Casing well acoustic-electromagnetic combined logging probe structure and logging method

Abstract

The invention belongs to the field of petroleum engineering well logging construction, and discloses a cased well acoustic-electromagnetic combined well logging probe structure and a well logging method.The probe structure comprises a magnetic well logging unit, a magnetic field distribution measuring unit, an array waveform measuring unit and a high-frequency sound wave emission probe which are fixedly connected in sequence. According to the probe structure, measurement of a magnetic field and measurement of an electric field are combined together in a transient response mode, acoustic-electromagnetic combined measurement is achieved at the same time, effective acoustic-electromagnetic measurement is achieved according to different receiving coil positions and arrays in the probe structure, the magnetic signal source distance is closest, the electric signal source distance is medium, the acoustic signal source distance is longest, and the measurement accuracy is high. The three parts are organically combined together and highly integrated.

Description

Technical Field

[0001] This application belongs to the field of logging operations in petroleum engineering, and particularly relates to a structure of an acoustic-electromagnetic combined logging probe for cased wells and a logging method. Background Art

[0002] Transcasing resistivity transient electromagnetic logging, transcasing acoustic logging, and casing magnetic logging can all be measured in a transient manner, where transient electric and magnetic fields coexist. The magnetic permeability and conductivity of the casing are very high, which has a great impact on electrical signals. Measuring the transient electromagnetic response magnetic field at the zero source distance of the casing can detect the casing characteristics. Increasing the source distance to measure the transient response of the cased well can measure the conductivity of the formation. Placing an acoustic receiving probe outside the receiving coil can measure the longitudinal and transverse wave slowness of the formation and the cementing quality. Magnetostrictive materials can not only increase the magnetic field energy storage but also excite vibrations, and can receive electromagnetic and acoustic fields simultaneously, enabling the measurement of casing corrosion, cementing, formation longitudinal and transverse wave slowness and resistivity, and the resistivity distribution around the well in a cased well. Based on the acoustic-electromagnetic logging principle, by designing the structure of the logging probe and integrating multiple transient electromagnetic field detection systems, an integrated instrument can be provided for deep well drilling and logging after casing installation under high pressure. Summary of the Invention

[0003] In order to overcome the defects existing in the above-mentioned prior art, the purpose of this application is to provide a structure of an acoustic-electromagnetic combined logging probe for cased wells and a logging method, which unify the three logging methods into one probe structure using the transient electromagnetic response, and realize the integration of the three logging methods in cased well logging.

[0004] To achieve the above purpose, this application provides the following technical solutions:

[0005] A structure of an acoustic-electromagnetic combined logging probe for cased wells includes a magnetic logging unit, a magnetic field distribution measurement unit, an array waveform measurement unit, and a high-frequency acoustic emission probe that are fixedly connected in sequence.

[0006] The magnetic logging unit includes a low-frequency emission probe centrally arranged in the cased well. The low-frequency emission probe consists of an emission coil and an internal magnetic core. A first receiving coil and a second receiving coil are arranged on the skeleton of the emission coil. A third receiving coil and a fourth receiving coil are arranged at both ends of the low-frequency emission probe.

[0007] On the side of the fourth receiving coil away from the low-frequency emission probe, a plurality of receiving coils are provided, which form a first receiving array with the fourth receiving coil. The parameters of each receiving coil in the first receiving array are the same.

[0008] The magnetic field distribution measurement unit includes a first receiving array and a second receiving array. The second receiving array is located on the side of the first receiving array away from the low-frequency emission probe. The second receiving array includes a plurality of receiving coils with the same parameters.

[0009] The array waveform measurement unit is located on the side of the second receiving array away from the first receiving array. The array waveform measurement unit includes multiple acoustic wave receiving probes with consistent parameters.

[0010] The high-frequency acoustic wave transmitting probe is located on the side of the array waveform measurement unit away from the second receiving array.

[0011] Adjacent receiving coils and transmitting coils, and between two adjacent receiving coils are connected by non-magnetic conductive connection blocks.

[0012] Further, the first receiving coil and the second receiving coil are symmetrically arranged with the center of the transmitting coil as the symmetry point.

[0013] The third receiving coil and the fourth receiving coil are symmetrically arranged with the center of the transmitting coil as the symmetry point.

[0014] The first receiving coil, the second receiving coil, the third receiving coil, and the fourth receiving coil are coaxial with the transmitting coil, and have the same number of turns around the coil and consistent parameters.

