received by the receiving coil R is TIV = V1 + V2 + V3 + V4 + V5, where V1 is the signal received by the receiving coil R from the first transmitting coil T1, V2 is the signal received by the receiving coil R from the second transmitting coil T2, V3 is the signal received by the receiving coil R from the autonomous transmitting coil T0, V4 is the signal received by the receiving coil R from the third transmitting coil T2', and V5 is the signal received by the receiving coil R from the fourth transmitting coil T1'.

[0050] Specifically, the four coils—the first transmitting coil T1, the second transmitting coil T2, the third transmitting coil T2', and the fourth transmitting coil T1'—work together to approximately, under the background conditions of the bushing, set up a virtual transmitting coil at the position of the main transmitting coil T0. This virtual transmitting coil has an equal number of turns in the opposite direction to the main transmitting coil T0. The virtual transmitting coil effectively compensates for the main transmitting coil T0, thus suppressing the background signal.

[0051] See Figure 6 According to a fifth aspect of the present invention, a method for measuring the resistivity of transient electromagnetic waves through a bushing is provided, employing the approximately equivalent compensation coil structure described in the third aspect of the present invention, the steps of which include: S1. Coil reciprocity step: Use the transmitting coil of the approximately equivalent compensation coil structure as the receiving coil, and use the receiving coil of the approximately equivalent compensation coil structure as the transmitting coil.

[0052] S2. Coil parameter adjustment steps: Under the set bushing background environment, adjust the coil parameters of the approximate equivalent compensation coil structure so that the bushing background signal in the measured signal is zero. The coil parameters at this time are the final coil parameters of the compensation differential coil structure.

[0053] S3. Signal measurement steps: Raise the approximate equivalent compensation coil structure along the wellbore, and measure the induced electromotive force at different formation locations through the approximate equivalent compensation coil structure.

[0054] S4. Drawing steps: Draw a curve reflecting the resistivity information of the formation based on the induced electromotive force.

[0055] S5. Resistivity determination steps: Convert the curves reflecting formation resistivity information into resistivity calibration charts.

[0056] The transient electromagnetic wave resistivity measurement method described in this embodiment not only reduces the complexity of circuit design but also suppresses background signals.

[0057] See Figure 7 According to a sixth aspect of the present invention, an approximately equivalent compensation coil structure is provided, including a compensation transmitting coil system and a receiving coil R, wherein the compensation transmitting coil system is disposed on one side of the receiving coil R. The compensation transmitting coil system includes a first transmitting coil T1, a second transmitting coil T2, a third transmitting coil T3, a main transmitting coil T0, a fourth transmitting coil T3', a fifth transmitting coil T2', and a sixth transmitting coil T1' arranged in sequence, wherein the six secondary transmitting coils are compensation transmitting coils.

[0058] Unlike the approximate equivalent compensation coil structure described in the first aspect of the present invention, the approximate equivalent compensation coil structure described in the present invention uses the combined action of six secondary transmitting coils to approximately equivalently set a virtual transmitting coil at the position of the main transmitting coil under the background conditions of the bushing. The virtual transmitting coil is in the opposite direction to the main transmitting coil with the same number of turns. The virtual transmitting coil is equivalent to the main transmitting coil in compensating for the background signal.

[0059] A seventh aspect embodiment of the present invention provides a method for measuring the resistivity of a controllable emitted transient electromagnetic wave through a bushing, employing the approximately equivalent compensation coil structure described in the sixth aspect embodiment of the present invention. The steps are essentially the same as those in the method for measuring the resistivity of a controllable emitted transient electromagnetic wave through a bushing described in the second aspect embodiment of the present invention, and will not be repeated here.

[0060] Unlike the controllable emission transient electromagnetic wave resistivity measurement method through a bushing described in the second aspect of the present invention, in this embodiment, the excitation time of the first transmitting coil T1 is t1, the excitation time of the second transmitting coil T2 is t2, the excitation time of the third transmitting coil T3 is t3, the excitation time of the main transmitting coil T0 is t4, the excitation time of the fourth transmitting coil T3' is t5, the excitation time of the fifth transmitting coil T2' is t6, and the excitation time of the sixth transmitting coil T1' is t7, where t1 = t2 + Δt1, t2 = t3 + Δt2, t3 = t4 + Δt3, t4 = t5 + Δt4, and t5 = t6 + Δt1. Δt5, t6 = t7 + Δt6, Δt1 is the transmission delay time when the second transmitting coil T2 transmits a signal relative to the first transmitting coil T1, Δt3 is the transmission delay time when the main transmitting coil T0 transmits a signal relative to the third transmitting coil T3, Δt4 is the transmission delay time when the fourth transmitting coil T3' transmits a signal relative to the main transmitting coil T0, Δt5 is the transmission delay time when the fifth transmitting coil T2' transmits a signal relative to the fourth transmitting coil T3', and Δt6 is the transmission delay time when the sixth transmitting coil T1' transmits a signal relative to the fifth transmitting coil T2'. All of the above transmission delay times can be 0.

