Approximately equivalent compensation coil structure, resistivity measurement method, formation property analysis method

Abstract

The present application belongs to the technical field of oil and gas exploration and development, and relates to a kind of approximate equivalent compensation coil structure, resistivity measurement method and formation property analysis method.The coil structure includes at least one compensation transmitting coil system and at least one receiving coil.The compensation transmitting coil system includes a main transmitting coil and at least two secondary transmitting coils.The secondary transmitting coils are arranged on both sides of the main transmitting coil, and the number of secondary coils on both sides of the main transmitting coil is the same.The secondary transmitting coils are compensation transmitting coils.The winding direction of the main transmitting coil is opposite to that of the secondary transmitting coil adjacent to it.The winding direction of the two adjacent secondary transmitting coils is the same or opposite.The winding direction of the receiving coil is the same as or opposite to that of the main transmitting coil.The method uses the approximate equivalent compensation coil structure.The present application can suppress the background signal of strong casing, improve the signal-to-noise ratio of formation signal, improve the response accuracy of transient electromagnetic wave through casing logging, and realize the extraction of formation resistivity under the influence of high-conductivity casing.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oil and gas exploration and development, and relates to electrical logging technology, in particular to a near-equivalent compensation coil structure, a resistivity measurement method and a formation property analysis method. BACKGROUND

[0002] In the exploration and development of oil and gas fields, through-casing resistivity measurement technology has important application value, especially in cased hole drilling, through-casing resistivity measurement is one of the important means for reservoir oiliness evaluation, reservoir dynamic monitoring and remaining oil distribution analysis, and has important significance for cased hole reservoir evaluation and production well development plan optimization, enhanced oil recovery, etc. As a new drilling method for oil and gas exploration and development, the conventional resistivity logging is difficult to be directly applied due to the existence of the casing, and how to realize accurate and efficient through-casing resistivity measurement has become a key problem in the industry.

[0003] At present, the through-casing resistivity logging method usually adopts the electrode method, and its basic principle is to infer the formation resistivity by measuring the weak current leaking inside and outside the casing. However, the electrode method has the following limitations: (1) greatly affected by the quality of the casing: the corrosion, thinning or deformation of the casing will significantly affect the contact quality between the electrode and the casing, thereby leading to inaccurate measurement data. (2) affected by the downhole environment: the scaling, waxing, rusting, etc. on the inner wall of the casing will interfere with the stability of the electrode method measurement, and it is necessary to spend time on preparation work such as well washing (e.g. descaling, oil removal, etc.), increasing the complexity of logging. (3) low logging efficiency: the electrode method usually adopts point measurement mode, and it needs a long time to establish stable measurement conditions, which cannot meet the real-time response demand of the rapid change of downhole environment, and the overall logging efficiency is low.

[0004] The transient electromagnetic wave technology provides a new solution for through-casing resistivity measurement, and its working principle is to arrange a transmitting coil and a receiving coil in the well, to emit a transient current pulse to the formation through the transmitting coil, the transient current pulse will generate an electromagnetic field varying with time, to excite the formation to generate an induced eddy current decaying with time, and to diffuse in different speeds in different media. After the current is turned off, the secondary induced electromagnetic field generated by the eddy current is measured to extract the formation resistivity information. The transient electromagnetic wave technology has the following advantages: (1) strong penetration: low-frequency signals can penetrate the casing shield, and can effectively collect the resistivity information of the formation. (2) continuous measurement: the transient electromagnetic wave has a wide frequency domain characteristic, and can work at multiple frequency bands at the same time, to obtain rich formation information and realize continuous logging. However, the transient electromagnetic wave logging also faces the following problems in practical application: (1) strong shielding effect of the metal casing: the high conductivity (10 7 - 10 10) and high relative permeability (50μ0- 100μ0) lead to its strong shielding effect on electromagnetic wave signals, and the signals measured by the receiving antenna mainly come from the casing, making it particularly difficult to extract the weak signals of the formation. (2) The use of receiving coil compensation method can suppress the casing background to a certain extent, but due to the transient electromagnetic wave propagation characteristics, the transient electromagnetic wave cannot synchronously reach multiple receiving coils, causing the time synchronization suppression of the multi-coil signal background to be difficult. (3) Higher engineering difficulty: related instruments are still in the stage of theoretical research and experimental development, lacking mature engineering equipment, and there is still a big gap from practical application.

[0005] Therefore, based on the controllable emission idea, designing a reasonable instrument structure to suppress the influence of the casing background has important theoretical value and practical significance for promoting the practical application of transient electromagnetic wave technology in casing resistivity measurement. SUMMARY

[0006] The present application provides a kind of approximate equivalent compensation coil structure, resistivity measurement method, formation analysis method to suppress strong casing background signal, improve the signal-to-noise ratio of formation signal, improve the response accuracy of transient electromagnetic wave through casing logging, realize the extraction of formation resistivity under the influence of high conductive casing, and formation property analysis.

[0007] The first aspect of the present application provides a kind of approximate equivalent compensation coil structure, comprising:

[0008] It includes at least one compensation transmitting coil system and at least one receiving coil;The compensation transmitting coil system includes a main transmitting coil and at least two secondary transmitting coils, the secondary transmitting coil is a compensation transmitting coil, the winding direction of the main transmitting coil and the secondary transmitting coil adjacent to it is opposite, and the winding direction of the two adjacent secondary transmitting coils is the same or opposite;The winding direction of the receiving coil and the main transmitting coil is the same or opposite.

[0009] In some embodiments, the receiving coil is provided with one, the compensation transmitting coil system is provided with one, and the compensation transmitting coil system is arranged on one side of the receiving coil;The compensation transmitting coil system includes at least a main transmitting coil and a first secondary transmitting coil and a second secondary transmitting coil arranged on both sides of the main transmitting coil, and the first secondary transmitting coil and the second secondary transmitting coil serve as compensation coils.

