Rock sample crack measurement method and system based on seismoelectric effect

Abstract

The invention discloses a rock sample crack measurement method and system based on the seismoelectric effect, and relates to the field of rock sample crack measurement, and the method comprises the steps: building a rock sample crack measurement system based on the seismoelectric effect, arranging hydrophones and electrodes in an array in a vertical direction, collecting sound field and electric field signals at the two sides of a rock sample, and carrying out the measurement of the rock sample crack. And then comparing and analyzing the electric field response difference between the complete rock sample and the crack-containing rock sample by adopting a sound source and electrode synchronous movement scanning technology so as to identify the crack interface. According to the rock sample crack measurement method based on the seismoelectric effect, the seismoelectric signals excited by the double interfaces are captured at the same time through the electrodes on the two sides, and effective identification of the crack interface is achieved through the signal amplitude difference, the attenuation characteristic and the waveform characteristic.

Description

Technical Field

[0001] The present invention relates to the field of rock sample crack measurement, and in particular to a rock sample crack measurement method and system based on seismoelectric effect. Background Art

[0002] As one of the most important electrokinetic coupling mechanisms, the seismoelectric effect describes the electromagnetic field induced by seismic waves propagating through fluid-saturated porous media. It comprises two distinct seismoelectric conversion signals: the accompanying electromagnetic field generated by the seismic wave, and the interfacial electromagnetic wave generated by the seismic wave at the dielectric boundary.

[0003] Therefore, seismic exploration has the dual response characteristics of reservoir elastic parameters and electrochemical properties. It shows great application potential in the fields of oil and gas resource exploration, geological disaster warning, etc., and has received widespread attention from the geophysics community.

[0004] However, existing seismoelectric experimental research mostly focuses on a single complete interface model, and lacks systematic observation of the coupling mechanism of multi-interface systems and the seismoelectric response of fracture interfaces, which seriously affects the application of seismoelectric exploration technology in actual complex formations.

[0005] In order to solve these problems, a rock sample crack measurement method and system based on seismoelectric effect is urgently needed. Summary of the Invention

[0006] To solve the above problems, this application proposes a rock sample fracture measurement system and method based on the seismoelectric effect, which measures rock sample fractures based on multi-interface seismoelectric coupling. By constructing a fluid-rock sample-fluid model to simulate the actual reservoir double-interface structure, a double-sided electrode array and a sound source synchronous moving scanning technology are used. By comparing the electric field signals of intact rock samples and rock samples containing fractures, the waveform characteristics of the seismoelectric response signal caused by the fracture interface are obtained.

[0007] A rock sample fracture measurement system based on seismoelectric effect, comprising a signal source, a high-voltage square wave pulse source, an acoustic source, a hydrophone, electrodes, a preamplifier, a filter, a data acquisition card, a rock sample and a data processing device; The rock samples include intact rock samples and rock samples containing fractures, and the hydrophone and electrodes constitute a receiver; The sound source, hydrophone, electrodes and rock samples are arranged in a water tank; The sound source hydrophone, electrode and rock sample are level in horizontal direction; The signal source is connected to the high-voltage square wave pulse source and the data acquisition card respectively through signal lines; The high-voltage square wave pulse source is connected to the sound source via a signal line; The preamplifier is connected to the filter and the hydrophone respectively through signal lines; The filter is connected to the data acquisition card via a signal line; The data acquisition card is connected to the data processing device via a signal line.

[0008] Preferably, the signal source is used to synchronously trigger the high-voltage square wave pulse and the data acquisition card; The sound source is provided by a sound source transducer; The high-voltage square wave pulse source is used to generate a pulse signal to excite the sound source transducer after being triggered by the receiving signal source; The sound source transducer generates fluid sound waves to form a sound source after being excited; The hydrophone and the electrode respectively record the acoustic field signal and the converted electric field signal and transmit the acoustic field signal and the converted electric field signal to the preamplifier through the signal line; The preamplifier is used to gain the sound field signal and the converted electric field signal to obtain a gain sound field signal and a gain electric field signal; The filter is used to process the gain sound field signal and the gain electric field signal; The data acquisition card is used to record the processed gain sound field signal and gain electric field signal.

[0009] Preferably, a rock sample crack measurement method based on seismoelectric effect comprises the following steps: S1. Conduct experimental testing on complete rock samples to obtain complete seismic-electrical response signals; S2. Conducting experimental testing on rock samples containing fractures to obtain fracture seismoelectric response signals; S3. Compare and analyze the complete electric field response and the crack electric field response to obtain the identification result of the crack interface.