[0061] Unlike the controllable emission transient electromagnetic wave resistivity measurement method described in the second aspect of the present invention, in this embodiment of the present invention, the total received signal TIV received by the receiving coil R is TIV = V1 + V2 + V3 + V4 + V5 + V6 + V7, where V1 is the signal received by the receiving coil R from the first transmitting coil T1, V2 is the signal received by the receiving coil R from the second transmitting coil T2, V3 is the signal received by the receiving coil R from the third transmitting coil T3, V4 is the signal received by the receiving coil R from the autonomous transmitting coil T0, V5 is the signal received by the receiving coil R from the fourth transmitting coil T3', V6 is the signal received by the receiving coil R from the fifth transmitting coil T2', and V7 is the signal received by the receiving coil R from the sixth transmitting coil T1'.

[0062] Specifically, the six coils—the first transmitting coil T1, the second transmitting coil T2, the third transmitting coil T3, the fourth transmitting coil T3', the fifth transmitting coil T2', and the sixth transmitting coil T1'—work together to approximately, under the background conditions of the bushing, set up a virtual transmitting coil at the position of the main transmitting coil T0. This virtual transmitting coil has an equal number of turns in the opposite direction to the main transmitting coil T0. The virtual transmitting coil effectively compensates for the main transmitting coil T0, suppressing the background signal.

[0063] See Figure 8According to an eighth aspect embodiment of the present invention, an approximately equivalent compensation coil structure is provided, including a compensation transmitting coil system and four receiving coils. The compensation transmitting coil system is disposed on one side of the receiving coil R. The compensation transmitting coil system includes a first transmitting coil T1, a main transmitting coil T0, and a second transmitting coil T2 arranged in sequence, with two secondary transmitting coils serving as compensation transmitting coils. The first receiving coil R1, the second receiving coil R2, the third receiving coil R3, and the fourth receiving coil R4 are arranged in sequence, and the winding directions of the four receiving coils may be the same or different.

[0064] Unlike the approximately equivalent compensation coil structure described in the first aspect of the present invention, the embodiments of the present invention... The device is equipped with four receiving coils, which receive signals respectively.

[0065] It should be noted that the number of receiving coils can be limited according to actual needs, and is not limited to four receiving coils; it can also be three (see [link to relevant documentation]). Figure 9 ), five, etc.

[0066] The approximate equivalent compensation coil structure of this invention can suppress the casing background in the intermediate time period, achieving high formation resolution (vertical stratification capability) and clearly distinguishing formations. This means it can be used for the identification, analysis, and evaluation of typical layered formations. Multiple receiving coils form a measurement array. When the formation properties remain unchanged, the differences in signals received by the multiple receiving coils can reflect the casing's heterogeneity among the receiving coils. Conversely, if the casing is homogeneous, the differences in signals received by the multiple receiving coils can reflect formation heterogeneity radially upwards near the well. If the formation and casing remain unchanged, averaging the multiple received signals can improve the signal-to-noise ratio and enable formation resistivity extraction under the influence of high-permeability casing.

[0067] A ninth aspect embodiment of the present invention provides a method for measuring the resistivity of a controllable emitted transient electromagnetic wave through a bushing, employing the approximately equivalent compensation coil structure described in the eighth aspect embodiment of the present invention. The steps are essentially the same as those in the method for measuring the resistivity of a controllable emitted transient electromagnetic wave through a bushing described in the second aspect embodiment of the present invention, and will not be repeated here.

[0068] Unlike the controllable emission transient electromagnetic wave resistivity measurement method described in the second aspect of the present invention, in this embodiment of the present invention, four formation resistivities can be obtained through four receiving coils. The four resistivities have differences. If the differences are caused by structural differences in the receiving coil structure, the average of the four formation resistivities is taken as the final measured formation resistivity. This can reduce noise, improve the signal-to-noise ratio, and enhance the accuracy of formation resistivity measurement.

