Compensation differential type coil structure and transient electromagnetic wave through casing resistivity logging instrument

Abstract

The utility model belongs to the technical field of oil-gas exploration and development, and relates to a compensation differential type coil structure and a transient electromagnetic wave through casing resistivity logging instrument, the compensation differential type coil structure comprises a transmitting coil and at least one compensation coil system, the compensation coil system at least comprises a first receiving coil and a second receiving coil which are sequentially arranged, the transmitting coil and the second receiving coil are wound in the forward direction, and the first receiving coil serves as a compensation coil and is wound in the reverse direction; and the transmitting coil and the compensating coil system are sequentially arranged from front to back. The instrument comprises a shell and a coil structure arranged in the shell, and the compensation differential type coil structure is adopted in the coil structure. According to the utility model, the transient electromagnetic wave through-casing logging response precision can be improved, and the formation resistivity extraction under the influence of a high-conductivity casing can be realized.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the oil and gas exploration and development technical field relates to the electrical logging technology, concretely relates to a kind of compensation difference type coil structure and transient electromagnetic wave through casing resistivity logging instrument, for measuring transient electromagnetic wave through casing resistivity. BACKGROUND

[0002] In the oil and gas field exploration and development, through casing resistivity measurement technology has important application value, especially in cased hole, through casing resistivity measurement is one of important means of reservoir oiliness evaluation, reservoir dynamic monitoring and remaining oil distribution analysis, and it has important significance for cased hole reservoir evaluation and production well exploitation scheme optimization, enhanced recovery and the like.Cased hole is a new drilling method for oil and gas exploration and development, and conventional resistivity logging cannot be directly applied due to the presence of casing, so how to realize accurate and efficient through casing resistivity measurement becomes a key problem in the industry.

[0003] At present, the through casing resistivity logging method usually adopts 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 casing quality: corrosion, thinning or deformation of the casing can significantly affect the contact quality between the electrode and the casing, resulting in inaccurate measurement data. (2) affected by downhole environment interference: scale, wax, rust spots and other contaminants on the inner wall of the casing can interfere with the stability of the electrode method measurement, which requires time-consuming preparation work such as well flushing (e.g. descaling, oil removal, etc.), increasing the complexity of logging. (3) low logging efficiency: the electrode method usually adopts point measurement mode, which requires a long time to establish stable measurement conditions, and cannot meet the real-time response demand of rapid changes in downhole environment, resulting in low overall logging efficiency.

[0004] Transient electromagnetic wave technology provides a new solution for through casing resistivity measurement, and its working principle is to arrange transmitting and receiving coils in the well, and transmit transient current pulses to the formation through the transmitting coil, which will generate time-varying electromagnetic field, excite the formation to generate time-decaying induced eddy current, and diffuse in different media at different speeds. After the current is turned off, the secondary induced electromagnetic field generated by the eddy current is measured to extract the formation resistivity information. 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: transient electromagnetic wave has wide frequency domain characteristics, can work in multiple frequency bands at the same time, and can obtain rich formation information to realize continuous logging. However, transient electromagnetic wave logging also faces the following problems in practical application: (1) strong shielding effect of metal casing: the high conductivity of steel casing (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, so it is particularly difficult to extract the weak signals of the formation.(2) Higher engineering difficulty: related instruments are still in the stage of theoretical research and experimental development, lack of mature engineering equipment, and there is still a big gap from practical application.

[0005] Therefore, clarifying the response law of transient electromagnetic wave logging in cased wells, suppressing the influence of metal casing, and designing a reasonable instrument structure have important theoretical value and practical significance for promoting the practical application of transient electromagnetic wave technology in cased well resistivity measurement. Practical new type content

[0006] The utility model provides a kind of compensation differential coil structure and transient electromagnetic wave through casing resistivity logging instrument for the problems existing in prior art, can improve transient electromagnetic wave through casing logging response precision, realize formation resistivity extraction under the influence of high conductive casing.

[0007] The utility model discloses a first aspect provides a kind of compensation differential coil structure, including a transmitting coil and at least one compensation coil system, the compensation coil system at least includes sequentially arranged first receiving coil and second receiving coil, transmitting coil and second receiving coil are forward winding, and first receiving coil is as compensation coil, and is reverse winding;Transmitting coil and compensation coil system are sequentially arranged according to front and back order.

[0008] In some embodiments, the compensation coil system is provided with a group, and the compensation coil system includes sequentially arranged first receiving coil, second receiving coil and third receiving coil, and the first receiving coil is adjacent to the transmitting coil;First receiving coil and third receiving coil are as compensation coil, and are reverse winding, and second receiving coil is forward winding.