[0015] Further, a magnetic core is placed inside the framework of the second receiving array.

[0016] Further, the excitation frequency of the high-frequency acoustic wave transmitting probe is designed based on the natural frequency of the casing wave. The response of the vibration excited by the high-frequency acoustic wave transmitting probe in the cased well is mainly the casing wave.

[0017] On the other hand, the present application discloses a method for acoustic-electromagnetic combined logging in a cased well, based on the above logging probe structure.

[0018] Further, the logging method includes:

[0019] Measuring the magnetic permeability and thickness of the casing using the magnetic logging unit;

[0020] Measuring the array response waveform using the magnetic field distribution measurement unit to describe the spatial distribution of formation conductivity;

[0021] Measuring the array waveform using the array waveform measurement unit to evaluate the cementing quality.

[0022] Further, measuring the magnetic permeability and thickness of the casing using the magnetic logging unit includes:

[0023] Using the transmitting coil and the casing to form a magnetic circuit, and obtaining the equivalent parameters of the casing thickness through the magnetic resistance calculation formula of the casing to describe the loss and corrosion of the casing.

[0024] Further, measuring the array response waveform using the magnetic field distribution measurement unit to describe the spatial distribution of formation conductivity includes:

[0025] Measure the first array response waveform using a first receiving array. The first array response waveform includes direct electromagnetic induction at different source distances and the transient response of a cased well. The response peak of the direct electromagnetic induction reflects the casing characteristics, the attenuation response of the direct electromagnetic induction reflects the conductivity of the casing and the formation, and the effective amplitude of the transient response of the cased well reflects the sensitivity of the formation.

[0026] Measure the second array response waveform using a second receiving array. The second array response waveform is used to describe the variation of formation eddy currents over time. The conductivity of formations at different radial depths is obtained from the responses re-excited by the formation eddy currents at different times.

[0027] Describe the spatial distribution of formation conductivity based on the first array response waveform and the second array response waveform.

[0028] Furthermore, measure the array waveform using an array waveform measurement unit to evaluate the cementing quality, including:

[0029] Measure the array waveform using an array waveform measurement unit. The array waveform is the response waveform of the cased well.

[0030] Obtain the time difference dispersion curve from the array waveform.

[0031] Separate the casing wave and the formation longitudinal wave in the time difference dispersion curve, and use the casing wave to evaluate the cementing quality.

[0032] Furthermore, use a transmitting coil to excite the built-in magnetic core to generate low-frequency vibrations through telescopic deformation, so that the cased well generates a response wave.

[0033] Use a high-frequency acoustic wave transmitting probe to excite vibrations, so that the response in the cased well is mainly the casing wave.

[0034] The technical effects and advantages of this application:

[0035] 1. The probe structure of this application combines the measurement of the magnetic field and the measurement of the electric field through the transient response method, and simultaneously realizes the combined measurement of sound, electricity and magnetism. Effective measurements of sound, electricity and magnetism are achieved based on the positions and arrays of different receiving coils in the probe structure. The magnetic signal has the closest source distance, the electrical signal has a medium source distance, and the acoustic signal has the longest source distance. The three are organically combined and highly integrated.

[0036] 2. This application uses a high-frequency transmitting probe to excite the resonant casing wave, obtains the time difference dispersion curve and the attenuation coefficient dispersion curve through the Prony method, and realizes the quantitative detection of cementing quality by using the monotonic relationship between the attenuation coefficient of the casing wave and the equivalent water layer thickness at the I interface. And retain the waveforms at 3-foot and 5-foot source distances, which is compatible with ordinary acoustic amplitude logging and retains the waveforms required for the original cementing quality evaluation.

[0037] 3. This application utilizes the low-frequency vibration excited by magnetostriction to measure the second Stoneley wave that appears when the bonding of the I interface in the cased well is very poor, and can judge the severe channeling situation.

[0038] 4. This application places coils in the sound insulation part of the long-spacing acoustic wave to measure the formation resistivity and casing permeability, effectively utilizes the spatial length, realizes the integration of different logging methods, shortens the instrument length, and is beneficial to actual construction and measurement in horizontal wells.

