阅读说明：本技术 一种水力压裂震电信号联合处理方法 (Hydraulic fracturing seismoelectric signal combined processing method ) 是由 王俊秋 雍皓 罗世豪 马立伟 孙佳 于 2020-05-27 设计创作，主要内容包括：本发明涉一种水力压裂震电信号联合处理方法,包括利用采集系统中的微地震信号与成像技术获取到裂缝的长度及宽度信息；利用采集系统中的震电信号获取到裂缝的方向信息；结合两种方法的数据处理结果,进行震电联合数据解释,获得裂缝完整的长度、宽度及走向参数。能在水力压裂过程中无需其他激发源的条件下,监测岩层破裂所产生的微地震信号以及震电效应所产生的震电信号,完成对压裂裂缝位置、方向、长度、宽度等参数信息的精确评估。(The invention relates to a hydraulic fracturing seismoelectric signal joint processing method, which comprises the steps of acquiring the length and width information of a crack by utilizing microseismic signals in an acquisition system and an imaging technology; acquiring the direction information of the crack by using a seismoelectric signal in an acquisition system; and (4) combining the data processing results of the two methods, and performing seismoelectric combination data interpretation to obtain the complete length, width and strike parameters of the crack. The method can monitor the micro seismic signals generated by rock stratum fracture and the seismic electric signals generated by the seismoelectric effect without other excitation sources in the hydraulic fracturing process, and complete accurate evaluation of parameter information such as the position, direction, length, width and the like of the fracturing fracture.)

1. A hydraulic fracturing seismoelectric signal combined processing method is characterized by comprising the following steps:

acquiring the length and width information of the crack by using a microseism signal and imaging technology in an acquisition system;

acquiring the direction information of the crack by using a seismoelectric signal in an acquisition system;

combining the data processing results of the two methods, performing seismoelectric combined data interpretation to obtain the complete length, width and trend parameters of the crack;

the method for acquiring the length and width information of the crack by using the micro seismic signal and the imaging technology in the acquisition system comprises the following steps:

s1, shifting the seismic wave data of each acquisition station to the earthquake occurrence time by a reverse time shift method, wherein the seismic waveforms of all the acquisition stations have the same phase after the travel time shift required by the seismic waves from the seismic source to the acquisition station;

s2, adding the multiple paths of seismic amplitudes subjected to reverse time offset, wherein if the phases are the same, the assignment of the signals is obviously increased, and if the phases are different, the signals are attenuated, so that the time and the position of energy focusing when a micro-seismic event occurs are obtained;

s3, using the successive dividing micro earthquake event positioning method to divide the area voxel with relatively large size in the time and position area of the energy focusing when the micro earthquake event happens, which is obtained in the step S2, selecting the local maximum value after all the voxel is scanned, if the voxel size meets the precision requirement, saving the local maximum value as the micro earthquake event, otherwise dividing the new target area into smaller voxel for scanning.

2. The joint processing method of hydraulic fracture seismoelectric signals according to claim 1,

the step S3 specifically includes:

step S31, dividing the target range according to the larger voxel size;

step S32, setting the concrete size of the voxel according to the resolution, and completing the division of the whole area to obtain a plurality of voxels with the same size;

s33, completing the calculation process of the distance between each voxel and the detector connected with the acquisition station, knowing the travel time of each detector according to the propagation velocity of the seismic wave, storing all the travel times and making into a time table;

step S34, the signals picked up by each detector move on the time axis according to the negative number of the corresponding travel time, and the signals picked up by other detectors are solved by the same method for the same voxel;

step S35, overlapping the translated data lines to obtain a data line overlapped relative to the current voxel to eliminate the travel time deviation from the current voxel to each detector, and judging whether a microseismic event occurs according to the overlapped waveform;

step S36, after all the voxels finish the above operation, obtaining a four-dimensional array in a target area, and processing each local maximum by a flood filling algorithm from the largest local maximum in the array to judge whether the local maximum is a real seismic source;

step S37, determining the size of the current voxel, if the current accuracy can be met, then taking the current source point as the final source point position, if the set accuracy requirement cannot be met, then replanning the target region with reference to the region division size in step S31 with the current source point as the center, and then repeating steps S32 to S36.

