Poynting vector and polarization vector hybrid imaging method and system for microseismic reverse time positioning

Abstract

The present invention belongs to the field of imaging technology, and discloses a hybrid imaging method of Poynting vector and polarization vector for reverse time positioning of microseismic. Based on the Poynting vector and velocity polarization vector of elastic wave field, the present invention proposes a hybrid imaging condition (PPMIC) of Poynting vector and polarization vector for reverse time imaging of microseismic. The imaging condition can use the time difference of P wave and S wave for imaging without decoupling P wave and S wave, which saves a lot of computing time and computer storage compared with traditional imaging conditions; at the same time, the imaging condition makes full use of the polarization and propagation direction information of the wave field, which can better suppress the imaging illusion and improve the accuracy of microseismic positioning. Combining PPMIC with the finite difference algorithm of arbitrary curve grid greatly expands the application scenario of microseismic reverse time imaging algorithm, and can accurately image the microseismic data collected in complex terrain areas without the need for complex static correction processing of seismic data.

Description

Technical Field

[0001] The present invention belongs to the technical field of microseismic imaging for oil and gas exploration, and in particular relates to a Poynting vector and polarization vector hybrid imaging method and system for microseismic reverse time positioning. Background Art

[0002] The time-reversal imaging technology of earthquake sources based on wave equation theory can realize high-precision earthquake source location of microseismic in complex geological models. In the time-reversal imaging method of earthquake sources, imaging conditions are extremely critical for positioning accuracy and imaging resolution. At present, the most commonly used imaging condition is the scalar cross-correlation imaging condition (SCCIC). However, the scalar cross-correlation imaging condition removes the directional information of the wave field through modulo operation to avoid the direct dot product operation of mutually orthogonal P waves and S waves, but this also makes it impossible to suppress imaging artifacts using the propagation direction of the wave field. For this reason, before the present invention, an imaging condition (PSEDPIC) based on the dot product of the energy flow density vector of P waves and S waves (i.e., Poynting vector) was proposed. This method makes full use of the wave field propagation direction information to suppress artifacts, but it is necessary to decouple P waves and S waves during the wave field back propagation process and additionally calculate the Poynting vector. In order to achieve artifact suppression while reducing the computational burden and memory usage, the present invention introduces the mixed imaging condition of Poynting vector and polarization vector (PPMIC). PPMIC utilizes the polarization and propagation direction information of the wave field by directly dot-producting the undecoupled velocity polarization vector and Poynting vector, avoiding the decoupling calculation of P-waves and S-waves and the additional memory requirements. Compared with SCCIC, this imaging condition can image low signal-to-noise ratio data more accurately. Synthetic data tests of the half-space model and the three-dimensional Marmousi model demonstrate the advantages of this method in suppressing imaging artifacts, as well as its high efficiency and ease of implementation.

[0003] As an important unconventional energy source, shale gas production is directly affected by the development of fracture networks generated by hydraulic fracturing. Microseismic monitoring can reveal the morphology and scale of underground fractures, providing key information for evaluating the effect of hydraulic fracturing and predicting production capacity. As an efficient method for microseismic monitoring, source time reversal imaging uses the entire microseismic waveform as input without picking up travel time, and can accurately locate events even under low signal-to-noise ratio conditions. The development of source time reversal imaging has made significant progress in the past few decades. Its theoretical basis is based on the symmetry principle of time reversal in the wave equation. With the improvement of computing power, source time reversal imaging can be applied to larger data sets and more complex scenarios. The current research focuses on automating the source time reversal imaging process, improving computing efficiency, and improving imaging quality under low signal-to-noise ratio conditions.