[0039] 5. This application designs a high-frequency probe based on the natural frequency and resonance characteristics of the casing wave to excite the resonance response of the cased well. Using the casing wave and formation longitudinal wave waveforms in the first arrival waveform of array acoustic logging, through the improved matrix method, the dispersion curves of travel time and attenuation coefficient are obtained simultaneously. The travel time is used to determine the casing wave, and the quantitative relationship between the attenuation coefficient of the casing wave and the equivalent thickness of the microcracks is used to evaluate the cementing quality. The original signals utilized are numerous and sufficient, transforming the evaluation of cementing quality from qualitative acoustic amplitude logging to quantitative description of attenuation coefficient.

[0040] 6. This application changes the magnetic logging from single-frequency steady-state measurement to transient and continuous spectrum measurement, obtains a broadband magnetic field response, and improves the spatial resolution of casing magnetic measurement through the response waveform differences at different positions on the transmitting coil skeleton.

[0041] 7. This application uses the spatial variation process of the transient electromagnetic field received by the array receiving coil for the processing of formation conductivity, records the transient electromagnetic response in all directions, develops the formation conductivity information in the array transient response waveform from multiple angles, and fully utilizes the time-varying response to calculate the distribution of formation conductivity at different radial depths.

[0042] 8. This application integrates long-spacing array acoustic logging and through-casing resistivity logging together. They are excited by the same transmitting probe, and the two physical fields are simultaneously excited by the same transmitting system. According to their respective equivalent parameters, different excitation waveforms are formed. However, both propagate and diffuse in the same model at the same time, the measured model is exactly the same, the physical field is distributed in the same model, the characteristics of the model are recorded by the two physical fields, the formation information of different physical fields is correlated, and the same model is measured from different sides, showing different physical field responses.

[0043] Other features and advantages of this application will be described in the subsequent specification, and part of them will become obvious from the specification or be understood by implementing this application. The objectives and other advantages of this application can be achieved and obtained through the structures pointed out in the specification, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1It is a schematic structural diagram of the acoustic electromagnetic combined logging probe structure of the present application;

[0045] Figure 2 It is the received waveforms of coils with different source distances inside a 5.5-inch casing;

[0046] Figure 3 It is the transient electromagnetic response waveforms of formations at different radial depths in the formation of a 5.5-inch casing well;

[0047] Figure 4 It is the moment when the formation eddy current is the largest in the transient electromagnetic response of formations at different radial depths in the formation of a 5.5-inch casing well;

[0048] Figure 5 It is the corresponding relationship diagram between the moment when the formation eddy current is the largest at different radial depths in the formation of a 5.5-inch casing well and the radial depth;

[0049] Figure 6 It is the time-depth relationship diagram of an open hole well;

[0050] Figure 7 It is the actual logging waveforms of receiving coils with four different source distances inside a 5.5-inch casing well;

[0051] Figure 8 It is the time difference dispersion curve of the acoustic wave response in the well when the cementing quality of the I interface in a 7-inch casing well is poor;

[0052] Figure 9 It is the actual casing well logging waveform, the first wave waveform, and the time difference dispersion curve after matrix method processing;

[0053] Figure 10 It is the mode wave distribution inside the casing well when the water layer thickness changes with poor cementing at the I interface of the simulated casing well;

[0054] Figure 11 It is the two-dimensional spectrum of the response inside the casing for two kinds of casing thicknesses.

[0055] Reference numerals: 1. Third receiving coil; 2. Transmitting coil; 3. First receiving coil; 4. Second receiving coil; 5. Fourth receiving coil; 6. First receiving array; 7. Second receiving array; 8. Array waveform measuring unit; 9. High-frequency acoustic wave transmitting probe. Detailed implementation manners

[0056] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0057] As Figure 1 shown, the present application provides a structure of a combined acoustic-electromagnetic logging tool for cased wells, including a magnetic logging unit, a magnetic field distribution measurement unit, an array waveform measurement unit, and a high-frequency acoustic wave transmitting probe 9 that are fixedly connected in sequence.

[0058] The magnetic logging unit includes a low-frequency transmitting probe disposed in the center of the cased well. The low-frequency transmitting probe is composed of a transmitting coil 2 and an internal magnetic core. A first receiving coil 3 and a second receiving coil 4 are disposed on the skeleton of the transmitting coil 2. A third receiving coil 1 and a fourth receiving coil 5 are disposed at both ends of the low-frequency transmitting probe.