[0009] In some embodiments, the compensation coil system is provided with N groups, N≥2, and the transmitting coil, the first group compensation coil system to the Nth group compensation coil system are sequentially arranged;Each group compensation coil system includes sequentially arranged first receiving coil, second receiving coil and third receiving coil, and first receiving coil and third receiving coil are as compensation coil, and are reverse winding, and second receiving coil is forward winding, and the first receiving coil of the first group compensation coil system is adjacent to the transmitting coil;In adjacent two groups of compensation coil systems, the third receiving coil of the previous group compensation coil system is adjacent to the first receiving coil of the subsequent group compensation coil system.

[0010] In some embodiments, the coil structure further comprises a pair of symmetric compensation coil systems, the pair of symmetric compensation coil systems comprises a fourth receiving coil and a fifth receiving coil, the two receiving coils are symmetrically arranged on two sides of the transmitting coil, the fourth receiving coil is arranged between the transmitting coil and the first receiving coil and is forward-wound, and the fifth receiving coil is a compensation coil and is reverse-wound.

[0011] In some embodiments, the compensation coil system comprises a first receiving coil and a second receiving coil, the first receiving coil is adjacent to the transmitting coil, the first receiving coil is a compensation coil and is reverse-wound, and the second receiving coil is forward-wound.

[0012] In some embodiments, the compensation coil system comprises N groups, N is greater than or equal to 2, the transmitting coil, the first group of compensation coil systems to the Nth group of compensation coil systems are sequentially arranged, each group of compensation coil systems comprises a first receiving coil and a second receiving coil which are sequentially connected, the first receiving coil is a compensation coil and is reverse-wound, the second receiving coil is forward-wound, and the first receiving coil of the first group of compensation coil systems is adjacent to the transmitting coil; in adjacent two groups of compensation coil systems, the second receiving coil of a previous group of compensation coil systems is adjacent to the first receiving coil of a subsequent group of compensation coil systems.

[0013] In some embodiments, the coil structure further comprises a pair of symmetric compensation coil systems, the pair of symmetric compensation coil systems comprises a third receiving coil and a fourth receiving coil, the two receiving coils are symmetrically arranged on two sides of the transmitting coil, the third receiving coil is arranged between the transmitting coil and the first receiving coil and is forward-wound, and the fourth receiving coil is a compensation coil and is reverse-wound.

[0014] The utility model discloses a second aspect provides a kind of transient electromagnetic wave over casing resistivity logging instrument, including shell and the coil structure being located in shell, the coil structure uses the compensation differential coil structure of the utility model first aspect.

[0015] Compared with the prior art, the utility model has the advantages and positive effects that:

[0016] (1) the compensation differential coil structure provided by the utility model suppresses middle background signal by compensation differential measurement mode, highlights useful signal (i.e. induced electromotive force related to formation resistivity), can improve transient electromagnetic wave over casing logging response precision, realizes formation resistivity extraction under the influence of high-conductivity casing, and the measurement of formation resistivity is accurate and high, and the blank of transient electromagnetic wave over casing resistivity logging is made up.

[0017] (2) the compensation differential coil structure provided by the utility model, compensation coil system adopts array design, can realize near-far well, near-middle-far well formation resistivity measurement, and improves transient electromagnetic wave over casing logging efficiency.

[0018] (3) The compensation differential type coil structure provided by the utility model can realize stratum interface identification, and can assist in determining stratum resistivity according to the identified stratum interface, thereby providing technical reference for transient electromagnetic wave through casing logging instrument development and data processing. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The structure diagram of the compensation differential type coil structure adopted by the first aspect embodiment of the utility model is shown in the figure.

[0020] Figure 2 The flow chart of measuring resistivity by the compensation differential type coil structure adopted by the first aspect embodiment of the utility model is shown in the figure.

[0021] Figure 3 The principle diagram of measuring resistivity by the compensation differential type coil structure adopted by the first aspect embodiment of the utility model is shown in the figure.

[0022] Figure 4 The structure diagram of the casing well three-layer columnar layered stratum model of the embodiment of the utility model is shown in the figure.

[0023] Figure 5 The measurement result diagram of measuring resistivity by the compensation differential type coil structure adopted by the first aspect embodiment of the utility model is shown in the figure.

[0024] Figure 6 The resistivity curve diagram obtained by measuring resistivity by the compensation differential type coil structure adopted by the first aspect embodiment of the utility model is shown in the figure.

[0025] Figure 7 The structure diagram of the compensation differential type coil structure adopted by the second aspect embodiment of the utility model is shown in the figure.

[0026] Figure 8 The flow chart of the stratum interface identified by the symmetric compensation coil system adopted by the embodiment of the utility model is shown in the figure.

[0027] Figure 9 The structure diagram of the stratum interface identified by the symmetric compensation coil system adopted by the second aspect embodiment of the utility model is shown in the figure.

[0028] Figure 10 The structure diagram of the compensation differential type coil structure adopted by the third aspect embodiment of the utility model is shown in the figure.

[0029] Figure 11 The structure diagram of the compensation differential type coil structure adopted by the fourth aspect embodiment of the utility model is shown in the figure.