[0010] Preferably, the experimental detection steps in S1 and S2 are the same, specifically including: Step 1: The rock sample includes two fluid-solid interfaces in the fluid, and the two fluid-solid interfaces are defined as a front interface and a rear interface respectively; Step 2: Arrange receivers in the vertical direction to record vertical interface seismoelectric signals; Step 3: Arrange receivers in the horizontal direction to record the seismoelectric signals of the horizontal interface; Step 4: Integrate the vertical interface seismoelectric signal and the horizontal interface seismoelectric signal to obtain an integrated seismoelectric response signal.

[0011] Preferably, in step 2, the receivers are arranged in the vertical direction, and the specific content of recording the vertical interface seismoelectric signal is: The connecting axis between the sound source center and the rock sample center is the z-axis, the front interface of the rock sample is the r-axis, and the intersection of the r-axis and the z-axis is the origin Z0. A sound source-receiver system distributed along the z-axis is established. The sound source is Z s19.5 cm from the front interface of the rock sample; The receiver array consists of 12 measurement points, with a spacing of 1 cm between measurement points on the same layer; The directions from the front interface of the rock sample to the sound source are receiving point 6, receiving point 5, receiving point 4, receiving point 3, receiving point 2, and receiving point 1; From the rear interface of the rock sample to the sound source in the opposite direction, they are receiving point 7, receiving point 8, receiving point 9, receiving point 10, receiving point 11, and receiving point 12; During the measurement process, the sound source remains fixed, and the converted electric field signals are collected at 12 measuring points in sequence by moving the electrodes, and the sound field signals are collected at 12 measuring points in sequence by moving the hydrophone. The converted electric field signals and sound field signals constitute the vertical interface seismoelectric signals.

[0012] Preferably, in step 3, the receivers are arranged horizontally to record the specific contents of the horizontal interface seismoelectric signal: A set of electrodes is arranged on the front interface and the rear interface of the rock sample; The sound source is Z s 19.5 cm from the front interface of the rock sample; With the front interface of the rock sample as the r axis and the center of the front interface of the rock sample as the origin Z0, a sound source-receiver system distributed along the r axis is established; During the measurement, keep the sound source and the electrode moving synchronously; The electrode starts from -6 cm in the horizontal direction and moves gradually to +6 cm at intervals of 0.5 cm, forming a scanning profile with a range of 12 cm to obtain the horizontal interface seismoelectric signal.

[0013] Preferably, the specific content of the identification result of the crack interface obtained by comparative analysis of the complete electric field response and the crack electric field response in step 4 is: The detection results of the front interface of the rock sample include the seismoelectric response of the front interface and the oblique wave group excited by the crack; The detection results of the rock sample rear interface include the signal attenuation area recorded by the rear electrode, which accurately corresponds to the crack position, realizing the spatial positioning of the crack.

[0014] In summary, the rock sample fracture measurement method and system based on the seismoelectric effect of the present invention have the following advantages over traditional technologies: (1) This application addresses the problem of the lack of fracture response signal measurement in existing seismoelectric effect research. By building a high-precision seismoelectric measurement system, miniature hydrophones and electrodes are arranged in a vertical array to collect acoustic and electric field signals on both sides of the rock sample. Subsequently, a synchronous mobile scanning technology of the sound source and electrodes is used to compare and analyze the differences in the electric field responses of intact rock samples and rock samples with fractures. The double-sided electrodes can simultaneously capture the seismoelectric signals excited by the dual interfaces, and the fracture interface can be effectively identified through the difference in signal amplitude, attenuation characteristics and waveform characteristics. (2) This application reveals the propagation law of multi-interface seismoelectric wave fields, providing experimental technical support for reservoir interface positioning and formation fracture identification, and has important application value in oil and gas exploration, geological disaster early warning and other fields; (3) This application not only verifies the spatial detectability of multi-interface seismoelectric signals, but also provides a high-precision experimental method for locating complex reservoir interfaces and identifying fractures, significantly enhancing the practical value of seismoelectric effects in resource exploration projects.