[0059] On the side of the fourth receiving coil 5 away from the low-frequency transmitting probe, a plurality of receiving coils are provided, which form a first receiving array 6 with the fourth receiving coil 5. The parameters of the receiving coils in the first receiving array 6 are the same.

[0060] The magnetic field distribution measurement unit includes a first receiving array 6 and a second receiving array 7. The second receiving array 7 is located on the side of the first receiving array 6 away from the low-frequency transmitting probe. The second receiving array 7 includes a plurality of receiving coils with the same parameters.

[0061] The array waveform measurement unit 8 is located on the side of the second receiving array away from the first receiving array. The array waveform measurement unit 8 includes a plurality of acoustic wave receiving probes with the same parameters.

[0062] The high-frequency acoustic wave transmitting probe 9 is located on the side of the array waveform measurement unit 8 away from the second receiving array 7.

[0063] Adjacent receiving coils and the transmitting coil 2, and between adjacent two receiving coils are connected by non-magnetic conductive connection blocks.

[0064] In some embodiments of the present application, the first receiving coil 3 and the second receiving coil 4 are symmetrically arranged with the center of the transmitting coil 2 as the symmetry point.

[0065] The third receiving coil 1 and the fourth receiving coil 5 are symmetrically arranged with the center of the transmitting coil 2 as the symmetry point.

[0066] The first receiving coil 3, the second receiving coil 4, the third receiving coil 1, and the fourth receiving coil 5 are coaxial with the transmitting coil 2, and have the same number of turns and the same parameters.

[0067] In some embodiments of the present application, a magnetic core is placed inside the skeleton of the second receiving array.

[0068] In some embodiments of the present application, the excitation frequency of the high-frequency acoustic wave transmitting probe 9 is designed according to the natural frequency of the casing wave. The response of the vibration excited by the high-frequency acoustic wave transmitting probe 9 in the cased well is mainly the casing wave.

[0069] On the other hand, the present application discloses a combined acoustic-electromagnetic logging method for cased wells, and the logging method is based on the above-mentioned logging probe structure.

[0070] In some embodiments of the present application, the logging method includes:

[0071] Measuring the magnetic permeability and thickness of the casing using a magnetic logging unit;

[0072] Measuring the array response waveform using a magnetic field distribution measurement unit to describe the spatial distribution of formation conductivity;

[0073] Measuring the array waveform using an array waveform measurement unit to evaluate the cementing bond quality.

[0074] In some embodiments of the present application, measuring the magnetic permeability and thickness of the casing using a magnetic logging unit includes:

[0075] Using the transmitting coil 2 and the casing to form a magnetic circuit, and obtaining the equivalent parameter of the casing thickness through the magnetic resistance calculation formula of the casing to describe the loss and corrosion of the casing.

[0076] Specifically, the 0-source distance response waveform (the waveform with the largest amplitude) of a 5.5-inch casing is as Figure 2 shown in a. The response reaches a maximum value instantaneously at conduction and then monotonically decays with time. The response waveforms received by the first receiving coil 3 and the second receiving coil 4, and the third receiving coil 1 and the fourth receiving coil 5 have opposite polarities and equal waveforms; when there is an abnormality in the casing, the magnetic fluxes passing through the two sets of symmetric receiving coils are inconsistent, and there is a difference between the two waveform signals, and the response difference shows the casing abnormality. The maximum amplitude of the response waveform of the casing has a monotonic relationship with the equivalent thickness of the casing, and the change shape of the response waveform depicts the abnormality of the casing.

[0077] In some embodiments of the present application, measuring the array response waveform using a magnetic field distribution measurement unit to describe the spatial distribution of formation conductivity includes:

[0078] Measuring the first array response waveform using the first receiving array 6. The first array response waveform includes direct electromagnetic induction and transient response of the cased well at different source distances. The response peak of the direct electromagnetic induction reflects the casing characteristics, the attenuation response of the direct electromagnetic induction reflects the conductivity of the casing and the formation, and the effective amplitude of the transient response of the cased well reflects the sensitivity of the formation;

[0079] Measuring the second array response waveform using the second receiving array 7. The second array response waveform is used to describe the change of formation eddy current with time, and the conductivity of formations at different radial depths is obtained through the response re-excited by the formation eddy current at different times;

[0080] Describing the spatial distribution of formation conductivity based on the first array response waveform and the second array response waveform.

