A rock sample crack measuring method and system based on seismoelectric effect

Abstract

The application discloses a rock sample crack measuring method and system based on a seismoelectric effect, relates to the rock sample crack measuring field, and comprises the following steps: a rock sample crack measuring system based on the seismoelectric effect is built, hydrophones and electrodes are arranged in an array in a vertical direction, sound field and electric field signals on both sides of the rock sample are collected, then a synchronous moving scanning technology of a sound source and the electrodes is adopted, differences in electric field responses of complete rock samples and rock samples containing cracks are compared and analyzed, and then a crack interface is identified. The rock sample crack measuring method based on the seismoelectric effect simultaneously captures seismoelectric signals excited by double interfaces by means of double electrodes, and effectively identifies the crack interface by means of signal amplitude difference, attenuation characteristics and waveform characteristics.

Description

Technical Field

[0001] This invention relates to the field of rock sample crack measurement, and in particular to a method and system for measuring rock sample cracks based on the seismoelectric effect. Background Technology

[0002] As an important electrodynamic coupling mechanism, the seismoelectric effect describes the characteristics of the electromagnetic field induced by seismic waves propagating in a fluid-saturated porous medium. It includes two different seismoelectric conversion signals: one is the accompanying electromagnetic field generated along with the seismic wave; the other is the interfacial radiated electromagnetic wave excited by the seismic wave at the medium boundary.

[0003] Therefore, seismic exploration has the dual response characteristics of reservoir elastic parameters and electrochemical properties, and it has shown great application potential in fields such as oil and gas resource exploration and geological disaster early warning, which has attracted widespread attention from the geophysical community.

[0004] However, existing seismoelectric experimental studies mostly focus on single complete interface models, lacking 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 strata.

[0005] To address these issues, there is an urgent need for a method and system for measuring rock sample cracks based on the seismoelectric effect. Summary of the Invention

[0006] To address the aforementioned issues, this application proposes a rock sample fracture measurement system and method based on seismoelectric effect. The system measures rock sample fractures based on multi-interface seismoelectric coupling. By constructing a fluid-rock-sample-fluid model to simulate the actual reservoir dual-interface structure, a dual-sided electrode array and acoustic source synchronous moving scanning technology are employed. By comparing the electric field signals of intact rock samples and fractured rock samples, the waveform characteristics of the seismoelectric response signal induced by the fracture interface are obtained.

[0007] A rock sample crack measurement system based on seismoelectric effect includes a signal source, a high-voltage square wave pulse source, a sound source, a hydrophone, electrodes, a preamplifier, a filter, a data acquisition card, a rock sample, and a data processing device.

[0008] The rock samples include intact rock samples and rock samples with fractures, and the hydrophone and electrodes constitute a receiver;

[0009] The sound source, hydrophone, electrodes, and rock sample are placed inside the water tank;

[0010] The acoustic source hydrophone, electrodes, and rock sample are horizontally aligned.

[0011] The signal source is connected to the high-voltage square wave pulse source and the data acquisition card respectively via signal lines;

[0012] The high-voltage square wave pulse source is connected to the sound source via a signal line;

[0013] The preamplifier is connected to the filter and the hydrophone via signal lines, respectively.

[0014] The filter is connected to the data acquisition card via a signal line;

[0015] The data acquisition card is connected to the data processing device via a signal cable.

[0016] Preferably, the signal source is used to synchronously trigger the high-voltage square wave pulse and the data acquisition card;

[0017] The sound source is provided through a sound source transducer;

[0018] 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.

[0019] The sound source transducer generates fluid sound waves after being excited, thus forming a sound source.

[0020] The hydrophone and electrodes 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;

[0021] The preamplifier is used to amplify the acoustic field signal and the converted electric field signal to obtain amplified acoustic field signal and amplified electric field signal;

[0022] The filter is obtained by processing the gain acoustic field signal and the gain electric field signal;

[0023] The data acquisition card is used to record the processed gain acoustic field signal and gain electric field signal.