[0015] The technical method of the present invention is further described in detail below through the accompanying drawings and examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the seismoelectric measurement system of the present invention; Figure 2 This is a schematic diagram of the vertical arrangement of receivers according to the present invention; Figure 3 This is a schematic diagram of the horizontal arrangement of receivers according to the present invention; Figure 4 This is a schematic diagram of rock sample cracks in the present invention. Figure 4 (a) is the top view of the rock sample. Figure 4 Middle (b) is a stereogram of the rock sample; Figure 5 The invention provides a method for measuring the seismic electric response signal of a rock sample containing fractures; Figure 6 is the measured acoustic and electrical signals of receiving points 1 to 6 of the present invention, Figure 6 (a) is the measured sound field signal. Figure 6 Middle (b) is the measured electric field signal; Figure 7 The measured acoustic and electrical signals at receiving points 7 to 12 of the present invention are: Figure 7 (a) is the measured sound field signal. Figure 7 Middle (b) is the measured electric field signal; Figure 8 is the seismoelectric signal of the front interface of the present invention, Figure 8 (a) is the front interface electric field of the complete rock sample. Figure 8 Middle (b) is the front interface electric field of the rock sample with fractures; Figure 9 is the seismoelectric signal of the rear interface of the present invention, Figure 9 (a) is the front interface electric field of the complete rock sample. Figure 9 Middle (b) shows the front interface electric field of a rock sample containing fractures. DETAILED DESCRIPTION

[0017] The technical method of the present invention is further described below through the accompanying drawings and embodiments. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and values described in these embodiments do not limit the scope of this application.

[0018] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present disclosure, its application, or uses.

[0019] Technologies, systems, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0020] In all examples shown and discussed herein, any specific values should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0021] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0022] A rock sample fracture measurement system based on seismoelectric effect, comprising a signal source, a high-voltage square wave pulse source, an acoustic source, a hydrophone, electrodes, a preamplifier, a filter, a data acquisition card, a rock sample and a data processing device; The rock samples include intact rock samples and rock samples with fractures, and the hydrophone and electrodes constitute the receiver; The sound source, hydrophone, electrodes and rock samples are set in the water tank (the rock sample is fixed at a fixed height by a spacer).

[0023] The sound source hydrophone, electrode and rock sample are level in horizontal direction.

[0024] The signal source is connected to the high-voltage square wave pulse source and the data acquisition card through signal lines.

[0025] The high-voltage square wave pulse source is connected to the sound source through a signal line.

[0026] The preamplifier is connected to the filter and the hydrophone through signal lines respectively.

[0027] The filter is connected to the data acquisition card through a signal line.

[0028] The data acquisition card is connected to the data processing device through a signal line.

[0029] Furthermore, the signal source is used to synchronously trigger the high voltage square wave pulse and the data acquisition card.

[0030] The sound source is provided by a sound source transducer.

[0031] The high-voltage square wave pulse source is used to generate a pulse signal to excite the sound source transducer after being triggered by the receiving signal source.

[0032] When the sound source transducer is excited, fluid sound waves are generated to form a sound source.

[0033] The hydrophone and the electrode record the acoustic field signal and the converted electric field signal respectively and transmit the acoustic field signal and the converted electric field signal to the preamplifier through the signal line.

[0034] The preamplifier is used to gain the sound field signal and the converted electric field signal to obtain a gain sound field signal and a gain electric field signal.

[0035] The filter is used to process the gain sound field signal and the gain electric field signal.

[0036] The data acquisition card is used to record the processed gain sound field signal and gain electric field signal.

[0037] Specifically, if Figure 1 As shown, it consists of a signal source HP3314A, a high-voltage square wave pulse source 5077, a sound source, a BK hydrophone, electrodes, a power amplifier 5660C, a filter (NF3628) and a NI data acquisition card.

[0038] During the experiment, the signal source synchronously triggers the high-voltage square wave pulse and the data acquisition card. Then the high-voltage pulse transmitter (100V) generates a 100kHz single-cycle square wave pulse signal to excite the sound source transducer, thereby generating fluid sound waves.

[0039] The BK hydrophone and electrodes record the acoustic field signal and the converted electric field signal, respectively. Because the converted seismoelectric signal is very weak, typically at the microvolt level, the measured electric field signal is amplified by a preamplifier with a gain of 60dB (1000 times), while the acoustic field signal is amplified by 40dB (100 times).

[0040] The amplified seismic signal and sound field signal are processed by bandpass filter and then Figure 1 High-precision NI data acquisition card recording in.