[0081] Specifically, the first receiving array 6 and the second receiving array 7 form a spatial distribution measurement system for the in-well transient electromagnetic field. Each receiving coil in the first receiving array 6 and the second receiving array 7 receives a transient waveform. The first array response waveform measured by the first receiving array 6 is as Figure 2 b, Figure 2 as shown in c. The pulse amplitude at the front mainly shows the casing characteristics. The magnetic permeability of the casing is very large. Most of the electromagnetic induction lines excited from the middle of the transmitting coil 2 pass through the casing to form a magnetic circuit. As the source distance increases, the intensity of the magnetic force lines along the axial direction decreases rapidly, and the directly coupled electromagnetic induction signal, that is, the pulse amplitude, decreases rapidly and approaches 0 at a certain source distance (0.4 m for a 5.5-foot casing). The subsequent waveform with slow change is the transient response of the cased well, without a directly coupled signal.

[0082] The second receiving array 7 mainly measures the transient response of the cased well. The measured second array response waveform is as Figure 2 shown in d, and the directly coupled pulse signal gradually disappears.

[0083] The shape of the transient response waveform of the cased well changes slowly. The response shape rises fast and falls slowly, which is consistent with the response waveform shape in the formation, as Figure 3 shown. The transient response of the cased well is determined by the process of the transient electromagnetic field passing through the casing.

[0084] By describing the waveform characteristics at different source distances in the formation through the first array response waveform and the second array response waveform, the eddy current response in the formation is obtained. From the response re-excited by the formation eddy current at different times, the conductivity of the formation at different radial depths is obtained. Figure 4 is the moment when the eddy current is the largest in the response of the formation at different radial depths. The response at each radial depth corresponds to such a moment, and the two constitute the Figure 5 time-depth correspondence relationship shown, and this relationship is significantly different from the Figure 6 time-depth correspondence relationship of the open-hole well. It has a time delay through the casing, and due to the relatively long time through the casing (the conductivity and magnetic permeability of the casing are large), the response change is slow, especially the response of the formation near the casing. Through this relationship, the radial depth corresponding to the main useful signal in the response at different times can be obtained. Figure 7 is the actual measured waveform at four source distances in a 5.5-inch cased well. At 0.6 m, the directly coupled response (the pulse corresponding to the excitation moment) basically disappears.

[0085] The first array response waveform and the second array response waveform together describe the spatial distribution of the transient electromagnetic field in a cased well with the source distance. This distribution can be measured and corresponds to the spatial distribution of the transient electromagnetic field in the formation. The two are connected together through equipotential surfaces. The spatial distribution in the formation is closely related to the formation conductivity. This relationship is recorded as an array response waveform along the wellbore through the coil structure. By establishing a processing method for the array response waveform, a specific example is provided for further describing the spatial distribution of the formation conductivity.

[0086] In some embodiments of the present application, an array waveform measurement unit is used to measure the array waveform and evaluate the cementing quality, including:

[0087] An array waveform measurement unit 8 is used to measure the array waveform, and the array waveform is the response waveform of the cased well;

[0088] The array waveform is processed by the matrix method or the Prony method to obtain a time difference dispersion curve;

[0089] The casing wave and the formation longitudinal wave in the time difference dispersion curve are separated, and the casing wave is used to evaluate the cementing quality.

[0090] Specifically, a long tubular, block-shaped (finally forming a long tubular) or strip-shaped magnetic core is placed inside the skeleton of the transmitting coil 2. When the transmitting coil 2 is turned on and off, the transient magnetic field excited in the magnetic core causes magnetostrictive deformation of the magnetic core to generate vibration. Because the magnetic core is relatively long, the vibration frequency in its length direction is relatively low. After passing through a certain mechanical structure in the probe, the vibration direction is converted, so that the radial vibration displacement in the response of the cased well is relatively large. The measurement of the acoustic wave time difference of the cased well when the I interface cementing is relatively poor is realized through the relatively large radial vibration displacement response. When the I interface cementing is poor, the micro-gap on the I interface is equivalently regarded as the water ring thickness to describe the cementing quality. The distribution of the extreme values of the response in the cased well along the frequency is measured when the water ring thicknesses are 5 mm (very poor cementing) and 1 mm (relatively poor cementing) respectively, where Figure 8 a is the extreme value distribution represented by the phase velocity, and the extreme values distributed along the horizontal longitudinal wave velocity line Vc and transverse wave velocity line Vs, and the velocities of its response waveforms are respectively equal to the longitudinal wave velocity and transverse wave velocity of the formation. Figure 8 b is the extreme value distribution represented by the time difference (the reciprocal of the velocity). When the cementing quality is relatively poor (equivalent water ring thickness of 1 mm), there are large sections of extreme value distributions along the formation longitudinal wave time difference line Vc and transverse wave time difference line Vs. Projecting these distributions onto the time difference will obtain the longitudinal and transverse wave time differences of the formation.