[0010] In some embodiments, the receiving coil is provided with N, N≥2, and the N receiving coils are sequentially arranged to form a measurement array, and the winding direction of the N receiving coils is the same;The compensation transmitting coil system is provided with one, and the compensation transmitting coil system is arranged on one side of the measurement array;The compensation transmitting coil system includes at least a main transmitting coil and a first secondary transmitting coil and a second secondary transmitting coil arranged on both sides of the main transmitting coil, and the first secondary transmitting coil and the second secondary transmitting coil serve as compensation coils.

[0011] In some embodiments, the receiving coils are provided in two, and the two receiving coils are sequentially arranged to form a measurement array, and the two receiving coils have the same winding direction; the compensation transmitting coil system is provided in two, and the two compensation transmitting coil systems are respectively arranged on the two sides of the measurement array and symmetrically arranged relative to the measurement array, the first compensation transmitting system is adjacent to the first receiving coil, and the second compensation transmitting system is adjacent to the second receiving coil; the compensation transmitting coil system at least includes a main transmitting coil, a first secondary transmitting coil and a second secondary transmitting coil arranged on the two sides of the main transmitting coil, and the first secondary transmitting coil and the second secondary transmitting coil serve as compensation coils.

[0012] In some embodiments, the compensation transmitting coil system includes a main transmitting coil and two secondary transmitting coils, one secondary transmitting coil is arranged on one side of the main transmitting coil, and the other secondary transmitting coil is arranged on the other side of the main transmitting coil.

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

[0014] In some embodiments, the compensation transmitting coil system is provided with a main transmitting coil and 2M secondary transmitting coils, M≥2, wherein M secondary transmitting coils are sequentially arranged to form a first group of secondary transmitting coils arranged on one side of the main transmitting coil, and M secondary transmitting coils are sequentially arranged to form a second group of secondary transmitting coils arranged on the other side of the main transmitting coil.

[0015] In some embodiments, the main transmitting coil and the receiving coil are forward winding, the first secondary transmitting coil and the second secondary transmitting coil are reverse winding; or the main transmitting coil is forward winding, the receiving coil, the first secondary transmitting coil and the second secondary transmitting coil are reverse winding; or the main transmitting coil and the receiving coil are reverse winding, the first secondary transmitting coil and the second secondary transmitting coil are forward winding; or the main transmitting coil is reverse winding, the receiving coil, the first secondary transmitting coil and the second secondary transmitting coil are forward winding.

[0016] In the second aspect of the present application, a controllable transmitting type transient electromagnetic wave through casing resistivity measurement method is provided, which adopts the approximately equivalent compensation coil structure of the first aspect of the present application, and the steps are as follows:

[0017] The coil parameter adjustment step: under the condition of setting the casing background environment, the transmitting coil parameters and the excitation time of the approximately equivalent compensation coil structure are adjusted, so that the casing background signals emitted by the transmitting coil are synchronously arrived at the receiving coil;

[0018] background signal measurement step: a transient electromagnetic wave signal is generated by the main transmitting coil as a background signal, and a transient electromagnetic wave signal opposite to the main transmitting coil is generated by the secondary transmitting coil as a counter background signal, under the casing background condition, the background signal and the counter background signal jointly act to make the total receiving signal received by the receiving coil minimum, at this time, the total receiving signal is the suppressed background signal;

[0019] actual response signal measurement step: under the same set casing background environment, the formation condition is changed, and the approximately equivalent compensation coil structure is pulled up along the wellbore, at this time, the total receiving signal measured by the receiving coil is the actual response signal;

[0020] calculation step: the formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal;

[0021] resistivity determination step: the formation anomaly signal is converted into the formation resistivity.

[0022] In a third aspect, the application provides a controllable transmitting transient electromagnetic wave through casing resistivity measurement method, which adopts the approximately equivalent compensation coil structure of the first aspect of the application, and the steps are as follows:

[0023] coil parameter adjustment step: under the set casing background environment, the transmitting coil parameters and the excitation time of the approximately equivalent compensation coil structure are adjusted, so that the casing background signals in the electromagnetic waves emitted by the transmitting coils in the first compensation transmitting coil system synchronously arrive at the second receiving coil, and the casing background signals in the electromagnetic waves emitted by the transmitting coils in the second compensation transmitting coil system synchronously arrive at the first receiving coil;

[0024] background signal measurement step: a transient electromagnetic wave signal is generated by the main transmitting coil in the first compensation transmitting coil system as a first background signal, and a transient electromagnetic wave signal opposite to the main transmitting coil is generated by the secondary transmitting coil as a first counter background signal, the first background signal and the first counter background signal jointly act to make the total receiving signal received by the second receiving coil minimum, at this time, the total receiving signal is the first suppressed background signal; a transient electromagnetic wave signal is generated by the main transmitting coil in the second compensation transmitting coil system as a second background signal, and a transient electromagnetic wave signal opposite to the main transmitting coil is generated by the secondary transmitting coil as a second counter background signal, the second background signal and the second counter background signal jointly act to make the total receiving signal received by the first receiving coil minimum, at this time, the total receiving signal is the second suppressed background signal; the mean value of the first suppressed background signal and the second suppressed background signal is the suppressed background signal;

[0025] Actual response signal measurement step: in the same casing background environment, changing the formation condition, the total receiving signal received by the first receiving coil and the total receiving signal received by the second receiving coil in the approximately equivalent compensation coil structure are approximately equivalent to the actual response signal;

[0026] Calculation step: the formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal;

[0027] Resistivity determination step: the formation anomaly signal is converted into the formation resistivity.

[0028] In the fourth aspect of the present application, a formation property analysis method is provided, which adopts the approximately equivalent compensation coil structure in the first aspect of the present application, and the steps are as follows:

[0029] Coil parameter adjustment step: in the casing background environment, the parameters of the transmitting coil and the excitation time of the approximately equivalent compensation coil structure are adjusted, so that the casing background signal in the electromagnetic wave emitted by the transmitting coil reaches the receiving coil synchronously;

[0030] Background signal measurement step: a transient electromagnetic wave signal is generated by the main transmitting coil as a background signal, and a transient electromagnetic wave signal opposite to the main transmitting coil is generated by the secondary transmitting coil as a reverse background signal, the background signal and the reverse background signal jointly act on the total receiving signal received by the receiving coil to minimize the total receiving signal, and the total receiving signal at this time is the suppressed background signal;

[0031] Actual response signal measurement step: in the same casing background environment, changing the formation condition, the total receiving signal received by the receiving coil in the approximately equivalent compensation coil structure is the actual response signal;

[0032] Calculation step: the formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal;

[0033] Resistivity determination step: the formation anomaly signal is converted into the formation resistivity.