[0041] During the experimental measurement process, the NI data acquisition card was set to a sampling rate of 1 Ms / s and a 22-bit resolution to meet the sampling requirements. Finally, the collected acoustic and electric field signals were exported and processed and analyzed using plotting software.

[0042] A rock sample crack measurement method based on seismoelectric effect comprises the following steps: S1. Conduct experimental testing on complete rock samples to obtain complete seismoelectric response signals, which provide benchmark data for identifying rock sample cracks.

[0043] S2. Experimental testing is performed on rock samples containing fractures to obtain the seismic electric response signal of the fractures.

[0044] Furthermore, the experimental testing steps in S1 and S2 are the same, including: Step 1: The rock sample forms two fluid-solid interfaces in the fluid. Therefore, the rock sample includes two fluid-solid interfaces in the fluid. The two fluid-solid interfaces are defined as the front interface and the rear interface, respectively.

[0045] Step 2: Arrange the receivers in the vertical direction to record the vertical interface seismoelectric signals.

[0046] Further, such as Figure 2 As shown in the figure, in step 2, the receivers are arranged in the vertical direction, and the specific content of the vertical interface seismoelectric signal recorded is: The connecting axis between the sound source center and the rock sample center is the z-axis, the front interface of the rock sample is the r-axis, and the intersection of the r-axis and the z-axis is the origin Z0. A sound source-receiver system distributed along the z-axis is established.

[0047] The sound source is Z s 19.5 cm from the front interface of the rock sample.

[0048] The receiver array consists of 12 measurement points, and the spacing between measurement points in the same layer is 1 cm.

[0049] The directions from the front interface of the rock sample to the sound source are receiving point 6, receiving point 5, receiving point 4, receiving point 3, receiving point 2, and receiving point 1.

[0050] From the rear interface of the rock sample to the sound source in the opposite direction, there are receiving points 7, 8, 9, 10, 11, and 12.

[0051] During the measurement process, the sound source remains fixed, and the converted electric field signals are collected at 12 measuring points in sequence by moving the electrodes, and the sound field signals are collected at 12 measuring points in sequence by moving the hydrophone. The converted electric field signals and sound field signals constitute the vertical interface seismoelectric signals.

[0052] Step 3: Arrange receivers horizontally to record horizontal interface seismoelectric signals.

[0053] Further, such as Figure 3 As shown, in step 3, the receivers are arranged horizontally, and the specific content of the horizontal interface seismoelectric signal recorded is: A set of electrodes is arranged on the front interface and the rear interface of the rock sample.

[0054] The sound source is Z s 19.5 cm from the front interface of the rock sample.

[0055] With the front interface of the rock sample as the r-axis and the center of the front interface of the rock sample as the origin Z0, a sound source-receiver system distributed along the r-axis is established.

[0056] Unlike the vertical measurement method, during the measurement process, the horizontal layout requires that the sound source and the electrode move synchronously, and the two are always aligned along the coaxial line to maintain the same relative position in space.

[0057] The electrode starts from -6 cm in the horizontal direction and moves gradually to +6 cm at intervals of 0.5 cm, forming a scanning profile with a range of 12 cm to obtain the horizontal interface seismoelectric signal.

[0058] Step 4: Integrate the vertical interface seismoelectric signal and the horizontal interface seismoelectric signal to obtain an integrated seismoelectric response signal.

[0059] S3. Compare and analyze the complete electric field response and the crack electric field response to obtain the identification result of the crack interface.

[0060] Furthermore, in S3, the specific content of the identification result of the crack interface obtained by comparing and analyzing the complete electric field response and the crack electric field response is as follows: The detection results of the front interface of the rock sample include the seismoelectric response of the front interface and the oblique wave group excited by the crack.

[0061] The detection results of the rock sample rear interface include the signal attenuation area recorded by the rear electrode, which accurately corresponds to the crack position, realizing the spatial positioning of the crack.

[0062] In order to systematically carry out seismic detection of cracked rock samples, this application prefabricated 1.5mm wide cracks based on the central axis of the rock sample. The processing flow is as follows: Figure 4 As shown in (a): Starting from point A, 3 cm to the left of the axis of the front surface, the sample is cut at a 45° angle and extended to point B, 3 cm to the right of the axis of the rear surface, forming a crack with a horizontal length of 6 cm. During processing, the bottom 2 cm section is retained as a support structure to maintain the integrity of the rock sample. The final morphology of the prepared cracked rock sample is as follows Figure 4 As shown in (b).