[0091] An array waveform measurement unit 8 is used to measure the array waveform. The array waveform is processed by an improved matrix method or the Prony method to obtain a time difference dispersion curve, that is, the time difference distribution. The time difference dispersion curves of the casing wave and the formation longitudinal wave are distributed in the same frequency range, such as Figure 8As shown in b, the bottom distribution is the casing wave, which is used for cementing quality evaluation, and the distribution above it is the formation longitudinal wave; Figure 9 a is the actual logging waveform and the first arrival waveform, Figure 9 b is processed by the improved matrix method Figure 9 The obtained time difference dispersion curve from a, where T is the time difference of the casing wave, used to evaluate the cementing bond quality; F is the time difference of the formation longitudinal wave, used for formation acoustic time difference measurement, and the two appear alternately. By changing the processed waveform, the obtained time difference dispersion curve also includes the distribution of the formation shear wave time difference (the straight section coinciding with the shear wave line), and thus the measurement of the formation longitudinal and shear wave time differences is obtained.

[0092] In some embodiments of the present application, the transmitting coil 2 is used to excite the built-in magnetic core to generate low-frequency vibration by telescopic deformation, so that the casing well generates a response wave;

[0093] The high-frequency acoustic wave transmitting probe 9 is used to excite vibration, so that the response in the casing well is mainly the casing wave 。

[0094] It should be noted that low-frequency excitation is beneficial to the measurement of the second Stoneley wave. As Figure 10 shown by the top three curves, from top to bottom, the water ring thicknesses are 5mm, 10mm, and 19mm respectively, which describe the acoustic waves generated in the liquid in the casing well when the water layer thickness outside the casing is relatively thick. The appearance of this mode of acoustic wave in the measured waveform often indicates serious channeling, and this feature can be used for the measurement of serious channeling in casing well cementing. The excitation frequency of the high-frequency acoustic wave transmitting probe 9 is designed according to the natural frequency of the casing wave, and the excited vibration has the casing wave as the main response in the casing well, mainly used for cementing quality detection. As Figure 8 shown, there is a peak in the response extreme value near 35kHz, and its amplitude is relatively large. It has a monotonic relationship with the water ring thickness, and its shape also changes with the water ring thickness. The peak is fitted with an exponential function to obtain the attenuation coefficient, and this attenuation coefficient also has a monotonic relationship with the water ring thickness. Using this monotonic relationship, the equivalent water ring thickness can be obtained to quantitatively evaluate the cementing quality.

[0095] Furthermore, Figure 11 is the two-dimensional spectrum of the liquid response in the casing well when the casing thickness is different. Near 15kHz, the extreme value distribution positions and amplitudes are significantly different, and these differences can be manifested by the break point positions of the time difference dispersion curve Figure 9 b, where the break point position D and the distance between the break points (the distance between two D points) can be used to evaluate the casing thickness.

[0096] Finally, it should be noted that the above are only the preferred embodiments of the present application and are not used to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A structure of a combined acoustic electromagnetic logging tool for cased wells, characterized in that, It includes a magnetic logging unit, a magnetic field distribution measurement unit, an array waveform measurement unit (8), and a high-frequency acoustic wave transmitting probe (9) that are fixedly connected in sequence. The magnetic logging unit includes a low-frequency transmitting probe centrally arranged in a cased well. The low-frequency transmitting probe is composed of a transmitting coil (2) and a built-in magnetic core. A first receiving coil (3) and a second receiving coil (4) are arranged on the skeleton of the transmitting coil (2). A third receiving coil (1) and a fourth receiving coil (5) are arranged at both ends of the low-frequency transmitting probe. On the side of the fourth receiving coil (5) away from the low-frequency transmitting probe, a plurality of receiving coils are arranged, forming a first receiving array (6) with the fourth receiving coil (5). The parameters of each receiving coil in the first receiving array (6) are the same. The magnetic field distribution measurement unit includes the first receiving array (6) and a second receiving array (7). The second receiving array (7) is located on the side of the first receiving array (6) away from the low-frequency transmitting probe. The second receiving array (7) includes a plurality of receiving coils with the same parameters. The array waveform measurement unit (8) is located on the side of the second receiving array away from the first receiving array. The array waveform measurement unit (8) includes a plurality of acoustic wave receiving probes with the same parameters. The high-frequency acoustic wave transmitting probe (9) is located on the side of the array waveform measurement unit (8) away from the second receiving array (7). Adjacent receiving coils and the transmitting coil (2), and adjacent two receiving coils are connected by non-magnetic conductive connection blocks.