[0030] Figure 12The structure diagram of the compensation differential type coil structure used in the fifth aspect of the present application is shown in the figure.

[0031] Figure 13 The measurement result comparison chart of the compensation differential type coil structure of the first aspect of the present application and the compensation differential type coil structure of the fifth aspect of the present application is shown in the figure.

[0032] Figure 14 The structure diagram of the compensation differential type coil structure used in the sixth aspect of the present application is shown in the figure.

[0033] Figure 15 The structure diagram of the compensation differential type coil structure used in the seventh aspect of the present application is shown in the figure.

[0034] Figure 16 The structure diagram of the compensation differential type coil structure used in the eighth aspect of the present application is shown in the figure.

[0035] In the figure, 1 is wellbore mud, 2 is casing, 3 is formation, 31 is first layer formation, 32 is second layer formation, and 33 is third layer formation. DETAILED DESCRIPTION

[0036] The present application will be described in detail below with reference to the accompanying drawings and exemplary embodiments. However, it should be understood that the elements, structures and features in one embodiment can be beneficially combined with other embodiments without further description.

[0037] Referring to Figure 1 The first aspect of the present application provides a compensation differential type coil structure, which comprises a transmitting coil T and a set of compensation coil systems. The transmitting coil T is forward-wound. The compensation coil system comprises a first receiving coil R2, a second receiving coil R3 and a third receiving coil R4 arranged in sequence. The first receiving coil R2 is adjacent to the transmitting coil T. The first receiving coil R2 and the third receiving coil R4 are reverse-wound compensation coils, and the second receiving coil R3 is forward-wound. Figure 1 In the figure, T2 is the coil distance between the transmitting coil T and the first receiving coil R2, T3 is the coil distance between the transmitting coil T and the second receiving coil R3, and T4 is the coil distance between the transmitting coil T and the third receiving coil R4. V R2 is the induced electromotive force of the first receiving coil R2, R3 is the induced electromotive force of the second receiving coil R3, R4is the induced electromotive force of the third receiving coil R4, N2 is the number of turns of the first receiving coil, N3 is the number of turns of the second receiving coil R3, N4 is the number of turns of the third receiving coil R4, and f is the differential induced electromotive force. In the resistivity measurement process, the second receiving coil R3 wound in the forward direction is differentiated with the compensation coil (i.e. the first receiving coil R2 and the third receiving coil R4) wound in the reverse direction, and the influence of the casing can be effectively suppressed by using the compensation effect of the compensation coil, and the useful signal (i.e. the induced electromotive force related to the formation resistivity) in the receiving coil can be highlighted.

[0038] Specifically, referring to Figure 2 , the method for measuring resistivity by using the compensation differential type coil structure in the embodiments of the present application is as follows:

[0039] S1, a coil parameter determination step: in the casing well formation model, under the set background environment, the coil parameters of the compensation differential type coil structure are adjusted so that the casing background signal in the measured signal is zero, and the coil parameters at this time are the final coil parameters of the compensation differential type coil structure;

[0040] S2, a signal measurement step: the compensation differential type coil structure is pulled up along the wellbore, and the induced electromotive force at different formation positions is measured by the compensation differential type coil structure;

[0041] S3, a drawing step: a curve reflecting the formation resistivity information is drawn according to the induced electromotive force;

[0042] S4, a resistivity determination step: the curve reflecting the formation resistivity information is converted into a resistivity calibration chart. According to Figure 1 , the coil parameters of the compensation differential type coil structure are determined under the background environment of the wellbore 1Ω·m, the casing 10 -6 Ω·m, and the formation 1Ω·m, that is, the casing background signal in the signal measured by the coil structure in a certain time period is as small as possible (zero), so that the casing signal is suppressed and the formation signal is differentially measured. The time domain response signals of the formation resistivity of 10Ω·m, 2Ω·m and 1Ω·m are simulated, and the difference value digital processing is performed on the 1Ω·m background signal. As shown in Figure 3 , the black solid line is the measurement result of the compensation differential type coil structure when the formation resistivity is 10Ω·m, corresponding to the left logarithmic coordinate axis; the purple and blue dashed lines are the processing results of the difference value of the measurement result and the background value, corresponding to the right linear coordinate axis. From 2x10 -4 s, the difference value signal starts to increase, indicating that the electromagnetic wave signal propagates to the formation; at the same time, the measurement result of the compensation differential type coil structure is relatively small near the peak value of the difference value signal, at this time the influence of the casing is almost completely suppressed, and the formation resistivity information can be reflected. Therefore, if the casing influence is detected in this time period, the casing influence can be effectively suppressed, and the signal-to-noise ratio of the formation signal can be greatly improved.

[0043] The following verifies the effectiveness of the compensated differential coil structure for measuring resistivity according to specific embodiments.