[0063] Seismic signal acquisition is performed on rock samples containing fractures. Figure 5 As shown, the sound source and the electrode perform a 12cm horizontal scan along the front interface of the rock sample. The receiving array starts at the axis position of -6cm, and the process of moving to the right covers three characteristic segments: the front non-crack area (0-3cm), the crack area (3-9cm), and the distal non-crack area (9-12cm). In order to enhance the accuracy of crack identification, this application adopts a 0.1cm ultra-high-density spatial sampling method to systematically characterize the seismoelectric wave field response characteristics of the crack interface by collecting 121 waveform signals on the front interface. In addition, when measuring the electric field signal on the rear side, this application sets the step distance of the electrode to 0.2cm. By comparing the seismoelectric response signal of the crack with the seismoelectric response signal of the intact rock sample, the shape and position information of the crack can be obtained.

[0064] (1) Seismoelectric wave field when electrodes are arranged in the vertical direction.

[0065] The hydrophones are placed at receiving points 1 to 6 to measure the sound field signal, with a spacing of 1 cm between each receiving point. The measurement results are as follows: Figure 6 As shown in (a), wave group A is the sound wave that directly reaches the fluid. Immediately after wave group A, there is a sound wave group B reflected from the front interface with an opposite slope.

[0066] Next, similarly place electrodes at receiving points 1 to 6 to measure the electric field signal. Figure 6 It can be found in (b) that the arrival time of the experimentally measured wave group signal EM1 is the same as the time when the direct sound wave arrives at the front interface, and it hardly changes with the change of the electrode position, indicating that the EM1 signal is the seismoelectric response signal generated by the front interface. As the electrode moves away from the front interface, the amplitude of the EM1 signal also decreases. This application extracts the amplitude of the EM1 signal. The results show that the amplitude of the EM1 signal of the 6th waveform is the largest (17.1mV), and the amplitude of the EM1 signal of the 1st waveform is the smallest (3.2mV). The amplitude of the EM1 signal decays exponentially with the increase of the distance between the electrode and the interface. There are some seismoelectric signals with smaller amplitudes after the wave group EM1. Figure 6 By calculating their arrival times, it can be inferred that EM2, EM3, and EM4 are the seismoelectric interface responses generated by the transmitted longitudinal wave propagating to the rear interface, the longitudinal wave returning to the front interface, and the longitudinal wave propagating to the rear interface again, respectively.

[0067] In the relevant studies on seismic-electrical interface response, most of the electrodes are placed near the front interface close to the sound source, but the electric field of the rear interface is lacking. Therefore, this application places hydrophones and electrodes at receiving points 7 to 12 on the rear side of the rock sample to measure and compare the acoustic and electric field signals. The hydrophone records the acoustic field signal on the rear side of the rock sample, such as Figure 7 As shown in (a) in the figure, it can be observed that the transmitted sound wave signal of the rear interface is not clearly displayed. By analyzing the waveform signal of the receiving point 7 closest to the rear interface, it can be found that its signal amplitude is 0.23V. However, the amplitude of the direct sound wave signal of the front interface receiving point 6 is 1.53V. Comparing the sound field signals on the rear and front sides, it can be seen that their amplitude ratio is about 0.15. Therefore, after the sound wave penetrates the front and rear interfaces, the energy will attenuate sharply, which leads to a decrease in the effective sound wave amplitude received by the hydrophone. Therefore, the transmitted sound wave of the rear interface is masked by the environmental noise and cannot clearly and effectively present the interface position information.

[0068] from Figure 7In (b) (electric field), it can be found that the first wave group signal EM1 arrives at the receiving points 7 to 12 almost simultaneously. This is the seismoelectric response generated by the direct sound wave at the front interface. The arrival time of the second wave group signal EM2 measured in the experiment is exactly when the transmitted longitudinal wave reaches the rear interface of the rock sample, indicating that this signal is the seismoelectric response generated by the transmitted longitudinal wave propagating to the rear interface. This application extracts Figure 7 The EM2 signal amplitude in (b) shows that the signal amplitude at receiving point 7 is the largest (4.9 mV) and the signal amplitude at receiving point 12 is the smallest (1.4 mV). Furthermore, the EM2 signal amplitude also decays exponentially with increasing distance. Comparing the EM2 signal amplitude at receiving point 7 (4.9 mV) with the EM1 signal amplitude at receiving point 6 (17.1 mV), we can see that the amplitude ratio of the seismoelectric conversion signal at the rear interface to the conversion signal at the front interface is approximately 0.286. This is because sound waves attenuate when propagating in the rock sample, so the converted seismoelectric signal EM1 generated by the direct fluid sound wave at the front interface is significantly stronger than the converted seismoelectric signal EM2 generated by the transmitted sound wave at the rear interface.