[0024] Preferably, a method for measuring rock sample fractures based on seismoelectric effects includes the following steps:

[0025] S1. Experimental testing was conducted on intact rock samples to obtain complete seismic response signals;

[0026] S2. Experimental testing was conducted on fractured rock samples to obtain the seismic-electric response signal of the fractures;

[0027] S3. Comparative analysis of the complete electric field response and the crack electric field response yields the crack interface identification results.

[0028] Preferably, the experimental detection steps in S1 and S2 are the same, specifically including:

[0029] Step 1: The rock sample in the fluid includes two fluid-solid interfaces, which are defined as the front interface and the back interface, respectively.

[0030] Step 2: Arrange the receiver vertically and record the seismic signal at the vertical interface;

[0031] Step 3: Arrange the receiver horizontally and record the seismic signal at the horizontal interface;

[0032] Step 4: Integrate the seismoelectric signals from the vertical and horizontal interfaces to obtain the integrated seismoelectric response signal.

[0033] Preferably, in step 2, the receiver is arranged vertically, and the specific content of the seismic signal at the vertical interface is recorded as follows:

[0034] A sound source-receiver system distributed along the z-axis is established with the axis connecting the sound source center and the rock sample center as the z-axis, the front interface of the rock sample as the r-axis, and the intersection of the r-axis and the z-axis as the origin Z0.

[0035] The sound source is Z s 19.5 cm from the front interface of the rock sample;

[0036] The receiver array consists of 12 measuring points, with a spacing of 1 cm between measuring points on the same layer;

[0037] From the front interface of the rock sample to the direction of the sound source, the receiver points are 6, 5, 4, 3, 2, and 1 respectively.

[0038] From the back interface of the rock sample to the opposite direction of the sound source, the receiver points are 7, 8, 9, 10, 11, and 12 respectively.

[0039] During the measurement process, the sound source remained fixed, and the converted electric field signal was collected at 12 measuring points by moving the electrode in sequence. The sound field signal was collected at 12 measuring points by moving the hydrophone in sequence. The converted electric field signal and the sound field signal constituted the vertical interface seismoelectric signal.

[0040] Preferably, in step 3, the receiver is arranged horizontally, and the specific content of the seismic signal at the horizontal interface is recorded as follows:

[0041] A set of electrodes was placed at both the front and rear interfaces of the rock sample.

[0042] The sound source is Z s 19.5 cm from the front interface of the rock sample;

[0043] With the rock sample front interface as the r-axis and the center of the rock sample front interface as the origin Z0, a sound source-receiver system distributed along the r-axis is established.

[0044] During the measurement process, the sound source and the electrodes should move synchronously.

[0045] The electrode is moved horizontally from -6cm to +6cm at 0.5cm intervals to form a scanning profile within a 12cm range, thus obtaining the horizontal interface seismoelectric signal.

[0046] Preferably, the specific content of the crack interface identification result obtained by comparing and analyzing the complete electric field response and the crack electric field response in step 4 is as follows:

[0047] The results of rock sample front interface testing include the front interface seismoelectric response and the oblique wave group excited by the crack;

[0048] The results of the rock sample back interface detection include the precise correspondence between the signal attenuation zone recorded by the back electrode and the fracture location, thus realizing the spatial positioning of the fracture.

[0049] In summary, the rock sample crack measurement method and system based on seismoelectric effect of the present invention has the following advantages compared with traditional technology:

[0050] (1) This application addresses the lack of crack response signal measurement in existing seismoelectric effect research. By constructing a high-precision seismoelectric measurement system, miniature hydrophones and electrodes are arrayed in the vertical direction to collect sound and electric field signals from both sides of the rock sample. Subsequently, a synchronous moving scanning technique of sound source and electrodes is used to compare and analyze the difference in electric field response between intact rock samples and rock samples with cracks. The electrodes on both sides can simultaneously capture the seismoelectric signals excited by the dual interfaces, and the crack interface can be effectively identified by the difference in signal amplitude, attenuation characteristics and waveform characteristics.