[0034] Formation property analysis step: the formation property is analyzed according to the change of the formation resistivity.

[0035] Compared with the prior art, the present application has the following advantages and positive effects:

[0036] (1) The approximately equivalent compensation coil structure provided by the present application suppresses the medium-term background signal through the approximately equivalent compensation transmission mode, highlights the useful signal (i.e. the induced electromotive force related to the formation resistivity), can improve the transient electromagnetic wave through-casing logging response accuracy, realizes the extraction of the formation resistivity under the influence of the high-conductivity casing, and the measurement of the formation resistivity is accurate and high.

[0037] (2) The approximate equivalent compensation coil structure provided by the application adopts an array design for the receiving coil, which can reduce noise and improve the signal-to-noise ratio of the formation signal on the one hand, and can realize near-far well, near-middle-far well formation resistivity measurement, thereby improving the efficiency of the transient electromagnetic wave through casing logging.

[0038] (3) The approximate equivalent compensation coil structure provided by the application can realize the correction of the influence of casing deformation through the design of the double receiving coil and the symmetric compensation transmitting coil system, thereby improving the effectiveness of the transient electromagnetic wave through casing logging.

[0039] (4) The controllable transmitting type transient electromagnetic wave through casing resistivity measurement method provided by the application can realize the synchronous arrival and compensation suppression of the casing background signal by adjusting the coil parameters (including the number of turns of the coil, the coil distance, etc.) and the excitation time, thereby improving the signal-to-noise ratio of the formation signal and improving the measurement accuracy of the through casing formation resistivity.

[0040] (5) The transient electromagnetic wave through casing resistivity measurement method provided by the application can realize the correction of the influence of casing deformation through the design of the double receiving coil and the symmetric compensation transmitting coil system of the approximate equivalent compensation coil structure, thereby improving the effectiveness of the transient electromagnetic wave through casing logging.

[0041] (6) The formation property analysis method provided by the application can measure the formation resistivity at different positions corresponding to the receiving coil of the approximate equivalent compensation coil structure, and can effectively determine the formation properties in the radial direction of the well according to the differences between the formation resistivities at different positions corresponding to the coil. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The structure diagram of the approximate equivalent compensation coil structure according to the first aspect of the application is shown in the figure.

[0043] Figure 2 The flowchart of the controllable transmitting type transient electromagnetic wave through casing resistivity measurement method according to the second aspect of the application is shown in the figure.

[0044] Figure 3 The working principle diagram of the approximate equivalent compensation coil structure according to the second aspect of the application is shown in the figure.

[0045] Figure 4 The schematic diagram of the approximate equivalent compensation casing background signal suppression principle according to the second aspect of the application is shown in the figure.

[0046] Figure 5 The structure diagram of the approximate equivalent compensation coil structure according to the third aspect of the application is shown in the figure.

[0047] Figure 6 A flowchart of the transient electromagnetic wave through casing resistivity measurement method according to the fifth aspect of the present application is shown in the figure;

[0048] Figure 7 A structure diagram of the approximately equivalent compensation coil structure according to the sixth aspect of the present application is shown in the figure;

[0049] Figure 8 A structure diagram of the approximately equivalent compensation coil structure according to the eighth aspect of the present application is shown in the figure;

[0050] Figure 9 A structure diagram of the approximately equivalent compensation coil structure containing three receiving coils according to the eighth aspect of the present application is shown in the figure;

[0051] Figure 10 A structure diagram of the approximately equivalent compensation coil structure according to the tenth aspect of the present application is shown in the figure;

[0052] Figure 11 A structure diagram of the approximately equivalent compensation coil structure according to the eleventh aspect of the present application is shown in the figure;

[0053] Figure 12 A flowchart of the controllable emission type transient electromagnetic wave through casing resistivity measurement method according to the twelfth aspect of the present application is shown in the figure;

[0054] Figure 13 A working principle diagram of the controllable emission type transient electromagnetic wave through casing resistivity measurement method according to the twelfth aspect of the present application is shown in the figure;

[0055] Figure 14 A principle diagram of casing anisotropy affecting the up and down measurement signals according to the present application is shown in the figure;

[0056] Figure 15 A principle diagram of taking mean value to reduce and correct casing anisotropy according to the present application is shown in the figure;

[0057] Figure 16 A structure diagram of the approximately equivalent compensation coil structure according to the thirteenth aspect of the present application is shown in the figure;

[0058] Figure 17 A flowchart of the formation property analysis method according to the fourteenth aspect of the present application is shown in the figure. DETAILED DESCRIPTION

[0059] The present application will now be described in greater detail by way of example, with reference to the accompanying drawings, wherein:

[0060] The transient electromagnetic wave signal is a time domain decay signal, and different time periods of early, middle and late reflect the properties of near and far media. The early time period mainly reflects casing information, the late time period mainly reflects formation information, the middle time period has both casing information and formation information, the relative contribution of the formation signal is greater and the corresponding detection depth is deepened, but the longitudinal resolution is reduced. For the middle time period, the application provides an approximately equivalent compensation coil structure, a resistivity measurement method and a formation analysis method, which suppresses the middle period background signal through the approximately equivalent compensation transmission mode, highlights the useful signal (i.e. the induced electromotive force related to the formation resistivity), can improve the transient electromagnetic wave through casing logging response accuracy, realizes the extraction of the formation resistivity under the influence of the high-conductivity casing, ensures the identification of the formation, and the measurement of the formation resistivity is accurate and high.