[0044] According to the above compensated differential measurement method, a three-layer columnar layered formation model of a cased hole is established as shown in Figure 4 The hole radius is 3-11 inch, i.e. 7.5-28 cm, the conductivity of the hole mud 1 depends on the mud type, the relative permeability of the casing 2 is 1-200, the casing thickness is 0.5-1.5 cm, and the formation 3 is a three-layered formation including a first layer 31, a second layer 32 and a third layer 33. Figure 4 , r i is the casing inner diameter, r o is the casing outer diameter, ρ1 is the first layer resistivity, ρ2 is the second layer resistivity, and ρ3 is the third layer resistivity. The layer interface positions of the first layer 31 and the second layer 32 and the layer interface positions of the second layer 32 and the third layer 33 are respectively l1=1.5 m and l2=-1.5 m, and the coil distance of the transmitting coil and the receiving coil is 0.3 m. Assuming that the formation resistivity from top to bottom is respectively 10 Ω·m, 5 Ω·m, 1 Ω·m and 100 Ω·m, 10 Ω·m, 1 Ω·m, the middle layer thickness is 3 m, the layer interface positions are respectively l1=1.5 m and l2=-1.5 m, the transmitting coil and the receiving coil distance is 0.3 m, and the instrument is pulled up along the hole, the transient electromagnetic signal at a certain time is given, in which the horizontal coordinate is the measured induction signal size, and the vertical coordinate is the measurement point position. The measurement result is shown in Figure 5 It can be seen from Figure 5 that the signal curve trend after the compensated differential measurement can reflect the change of the formation resistivity. Meanwhile, the values of the two different formation conditions of the cased three-layer model at 1 Ω·m and 10 Ω·m are similar, which shows that the influence of the model change is small, and the compensated differential measurement can be used for calibrating the formation resistivity. The value of 1 Ω·m is set as a background base value, the difference between different formation resistivities and the background base value is calculated respectively, and the resistivity curve is drawn, and the result is shown in Figure 6 It can be seen that when the formation resistivity is below 50 Ω·m, the difference signal changes obviously, which shows that the transient electromagnetic wave through the cased hole logging response is more sensitive to low-resistance formation. Between 0 and 200 Ω·m, the formation resistivity and the difference signal present a good logarithmic relationship, which can effectively calibrate the formation resistivity.

[0045] The compensated differential coil structure described in the above embodiment is suitable for measuring the formation resistivity in any position logging. Referring to Figure 7The utility model discloses a second aspect embodiment provides a kind of compensation differential coil structure, including a transmitting coil T, a set of compensation coil system and a pair of symmetric compensation coil system, the transmitting coil T is forward winding.The compensation coil system includes sequentially arranged first receiving coil R2, second receiving coil R3 and third receiving coil R4, first receiving coil R2 with the transmitting coil T adjacent;First receiving coil R2 and third receiving coil R4 as compensation coil, are reverse winding, and second receiving coil R3 is forward winding.The symmetric compensation coil system includes receiving coil R1 and receiving coil R1', two receiving coils are symmetrically arranged in the two sides of transmitting coil T, and receiving coil R1 is between transmitting coil T and first receiving coil R2 and is forward winding, and receiving coil R1' as compensation coil, is reverse winding.In resistivity measurement process, the second receiving coil R3 of forward winding and the compensation coil (i.e. first receiving coil R2 and third receiving coil R4) of reverse winding are differentially, using the offset effect of compensation coil, the influence of casing can be effectively suppressed, and the useful signal (i.e. the induced electromotive force related to formation resistivity) in receiving coil is highlighted.

[0046] The method for measuring resistivity using the compensation differential coil structure described in the embodiment is basically the same as the method for measuring resistivity using the compensation differential coil structure described in the first aspect embodiment of the utility model.

[0047] According to Figure 7 The compensation differential coil structure shown in the figure is used to determine coil parameters under the background environment of wellbore 1Ω·m, casing 10 -6 Ω·m and formation 1Ω·m, i.e. to make the casing background signal in the signal measured by the coil structure in a certain period as small as possible (zero), so as to realize the compensation suppression of casing signal and the differential measurement of formation signal. In the embodiment, the above-mentioned compensation differential coil structure can also be used for formation interface identification, referring to Figure 8 The method for identifying formation interface using the above-mentioned compensation differential coil structure is as follows:

[0048] S1, signal measurement step: in the casing well formation model, the compensation differential coil structure is pulled up along the wellbore, and the induced electromotive force at different formation positions is measured by the symmetric compensation coil system (i.e. receiving coil R1 and receiving coil R1').

[0049] S2, identification step: according to the measured induced electromotive force, a curve graph of the change of induced electromotive force with depth is drawn, and the peak value of induced electromotive force is the formation interface.