[0004] Seismic source reverse time imaging usually includes two main steps: back propagation of station data and application of imaging conditions. Imaging conditions significantly affect the accuracy of source location results and the ability to detect seismic events. For seismic source reverse time imaging, the polarization directions of P waves and S waves are approximately orthogonal at the source point. The vector dot product cross-correlation imaging conditions commonly used in traditional reverse time migration lead to the attenuation of the energy of the source point, so they are not suitable for direct application in seismic source reverse time imaging. In order to meet the challenges of microseismic source reverse time imaging, researchers have developed a variety of imaging conditions, including maximum energy imaging conditions, interference imaging conditions, and scalar cross-correlation imaging conditions (SCCIC). Among them, the scalar cross-correlation imaging conditions remove the polarization information by taking the modulus of the wave field, avoiding the inability to focus the imaging results due to the dot product of the approximately orthogonal vector wave field, and achieved good results.

[0005] In the field of reverse time positioning of microseismic earthquakes, traditional imaging conditions have been developed for many years, especially the scalar cross-correlation imaging condition, which solves the problem that the energy of the imaging result cannot be focused due to the direct dot product of the vector wave field with mutually orthogonal polarization directions, and has been widely used. However, the directional information of the wave field is a key component of the vector elastic wave field, which provides additional constraints for the wave equation imaging process and is widely used in the noise suppression of the reverse time migration of the active source velocity structure. Since the current imaging conditions for reverse time imaging of earthquake sources do not make full use of the directional information of the wave field, a dot product imaging condition (PSEDPIC) based on the energy flow density vector (Poynting vector) of P waves and S waves has been proposed before the present invention. Compared with the scalar cross-correlation imaging condition, this new imaging condition makes full use of the propagation direction information of P waves and S waves at the earthquake source point, and suppresses the imaging artifacts caused by the inconsistent propagation direction of the wave field. In addition, it also provides higher imaging resolution and can be considered as an ideal imaging condition for reverse time imaging of earthquake sources. However, the realization of this imaging condition requires the decoupling of P waves and S waves in the wave field based on the solution of the traditional wave equation. In addition, the Poynting vector of the decoupled wave field needs to be calculated, which introduces additional computational complexity and storage requirements to the source time-reversal imaging process. There is still room for optimization in terms of computational complexity and memory usage.

[0006] Through the above analysis, the problems and defects of the prior art are as follows:

[0007] The realization of existing imaging conditions requires decoupling of P waves and S waves in the wave field based on the solution of the traditional wave equation. In addition, the Poynting vector of the decoupled wave field needs to be calculated, which introduces additional computational complexity and storage requirements to the source time-reverse imaging process. Summary of the invention

[0008] In view of the problems existing in the prior art, the present invention provides a Poynting vector and polarization vector hybrid imaging method for microseismic reverse time positioning.

[0009] The present invention is implemented as follows: a Poynting vector and polarization vector hybrid imaging method for microseismic reverse time positioning includes:

[0010] Step 1: Time-reverse propagation of the teleseismic wave field.

[0011] Taking advantage of the time symmetry and consistency of the wave field in forward and reverse propagation, the first step of source reverse time imaging is to load the seismic data as boundary conditions into the elastic wave equation in the form of a force source; then the wave field is reversely propagated to reconstruct the reverse time wave field.

[0012] Step 2: Solve the wave equation using the curved grid finite difference format.

[0013] The above equation is discretized using arbitrary curve grid finite difference scheme to solve the wave equation.

[0014] Step 3, applying the mixed imaging condition of Poynting vector and polarization vector to perform imaging.

[0015] For elastic wave fields, the direction of the wave field vector itself represents their polarization direction, and the propagation direction of the wave field can be represented by the Poynting vector. By performing a dot product of the solved wave field polarization vector and the Poynting vector, the imaging of the microseismic source can be achieved.

[0016] Step 4: Four-dimensional search and positioning of the maximum energy of microseismic imaging.

[0017] After imaging using the mixed imaging conditions of Poynting vector and polarization vector, a four-dimensional search for the maximum imaging energy is performed in the global spatial dimension and time dimension of imaging to determine the final spatial position and occurrence time of the microearthquake.