[0061] Referring to Figure 1 In a first aspect of the embodiments of the application, an approximately equivalent compensation coil structure is provided, which comprises a compensation transmission coil system and a receiving coil R, and the compensation transmission coil system is arranged on one side of the receiving coil R. The compensation transmission coil system comprises a first transmission coil T1, a main transmission coil T0 and a second transmission coil T2 arranged in sequence, and the first transmission coil T1 and the second transmission coil T2 are compensation transmission coils.

[0062] It should be noted that in the compensation transmission coil system, the first transmission coil T1 and the second transmission coil T2 jointly act, and under the casing background condition, an imaginary transmission coil is approximately equivalent to being arranged at the position of the main transmission coil, which has an opposite number of turns with the main transmission coil, and the imaginary transmission coil and the main transmission coil are equivalent compensation, which suppresses the background signal. This compensation transmission coil system structure layout uses the response signal of the transient electromagnetic wave signal and the suppressed background signal to suppress the strong background and improve the signal-to-noise ratio of the weak formation signal.

[0063] In a specific embodiment, the winding mode of the coil is that the main transmission coil T0 and the receiving coil R are forward winding, and the first transmission coil T1 and the second transmission coil T2 are reverse winding.

[0064] Alternatively, the winding mode of the coil is that the main transmission coil T0 is forward winding, and the receiving coil R, the first transmission coil T1 and the second transmission coil T2 are reverse winding.

[0065] In another specific embodiment, the winding mode of the coil is that the main transmission coil T0 and the receiving coil R are reverse winding, and the first transmission coil T1 and the second transmission coil T2 are forward winding.

[0066] Alternatively, the winding mode of the coil is that the main transmission coil T0 is reverse winding, and the receiving coil R, the first transmission coil T1 and the second transmission coil T2 are forward winding.

[0067] When the approximately equivalent compensation coil structure described in the embodiment of the present application is used for background signal suppression, in the setting of the casing background, the parameters (including the number of turns and the coil spacing) and the excitation time of the transmitting coil are adjusted, so that the casing background signals in the electromagnetic waves transmitted by the main transmitting coil and the secondary transmitting coil reach the receiving coil synchronously, and the signals transmitted by the transmitting coils in the casing background are compensated and offset, the signal-to-noise ratio of the formation signal is improved, the response accuracy of the transient electromagnetic wave through the casing logging is improved, the formation resistivity extraction under the influence of the high-conductivity casing is realized, and the measurement of the formation resistivity is accurate and high.

[0068] Referring to Figure 2 , the second aspect embodiment of the present application provides a controllable transmitting type transient electromagnetic wave through casing resistivity measurement method, which uses the approximately equivalent compensation coil structure described in the first aspect of the present application, and the steps are as follows:

[0069] S1, coil parameter adjustment step: in the setting of the casing background environment, the parameters and the excitation time of the transmitting coil of the approximately equivalent compensation coil structure are adjusted, so that the casing background signals in the electromagnetic waves transmitted by the transmitting coil reach the receiving coil synchronously.

[0070] Specifically, as Figure 3 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, Δt1 is the transmission delay time of the main transmitting coil T0 relative to the first transmitting coil T1 transmitting the signal, and Δt2 is the transmission delay time of the second transmitting coil T2 relative to the main transmitting coil T0 transmitting the signal.

[0071] S2, background signal measurement step: a transient electromagnetic wave signal is generated by the main transmitting coil as a background signal, and a transient electromagnetic wave signal opposite to the main transmitting coil is generated by the secondary transmitting coil as a counter background signal, under the casing background condition, the background signal and the counter background signal jointly act on the total receiving signal received by the receiving coil to make it minimum, and the total receiving signal at this time is the suppressed background signal.

[0072] Specifically, continuing to refer to Figure 3 , the main transmitting coil T0 transmits a transient electromagnetic wave signal TC, i.e. a background signal, the first transmitting coil T1 and the second transmitting coil T2 transmit a transient electromagnetic wave signal TC opposite to the main transmitting coil T0, i.e. a counter background signal, and the three transmitting signals jointly act on the total receiving signal TIV received by the receiving coil R to make it minimum, TIV=V1+V2+V3, wherein 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.

[0073] Specifically, the signal of the transmitting coil received by the receiving coil is an induced electromotive force.

[0074] Specifically, the first transmitting coil T1 and the second transmitting coil T2 jointly act, and in the casing background condition, approximately equivalent to setting a virtual transmitting coil at the position of the main transmitting coil T0, which is in an inverse number of turns relationship with the main transmitting coil T0, and the virtual transmitting coil and the main transmitting coil T0 are equivalent compensation, and the background signal is suppressed.

[0075] It should be noted that the approximate equivalence is not required to be all 0, but only to minimize the intermediate transient signal in a certain time period, as shown in the figure. Figure 4 The approximate equivalent compensation casing background signal suppression principle is shown in the figure, and the background signal suppression is obvious within 0.004 s and is relatively stable.

[0076] S3, an actual response signal measurement step: in the same set casing background environment, changing the formation condition, the total receiving signal received by the receiving coil in the approximately equivalent compensation coil structure is the actual response signal.

[0077] S4, a calculation step: the formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal.

[0078] S5, a resistivity determination step: converting the formation anomaly signal into the formation resistivity.

[0079] It should be noted that when the casing well formation property is different from the casing well background, the transient electromagnetic signal generated by the compensation transmitting coil system in the approximately equivalent compensation coil structure deviates from the casing background condition, and the difference reflects the electrical property of the formation outside the casing. The above-mentioned method of the embodiment of the present application realizes the casing background suppression deduction and the formation effective signal measurement, and improves the signal-to-noise ratio of the formation signal.

[0080] Referring to Figure 5 The third aspect of the present application provides an approximately equivalent compensation coil structure, which comprises a compensation transmitting coil system and a receiving coil R, and the compensation transmitting coil system is arranged on one side of the receiving coil R. The compensation transmitting coil system comprises 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 transmitting coils are compensation transmitting coils.