3. The joint processing method of hydraulic fracture seismoelectric signals according to claim 1,

the method for acquiring the direction information of the crack by using the seismoelectric signals in the acquisition system comprises the following steps:

s4, eliminating the error of the distance between two electrodes caused by the high difference of the terrain for the seismoelectric signal by using the terrain correction technology;

s5, filtering the 50Hz power frequency interference of the signal after the error is eliminated in the step S4 by adopting a low-pass filtering method;

s6, processing the data filtered in the step S5 by utilizing a parallax component potential gradient imaging technology to obtain a potential gradient change curve for displaying potential anomaly of the target area, wherein the curve directly displays the trend of the crack in the horizontal direction, and potential gradient values before and after fracturing or water injection are solved by the following formula:

setting the potential gradient value before fracturing or water injection as

Technical Field

The invention belongs to the technical field of geophysical exploration and research related to hydraulic fracturing, and particularly relates to a hydraulic fracturing seismoelectric signal combined processing method.

Background

With the development of society, the demand of China for petroleum rises year by year, but the domestic petroleum exploitation amount is not obviously improved, and the demand of China only depends on imported petroleum in order to meet the huge petroleum demand. At present, the yield of an oil field can be effectively increased by a hydraulic fracturing method in the world, and artificial fractures are formed by injecting fracturing fluid underground, so that the permeability condition of an oil layer is improved, the blockage is dredged, and the yield of an oil well is increased. Accurate description of fracturing fracture parameters will directly relate to evaluation of fracturing effect and selection of next fracturing construction. The microseism method is a commonly used monitoring method in the hydraulic fracturing process, and mainly obtains information such as the direction, the length, the position, the change, the development degree and the like of a fracture by monitoring a microseism event generated by rock stratum fracture in the fracturing process.

During the hydraulic fracturing process, a large amount of fracturing fluid which contains proppant and has low resistivity and certain viscosity is injected into the stratum, so that the resistivity of a reservoir and surrounding rocks is obviously changed. When seismic wave propagation encounters an interface with electrochemical properties or elastic differences, a second type of seismoelectric effect is induced, and at the moment, charge balance is disturbed, so that asymmetry of charge distribution is caused, and an interface electromagnetic field is formed. The generated seismoelectric signal (an electromagnetic signal) can reflect the key parameters of the fluid-containing reservoir such as porosity, permeability and the like, and can also directly reflect the property of the reservoir fluid, so that the seismoelectric effect has great significance for the exploration of underground oil and gas reservoirs.

The single detection method has the problems of inaccurate crack interpretation and incomplete stratum parameter evaluation, and simultaneously monitors two geophysical signals of vibration and electromagnetism, so that the fracturing crack can be more accurately interpreted and analyzed, and the oil-gas exploration and development are effectively promoted.

CN205562840U discloses a hydraulic fracturing seismoelectric combined detection system combining seismic data and electrical data. Although the system combines the micro seismic method and the electrical method to explain fracturing fractures in a multi-angle and more comprehensive manner in the hydraulic fracturing process, the vibration signal and the electromagnetic signal can be mutually converted in a fluid-containing medium, so that the cause of the acquired signal is complex, and the accuracy of a data processing result is influenced.

CN205620357U discloses an experimental measurement system for seismoelectric signals, which provides a test platform capable of performing laboratory seismoelectric signal measurement, and is convenient for experimental research of seismoelectric signals. However, the system needs an ultrasonic transducer as an active excitation source, and is not suitable for the situation that no active source is available in the hydraulic fracturing process, and in addition, a professional acquisition system is needed for acquiring, processing and storing the field seismoelectric signals.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a hydraulic fracturing seismoelectric signal combined processing method, which solves the defects that in the background technology, fluid medium containing vibration signals and electromagnetic signals are easy to be mutually converted, signal acquisition is inconvenient, data is difficult to process, an ultrasonic transducer is required to be used as an active excitation source, and the like.

The present invention is achieved in such a way that,

a hydraulic fracturing seismoelectric signal combined processing method comprises the following steps:

acquiring the length and width information of the crack by using a microseism signal and imaging technology in an acquisition system;

acquiring the direction information of the crack by using a seismoelectric signal in an acquisition system;

combining the data processing results of the two methods, performing seismoelectric combined data interpretation to obtain the complete length, width and trend parameters of the crack;

the method for acquiring the length and width information of the crack by using the micro seismic signal and the imaging technology in the acquisition system comprises the following steps:

s1, shifting the seismic wave data of each acquisition station to the earthquake occurrence time by a reverse time shift method, wherein the seismic waveforms of all the acquisition stations have the same phase after the travel time shift required by the seismic waves from the seismic source to the acquisition station;

s2, adding the multiple paths of seismic amplitudes subjected to reverse time offset, wherein if the phases are the same, the assignment of the signals is obviously increased, and if the phases are different, the signals are attenuated, so that the time and the position of energy focusing when a micro-seismic event occurs are obtained;

s3, using the successive dividing micro earthquake event positioning method to divide the area voxel with relatively large size in the time and position area of the energy focusing when the micro earthquake event happens, which is obtained in the step S2, selecting the local maximum value after all the voxel is scanned, if the voxel size meets the precision requirement, saving the local maximum value as the micro earthquake event, otherwise dividing the new target area into smaller voxel for scanning.