[0069] See Figure 10According to a tenth aspect of the present invention, an approximately equivalent compensation coil structure is provided, including a compensation transmitting coil system and four receiving coils, wherein the compensation transmitting coil system is disposed on one side of the receiving coil R. The compensation transmitting coil system includes a first transmitting coil T1, a second transmitting coil T2, a main transmitting coil T0, a third transmitting coil T2', and a fourth transmitting coil T1' arranged in sequence, and the four secondary transmitting coils are compensation transmitting coils. The first receiving coil R1, the second receiving coil R2, the third receiving coil R3, and the fourth receiving coil R4 are arranged in sequence.

[0070] Unlike the approximately equivalent compensation coil structure described in the eighth aspect embodiment of the present invention, the embodiments of the present invention... In this process, through the combined action of four secondary transmitting coils, under the background conditions of the bushing, a virtual transmitting coil is approximately equivalent to being set at the position of the main transmitting coil. The virtual transmitting coil has an equal number of turns in the opposite direction to the main transmitting coil. The virtual transmitting coil is equivalent to the main transmitting coil in compensating for and suppressing the background signal.

[0071] See Figure 11 According to an eleventh aspect of the present invention, an approximately equivalent compensation coil structure is provided, comprising two compensation transmitting coil systems and two receiving coils. The two receiving coils (i.e., a first receiving coil R1 and a second receiving coil R2) are arranged sequentially to form a measurement array, with the two receiving coils wound in the same direction. The two compensation transmitting coil systems are respectively disposed on both sides of the measurement array and are symmetrically arranged relative to the measurement array. The first compensation transmitting coil system is adjacent to the first receiving coil R1, and the second compensation transmitting coil system is adjacent to the second receiving coil R2. The compensation transmitting coil system includes a main transmitting coil T0 and a first transmitting coil T1 and a second transmitting coil T2 disposed on both sides of the main transmitting coil, the first transmitting coil and the second transmitting coil serving as compensation coils.

[0072] In the compensated transmitting coil system, the first transmitting coil T1 and the second transmitting coil T2 work together. Under casing background conditions, a virtual transmitting coil is approximately equivalent to being set at the location of the main transmitting coil, with the virtual transmitting coil having the same number of turns in the opposite direction to the main transmitting coil. The virtual transmitting coil effectively compensates for the main transmitting coil, suppressing the background signal. This compensated transmitting coil system structure utilizes the difference between the response signal of the transient electromagnetic wave signal and the suppressed background signal to suppress strong background and improve the signal-to-noise ratio of weak formation signals.

[0073] In one specific embodiment, the coil is wound as follows: the main transmitting coil T0 and the receiving coil R are wound in the forward direction, while the first transmitting coil T1 and the second transmitting coil T2 are wound in the reverse direction.

[0074] Alternatively, the coils can be wound in the following way: the main transmitting coil T0 is wound in the forward direction, while the receiving coil R, the first transmitting coil T1, and the second transmitting coil T2 are wound in the reverse direction.

[0075] In another specific embodiment, the coils are wound in the following manner: the main transmitting coil T0 and the receiving coil R are wound in opposite directions, while the first transmitting coil T1 and the second transmitting coil T2 are wound in the forward direction.

[0076] Alternatively, the coils can be wound in the following way: the main transmitting coil T0 is wound in the reverse direction, while the receiving coil R, the first transmitting coil T1, and the second transmitting coil T2 are wound in the forward direction.

[0077] When performing formation resistivity measurements using the approximate equivalent compensation coil structure described in this embodiment of the invention, based on suppressing the mid-term background signal through the approximate compensation transmission method of the compensation transmission system, the method of transmitting signals through the first compensation transmission system and receiving signals through the second receiving coil, and the method of transmitting signals through the second compensation transmission system and receiving signals through the first receiving coil, can eliminate or reduce the influence of casing inhomogeneity to a certain extent, and improve the effectiveness of formation signal measurement, since casing inhomogeneity has the opposite effect on the measurement results of the receiving coil.