[0081] Different from the approximately equivalent compensation coil structure described in the first aspect of the present application, the approximately equivalent compensation coil structure described in the embodiment of the present application, through the joint action of the four secondary transmitting coils, approximately equivalently sets a virtual transmitting coil at the position of the main transmitting coil under the casing background condition, which is in an inverse equal number of turns relationship with the main transmitting coil, and the virtual transmitting coil and the main transmitting coil are equivalent compensation, which suppresses the background signal.

[0082] The fourth aspect of the present application provides a controllable transmitting type transient electromagnetic wave through casing resistivity measurement method, which adopts the approximately equivalent compensation coil structure described in the third aspect of the present application, and the steps are basically the same as those of the controllable transmitting type transient electromagnetic wave through casing resistivity measurement method described in the second aspect of the present application, which will not be repeated here.

[0083] Different from the controllable transmitting type transient electromagnetic wave through casing resistivity measurement method described in the second aspect of the present application, in the embodiment of the present application, 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 of the second transmitting coil T2 relative to the first transmitting coil T1, Δt2 is the transmission delay time of the main transmitting coil T0 relative to the second transmitting coil T2, Δt3 is the transmission delay time of the third transmitting coil T2' relative to the main transmitting coil T0, and Δt4 is the transmission delay time of the fourth transmitting coil T1' relative to the third transmitting coil T2', and the above transmission delay times can also be 0.

[0084] Different from the controllable transmitting type transient electromagnetic wave through casing resistivity measurement method described in the second aspect of the present application, in the embodiment of the present application, the total receiving signal TIV received by the receiving coil R is V1+V2+V3+V4+V5, wherein 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 main 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'.

[0085] Specifically, the first transmitting coil T1, the second transmitting coil T2, the third transmitting coil T2', and the fourth transmitting coil T1' jointly act, under the casing background condition, to approximately equivalently set a virtual transmitting coil at the position of the main transmitting coil T0, which is in the inverse equal-turn relationship with the main transmitting coil T0, and the virtual transmitting coil equivalently compensates the main transmitting coil T0 to suppress the background signal.

[0086] Referring to Figure 6 The fifth aspect embodiment of the present application provides a transient electromagnetic wave through-casing resistivity measurement method, which adopts the approximately equivalent compensation coil structure of the third aspect embodiment of the present application, and the steps include:

[0087] S1, coil reciprocity step: taking the transmitting coil of the approximately equivalent compensation coil structure as a receiving coil, and taking the receiving coil of the approximately equivalent compensation coil structure as a transmitting coil.

[0088] S2, coil parameter adjustment step: under the set casing background environment, adjusting the coil parameters of the approximately equivalent compensation coil structure to make the casing background signal in the measured signal zero, and the coil parameters at this time are the final coil parameters of the compensation differential coil structure.

[0089] S3, signal measurement step: lifting the approximately equivalent compensation coil structure along the borehole, and measuring the induced electromotive force at different formation positions through the approximately equivalent compensation coil structure.

[0090] S4, drawing step: drawing a curve reflecting the formation resistivity information according to the induced electromotive force.

[0091] S5, resistivity determination step: converting the curve reflecting the formation resistivity information into a resistivity calibration chart.

[0092] The transient electromagnetic wave through-casing resistivity measurement method in the embodiment can not only reduce the trouble of circuit design, but also suppress the background signal.

[0093] Referring to Figure 7 The sixth aspect embodiment of the present application provides an approximately equivalent compensation coil structure, which includes a compensation transmitting coil system and a receiving coil R, and the compensation transmitting coil system is arranged 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, and the six transmitting coils are compensation transmitting coils.

[0094] Different from the approximately equivalent compensation coil structure described in the first aspect of the present application, the approximately equivalent compensation coil structure described in the embodiment of the present application, through the joint action of the six secondary transmitting coils, approximately equivalently sets a virtual transmitting coil at the position of the main transmitting coil under the casing background condition, which is in an inverse equal number of turns relationship with the main transmitting coil, and the virtual transmitting coil and the main transmitting coil are equivalent compensation, which suppresses the background signal.

[0095] The seventh aspect of the present application provides a controllable transmitting type transient electromagnetic wave through casing resistivity measurement method, which adopts the approximately equivalent compensation coil structure described in the sixth aspect of the present application, and the steps are basically the same as those of the controllable transmitting type transient electromagnetic wave through casing resistivity measurement method described in the second aspect of the present application, which will not be repeated here.

[0096] Different from the controllable transmitting type transient electromagnetic wave through casing resistivity measurement method described in the second aspect of the present application, in the embodiment of the present application, 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, the excitation time of the sixth transmitting coil T1' is t7, t1=t2+Δt1, t2=t3+Δt2, t3=t4+Δt3, t4=t5+Δt4, t5=t6+Δt5, t6=t7+Δt6, Δt1 is the transmission delay time of the second transmitting coil T2 relative to the first transmitting coil T1, Δt3 is the transmission delay time of the main transmitting coil T0 relative to the third transmitting coil T3, Δt4 is the transmission delay time of the fourth transmitting coil T3' relative to the main transmitting coil T0, Δt5 is the transmission delay time of the fifth transmitting coil T2' relative to the fourth transmitting coil T3', and Δt6 is the transmission delay time of the sixth transmitting coil T1' relative to the fifth transmitting coil T2', and the above transmission delay times can be 0.

[0097] The total receiving signal TIV received by the receiving coil R in the embodiment of the present application is TIV=V1+V2+V3+V4+V5+V6+V7, wherein 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 self-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'.

[0098] Specifically, 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' jointly act to approximately equivalently set a virtual transmitting coil at the position of the self-transmitting coil T0 under the casing background condition, and the virtual transmitting coil has an inverse equal number of turns relationship with the self-transmitting coil T0, equivalently compensates the virtual transmitting coil and the self-transmitting coil T0, and suppresses the background signal.

[0099] Referring to Figure 8 , the eighth aspect of the present application provides a coil structure for approximately equivalent compensation, which comprises a compensation transmitting coil system and four receiving coils, and the compensation transmitting coil system is arranged on one side of the receiving coil R. The compensation transmitting coil system comprises a first transmitting coil T1, a self-transmitting coil T0 and a second transmitting coil T2 arranged in sequence, and the two 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, and the winding directions of the four receiving coils are the same or different.