2. The structure of a combined acoustic electromagnetic logging tool for cased wells according to claim 1, characterized in that, The first receiving coil (3) and the second receiving coil (4) are symmetrically arranged with the center of the transmitting coil (2) as the symmetry point. The third receiving coil (1) and the fourth receiving coil (5) are symmetrically arranged with the center of the transmitting coil (2) as the symmetry point. The first receiving coil (3), the second receiving coil (4), the third receiving coil (1), and the fourth receiving coil (5) are coaxial with the transmitting coil (2), and have the same number of turns and the same parameters.

3. The structure of a combined acoustic electromagnetic logging tool for cased wells according to claim 1, characterized in that, A magnetic core is placed inside the skeleton of the second receiving array (7).

4. The structure of a combined acoustic electromagnetic logging tool for cased wells according to claim 1, characterized in that, The excitation frequency of the high-frequency acoustic wave transmitting probe (9) is designed according to the natural frequency of the casing wave. The response of the vibration excited by the high-frequency acoustic wave transmitting probe (9) in the cased well is mainly the casing wave.

5. A method for combined acoustic electromagnetic logging in cased wells, characterized in that, The logging method is based on the logging probe structure described in any one of claims 1-4.

6. The method for combined acoustic electromagnetic logging in cased wells according to claim 5, characterized in that, It includes: Measuring the magnetic permeability and thickness of the casing using the magnetic logging unit; Measuring the array response waveform using the magnetic field distribution measurement unit to describe the spatial distribution of formation conductivity; Measuring the array waveform using the array waveform measurement unit to evaluate the cementing quality.

7. The method for combined acoustic electromagnetic logging in cased wells according to claim 6, characterized in that, The measuring the magnetic permeability and thickness of the casing using the magnetic logging unit includes: Using the transmitting coil (2) and the casing to form a magnetic circuit, and obtaining the equivalent parameter of the casing thickness through the magnetic resistance calculation formula of the casing to describe the loss and corrosion of the casing.

8. The method for combined acoustic electromagnetic logging in cased wells according to claim 6, characterized in that, The measuring the array response waveform using the magnetic field distribution measurement unit to describe the spatial distribution of formation conductivity includes: Measure the first array response waveform using the first receiving array (6), where the first array response waveform includes direct electromagnetic induction at different source distances and the transient response of the cased well. The response peak of the direct electromagnetic induction reflects the casing characteristics, the attenuation response of the direct electromagnetic induction reflects the conductivity of the casing and the formation, and the effective amplitude of the transient response of the cased well reflects the sensitivity of the formation; Measure the second array response waveform using the second receiving array (7), where the second array response waveform is used to describe the variation of formation eddy currents over time, and the conductivity of formations at different radial depths is obtained through the responses re-excited by the formation eddy currents at different times; Describe the spatial distribution of formation conductivity based on the first array response waveform and the second array response waveform.

9. The method for combined acoustic electromagnetic logging in cased wells according to claim 5, characterized in that, The method of measuring the array waveform using the array waveform measurement unit to evaluate the cementing quality includes: Measure the array waveform using the array waveform measurement unit (8), where the array waveform is the response waveform of the cased well; Obtain the time difference dispersion curve through the array waveform; Separate the casing wave and the formation longitudinal wave in the time difference dispersion curve, and use the casing wave to evaluate the cementing quality.

10. A casing well acoustic-electromagnetic combined logging method according to claim 5, characterized in that, It includes: Use the transmitting coil (2) to excite the built-in magnetic core to generate low-frequency vibration by telescopic deformation, so that the cased well generates a response wave; Use the high-frequency acoustic wave transmitting probe (9) to excite vibration, so that the response in the cased well is mainly the casing wave.

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