[0078] See Figure 12 According to the twelfth aspect of the present invention, a method for measuring the resistivity of a controllable emission transient electromagnetic wave through a bushing is provided, employing the approximately equivalent compensation coil structure described in the eleventh aspect of the present invention. The steps are as follows: S1. Coil parameter adjustment steps: Under the set bushing background environment, adjust the transmitting coil parameters and excitation time of the approximate equivalent compensation coil structure so that the bushing background signal in the electromagnetic wave emitted by the transmitting coil of the first compensation transmitting coil reaches the second receiving coil R2 synchronously, and so that the bushing background signal in the electromagnetic wave emitted by the transmitting coil of the second compensation transmitting coil reaches the first receiving coil R1 synchronously.

[0079] S2. Background signal measurement steps: A transient electromagnetic wave signal is generated by the main transmitting coil in the first compensated transmitting coil system as the first background signal. At the same time, a transient electromagnetic wave signal in the opposite direction to the main transmitting coil is generated by the secondary transmitting coil as the first anti-background signal. The first background signal and the first anti-background signal work together to minimize the total received signal received by the second receiving coil R2. The total received signal at this time is the first suppressed background signal. A transient electromagnetic wave signal is generated by the main transmitting coil in the second compensated transmitting coil system as the second background signal. At the same time, a transient electromagnetic wave signal in the opposite direction to the main transmitting coil is generated by the secondary transmitting coil as the second anti-background signal. The second background signal and the second anti-background signal work together to minimize the total received signal received by the first receiving coil R1. The total received signal at this time is the second suppressed background signal. The average of the first suppressed background signal and the second suppressed background signal is the suppressed background signal.

[0080] S3. Actual Response Signal Measurement Steps: Under the same casing background environment, change the formation conditions and raise the approximate equivalent compensation coil structure along the wellbore. The average of the total received signal Raa received by the first receiving coil and the total received signal Rab received by the second receiving coil at this time is taken as the actual response signal Raa (see...). Figure 13 ).

[0081] S4. Calculation steps: The formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal. S5. Resistivity determination steps: Convert formation anomaly signals into formation resistivity.

[0082] The resistivity measurement method described in this embodiment of the invention, based on the suppression of the mid-term background signal through an approximate compensation emission method using a compensated emission system, also employs upper emission with lower reception and lower emission with upper reception. The non-homogeneity of the bushing (such as deformation) has opposite effects on their measurement results (see...). Figure 14 Taking the average of the two values ​​can, to some extent, eliminate or reduce the influence of casing heterogeneity (see...). Figure 15 This will improve the effectiveness of formation signal measurement.

[0083] See Figure 16 According to a thirteenth aspect embodiment of the present invention, an approximately equivalent compensation coil structure is provided, comprising two compensation transmitting coil systems and two receiving coils. The two receiving coils (i.e., a first receiving coil R1 and a second receiving coil R2) are arranged sequentially to form a measurement array, with the two receiving coils wound in the same direction. The two compensation transmitting coil systems are respectively disposed on both sides of the measurement array and are symmetrically arranged relative to the measurement array. The first compensation transmitting coil system is adjacent to the first receiving coil R1, and the second compensation transmitting coil system is adjacent to the second receiving coil R2. The compensation transmitting coil systems include a first transmitting coil T1, a second transmitting coil T2, a main transmitting coil T0, a third transmitting coil T2', and a fourth transmitting coil T1' arranged sequentially, with the four secondary transmitting coils serving as compensation transmitting coils.

[0084] Unlike the approximate equivalent compensation coil structure described in the eleventh aspect embodiment of the present invention, the approximate equivalent compensation coil structure described in the embodiment of the present invention, through the joint action of four secondary transmitting coils, approximately equivalently sets a virtual transmitting coil at the position of the main transmitting coil, which has an equal number of turns in the opposite direction to the main transmitting coil. The virtual transmitting coil is equivalent to the main transmitting coil in compensating for and suppressing the background signal.

[0085] See Figure 17 According to the fourteenth aspect of the present invention, a method for analyzing formation properties is provided, employing the approximately equivalent compensation coil structure described in the eighth or tenth aspect of the present invention, the steps of which are as follows: S1. Coil parameter adjustment steps: Under the set bushing background environment, adjust the transmitting coil parameters and excitation time of the approximate equivalent compensation coil structure so that the bushing background signal in the electromagnetic wave emitted by the transmitting coil reaches the receiving coil synchronously.

[0086] S2. Background signal measurement steps: A transient electromagnetic wave signal is generated by the main transmitting coil as the background signal, and a transient electromagnetic wave signal opposite to that of the main transmitting coil is generated by the secondary transmitting coil as the anti-background signal. The background signal and the anti-background signal work together to minimize the total received signal received by the receiving coil. At this time, the total received signal is the suppressed background signal.