[0100] Different from the coil structure for approximately equivalent compensation in the first aspect of the present application, the embodiment of the present application

[0101] In the embodiment of the present application, four receiving coils are arranged, and the four receiving coils respectively receive signals.

[0102] 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, but can also be three (see Figure 9 ), five, etc.

[0103] The approximate equivalent compensation coil structure of the embodiment of the present application can suppress the casing background in the middle time period, can have higher formation resolution (longitudinal layering ability), and can distinguish the formation more clearly, that is, can be used for identification, analysis and evaluation of the general layered formation. The plurality of receiving coils form a measurement array. When the formation property does not change, the difference between the signals received by the plurality of receiving coils can reflect the casing inhomogeneity between the receiving coils. Conversely, if the casing is of uniform property, the difference between the signals received by the plurality of receiving coils can reflect the formation inhomogeneity in the radial direction of the well. If the formation and the casing do not change, the average of the plurality of receiving signals can improve the signal-to-noise ratio and realize the formation resistivity extraction under the influence of the high-permeability casing.

[0104] The ninth aspect embodiment of the present application provides a controllable transmitting transient electromagnetic wave through-casing resistivity measurement method. The approximate equivalent compensation coil structure of the eighth aspect embodiment of the present application is used, and the steps are basically the same as those of the controllable transmitting transient electromagnetic wave through-casing resistivity measurement method of the second aspect embodiment of the present application, which will not be repeated here.

[0105] Different from the controllable transmitting transient electromagnetic wave through-casing resistivity measurement method of the second aspect embodiment of the present application, in the embodiment of the present application, four formation resistivities can be obtained through the four receiving coils. The four resistivities are different. If the difference is caused by the structural difference of the receiving coil structure, the average of the four formation resistivities is taken as the final measured formation resistivity, which can reduce the noise, improve the signal-to-noise ratio, and improve the accuracy of the formation resistivity measurement.

[0106] Referring to Figure 10 The tenth aspect embodiment of the present application provides an approximate equivalent compensation coil structure. The approximate equivalent compensation coil structure comprises a compensation transmitting coil system and four receiving coils. The compensation transmitting coil system is arranged on the side of the receiving coil R. The compensation transmitting coil system comprises 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. The four 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.

[0107] Different from the approximate equivalent compensation coil structure of the eighth aspect embodiment of the present application, in the embodiment of the present application

[0108] In the embodiment of the present application, the four secondary transmitting coils jointly act to approximately equivalently set a virtual transmitting coil at the position of the main transmitting coil under the casing background condition, and the virtual transmitting coil has an inverse number of turns with the main transmitting coil. The virtual transmitting coil and the main transmitting coil equivalently compensate each other and suppress the background signal.

[0109] Referring to Figure 11In the eleventh aspect of the present application, an approximately equivalent compensation coil structure is provided, which comprises 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 sequentially arranged to form a measurement array, and the winding directions of the two receiving coils are the same. The two compensation transmitting coil systems are respectively arranged on the two sides of the measurement array and symmetrically arranged relative to the measurement array. The first compensation transmitting system is adjacent to the first receiving coil R1, and the second compensation transmitting system is adjacent to the second receiving coil R2. The compensation transmitting coil system comprises a main transmitting coil T0, a first secondary transmitting coil T1 and a second secondary transmitting coil T2 arranged on the two sides of the main transmitting coil, and the first secondary transmitting coil and the second secondary transmitting coil serve as compensation coils.

[0110] In the compensation transmitting coil system, the first secondary transmitting coil T1 and the second secondary transmitting coil T2 jointly act to approximately equivalently set a virtual transmitting coil at the position of the main transmitting coil under the sleeve background condition, and the virtual transmitting coil and the main transmitting coil are in an inverse equivalent number of turns relationship. The virtual transmitting coil and the main transmitting coil equivalently compensate each other to suppress the background signal. The compensation transmitting coil system structure layout uses the response signal of the transient electromagnetic wave signal and the suppressed background signal to suppress the strong background and improve the signal-to-noise ratio of the weak signal of the formation.

[0111] In a specific embodiment, the winding mode of the coil is that the main transmitting coil T0 and the receiving coil R are forward winding, and the first secondary transmitting coil T1 and the second secondary transmitting coil T2 are reverse winding.

[0112] Alternatively, the winding mode of the coil is that the main transmitting coil T0 is forward winding, and the receiving coil R, the first secondary transmitting coil T1 and the second secondary transmitting coil T2 are reverse winding.

[0113] In another specific embodiment, the winding mode of the coil is that the main transmitting coil T0 and the receiving coil R are reverse winding, and the first secondary transmitting coil T1 and the second secondary transmitting coil T2 are forward winding.

[0114] Alternatively, the winding mode of the coil is that the main transmitting coil T0 is reverse winding, and the receiving coil R, the first secondary transmitting coil T1 and the second secondary transmitting coil T2 are forward winding.

[0115] When the approximately equivalent compensation coil structure described in the embodiments of the present application is used for formation resistivity measurement, on the basis of approximately compensating the intermediate background signal by the compensation transmitting system, the first compensation transmitting system transmits a signal, the second receiving coil receives a signal, and the second compensation transmitting system transmits a signal, and the first receiving coil receives a signal. The effects of the casing heterogeneity on the measurement results of the receiving coils are opposite, the mean value of the two receiving coils can eliminate or reduce the influence of the casing heterogeneity to a certain extent, and the effectiveness of the formation signal measurement is improved.

[0116] Referring to Figure 12 In the twelfth aspect of the present application, a controllable transmitting transient electromagnetic wave through casing resistivity measurement method is provided, which adopts the approximately equivalent compensation coil structure of the eleventh aspect of the present application, and the steps are as follows:

[0117] S1, coil parameter adjustment step: under the set casing background environment, the transmitting coil parameters and excitation time of the approximately equivalent compensation coil structure are adjusted, so that the casing background signals in the electromagnetic waves emitted by the transmitting coils in the first compensation transmitting coil system synchronously arrive at the second receiving coil R2, and the casing background signals in the electromagnetic waves emitted by the transmitting coils in the second compensation transmitting coil system synchronously arrive at the first receiving coil R1.