[0050] Taking the 10-5-1Ω·m formation model under the condition of the earth as an example, the formation interface is identified according to the above-mentioned formation interface identification step, and the identification result is shown in Figure 9 Figure 9 ​It can be seen that the signal at the position of the layer interface is obviously higher than that at other positions, i.e. l1=1.5m and l2=-1.5m. It is illustrated that the total signal received by the two symmetrical receiving coils depends on the existence of the layer interface, because the signal in the uniform infinite medium should be 0. Therefore, when the layer resistivity changes, the signal received by the symmetrical coils will be different. Meanwhile, the amplitude and time of the signal are controlled by the medium resistivity and the resistivity contrast of the media on both sides of the interface, so the signal can also be used to determine the resistivity distribution change of the layer in combination with the compensated differential measurement method.

[0051] The compensated differential coil structure described in the embodiment above is suitable for the measurement of the layer resistivity in any position logging. The symmetrical compensated coil system is also provided, which can identify the layer interface and determine the resistivity distribution change of the layer in combination with the compensated differential measurement method.

[0052] Referring to Figure 10 The third aspect of the utility model provides a kind of compensated differential coil structure, including a transmitting coil T and two groups of compensation coil systems, transmitting coil T, first group of compensation coil systems, second group of compensation coil systems are sequentially arranged, and the transmitting coil T is forward winding.The first group of compensation coil systems includes sequentially arranged R2, second receiving coil R3 and third receiving coil R4, and the first receiving coil R2 and the third receiving coil R4 are used as compensation coil, and are reverse winding, and the second receiving coil R3 is forward winding, and the first receiving coil R2 is adjacent to the transmitting coil T.The second group of compensation coil systems includes sequentially arranged fourth receiving coil R5, fifth receiving coil R6 and sixth receiving coil R7, and the fourth receiving coil R5 and the sixth receiving coil R7 are used as compensation coil, and are reverse winding, and the fifth receiving coil R6 is forward winding, and the fourth receiving coil R5 is adjacent to the third receiving coil R4.

[0053] The method for measuring resistivity using the compensated differential coil structure described in the embodiment is basically the same as the method for measuring resistivity using the compensated differential coil structure described in the first aspect of the utility model.

[0054] According to Figure 10 The coil structure shown in the drawing determines the coil parameters of each compensation coil system under the background environment of wellbore 1 Ω·m, casing 10 -6 Ω·m, layer 1 Ω·m, i.e. different compensation coil systems select their corresponding time periods, so that the casing background signal in the total signal of each compensation coil system is as small as possible (zero), so as to realize the suppression of casing signal and the differential measurement of layer signal. The time period is preferably set from medium to late period, with high resolution and shallow detection depth in front, and large detection depth in back.

[0055] In the embodiment, two groups of compensation coil systems are provided, which can realize near-far well layer resistivity measurement.

[0056] It should be noted that the above compensation coil system can also be provided with three groups, and the measurement principle is the same as that of the two groups of compensation coil systems, and near-mid-far well formation resistivity measurement can be realized. Specifically, the number of compensation coil systems can be set according to actual needs to realize formation resistivity measurement of different well sections.

[0057] Referring to Figure 11 , the fourth aspect of the utility model provides a kind of compensation differential coil structure, including a transmitting coil T, two groups of compensation coil system and a symmetric coil compensation system, transmitting coil T, first group of compensation coil system, second group of compensation coil system are sequentially arranged in order, and the transmitting coil T is forward winding.The first group of compensation coil system includes sequentially arranged R2, second receiving coil R3 and third receiving coil R4, and the first receiving coil R2 and the third receiving coil R4 are used as compensation coil, and are reverse winding, and the second receiving coil R3 is forward winding, and the first receiving coil R2 is adjacent to the transmitting coil T.The second group of compensation coil system includes sequentially arranged fourth receiving coil R5, fifth receiving coil R6 and sixth receiving coil R7, and the fourth receiving coil R5 and the sixth receiving coil R7 are used as compensation coil, and are reverse winding, and the fifth receiving coil R6 is forward winding, and the fourth receiving coil R5 is adjacent to the third receiving coil R4.The symmetric compensation coil system includes receiving coil R1 and receiving coil R1 ', and the two receiving coils are symmetrically arranged on the two sides of the transmitting coil T, and the receiving coil R1 is located between the transmitting coil T and the first receiving coil R2 and is forward winding, and the receiving coil R1'is used as compensation coil and is reverse winding.

[0058] The method for measuring resistivity using the compensation differential coil structure described in the embodiment is basically the same as the method for measuring resistivity using the compensation differential coil structure described in the first aspect of the utility model.

[0059] According to Figure 11 , the coil structure is used to determine the coil parameters of each compensation coil system under the background environment of wellbore 1Ω·m, casing 10 -6 Ω·m, formation 1Ω·m, that is, each compensation coil system selects its corresponding time period, so that the casing background signal in the total signal of each compensation coil system is as small as possible (zero), thereby realizing the suppression of casing signal and the differential measurement of formation signal. The time period is preferably set from the middle period to the late period, with high resolution and shallow detection depth at the front, and large detection depth at the back.