Further, the air conditioner is provided with a fan,

the step S3 specifically includes:

step S31, dividing the target range according to the larger voxel size;

step S32, setting the concrete size of the voxel according to the resolution, and completing the division of the whole area to obtain a plurality of voxels with the same size;

s33, completing the calculation process of the distance between each voxel and the detector connected with the acquisition station, knowing the travel time of each detector according to the propagation velocity of the seismic wave, storing all the travel times and making into a time table;

step S34, the signals picked up by each detector move on the time axis according to the negative number of the corresponding travel time, and the signals picked up by other detectors are solved by the same method for the same voxel;

step S35, overlapping the translated data lines to obtain a data line overlapped relative to the current voxel to eliminate the travel time deviation from the current voxel to each detector, and judging whether a microseismic event occurs according to the overlapped waveform;

step S36, after all the voxels finish the above operation, obtaining a four-dimensional array in a target area, and processing each local maximum by a flood filling algorithm from the largest local maximum in the array to judge whether the local maximum is a real seismic source;

step S37, determining the size of the current voxel, if the current accuracy can be met, then taking the current source point as the final source point position, if the set accuracy requirement cannot be met, then replanning the target region with reference to the region division size in step S31 with the current source point as the center, and then repeating steps S32 to S36.

Further, the air conditioner is provided with a fan,

the method for acquiring the direction information of the crack by using the seismoelectric signals in the acquisition system comprises the following steps:

s4, eliminating the error of the distance between two electrodes caused by the high difference of the terrain for the seismoelectric signal by using the terrain correction technology;

s5, filtering the 50Hz power frequency interference of the signal after the error is eliminated in the step S4 by adopting a low-pass filtering method;

s6, processing the data filtered in the step S5 by utilizing a parallax component potential gradient imaging technology to obtain a potential gradient change curve for displaying potential anomaly of the target area, wherein the curve directly displays the trend of the crack in the horizontal direction, and potential gradient values before and after fracturing or water injection are solved by the following formula:

setting the potential gradient value before fracturing or water injection as

The electric potential gradient value after fracturing or water injection is

According toPotential gradient difference value can be obtained

Finally, the potential gradient value of parallax components in all directions in the area is obtained.

Compared with the prior art, the invention has the beneficial effects that: the method fully utilizes the physical characteristics of the fluid-containing stratum on the basis of the traditional hydraulic fracturing microseism method, adds a method for monitoring the seismoelectric signal generated by the seismoelectric effect, does not interfere with each other, and ensures that the parameter information of the fracturing fracture is more accurate through the mutual verification of the two detection methods; the acquisition system is more integrated, does not need a signal excitation source, saves manpower and material resources to a certain extent, and enhances the practicability of field exploration; the data processing method can greatly improve the calculation efficiency on the premise of ensuring the positioning precision.

Drawings

FIG. 1 is a schematic diagram of a structural frame of a hydraulic fracturing seismoelectric signal acquisition system according to the present invention;

FIG. 2 is a block diagram of the structure of the acquisition station unit of the present invention;

FIG. 3 is a schematic view of seismic amplitude stacking according to the present invention;

FIG. 4 is a flow chart of positioning in the method of the present invention;

FIG. 5 is a schematic diagram of stepwise splitting of voxels according to the method of the present invention, wherein (a) is a previous stage of splitting, and (b) a smaller voxel is split.