[0018] Furthermore, the teleseismic wave field is transmitted in reverse time:

[0019] Back propagation of the wavefield to reconstruct the reverse time wavefield is expressed by the following formula:

[0020] (1)

[0021] in represents the time-reverse reconstruction of the wave field, From the station location To any point in space The Green function of It is the station data transmitted in reverse time. It's time. is the total time length of the data, Represents the convolution operator.

[0022] In the Cartesian coordinate system, the first-order velocity-stress elastic wave equation of an isotropic medium expressed in the form of tensor components can be expressed as:

[0023] (2)

[0024] in, It is the velocity wave field No. i Quantity, is the stress component, and the time derivative is represented by the subscript t express, λ and μ is the Lamé constant, ρ is the medium density, is the Kronecker symbol. Note that the above expressions all omit the physical terms (source terms) and use the Einstein summation convention.

[0025] Furthermore, the curved grid finite difference format solves the wave equation.

[0026] Assume that the grid points in the computational domain are , the corresponding physical grid point is , the mapping relationship between the two can be expressed as:

[0027] (3)

[0028] According to the above mapping relationship, the coordinate transformation coefficient can be calculated as follows:

[0029] (4)

[0030] in represents a linear difference operator and can be computed using the same difference format used to solve the governing equations;

[0031] by For example, the control equation in the curvilinear coordinate system can be written as:

[0032] (5)

[0033] in, , , , , , , , , The spatial differential term in the above equation is solved using the DRP / opt MacCormack format with a collocated grid, and the temporal differential term is solved using the fourth-order Runge-Kutta format.

[0034] Furthermore, the imaging is performed using mixed imaging conditions of Poynting vector and polarization vector.

[0035] The Poynting vector of the wave field before decoupling can be expressed as:

[0036] (6)

[0037] in Poynting vector representing the wavefield before decoupling No. Quantity, are the components of the stress tensor, is the component of the velocity vector. For formula (6), since the P wave and S wave are not decoupled in the wave field, the calculated Poynting vector includes the contribution of both the P wave and the S wave, corresponding to the propagation directions of the P wave and the S wave in the entire velocity wave field, respectively.

[0038] The specific formula for imaging conditions can be written as:

[0039] (7)

[0040] in, In this hybrid imaging condition, the present invention directly calculates the polarization velocity of the original wave field. and Poynting vector The dot product of is taken and the square is used as the imaging value.

[0041] By converting the velocity wave field Expressed as , and the Poynting vector Expressed as , the formula (7) for the mixed imaging condition of the Poynting vector and the polarization vector can be decomposed into four parts:

[0042] (8)

[0043] Since the polarization direction of the S wave at the earthquake source is approximately orthogonal to the propagation direction of the P wave and the S wave, and The term can be ignored. Therefore, the mixed imaging condition of Poynting vector and polarization vector can be simplified as:

[0044] (9).

[0045] Furthermore, the microseismic imaging energy maximum value is searched and located in four dimensions.

[0046] The first step is to, at each moment after the wave field is reversed and the imaging condition is applied, for each fixed time , find the image body at The maximum value in space and its corresponding spatial coordinates:

[0047] (10)

[0048] here, Indicates at time Moment, imaging body The spatial coordinate corresponding to the maximum value of .

[0049] The second step is to In the first step, compare the maximum values ​​of each moment and find the global maximum value and its corresponding time. .

[0050] Further, the (11).

[0051] At the same time, the final spatial coordinates are obtained:

[0052] (12)

[0053] but It is the time when the micro-earthquake occurs. It is the three-dimensional spatial coordinate of the microearthquake.

[0054] Another object of the present invention is to provide a Poynting vector and polarization vector hybrid imaging system for microseismic reverse time positioning, comprising:

[0055] The reverse time propagation module is used to utilize the time symmetry and consistency of the forward and reverse propagation of the wave field. The first step of reverse time imaging of the source is to load the seismic data as boundary conditions into the elastic wave equation in the form of a force source; then the wave field is reversely propagated to reconstruct the reverse time wave field.