[0051] (2) This application reveals the propagation law of multi-interface seismic wave field, providing experimental technical support for reservoir interface location and formation fracture identification, and has important application value in oil and gas exploration, geological disaster early warning and other fields;

[0052] (3) This application not only verifies the spatial detectability of multi-interface seismic signals, but also provides a high-precision experimental means for locating complex reservoir interfaces and identifying fractures, significantly improving the practical value of seismic effects in resource exploration engineering.

[0053] The technical method of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the seismoelectric measurement system of the present invention;

[0055] Figure 2 This is a schematic diagram of the receiver arranged vertically according to the present invention;

[0056] Figure 3 This is a schematic diagram of the receiver arranged horizontally according to the present invention;

[0057] Figure 4 This is a schematic diagram of rock sample cracks according to the present invention. Figure 4 (a) is a top view of the rock sample. Figure 4 (b) is a three-dimensional view of the rock sample;

[0058] Figure 5 Measurement of seismic-electric response signals of fractured rock samples in this invention;

[0059] Figure 6 The measured acoustic and electrical signals received at points 1 to 6 of this invention are... Figure 6 In the middle (a), the measured sound field signal is shown. Figure 6 (b) is the measured electric field signal;

[0060] Figure 7 The measured acoustic-electric signals received at points 7 to 12 in this invention are... Figure 7 In the middle (a), the measured sound field signal is shown. Figure 7 (b) is the measured electric field signal;

[0061] Figure 8 The electrical signal of the front interface of this invention. Figure 8 In (a), the frontal electric field of the intact rock sample is shown. Figure 8 (b) shows the electric field at the front interface of the fractured rock sample;

[0062] Figure 9 This refers to the electro-optical signal at the interface of the present invention. Figure 9 In (a), the frontal electric field of the intact rock sample is shown. Figure 9 (b) shows the electric field at the front interface of the fractured rock sample. Detailed Implementation

[0063] The technical method of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of this application.

[0064] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the scope of this application and its application or use.

[0065] Techniques, systems, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the instruction manual.

[0066] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0067] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0068] A rock sample crack measurement system based on seismoelectric effect includes a signal source, a high-voltage square wave pulse source, a sound source, a hydrophone, electrodes, a preamplifier, a filter, a data acquisition card, a rock sample, and a data processing device.

[0069] Rock samples include intact rock samples and rock samples with fractures; the receiver consists of a hydrophone and electrodes.

[0070] The sound source, hydrophone, electrodes and rock sample are placed in the water tank (the rock sample is fixed at a fixed height by pads).

[0071] The sound source hydrophone, electrodes, and rock sample are level in the horizontal direction.

[0072] The signal source is connected to the high-voltage square wave pulse source and the data acquisition card via signal lines.

[0073] The high-voltage square wave pulse source is connected to the sound source via a signal line.

[0074] The preamplifier is connected to the filter and hydrophone via signal lines.

[0075] The filter is connected to the data acquisition card via signal lines.

[0076] The data acquisition card is connected to the data processing device via a signal cable.

[0077] Furthermore, the signal source is used to synchronously trigger the high-voltage square wave pulse and the data acquisition card.

[0078] The sound source is provided through a sound source transducer.

[0079] A high-voltage square wave pulse source is used to generate a pulse signal to excite the sound source transducer after being triggered by a receiving signal source.

[0080] When the sound source transducer is excited, it generates fluid sound waves to form a sound source.

[0081] The hydrophone and electrodes 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.

[0082] The preamplifier is used to gain the sound field signal and the converted electric field signal to obtain the gained sound field signal and the gained electric field signal.

[0083] The filter is obtained by processing the gain acoustic field signal and the gain electric field signal.

[0084] The data acquisition card is used to record the processed gain acoustic field signal and gain electric field signal.

[0085] Specifically, such as Figure 1As 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 an NI data acquisition card.

[0086] During the experiment, the signal source synchronously triggers the high-voltage square wave pulse and the data acquisition card. Subsequently, 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.

[0087] The BK hydrophone and electrodes record the acoustic field signal and the converted electric field signal, respectively. Since the converted electric field signal is very weak, usually at the microvolt level, the measured electric field signal will be amplified by 60dB (1000 times) by a preamplifier, while the acoustic field signal will be amplified by 40dB (100 times).