[0087] S3. Actual response signal measurement steps: Under the same casing background environment, change the formation conditions, and the total received signal received by the receiving coil in the approximate equivalent compensation coil structure is the actual response signal.

[0088] S4. Calculation steps: The formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal.

[0089] S5. Resistivity determination steps: Convert formation anomaly signals into formation resistivity.

[0090] It should be noted that the approximate equivalent compensation coil structure can obtain multiple receiving results through multiple receiving coils, and multiple formation resistivities can be obtained based on the receiving structure.

[0091] S6. Steps for analyzing formation properties: Analyze the formation properties based on the changes in formation resistivity.

[0092] Specifically, when the difference in resistivity between two adjacent formations is greater than the deviation caused by the receiving coil structure, it indicates that the formation is radially heterogeneous near the well, or that the casing between the receiving coils is heterogeneous (e.g., the casing is deformed). If the casing is homogeneous, the difference in the signals received by multiple receiving coils can reflect radially heterogeneous formations near the well.

[0093] The above embodiments are used to explain the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. An approximately equivalent compensation coil structure for measuring the resistivity of transient electromagnetic waves through a bushing, characterized in that, It includes at least one compensating transmitting coil system and at least one receiving coil; the compensating transmitting coil system includes a main transmitting coil and at least two secondary transmitting coils, the secondary transmitting coils being compensating transmitting coils, the main transmitting coil and its adjacent secondary transmitting coils having opposite winding directions, and the winding directions of two adjacent secondary transmitting coils being the same or opposite; the receiving coil and the main transmitting coil having the same or opposite winding directions.

2. The approximately equivalent compensation coil structure as described in claim 1, characterized in that, The receiving coil is provided, and the compensating transmitting coil is provided, with the compensating transmitting coil located on one side of the receiving coil; the compensating transmitting coil includes at least a main transmitting coil and a first transmitting coil and a second transmitting coil located on both sides of the main transmitting coil, with the first transmitting coil and the second transmitting coil serving as compensating coils.

3. The approximately equivalent compensation coil structure as described in claim 1, characterized in that, The receiving coil has N coils, where N≥2, and the N receiving coils are arranged sequentially to form a measurement array. The winding direction of the N receiving coils is the same. The compensation transmitting coil has one coil, which is located on one side of the measurement array. The compensation transmitting coil includes at least a main transmitting coil and a first transmitting coil and a second transmitting coil located on both sides of the main transmitting coil. The first transmitting coil and the second transmitting coil serve as compensation coils.

4. The approximately equivalent compensation coil structure as described in claim 1, characterized in that, The system comprises two receiving coils arranged sequentially to form a measurement array, with the two receiving coils wound in the same direction. It also comprises two compensation transmitting coil systems, each located on one side of the measurement array and symmetrically arranged relative to the array. The first compensation transmitting coil system is adjacent to the first receiving coil, and the second compensation transmitting coil system is adjacent to the second receiving coil. The compensation transmitting coil system includes at least a main transmitting coil and a first transmitting coil and a second transmitting coil located on either side of the main transmitting coil, with the first and second transmitting coils serving as compensation coils.

5. The approximately equivalent compensation coil structure as described in any one of claims 2 to 4, characterized in that, The compensation transmitting coil system includes a main transmitting coil and two secondary transmitting coils. One secondary transmitting coil is located on one side of the main transmitting coil, and the other secondary transmitting coil is located on the other side of the main transmitting coil.

6. The approximately equivalent compensation coil structure as described in any one of claims 2 to 4, characterized in that, The compensation transmitting coil system includes a main transmitting coil and 2M secondary transmitting coils, where M ≥ 2. The M secondary transmitting coils are arranged sequentially to form a first group of secondary transmitting coils, located on one side of the main transmitting coil, and the M secondary transmitting coils are arranged sequentially to form a second group of secondary transmitting coils, located on the other side of the main transmitting coil.