[0056] The solution module is used to solve the wave equation using the curved grid finite difference format; the above equation is discretized using the arbitrary curved grid finite difference format.

[0057] The imaging module is used to perform imaging using mixed imaging conditions of Poynting vector and polarization vector. For elastic wave fields, the directions of the wave field vectors themselves represent their polarization directions, while the propagation direction of the wave field can be represented by the Poynting vector.

[0058] The search and positioning module is used for the four-dimensional search and positioning of the maximum energy of microseismic imaging. After imaging using the mixed imaging conditions of Poynting vector and polarization vector, a four-dimensional search for the maximum imaging energy is performed in the global spatial dimension and time dimension of the imaging to determine the final spatial position and occurrence time of the microseism.

[0059] Another object of the present invention is to provide a computer device, which includes a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the Poynting vector and polarization vector hybrid imaging method for microseismic reverse time positioning.

[0060] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, enables the processor to execute the steps of the Poynting vector and polarization vector hybrid imaging method for microseismic reverse time positioning.

[0061] Another object of the present invention is to provide an information data processing terminal, which is used to implement the Poynting vector and polarization vector hybrid imaging system for microseismic reverse time positioning.

[0062] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0063] First, in the present invention, a new imaging condition is proposed for the time-reverse imaging of the earthquake source, namely, the mixed imaging condition of Poynting vector and polarization vector (PPMIC). This imaging condition directly uses the Poynting vector and velocity polarization vector (relative to the decoupled P-wave and S-wave wave fields) of the original wave field for dot product imaging. Considering that at the earthquake source point, the polarization direction of the P wave in the original wave field is almost parallel to the propagation direction represented by the Poynting vector, directly performing the dot product operation can enhance the energy value of the earthquake source imaging. The polarization direction of the S wave in the original wave field is almost orthogonal to the propagation direction represented by the Poynting vector, so their dot product can be ignored. PPMIC does not need to decouple the P wave and the S wave, nor does it need to introduce variables beyond the original wave equation, thereby saving a lot of computational load and memory usage in the time-reverse imaging of the earthquake source. In addition, it realizes the simultaneous use of the wave field polarization information and the propagation direction information, effectively suppressing the imaging artifacts caused by the inconsistent wave field propagation direction. Compared with the traditional scalar cross-correlation imaging condition (SCCIC), PPMIC can accurately determine the earthquake source position in data with low signal-to-noise ratio. The synthetic data imaging results of the 3D Marmousi model with surface undulations demonstrate the effectiveness of the proposed method.

[0064] The directional information of the wave field is crucial to improving the imaging results of source time reversal imaging (TRI). In order to avoid the attenuation of imaging energy at the source point, the traditional polarity-corrected scalar imaging condition (SCCIC) removes the directional information of the imaging wave field through modulo operation, so it is impossible to use the directional information of the wave field to suppress imaging artifacts. In order to further reduce imaging artifacts and eliminate the influence of terrain on imaging results, the present invention adopts a curved grid finite difference (FD) scheme to solve the wave equation in TRI, and proposes a Poynting vector and polarization vector hybrid imaging condition (PPMIC). Compared with conventional technical solutions, the technical solution of the present invention has the following advantages:

[0065] 1. The PPMIC proposed in the present invention can make full use of the polarization and propagation direction information of the imaging wave field, and further suppress the imaging artifacts that do not conform to the physical laws of imaging while ensuring the imaging resolution. Synthetic data imaging tests show that compared with traditional SCCIC, PPMIC performs better in artifact suppression. In the half-space and three-dimensional Marmousi models, the effect of PPMIC in artifact suppression is improved by about 2 times.