[0088] The amplified vibratory signal and sound field signal, after being processed by a bandpass filter, will be... Figure 1 Recorded using a high-precision NI data acquisition card.

[0089] During the experimental measurements, the NI data acquisition card was set to a sampling rate of 1Ms / s and a resolution of 22 bits to meet the sampling requirements. Finally, the acquired sound and electric field signals were exported, and data processing and result analysis were performed using plotting software.

[0090] A method for measuring rock sample fractures based on seismoelectric effects includes the following steps:

[0091] S1. Experimental testing is performed on intact rock samples to obtain complete seismic-electric response signals. These signals provide benchmark data for identifying cracks in the rock samples.

[0092] S2. Experimental testing was conducted on fractured rock samples to obtain the seismic-electric response signal of the fractures.

[0093] Furthermore, the experimental detection steps in S1 and S2 are the same, specifically including:

[0094] Step 1: Rock samples will form two fluid-solid interfaces in the fluid. Therefore, rock samples in the fluid include two fluid-solid interfaces, which are defined as the front interface and the back interface, respectively.

[0095] Step 2: Arrange the receiver vertically and record the seismic signal at the vertical interface.

[0096] Furthermore, such as Figure 2 As shown, in step 2, the receiver is arranged vertically to record the specific content of the vertical interface seismic signal:

[0097] A sound source-receiver system distributed along the z-axis is established, with the axis connecting the sound source center and the rock sample center as the z-axis, the front interface of the rock sample as the r-axis, and the intersection of the r-axis and the z-axis as the origin Z0.

[0098] The sound source is Z s 19.5 cm from the front interface of the rock sample.

[0099] The receiver array consists of 12 measuring points, with a spacing of 1 cm between measuring points on the same layer.

[0100] From the front interface of the rock sample to the direction of the sound source, the receiver points are 6, 5, 4, 3, 2, and 1 respectively.

[0101] From the back interface of the rock sample to the opposite direction of the sound source, the receiver points are 7, 8, 9, 10, 11, and 12 respectively.

[0102] During the measurement process, the sound source remained fixed, and the converted electric field signal was collected at 12 measuring points by moving the electrode in sequence. The sound field signal was collected at 12 measuring points by moving the hydrophone in sequence. The converted electric field signal and the sound field signal constituted the vertical interface seismoelectric signal.

[0103] Step 3: Arrange the receiver horizontally and record the seismic signal at the horizontal interface.

[0104] Furthermore, such as Figure 3 As shown, in step 3, the receiver is arranged horizontally to record the specific content of the horizontal interface seismic signal:

[0105] A set of electrodes was placed on both the front and back interfaces of the rock sample.

[0106] The sound source is Z s 19.5 cm from the front interface of the rock sample.

[0107] A sound source-receiver system distributed along the r-axis is established with the rock sample front interface as the r-axis and the center of the rock sample front interface as the origin Z0.

[0108] Unlike vertical measurement methods, horizontal setups require the sound source and electrodes to move synchronously and remain aligned along the same axis to maintain their relative spatial position.

[0109] The electrode is moved horizontally from -6cm to +6cm at 0.5cm intervals to form a scanning profile within a 12cm range, thus obtaining the horizontal interface seismoelectric signal.

[0110] Step 4: Integrate the seismoelectric signals from the vertical and horizontal interfaces to obtain the integrated seismoelectric response signal.

[0111] S3. Comparative analysis of the complete electric field response and the crack electric field response yields the crack interface identification results.

[0112] Furthermore, the specific details of the crack interface identification results obtained by comparing and analyzing the complete electric field response and the crack electric field response in S3 are as follows:

[0113] The results of the rock sample front interface test include the front interface seismoelectric response and the oblique wave group excited by the crack.

[0114] The results of the rock sample back interface detection include the precise correspondence between the signal attenuation zone recorded by the back electrode and the fracture location, thus realizing the spatial positioning of the fracture.