FIG. 6 is a distribution diagram of the acquisition station units of the present invention;

fig. 7 is a coordinate system in step S4 of the method of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Referring to fig. 1 and fig. 2, a hydraulic fracture seismoelectric signal acquisition system is mainly composed of a plurality of hydraulic fracture seismoelectric signal acquisition station units 21 with the same function, which are arranged and arranged outwards in a star array (see fig. 6) by taking the hydraulic fracture seismoelectric signal acquisition station units 21 as centers, wherein each acquisition station unit 21 comprises an STM32 central control unit 13, a real-time clock 14, an SD card 15, a network communication module 16 and the like, and two input ends of the STM32 central control unit 13 are respectively connected with a micro seismic signal processing channel 17 and a seismoelectric signal processing channel 20; the input end of the micro-seismic signal processing channel 17 is provided with a single-component wave detector 1, a micro-seismic signal conditioning circuit 18 is arranged behind the single-component wave detector, and the tail end of the micro-seismic signal processing channel is provided with a first analog-to-digital conversion circuit 5 of the micro-seismic signal processing channel; the front end of the micro-seismic signal conditioning circuit 18 is provided with a filter network 2, the middle of the micro-seismic signal conditioning circuit is provided with a first analog switch 3 of a micro-seismic signal processing channel, and the tail end of the micro-seismic signal conditioning circuit is provided with a micro-seismic signal processing channel fully-differential amplifier 4; the input end of the seismoelectric signal processing channel 20 is provided with a pair of Pb/PbCl2 receiving electrodes 6, the rear end is provided with a seismoelectric signal conditioning circuit 19, and the tail end is provided with a secondary analog-to-digital conversion circuit 12 of the seismoelectric signal processing channel; the front end of the seismoelectric signal conditioning circuit 19 is provided with a preprocessing circuit 7, and then a second analog switch 8, a preamplifier 9 of the seismoelectric signal processing channel and a band-pass filter circuit 10 of the seismoelectric signal processing channel are sequentially arranged, and the tail end is provided with a buffer isolating circuit 11.

The single-component micro-seismic detector 1 is used for acquiring micro-seismic signals in the vertical direction; the Pb/PbCl2 receiving electrode 6 is used to collect seismoelectric signals in the form of potential differences.

In the microseism signal conditioning circuit 18, a filter network 2 carries out filtering processing on microseism signals, an analog switch 3 controls the working state of a channel, and a fully differential amplifier 4 amplifies weak signals and drives a rear-end microseism signal analog-to-digital conversion circuit 5; the microseism signal conditioning circuit 18 is connected with the analog-to-digital conversion circuit 5, and the analog-to-digital conversion circuit 5 converts effective microseism signals into digital signals capable of being stored.

In the seismoelectric signal conditioning circuit 19, the preprocessing circuit 7 can eliminate the interference of direct current level signals received by the electrodes, high-frequency signals radiated in space and the like, the analog switch 8 controls the working state of a seismoelectric signal channel, the preamplifier 9 amplifies extremely weak seismoelectric signals, the passband range of the band-pass filter circuit 10 is 5 kHz-25 kHz, and allows seismoelectric signals with the central frequency of 15kHz to pass through, the buffer isolation circuit 11 can eliminate the mutual interference between the seismoelectric signal conditioning circuit 19 and the analog-to-digital conversion circuit 12, and reduce the interference on the seismoelectric signal conditioning circuit 19; the seismoelectric signal conditioning circuit 19 is connected to the analog-to-digital conversion circuit 12, and the analog-to-digital conversion circuit 12 converts the processed seismoelectric signal into a storable digital signal.

The input end of the STM32 central control unit 13 is respectively connected with the output ends of the micro seismic signal processing channel analog-to-digital conversion circuit 5 and the seismoelectric signal processing channel analog-to-digital conversion circuit 12, which are the main control and processing units of the system and can control the analog-to-digital conversion processing and data storage of two signals. The real-time clock 14 can accurately set real-time to ensure the synchronism of the acquisition stations; the SD card 15 is used for storing data cached in the STM32 central control unit 13; the network communication module 16 may be connected to a switch 22 and the PC connected to retrieve the collected data.

The acquisition method of the hydraulic fracturing seismoelectric signal acquisition system of the invention is explained in detail by specific field tests as follows:

1) arranging acquisition systems around the fracturing well according to a detection plan, and recording the position and the corresponding station number of each acquisition station 21; and connecting each station with the embedded single component detector 1 and the electrode pair 6, wherein a proper amount of concentrated saline is poured into the pit position where the electrode pair 6 is embedded in advance to enhance the conductivity and the coupling property of the electrode and the ground.

2) Before oil field fracturing, each acquisition station 21 is started to start data acquisition and record a background noise field.

3) The oil field begins hydraulic fracturing, the real-time clock 14 records the time of fracturing, and the acquisition system begins to acquire microseismic and seismoelectric signals generated in the fracturing process.

4) After fracturing is complete, the collection station 21 is closed and the instruments are recovered.

5) The collection station 21, the switch 22, and the PC are connected properly, and data is collected.