[0060] In the embodiment, the above-mentioned compensation differential coil structure can also be used for formation interface identification, referring to Figure 8 , the method for identifying formation interface using the above-mentioned compensation differential coil structure is as follows:

[0061] S1, signal measurement step: in the casing well formation model, the compensated differential coil structure is pulled up along the wellbore, and the inductive electromotive force of different formation positions is measured through the symmetrical compensated coil system (i.e. the receiving coil R1 and the receiving coil R1');

[0062] S2, identification step: a curve of the inductive electromotive force changing with depth is drawn according to the measured inductive electromotive force, and the peak of the inductive electromotive force is the formation interface.

[0063] In the embodiment, two groups of compensated coil systems are provided, which can realize near-far well formation resistivity measurement. The symmetrical compensated coil system can identify the formation interface, and the formation resistivity distribution change can also be determined in combination with the compensated differential measurement mode.

[0064] It should be noted that the above-mentioned compensated coil system can also be provided with three groups, and the measurement principle is the same as that of the two groups of compensated coil systems, which can realize near-middle-far well formation resistivity measurement. Specifically, the number of compensated coil systems can be set according to actual needs to realize formation resistivity measurement of different well sections.

[0065] Referring to Figure 12 , the fifth aspect of the utility model provides a kind of compensated differential coil structure, including a transmitting coil T and a group of compensated coil system, the transmitting coil T is forward winding, and the compensated coil system includes first receiving coil R2, second receiving coil R3 in turn sequentially arranged, and first receiving coil R2 is adjacent with the transmitting coil T;First receiving coil R2 is as compensation coil, and it is reverse winding, and second receiving coil R3 is forward winding. Figure 12 , T2 is the coil distance between transmitting coil T and first receiving coil R2, T3 is the coil distance between transmitting coil T and second receiving coil R3, V R2 is the inductive electromotive force of first receiving coil R2, V R3 is the inductive electromotive force of second receiving coil R3, N2 is the number of turns of first receiving coil, N3 is the number of turns of second receiving coil R3, and f is differential inductive electromotive force.In the process of resistivity measurement, second receiving coil R3 of forward winding and compensation coil (i.e. first receiving coil R2) of reverse winding are different, and the influence of casing can be effectively suppressed by using the offsetting effect of compensation coil, and the useful signal (i.e. the inductive electromotive force related to formation resistivity) in receiving coil is highlighted.

[0066] The method for measuring resistivity using the compensated differential coil structure described in the embodiment is basically the same as the method for measuring resistivity using the compensated differential coil structure described in the first aspect of the utility model.

[0067] In the embodiment, the compensation coil system composed of double coils is used for compensation, only one receiving coil is used for compensation, that is, single compensation coil compensation is used. When measuring the formation resistivity, the coil parameters are determined through the first aspect of the embodiment of the utility model background environment, and the formation resistivity information is extracted through the above-mentioned compensation coil system of the embodiment. Referring to Figure 13 Compared with the compensation coil system of the double compensation coil compensation of the first aspect of the utility model embodiment, the measurable time is reduced, but the coil structure is simplified.

[0068] The above-mentioned compensation differential coil structure of the embodiment is suitable for the measurement of formation resistivity in any position logging. Referring to Figure 14 The sixth aspect of the utility model provides a compensation differential coil structure, which comprises a transmitting coil T, a set of compensation coil systems and a symmetrical compensation coil system, the transmitting coil T is forward winding. The compensation coil system comprises a first receiving coil R2, a second receiving coil R3 arranged in sequence, the first receiving coil R2 is adjacent to the transmitting coil T; the first receiving coil R2 is used as a compensation coil and is reverse winding, and the second receiving coil R3 is forward winding. The symmetrical compensation coil system comprises a receiving coil R1 and a receiving coil R1', the two receiving coils are symmetrically arranged on both sides of the transmitting coil T, the receiving coil R1 is located between the transmitting coil T and the first receiving coil R2 and is forward winding, and the receiving coil R1' is used as a compensation coil and is reverse winding. In the resistivity measurement process, the second receiving coil R3 of forward winding and the compensation coil (that is, the first receiving coil R2) of reverse winding are differentially connected, the influence of the casing can be effectively suppressed by using the compensation effect of the compensation coil, and the useful signal (that is, the induced electromotive force related to the formation resistivity) in the receiving coil can be highlighted.

[0069] The method for measuring resistivity by using the compensation differential coil structure of the embodiment is basically the same as the method for measuring resistivity by using the compensation differential coil structure of the fifth aspect of the utility model embodiment.