[0115] To systematically conduct seismic-electric detection on fractured rock samples, this application prefabricates a 1.5mm wide fracture based on the central axis of the rock sample. The processing procedure is as follows: Figure 4 As shown in (a): Starting from point A, 3 cm to the left of the front surface axis, a 45° oblique cut is made, extending to point B, 3 cm to the right of the rear surface axis, forming a 6 cm transverse crack. During processing, the bottom 2 cm uncut section is retained as a supporting structure to maintain the integrity of the rock sample. The final morphology of the cracked rock sample is as follows. Figure 4 As shown in (b).

[0116] Seismic electrical signal acquisition was performed on fractured rock samples. For example... Figure 5 As shown, the sound source and electrodes perform a 12cm horizontal scan along the front interface of the rock sample. The receiving array starts at -6cm from the axis and moves to the right, covering three characteristic segments: the front non-crack region (0-3cm), the crack region (3-9cm), and the distal non-crack region (9-12cm). To enhance crack identification accuracy, this application employs a 0.1cm ultra-high density spatial sampling method, systematically characterizing the seismoelectric wave field response features of the crack interface by acquiring 121 waveform signals from the front interface. Furthermore, when measuring the electric field signal on the rear side, this application sets the electrode step distance to 0.2cm. By comparing the seismoelectric response signal containing cracks with that of intact rock samples, the shape and location information of the cracks can be obtained.

[0117] (1) Electromagnetic wave field when electrodes are arranged in the vertical direction.

[0118] The hydrophone was placed sequentially at receiving points 1 to 6 to measure the sound field signal, with each receiving point spaced 1 cm apart. The measurement results are as follows. Figure 6 As shown in Figure (a), wave group A is a direct fluid acoustic wave. Immediately following wave group A, there is a front interface reflected acoustic wave group B with an opposite slope.

[0119] Next, the electrodes were similarly placed at receiving points 1 to 6 to measure the electric field signal. From Figure 6As shown in (b), the arrival time of the experimentally measured wave group signal EM1 is the same as the arrival time of the direct sound wave at the front interface, and it hardly changes with the change of electrode position, indicating that the EM1 signal is the seismoelectric response signal generated by the front interface. As the electrode moves further 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 EM1 signal amplitude is largest in the 6th waveform (17.1 mV), and smallest in the 1st waveform (3.2 mV). The amplitude of the EM1 signal decreases exponentially with increasing distance between the electrode and the interface. Following the wave group EM1, there are some seismoelectric signals with smaller amplitudes. Figure 6 As shown in the dashed box in (b), by calculating their arrival times, it can be inferred that EM2, EM3, and EM4 are the seismoelectric interface responses generated by the propagation of the transmitted longitudinal wave to the rear interface, the return of the longitudinal wave to the front interface, and the propagation of the longitudinal wave to the rear interface again, respectively.

[0120] In related studies of seismoelectric interface response, most methods place electrodes near the front interface close to the sound source, while neglecting to study the electric field at the rear interface. Therefore, this application places the hydrophone and electrodes at receiving points 7 to 12 on the rear side of the rock sample to measure and compare the sound and electric field signals. The hydrophone records the sound field signal on the rear side of the rock sample as follows: Figure 7 As shown in Figure (a), the transmitted sound wave signal at the rear interface is not clearly displayed. Analysis of the waveform signal at receiver point 7, closest to the rear interface, reveals an amplitude of 0.23V. However, the direct sound wave signal amplitude at receiver point 6 at the front interface is 1.53V. Comparing the sound field signals at the rear and front sides shows an amplitude ratio of approximately 0.15. Therefore, the sound wave energy attenuates sharply after penetrating both the front and rear interfaces, resulting in a reduction in the effective sound wave amplitude received by the hydrophone. Consequently, the transmitted sound wave at the rear interface is masked by environmental noise, failing to clearly and effectively represent the interface location information.