[0118] S2, background signal measurement step: a transient electromagnetic wave signal is generated by the main transmitting coil in the first compensation transmitting coil system as a first background signal, and a transient electromagnetic wave signal opposite to the main transmitting coil is generated by the secondary transmitting coil as a first reverse background signal, the first background signal and the first reverse background signal jointly act on the total receiving signal received by the second receiving coil R2 to make the total receiving signal minimum, and the total receiving 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 compensation transmitting coil system as a second background signal, and a transient electromagnetic wave signal opposite to the main transmitting coil is generated by the secondary transmitting coil as a second reverse background signal, the second background signal and the second reverse background signal jointly act on the total receiving signal received by the first receiving coil R1 to make the total receiving signal minimum, and the total receiving 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.

[0119] S3, actual response signal measurement step: under the same set casing background environment, the formation condition is changed, and the approximately equivalent compensation coil structure is pulled up along the borehole, and the average of the total receiving signal Ra received by the first receiving coil and the total receiving signal Ra received by the second receiving coil at this time is the actual response signal Ra (see Figure 13 ).

[0120] S4, calculation step: the formation abnormal signal is obtained by subtracting the actual response signal from the suppressed background signal;

[0121] S5, resistivity determination step: the formation abnormal signal is converted into the formation resistivity.

[0122] The resistivity measurement method of the present application embodiment is based on the suppression of the intermediate background signal by the compensation transmitting system, and through the upper transmitting and lower receiving and the lower transmitting and upper receiving, the effects of casing heterogeneity (such as deformation) on their measurement results are opposite (see Figure 14), the average of both can eliminate or reduce the casing heterogeneity (see Figure 15 ), and improve the effectiveness of formation signal measurement.

[0123] Referring to Figure 16 , the thirteenth aspect of the present application provides a kind of approximately equivalent compensation coil structure, including two compensation transmitting coil systems and two receiving coils.Two receiving coils (i.e. first receiving coil R1 and second receiving coil R2) are sequentially arranged to form a measurement array, and the winding direction of the two receiving coils is the same.Two compensation transmitting coil systems are respectively arranged on the two sides of the measurement array, and are symmetrically arranged relative to the measurement array, the first compensation transmitting system is adjacent to the first receiving coil R1, and the second compensation transmitting system is adjacent to the second receiving coil R2.The compensation transmitting coil system includes first transmitting coil T1, second transmitting coil T2, main transmitting coil T0, third transmitting coil T2' and fourth transmitting coil T1' arranged in sequence, and the four secondary transmitting coils are compensation transmitting coils.

[0124] Unlike the approximately equivalent compensation coil structure described in the eleventh aspect of the present application, the approximately equivalent compensation coil structure described in the embodiment of the present application approximately equivalently sets a virtual transmitting coil at the position of the main transmitting coil through the joint action of the four secondary transmitting coils, which has an inverse number of turns relationship with the main transmitting coil, and the virtual transmitting coil and the main transmitting coil are equivalent compensation, which suppresses the background signal.

[0125] Referring to Figure 17 , the fourteenth aspect of the present application provides a kind of formation property analysis method, which uses the approximately equivalent compensation coil structure described in the eighth aspect or the tenth aspect of the present application, and the steps are as follows:

[0126] S1, coil parameter adjustment step: under the condition of setting casing background environment, the transmitting coil parameters and excitation time of the approximately equivalent compensation coil structure are adjusted, so that the casing background signal in the electromagnetic wave emitted by the transmitting coil reaches the receiving coil synchronously.

[0127] S2, background signal measurement step: a transient electromagnetic wave signal is generated by the main transmitting coil as a background signal, and a transient electromagnetic wave signal opposite to the main transmitting coil is generated by the secondary transmitting coil as an anti-background signal, the total receiving signal received by the receiving coil is minimized by the joint action of the background signal and the anti-background signal, and the total receiving signal at this time is the suppressed background signal.

[0128] S3, actual response signal measurement step: under the same condition of setting casing background environment, the formation condition is changed, and the total receiving signal received by the receiving coil in the approximately equivalent compensation coil structure is the actual response signal.

[0129] S4, calculation step: the formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal.

[0130] S5, resistivity determining step: converting the formation abnormal signal into formation resistivity.

[0131] It should be noted that the approximately equivalent compensation coil structure can obtain multiple receiving results through multiple receiving coils, and multiple formation resistivities can be obtained according to the receiving structure.

[0132] S6, formation property analyzing step: analyzing the formation property according to the change of the formation resistivity.

[0133] Specifically, when the difference between the resistivities of the two adjacent formations is greater than the deviation caused by the receiving coil structure, it indicates that the formation is heterogeneous in the radial direction of the well, or the casing is heterogeneous between the receiving coils (for example, the casing is deformed). If the casing is homogeneous in property, the difference in the signals received by the multiple receiving coils can reflect the heterogeneity of the formation in the radial direction of the well.

[0134] The above embodiments are used to explain the present application, but not to limit the present application, and any modification and change made to the present application within the spirit and protection scope of the claims of the present application, falls into the protection scope of the present application.

Claims

1. An approximately equivalent compensating coil configuration for measuring transient electromagnetic wave through casing resistivity, characterized in that, The compensation transmitting coil system comprises a main transmitting coil and at least two secondary transmitting coils, the secondary transmitting coils are compensation transmitting coils, when the secondary transmitting coils are two, one secondary transmitting coil is arranged on one side of the main transmitting coil, and the other secondary transmitting coil is arranged on the other side of the main transmitting coil; when the secondary transmitting coils are 2M (M is greater than or equal to 2), the M secondary transmitting coils are sequentially arranged to form a first group of secondary transmitting coils and are arranged on one side of the main transmitting coil, and the M secondary transmitting coils are sequentially arranged to form a second group of secondary transmitting coils and are arranged on the other side of the main transmitting coil; the winding direction of the main transmitting coil is opposite to that of the secondary transmitting coil adjacent to the main transmitting coil, and the winding directions of two adjacent secondary transmitting coils are the same or opposite; the two or two groups of secondary transmitting coils jointly act on the background of the sleeve to approximately equivalently set a virtual transmitting coil at the position of the main transmitting coil, the virtual transmitting coil and the main transmitting coil are in a reverse equal-turn relationship, the virtual transmitting coil and the main transmitting coil are equivalent compensation, and the background signal is suppressed; and the winding direction of the receiving coil is the same as or opposite to that of the main transmitting coil.