[0070] According to Figure 14 The compensation differential coil structure is used to determine the coil parameters in the wellbore 1Ω·m, the casing 10 -6 Ω·m, and the formation 1Ω·m background environment, that is, the casing background signal in the signal measured by the coil structure in a certain period of time is as small as possible (zero), so as to realize the compensation suppression of the casing signal and the differential measurement of the formation signal. In the embodiment, the above-mentioned compensation differential coil structure can also be used for formation interface identification, referring to Figure 8 The method for identifying the formation interface by using the above-mentioned compensation differential coil structure is as follows:

[0071] S1, signal measurement step: in the casing well formation model, the compensated differential coil structure is pulled up along the wellbore, and the inductive electromotive force of different formation positions is measured through the symmetrical compensation coil system (i.e. the receiving coil R1 and the receiving coil R1');

[0072] S2, identification step: according to the measured inductive electromotive force, a curve graph of the inductive electromotive force changing with depth is drawn, and the peak value of the inductive electromotive force is the formation interface.

[0073] The compensated differential coil structure described in the embodiment is suitable for measuring the formation resistivity in any position logging. The symmetrical compensation coil system can identify the formation interface, and the compensated differential measurement method can also be used to determine the change of the formation resistivity distribution.

[0074] Referring to Figure 15 , the seventh aspect of the utility model provides a compensated differential coil structure, which comprises a transmitting coil T and two sets of compensation coil systems, the transmitting coil T, the first set of compensation coil systems and the second set of compensation coil systems are sequentially arranged, and the transmitting coil T is forward wound. The first set of compensation coil systems comprises R2 and a second receiving coil R3 which are sequentially arranged, the first receiving coil R2 is a compensation coil and is reversely wound, the second receiving coil R3 is forward wound, and the first receiving coil R2 is adjacent to the transmitting coil T. The second set of compensation coil systems comprises a third receiving coil R4 and a fourth receiving coil R5 which are sequentially arranged, the third receiving coil R4 is a compensation coil and is reversely wound, the fourth receiving coil R5 is forward wound, and the second receiving coil R3 is adjacent to the third receiving coil R4.

[0075] The method for measuring resistivity by using the compensated differential coil structure described in the embodiment is basically the same as the method for measuring resistivity by using the compensated differential coil structure described in the fifth aspect of the utility model.

[0076] According to Figure 15 , the coil structure is used to determine the coil parameters of each compensation coil system in the background environment of the wellbore 1Ω·m, the casing 10 -6 Ω·m and the formation 1Ω·m, that is, each compensation coil system selects a corresponding time period, so that the casing background signal in the total signal of each compensation coil system is as small as possible (zero), so as to realize the suppression of the casing signal and the differential measurement of the formation signal. The time period is preferably set from the middle period to the late period, the resolution is high at the front, and the detection depth is shallow at the back.

[0077] In the embodiment, there are two sets of compensation coil systems, which can realize near-far well formation resistivity measurement.

[0078] It should be noted that the above compensation coil system can also be provided with three groups, and the measurement principle is the same as that of the two-group compensation coil system, and near-mid-far well formation resistivity measurement can be realized. Specifically, the number of compensation coil systems can be set according to actual needs to realize formation resistivity measurement of different well sections.

[0079] Referring to Figure 16 , the eighth aspect of the utility model provides a compensation differential type coil structure, including a transmitting coil T, two groups of compensation coil systems and a symmetric compensation coil system, the transmitting coil T, the first group of compensation coil systems, the second group of compensation coil systems are sequentially arranged, the transmitting coil T is forward winding. The first group of compensation coil systems includes R2, the second receiving coil R3 sequentially arranged, the first receiving coil R2 is used as a compensation coil, and is reverse winding, the second receiving coil R3 is forward winding, and the first receiving coil R2 is adjacent to the transmitting coil T. The second group of compensation coil systems includes the third receiving coil R4, the fourth receiving coil R5 sequentially arranged, the third receiving coil R4 is used as a compensation coil, and is reverse winding, the fourth receiving coil R5 is forward winding, and the second receiving coil R3 is adjacent to the third receiving coil R4. The symmetric compensation coil system includes receiving coil R1 and receiving coil R1', and the two receiving coils are symmetrically arranged on both sides of the transmitting coil T, the receiving coil R1 is located between the transmitting coil T and the first receiving coil R2 and is forward winding, and the receiving coil R1' is used as a compensation coil and is reverse winding.

[0080] The method for measuring resistivity by using the compensation differential type coil structure in the embodiment is basically the same as the method for measuring resistivity by using the compensation differential type coil structure in the fifth aspect of the utility model.

[0081] According to Figure 16 , the coil structure is used to determine the coil parameters of each compensation coil system under the background environment of the borehole 1Ω·m, the casing 10 -6 Ω·m and the formation 1Ω·m, that is, different compensation coil systems select their corresponding time periods, so that the casing background signal in the total signal of each compensation coil system is as small as possible (zero), so that the casing signal is suppressed and the formation signal is differentially measured. The time period is preferably set from the middle period to the late period, and the resolution is high and the detection depth is shallow in the front, and the detection depth is large in the rear.