[0121] from Figure 7 In the middle (b) (electric field), it can be observed that the first wave group signal EM1 arrives at 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, as measured in the experiment, coincides with the time when the transmitted P-wave arrives at the back interface of the rock sample. This indicates that this signal is the seismoelectric response generated by the propagation of the transmitted P-wave to the back interface. This application extracts... Figure 7In (b), the EM2 signal amplitude was found to be the largest at receiver 7 (4.9 mV) and the smallest at receiver 12 (1.4 mV). Furthermore, the EM2 signal amplitude decreased exponentially with increasing distance. Comparing the EM2 signal amplitude (4.9 mV) at receiver 7 with the EM1 signal amplitude (17.1 mV) at receiver 6, it can be seen that the amplitude ratio of the seismoelectric conversion signal at the rear interface to that at the front interface is approximately 0.286. This is because sound waves attenuate as they propagate through the rock sample; therefore, 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.

[0122] To further explore the acoustic-electric signals at the back interface, Figure 7 (a) (sound field) and Figure 7 By comparing and analyzing the electric field in (b), we can find that... Figure 7 The acoustic field experimental data in (a) did not effectively reflect the interface information of the rock sample; however, in Figure 7 In (b), the acoustic waves excited distinct transducer signals EM1 and EM2 at both the front and rear interfaces. By analyzing the arrival times of these two interface signals and the propagation speed of the acoustic waves in the fluid and rock sample, the location information of the front and rear interfaces of the rock sample can be deduced. This demonstrates the feasibility and superiority of using interface electromagnetic waves for stratigraphic exploration. Therefore, interface electromagnetic waves show promising prospects in detecting stratigraphic interfaces and exploring oil and gas reservoirs.

[0123] (2) Seismic-electric response signal of fractured rock sample:

[0124] Figure 8 (a) shows the horizontal electric field measurement results of the front interface of the complete rock sample. A seismoelectric signal cluster appears at approximately 0.13 ms, confirming the effectiveness of seismoelectric technology in locating the front interface. Comparative experiments show ( Figure 8 In (b), the fractured rock sample also exhibited frontal interface waveform characteristics within the same timeframe, with phase and amplitude highly consistent with the intact sample. When the electrode scanned in the non-fractured region (-6cm to -3cm), only a single frontal interface signal was recorded in the first 30 channels. Figure 8 (b) No subsequent wavefield disturbances were detected in channels 1-30. However, when the measuring point was moved to the fracture region (starting from channel 31), a slanted wave train with obvious time difference characteristics appeared behind the front interface signal. Comparative analysis revealed that intact rock samples did not exhibit this type of slanted wavefield characteristic. Under experimental conditions where the parameters of the acoustic-electric system and the spatial relationship between the rock sample and the sound source were uncertain, it can be confirmed that the slanted wave train is a seismoelectric conversion signal excited by the fracture interface.

[0125] Figure 9In the middle (a), the electric field signal of the back interface of the intact rock sample was measured by electrodes arranged in the horizontal direction. It can be seen that the seismoelectric response signal excited by the back interface was generated at about 0.17ms. Figure 9 (b) shows the electric field signal at the back interface of a fractured rock sample measured with horizontally arranged electrodes. When the receiver is not in the fracture zone, the seismoelectric response signal at the back interface is clearly distinguishable. However, when the electrode moves to the area behind the fracture, the seismoelectric signal attenuates. Analysis shows that the acoustic scattering caused by the fracture significantly reduces the effective acoustic energy propagating to the back interface, resulting in a significant decrease in the seismoelectric conversion efficiency at the back interface, which in turn weakens the electric field at the back interface. As the electrode continues to move to the right beyond the fracture zone, the acoustic propagation path avoids the fracture structure, and the waveform at the end measuring point returns to normal.

[0126] 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 zone recorded by the rear electrode corresponds precisely to the crack location, realizing the spatial localization of the crack.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical methods of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical methods of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical methods to deviate from the spirit and scope of the technical methods of the present invention.