6) And performing data processing, and performing inversion interpretation on a background noise field before fracturing according to the difference of the microseism data after fracturing and the seismoelectric data to obtain the parameter information of the fracturing fracture.

The hydraulic fracturing seismoelectric signal combined treatment method of the invention is explained in detail by concrete data processing, and comprises the following steps:

and acquiring information such as the length, the width and the like of the crack by using a microseism data processing and imaging technology.

Acquiring direction information of the crack by using a seismoelectric monitoring method;

and the data processing results of the two methods are combined to carry out seismoelectric combined data interpretation so as to make up the defects brought by a single method and realize accurate monitoring of the cracks generated in the hydraulic fracturing process.

The method for acquiring the information such as the length and the width of the crack by using the micro seismic data processing and imaging technology comprises the following steps:

s1, the seismic wave data of each acquisition station is shifted to the earthquake occurrence time by a reverse time shift method, wherein the time is the travel time required by the seismic wave from the seismic source to the acquisition station, and the seismic wave forms of all the acquisition stations after the shift have the same phase.

S2, adding the multiple seismic amplitudes after the inverse time offset by using a seismic amplitude superposition method, wherein assignment of signals is obviously increased if the phases are the same, and the signals are attenuated if the phases are different. Thereby obtaining the time and position of energy focusing when the micro-seismic event occurs; the schematic view of amplitude stacking is shown in fig. 3.

S3, using the method of positioning the successive dividing micro-seismic event to divide the voxel of the relatively larger area in the time and position area of the energy focusing when the micro-seismic event happens, which is obtained in the step S2, selecting the local maximum value after all the voxels are scanned, if the voxel size meets the precision requirement, saving the voxel as the micro-seismic event, otherwise, dividing the new target area into smaller voxels for scanning. The positioning process is shown in fig. 4.

Further, the step S3 specifically includes:

1) dividing the target range according to the larger voxel size;

2) in order to achieve the ideal resolution, the specific size of the voxel is set, and the whole area is divided to obtain a plurality of voxels with the same size;

3) and finishing the calculation process of the distance from each voxel to the detector, and knowing the travel time of each detector according to the propagation speed of the seismic wave. Storing all travel times to make a time-out table;

4) the signals picked up by each detector move on the time axis according to the negative number of the corresponding travel time, and the signals picked up by other detectors are solved by the same method for the same voxel.

5) And superposing the translated data lines to obtain a superposed data line relative to the voxel so as to eliminate the travel time deviation from the current voxel to each detector. And judging whether the microseismic event occurs according to the superposed waveform.

6) After all the voxels complete the above operation, a four-dimensional array in a target region can be obtained, and from the largest local maximum in the array, each local maximum is processed by a flood filling algorithm to determine whether it is a real seismic source.

7) Judging the size of the current voxel, if the current accuracy can be met, taking the current seismic source point as the final seismic source point position, if the set accuracy requirement cannot be met, taking the current seismic source point as the center, replanning the target region by referring to the region division size in the previous step, and then repeating the step (2-6). The voxel progressive subdivision schematic diagram is shown in fig. 5(a) and (b).

The acquiring of the direction information of the crack by using the seismoelectric signal in the acquisition system comprises the following steps:

s4, eliminating the error of the distance between two electrodes caused by the high difference of the terrain by using the terrain correction technology; in the process of electric potential gradientWhen calculating, the components in the three directions of xyz are calculated separatelyTo simplify the calculation, a three-dimensional rectangular coordinate system is established such thatIn the xoz plane, at this time

The component in the y-direction is zero as shown in fig. 7. M, N are two measurement electrodes, and in order to determine M, N the gradient value of the electrode in the horizontal direction, the equivalent distance of the distance L between M, N in the horizontal direction (ox) needs to be found by terrain correction.

The data measured in the actual measurement process is the potential difference between M, N, and due to the existence of the height difference, the projection L · cos α of the distance L between M, N in the ox direction is first obtained, so as to obtain the magnitude of the potential gradient along the ox direction.

In the formula (I), the compound is shown in the specification,in order to be the total potential gradient,is the potential gradient after the terrain correction.

S5 filtering the 50Hz power frequency interference by adopting a low-pass filtering method.

S6, obtaining the potential gradient change curve showing the potential abnormity of the target area by using the parallax partial potential gradient imaging technology. The potential gradient values before and after fracturing or flooding can be solved by the following formula:

setting the potential gradient value before fracturing or water injection as

The electric potential gradient value after fracturing or water injection isAccording toPotential gradient difference value can be obtained

Finally, the potential gradient value of parallax components in all directions in the area is obtained.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.