[0069] In order to further explore the experimental acoustic and electrical signals of the rear interface, Figure 7 Middle (a) (sound field) and Figure 7 By comparing and analyzing (b) (electric field), we can find that Figure 7 The acoustic field experimental data in (a) does not effectively reflect the interface information of the rock sample. Figure 7 In (b), the acoustic wave generates distinct converted seismoelectric signals EM1 and EM2 at both the front and rear interfaces. The arrival times of these two interface signals and the propagation speed of the acoustic wave in the fluid and rock sample allow the position of the two interfaces to be inferred. This demonstrates the feasibility and superiority of using interfacial electromagnetic waves for formation exploration. Therefore, interfacial electromagnetic waves hold great promise for detecting formation interfaces and exploring for oil and gas reservoirs.

[0070] (2) Seismoelectric response signal of rock samples containing fractures: Figure 8 (a) shows the horizontal electric field measurement results of the front interface of the intact rock sample. The seismoelectric signal wave group appears at around 0.13ms, which confirms the effectiveness of seismoelectric technology in locating the front interface. Figure 8 In (b), the fractured rock sample also has front interface waveform characteristics during the same period of time, and its phase and amplitude are highly consistent with those of the intact sample. When the electrode scans in the non-fracture area (-6cm to -3cm), the first 30 data records only a single front interface signal ( Figure 8In traces 1-30 (b), no subsequent wavefield disturbances were detected. However, when the measurement point was moved to the fracture region (starting at trace 31), an oblique wave train with a distinct time-lag characteristic appeared behind the front interface signal. Comparative analysis revealed that intact rock samples did not exhibit these oblique wavefield characteristics. Under experimental conditions that ensured that the acoustic-electric system parameters and the spatial relationship between the rock sample and the sound source were not fixed, the oblique wave group was confirmed to be a seismoelectric conversion signal excited by the fracture interface.

[0071] Figure 9 Middle (a) shows the electric field signal of the back interface of the intact rock sample measured by horizontally arranged electrodes. It can be seen that the seismoelectric response signal of the back interface excitation is generated at around 0.17ms. Figure 9 Figure (b) shows the electric field signal at the rear interface of a fractured rock sample measured using horizontally arranged electrodes. When the receiver does not enter the fracture zone, the seismoelectric response signal at the rear interface is clearly discernible. However, when the electrode is moved to the area behind the fracture, the seismoelectric signal attenuates. Analysis shows that acoustic wave scattering caused by the fracture significantly reduces the effective acoustic energy propagating to the rear interface, resulting in a significant decrease in the seismoelectric conversion efficiency at the rear interface and a partial weakening of the electric field at the rear interface. As the electrode continues to move right beyond the fracture zone, the acoustic wave propagation path avoids the fracture structure, and the waveform at the end measurement point returns to normal levels.

[0072] Experimental data show that the electric field on the front side of the rock sample not only includes the seismoelectric response of the front interface, but also detects the oblique wave group excited by the crack; the signal attenuation area recorded by the rear electrode accurately corresponds to the crack position, realizing the spatial positioning of the crack.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical method of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical method of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical method to deviate from the spirit and scope of the technical method of the present invention.

Claims

1. A rock sample crack measurement system based on seismoelectric effect, characterized in that: It includes signal source, high-voltage square wave pulse source, sound source, hydrophone, electrode, preamplifier, filter, data acquisition card, rock sample and data processing device; The rock samples include intact rock samples and rock samples containing fractures, and the hydrophone and electrodes constitute a receiver; The sound source, hydrophone, electrodes and rock samples are arranged in a water tank; The sound source hydrophone, electrode and rock sample are level in horizontal direction; The signal source is connected to the high-voltage square wave pulse source and the data acquisition card respectively through signal lines; The high-voltage square wave pulse source is connected to the sound source via a signal line; The preamplifier is connected to the filter and the hydrophone respectively through signal lines; The filter is connected to the data acquisition card via a signal line; The data acquisition card is connected to the data processing device via a signal line.