Claims

1. A rock sample crack measurement system based on seismoelectric effect, characterized in that, Includes signal source, high-voltage square wave pulse source, sound source, hydrophone, electrodes, preamplifier, filter, data acquisition card, rock sample and data processing device; The rock samples include intact rock samples and rock samples with fractures, and the hydrophone and electrodes constitute a receiver; The sound source, hydrophone, electrodes, and rock sample are placed inside the water tank; The sound source, hydrophone, electrodes, and rock sample are horizontally aligned. The signal source is connected to the high-voltage square wave pulse source and the data acquisition card respectively via 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 via signal lines, respectively. 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 cable; The signal source is used to synchronously trigger the high-voltage square wave pulse and the data acquisition card; The sound source is provided through 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 after being excited, thus forming a sound source. The hydrophone and electrodes 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; The preamplifier is used to amplify the acoustic field signal and the converted electric field signal to obtain amplified acoustic field signal and amplified electric field signal; The filter is used to process the gain acoustic field signal and the gain electric field signal; The data acquisition card is used to record the processed gain acoustic field signal and gain electric field signal; The rock sample fracture measurement system based on seismoelectric effect is used to measure rock sample fractures. The measurement method includes the following steps: S1. Experimental testing was conducted on intact rock samples to obtain complete seismic response signals; S2. Experimental testing was conducted on fractured rock samples to obtain the seismic-electric response signal of the fractures; S3. Comparative analysis of the complete electric field response and the crack electric field response yields the crack interface identification results.

2. The rock sample crack measurement system based on seismoelectric effect according to claim 1, characterized in that, The experimental detection steps in S1 and S2 are the same, and the specific content includes: Step 1: The rock sample in the fluid includes two fluid-solid interfaces, which are defined as the front interface and the back interface, respectively. Step 2: Arrange the receiver vertically and record the seismic signal at the vertical interface; Step 3: Arrange the receiver horizontally and record the seismic signal at the horizontal interface; Step 4: Integrate the seismoelectric signals from the vertical and horizontal interfaces to obtain the integrated seismoelectric response signal.

3. The rock sample crack measurement system based on seismoelectric effect according to claim 2, characterized in that, In step 2, the receiver is arranged vertically, and the specific details of the seismic signal at the vertical interface are recorded as follows: A sound source-receiver system distributed along the z-axis is established with the axis connecting the sound source center and the rock sample center as the z-axis, the front interface of the rock sample as the r-axis, and the intersection of the r-axis and the z-axis as the origin Z0. The sound source is Z s 19.5 cm from the front interface of the rock sample; The receiver array consists of 12 measuring points, with a spacing of 1 cm between measuring points on the same layer; From the front interface of the rock sample to the direction of the sound source, the receiver points are 6, 5, 4, 3, 2, and 1 respectively. From the back interface of the rock sample to the opposite direction of the sound source, the receiver points are 7, 8, 9, 10, 11, and 12 respectively. During the measurement process, the sound source remained fixed, and the converted electric field signal was collected at 12 measuring points by moving the electrode in sequence. The sound field signal was collected at 12 measuring points by moving the hydrophone in sequence. The converted electric field signal and the sound field signal constituted the vertical interface seismoelectric signal.

4. The rock sample crack measurement system based on seismoelectric effect according to claim 3, characterized in that, In step 3, the receiver is arranged horizontally, and the specific details of the seismic signal at the horizontal interface are recorded as follows: A set of electrodes was placed at both the front and rear interfaces of the rock sample. The sound source is Z s 19.5 cm from the front interface of the rock sample; With the rock sample front interface as the r-axis and the center of the rock sample front interface as the origin Z0, a sound source-receiver system distributed along the r-axis is established. During the measurement process, the sound source and the electrodes should move synchronously. The electrode is moved horizontally from -6cm to +6cm at 0.5cm intervals to form a scanning profile within a 12cm range, thus obtaining the horizontal interface seismoelectric signal.

5. The rock sample crack measurement system based on seismoelectric effect according to claim 1, characterized in that, The specific details of the crack interface identification results obtained by comparing and analyzing the complete electric field response and the crack electric field response in S3 are as follows: The results of rock sample front interface testing include the front interface seismoelectric response and the oblique wave group excited by the crack; The results of the rock sample back interface detection include the precise correspondence between the signal attenuation zone recorded by the back electrode and the fracture location, thus realizing the spatial positioning of the fracture.

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