[0082] In the embodiment, the above-mentioned compensation differential type coil structure can also be used for formation interface identification, referring to Figure 8 , the method for identifying the formation interface by using the above-mentioned compensation differential type coil structure is as follows:

[0083] S1, signal measurement step: in the casing well formation model, the compensation differential type coil structure is pulled up along the borehole, and the symmetric compensation coil system (i.e. receiving coil R1 and receiving coil R1') measures the induced electromotive force at different formation positions;​

[0084] S2, identifying step: according to the measured induced electromotive force, the curve of which changes with depth is drawn, and the peak of the induced electromotive force is the formation interface.

[0085] In the embodiment, two sets of compensation coil systems are provided, which can realize near-far well formation resistivity measurement. A symmetric compensation coil system is also provided, which can identify the formation interface and can also determine the formation resistivity distribution change in combination with the compensation differential measurement mode.

[0086] It should be noted that the above compensation coil system can also be provided with three sets, and the measurement principle is the same as that of the two sets of compensation coil systems, which can realize near-middle-far well formation resistivity measurement. Specifically, the number of compensation coil systems can be set according to actual needs to realize formation resistivity measurement of different well sections.

[0087] The ninth aspect of the utility model provides a kind of transient electromagnetic wave through casing resistivity logging instrument, including shell and the coil structure being located in shell, the coil structure uses the compensation differential type coil structure described in any one of the first aspect to the eighth aspect of the utility model.

[0088] The above embodiments are used to explain the utility model, rather than limit the utility model, and any modification and change made to the utility model within the spirit and protection scope of the claims falls within the protection scope of the utility model.

Claims

1. A compensated differential coil configuration for measuring transient electromagnetic wave through casing resistivity, characterized in that, The coil structure comprises a transmitting coil and at least one compensation coil system, the compensation coil system comprises a first receiving coil and a second receiving coil arranged in sequence, the transmitting coil and the second receiving coil are forward winding, the first receiving coil is reverse winding as a compensation coil.

2. The compensated differential coil structure of claim 1, wherein, The compensation coil system comprises a first receiving coil, a second receiving coil and a third receiving coil arranged in sequence, the first receiving coil is adjacent to the transmitting coil, the first receiving coil and the third receiving coil are reverse winding as compensation coils, and the second receiving coil is forward winding.

3. The compensated differential coil structure of claim 1, wherein, The compensation coil system comprises N groups, N≥2, the transmitting coil, the first compensation coil system to the Nth compensation coil system are arranged in sequence, each compensation coil system comprises a first receiving coil, a second receiving coil and a third receiving coil arranged in sequence, the first receiving coil and the third receiving coil are reverse winding as compensation coils, and the second receiving coil is forward winding, the first receiving coil of the first compensation coil system is adjacent to the transmitting coil, and the third receiving coil of the previous compensation coil system is adjacent to the first receiving coil of the next compensation coil system in the adjacent two compensation coil systems.

4. A compensated differential coil structure as claimed in claim 2 or 3, wherein, The coil structure further comprises a symmetric compensation coil system, the symmetric compensation coil system comprises a fourth receiving coil and a fifth receiving coil, the two receiving coils are symmetrically arranged on both sides of the transmitting coil, the fourth receiving coil is between the transmitting coil and the first receiving coil and is forward winding, and the fifth receiving coil is reverse winding as a compensation coil.

5. The compensated differential coil structure of claim 1, wherein, The compensation coil system comprises a first receiving coil and a second receiving coil, the first receiving coil is adjacent to the transmitting coil, the first receiving coil is reverse winding as a compensation coil, and the second receiving coil is forward winding.

6. The compensated differential coil structure of claim 1, wherein, The compensation coil system comprises N groups, N≥2, the transmitting coil, the first compensation coil system to the Nth compensation coil system are arranged in sequence, each compensation coil system comprises a first receiving coil and a second receiving coil connected in sequence, the first receiving coil is reverse winding as a compensation coil, and the second receiving coil is forward winding, the first receiving coil of the first compensation coil system is adjacent to the transmitting coil, and the second receiving coil of the previous compensation coil system is adjacent to the first receiving coil of the next compensation coil system in the adjacent two compensation coil systems.

7. A compensated differential coil structure as claimed in claim 5 or 6, characterised in that, The coil structure further comprises a symmetric compensation coil system, the symmetric compensation coil system comprises a third receiving coil and a fourth receiving coil, the two receiving coils are symmetrically arranged on both sides of the transmitting coil, the third receiving coil is between the transmitting coil and the first receiving coil and is forward winding, and the fourth receiving coil is reverse winding as a compensation coil.

8. A transient electromagnetic borehole resistivity logging instrument characterized by, The coil structure comprises a transmitting coil and at least one compensation coil system, the compensation coil system comprises a first receiving coil and a second receiving coil arranged in sequence, the transmitting coil and the second receiving coil are forward winding, the first receiving coil is reverse winding as a compensation coil.

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