2. The approximately equivalent compensating coil structure of claim 1, wherein, The receiving coil is provided with one, the compensation transmitting coil system is provided with one, and the compensation transmitting coil system is arranged on one side of the receiving coil; the compensation transmitting coil system at least comprises a main transmitting coil and first and second secondary transmitting coils arranged on two sides of the main transmitting coil, and the first and second secondary transmitting coils act as compensation coils.

3. The approximately equivalent compensating coil structure of claim 1, wherein, The receiving coil is provided with N (N is greater than or equal to 2), N receiving coils are sequentially arranged to form a measurement array, and the winding directions of the N receiving coils are the same; the compensation transmitting coil system is provided with one, and the compensation transmitting coil system is arranged on one side of the measurement array; the compensation transmitting coil system at least comprises a main transmitting coil and first and second secondary transmitting coils arranged on two sides of the main transmitting coil, and the first and second secondary transmitting coils act as compensation coils.

4. The approximately equivalent compensating coil structure of claim 1, wherein, The receiving coil is provided with two, two receiving coils are sequentially arranged to form a measurement array, and the winding directions of the two receiving coils are the same; the compensation transmitting coil system is provided with two, two compensation transmitting coil systems are respectively arranged on two sides of the measurement array and are symmetrically arranged relative to the measurement array, a first compensation transmitting system is adjacent to a first receiving coil, and a second compensation transmitting system is adjacent to a second receiving coil; the compensation transmitting coil system at least comprises a main transmitting coil and first and second secondary transmitting coils arranged on two sides of the main transmitting coil, and the first and second secondary transmitting coils act as compensation coils.

5. A quasi-isodynamic compensation coil structure according to any one of claims 2 to 4, wherein The main transmitting coil and the receiving coil are forwardly wound, the first and second secondary transmitting coils are reversely wound; or the main transmitting coil is forwardly wound, and the receiving coil, the first and second secondary transmitting coils are reversely wound; or the main transmitting coil and the receiving coil are reversely wound, and the first and second secondary transmitting coils are forwardly wound; or the main transmitting coil is reversely wound, and the receiving coil, the first and second secondary transmitting coils are forwardly wound.

6. A method for controlled-source transient electromagnetic wave through casing resistivity measurement, using the approximately equivalent compensation coil structure of claim 2 or 3, characterized in that, The steps are as follows: The coil parameter adjustment step: under the condition of setting the casing background environment, the transmitting coil parameters and the excitation time of the approximately equivalent compensation coil structure are adjusted so that the casing background signals in the electromagnetic waves transmitted by the transmitting coil reach the receiving coil synchronously; The background signal measurement step: a transient electromagnetic wave signal is generated by the main transmitting coil as a background signal, and a transient electromagnetic wave signal opposite to the main transmitting coil is generated by the secondary transmitting coil as a background signal, the background signal and the background signal together make the total receiving signal received by the receiving coil minimum, and the total receiving signal at this time is the suppressed background signal; The actual response signal measurement step: under the same condition of setting the casing background environment, the formation condition is changed, and the total receiving signal received by the receiving coil in the approximately equivalent compensation coil structure is the actual response signal; The calculation step: the formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal; The resistivity determination step: the formation anomaly signal is converted into the formation resistivity.

7. A method for controlled-source transient electromagnetic (CSEM) cross-hole resistivity surveying using the approximately equivalent compensating coil structure of claim 4, wherein, The steps are: The coil parameter adjustment step: under the condition of setting the casing background environment, the transmitting coil parameters and the excitation time of the approximately equivalent compensation coil structure are adjusted so that the casing background signals in the electromagnetic waves transmitted by the transmitting coil reach the receiving coil synchronously; The background signal measurement step: a transient electromagnetic wave signal is generated by the main transmitting coil as a background signal, and a transient electromagnetic wave signal opposite to the main transmitting coil is generated by the secondary transmitting coil as a background signal, the background signal and the background signal together make the total receiving signal received by the receiving coil minimum, and the total receiving signal at this time is the suppressed background signal; The actual response signal measurement step: under the same condition of setting the casing background environment, the formation condition is changed, and the total receiving signal received by the receiving coil in the approximately equivalent compensation coil structure is the actual response signal; The calculation step: the formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal; The resistivity determination step: the formation anomaly signal is converted into the formation resistivity.

8. A method of formation property analysis using the approximately equivalent compensating coil structure of claim 3, characterized by, The steps are: The coil parameter adjustment step: under the condition of setting the casing background environment, the transmitting coil parameters and the excitation time of the approximately equivalent compensation coil structure are adjusted so that the casing background signals in the electromagnetic waves transmitted by the transmitting coil reach the receiving coil synchronously; The background signal measuring step: a transient electromagnetic wave signal is generated by the main transmitting coil as a background signal, and a transient electromagnetic wave signal opposite to the main transmitting coil is generated by the secondary transmitting coil as a reverse background signal, the background signal and the reverse background signal jointly act on the total receiving signal received by the receiving coil to minimize the total receiving signal, and the total receiving signal at this time is the suppressed background signal; The actual response signal measuring step: in the same setting sleeve background environment, the formation condition is changed, and the total receiving signal received by the receiving coil in the approximately equivalent compensation coil structure is the actual response signal; The calculating step: the formation anomaly signal is obtained by subtracting the actual response signal from the suppressed background signal; The resistivity determining step: the formation anomaly signal is converted into the formation resistivity; The formation property analyzing step: the formation property is analyzed according to the change of the formation resistivity.

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