2. A rock sample crack measurement system based on seismoelectric effect according to claim 1, characterized in that: The signal source is used to synchronously trigger the high-voltage square wave pulse and the data acquisition card; The sound source is provided by a sound source transducer; The high-voltage square wave pulse source is used to generate a pulse signal to excite the sound source transducer after being triggered by the receiving signal source; The sound source transducer generates fluid sound waves to form a sound source after being excited; The hydrophone and the electrode respectively record the acoustic field signal and the converted electric field signal and transmit the acoustic field signal and the converted electric field signal to the preamplifier through the signal line; The preamplifier is used to gain the sound field signal and the converted electric field signal to obtain a gain sound field signal and a gain electric field signal; The filter is used to process the gain sound field signal and the gain electric field signal; The data acquisition card is used to record the processed gain sound field signal and gain electric field signal.

3. A rock sample crack measurement method based on seismoelectric effect, applied to a rock sample crack measurement system based on seismoelectric effect as described in claim 1-2, characterized in that: The following steps are involved: S1. Conduct experimental testing on complete rock samples to obtain complete seismic-electrical response signals; S2. Conducting experimental testing on rock samples containing fractures to obtain fracture seismoelectric response signals; S3. Compare and analyze the complete electric field response and the crack electric field response to obtain the identification result of the crack interface.

4. The rock sample crack measurement method based on seismoelectric effect according to claim 3 is characterized in that: The experimental testing steps in S1 and S2 are the same, including: Step 1: The rock sample includes two fluid-solid interfaces in the fluid, and the two fluid-solid interfaces are defined as a front interface and a rear interface respectively; Step 2: Arrange receivers in the vertical direction to record vertical interface seismoelectric signals; Step 3: Arrange receivers in the horizontal direction to record the seismoelectric signals of the horizontal interface; Step 4: Integrate the vertical interface seismoelectric signal and the horizontal interface seismoelectric signal to obtain an integrated seismoelectric response signal.

5. The rock sample crack measurement method based on seismoelectric effect according to claim 4, characterized in that: In step 2, the receivers are arranged vertically to record the vertical interface seismoelectric signals. The connecting axis between the sound source center and the rock sample center is the z-axis, the front interface of the rock sample is the r-axis, and the intersection of the r-axis and the z-axis is the origin Z0. A sound source-receiver system distributed along the z-axis is established. The sound source is Z s 19.5 cm from the front interface of the rock sample; The receiver array consists of 12 measurement points, with a spacing of 1 cm between measurement points on the same layer; The directions from the front interface of the rock sample to the sound source are receiving point 6, receiving point 5, receiving point 4, receiving point 3, receiving point 2, and receiving point 1; From the rear interface of the rock sample to the sound source in the opposite direction, they are receiving point 7, receiving point 8, receiving point 9, receiving point 10, receiving point 11, and receiving point 12; During the measurement process, the sound source remains fixed, and the converted electric field signals are collected at 12 measuring points in sequence by moving the electrodes, and the sound field signals are collected at 12 measuring points in sequence by moving the hydrophone. The converted electric field signals and sound field signals constitute the vertical interface seismoelectric signals.

6. The rock sample crack measurement method based on seismoelectric effect according to claim 5, characterized in that: In step 3, the receivers are arranged horizontally to record the seismoelectric signals of the horizontal interface: A set of electrodes is arranged on the front interface and the rear interface of the rock sample; The sound source is Z s 19.5 cm from the front interface of the rock sample; With the front interface of the rock sample as the r axis and the center of the front interface of the rock sample as the origin Z0, a sound source-receiver system distributed along the r axis is established; During the measurement, the sound source and the electrode are kept moving synchronously; The electrode starts from -6 cm in the horizontal direction and moves gradually to +6 cm at intervals of 0.5 cm, forming a scanning profile with a range of 12 cm to obtain the horizontal interface seismoelectric signal.

7. The rock sample crack measurement method based on seismoelectric effect according to claim 4, characterized in that: The specific content of the crack interface identification results obtained by comparing and analyzing the complete electric field response and the crack electric field response in S3 is as follows: The detection results of the front interface of the rock sample include the seismoelectric response of the front interface and the oblique wave group excited by the crack; The detection results of the rock sample rear interface include the signal attenuation area recorded by the rear electrode, which accurately corresponds to the crack position, realizing the spatial positioning of the crack.

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