7. The approximately equivalent compensation coil structure as described in any one of claims 2 to 4, characterized in that, The main transmitting coil and the receiving coil are wound in the forward direction, and the first transmitting coil and the second transmitting coil are wound in the reverse direction; or the main transmitting coil is wound in the forward direction, and the receiving coil, the first transmitting coil, and the second transmitting coil are wound in the reverse direction; or the main transmitting coil and the receiving coil are wound in the reverse direction, and the first transmitting coil and the second transmitting coil are wound in the forward direction; or the main transmitting coil is wound in the reverse direction, and the receiving coil, the first transmitting coil, and the second transmitting coil are wound in the forward direction.

8. A method for measuring the resistivity of a controllable emission type transient electromagnetic wave through a bushing, employing the approximately equivalent compensation coil structure described in claim 2 or 3, characterized in that, The steps are as follows: Coil parameter adjustment steps: Under the set bushing background environment, adjust the transmitting coil parameters and excitation time of the approximate equivalent compensation coil structure so that the bushing background signal in the electromagnetic wave emitted by the transmitting coil reaches the receiving coil synchronously. Background signal measurement steps: A transient electromagnetic wave signal is generated by the main transmitting coil as the background signal, and a transient electromagnetic wave signal opposite to that of the main transmitting coil is generated by the secondary transmitting coil as the anti-background signal. The background signal and the anti-background signal work together to minimize the total received signal received by the receiving coil. At this time, the total received signal is the suppressed background signal. Actual response signal measurement steps: Under the same casing background environment, change the formation conditions, and the total received signal received by the receiving coil in the approximate equivalent compensation coil structure is the actual response signal; Calculation steps: The formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal; Resistivity determination steps: Convert formation anomaly signals into formation resistivity.

9. A method for measuring the resistivity of a controllable emission type transient electromagnetic wave through a bushing, employing the approximately equivalent compensation coil structure described in claim 4, characterized in that... The steps are as follows: Coil parameter adjustment steps: Under the set bushing background environment, adjust the transmitting coil parameters and excitation time of the approximately equivalent compensation coil structure so that the bushing background signal in the electromagnetic wave emitted by the transmitting coil in the first compensation transmitting coil reaches the second receiving coil synchronously, and so that the bushing background signal in the electromagnetic wave emitted by the transmitting coil in the second compensation transmitting coil reaches the first receiving coil synchronously. Background signal measurement steps: A transient electromagnetic wave signal is generated by the main transmitting coil in the first compensated transmitting coil as the first background signal. Simultaneously, a transient electromagnetic wave signal in the opposite direction to the main transmitting coil is generated by the secondary transmitting coil as the first anti-background signal. The combined effect of the first background signal and the first anti-background signal minimizes the total received signal received by the second receiving coil. This total received signal is the first suppressed background signal. A transient electromagnetic wave signal is generated by the main transmitting coil in the second compensated transmitting coil as the second background signal. Simultaneously, a transient electromagnetic wave signal in the opposite direction to the main transmitting coil is generated by the secondary transmitting coil as the second anti-background signal. The combined effect of the second background signal and the second anti-background signal minimizes the total received signal received by the first receiving coil. This total received signal is the second suppressed background signal. The average of the first suppressed background signal and the second suppressed background signal is the suppressed background signal. Actual response signal measurement steps: Under the same casing background environment, change the formation conditions, and the average of the total received signal received by the first receiving coil and the total received signal received by the second receiving coil in the approximate equivalent compensation coil structure is the actual response signal; Calculation steps: The formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal; Resistivity determination steps: Convert formation anomaly signals into formation resistivity.

10. A method for analyzing formation properties, employing the approximately equivalent compensation coil structure described in claim 3, characterized in that, The steps are as follows: Coil parameter adjustment steps: Under the set bushing background environment, adjust the transmitting coil parameters and excitation time of the approximate equivalent compensation coil structure so that the bushing background signal in the electromagnetic wave emitted by the transmitting coil reaches the receiving coil synchronously. Background signal measurement steps: A transient electromagnetic wave signal is generated by the main transmitting coil as the background signal, and a transient electromagnetic wave signal opposite to that of the main transmitting coil is generated by the secondary transmitting coil as the anti-background signal. The background signal and the anti-background signal work together to minimize the total received signal received by the receiving coil. At this time, the total received signal is the suppressed background signal. Actual response signal measurement steps: Under the same casing background environment, change the formation conditions, and the total received signal received by the receiving coil in the approximate equivalent compensation coil structure is the actual response signal; Calculation steps: The formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal; Resistivity determination steps: Convert formation anomaly signals into formation resistivity; Steps for analyzing formation properties: Analyze formation properties based on changes in formation resistivity.

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