[0066] 2. The technical solution proposed in the present invention based on the combination of the curve grid finite difference method and PPMIC can adapt to the situation of complex undulating terrain in the reverse time positioning of microseismic data without the need for additional static correction processing of the data; at the same time, PPMIC can also accurately locate the position and occurrence time of each microseismic event when multiple microseismic sources are excited.

[0067] 3. Since the present invention does not need to decouple P waves and S waves, no additional variables are introduced in solving the wave equation, which can greatly save the computing time and computer storage of imaging. After testing, under the same hardware conditions, the computing time used for a single imaging of PPMIC is about 80.44% of that of traditional SCCIC; the computer video memory consumed by the GPU accelerated computing code is about 71.96% of that of traditional SCCIC.

[0068] In microseismic time-reverse imaging, the PPMIC proposed in the present invention is combined with a curve grid difference algorithm to use the time difference for imaging without decoupling the P-wave and S-wave, making full use of the polarization and propagation direction information of the wave field, significantly improving the imaging quality, especially in terms of false image suppression; at the same time, since there is no need to decouple the P-wave and S-wave, PPMIC also has advantages in computational efficiency and resource utilization, and compared with traditional imaging conditions, the computational time for each imaging is shortened and the memory consumption is lower. Therefore, the technical solution proposed in the present invention not only provides higher imaging accuracy, but also has lower computational cost and wider applicability, and is a more ideal solution for microseismic monitoring source time-reverse imaging.

[0069] Based on the Poynting vector and velocity polarization vector of the elastic wave field, a hybrid imaging condition of Poynting vector and polarization vector (PPMIC) for microseismic time-reverse imaging is proposed. This imaging condition can use the time difference between P waves and S waves for imaging without decoupling P waves and S waves, which saves a lot of computing time and computer storage compared with traditional imaging conditions. At the same time, this imaging condition makes full use of the polarization and propagation direction information of the wave field, which can better suppress imaging artifacts and improve the accuracy of microseismic positioning.

[0070] Combining PPMIC with the arbitrary curve grid finite difference algorithm has greatly expanded the application scenarios of the microseismic reverse time imaging algorithm. It can accurately image the microseismic data collected in complex terrain areas without the need for complex static correction processing of the seismic data. At the same time, PPMIC can also adapt to the situation where one microseismic data contains multiple microseismic events and accurately image and locate each microseismic event.

[0071] Second, the technical solution of the present invention fills the technical gap in the rapid and accurate reverse time positioning of microseismic data with extremely low signal-to-noise ratio at home and abroad.

[0072] Compared with traditional earthquake positioning methods, source reverse time imaging uses the overall seismic waveform as input, does not need to pick up earthquake travel time, and can locate seismic data with a lower signal-to-noise ratio; at the same time, based on the wave equation theory, the positioning process does not require any assumptions about the velocity medium, and is theoretically applicable to any complex medium. However, when the noise in the seismic data reaches a certain level, source reverse time imaging will also face the interference problem of imaging illusions. With the gradual increase in the difficulty of shale oil and gas extraction, the demand for rapid and accurate positioning of seismic data with extremely low signal-to-noise ratios and more complex surface receiving environments is becoming more and more urgent. For source reverse time imaging, developing more accurate, noise-resistant, and computationally efficient imaging conditions is the key to filling the gap in high-precision reverse time positioning technology for microseismic conditions with extremely low signal-to-noise ratios at home and abroad.

[0073] The polarization vector hybrid imaging condition (PPMIC) proposed in the present invention can simultaneously utilize the polarization direction and propagation direction information of the wave field during the reverse time imaging of microseismic data, constrain the wave field involved in the imaging, and avoid the imaging artifacts caused by data noise interfering with the microseismic positioning results, thereby achieving high-precision reverse time positioning of microseisms even when the data noise is very high; at the same time, the PPMIC proposed in the present invention does not require decoupling of the wave equation, greatly reducing the amount of calculation and computer storage used in the reverse time imaging of the earthquake source, and effectively filling the technical gap in fast and accurate microseismic positioning at home and abroad under extremely low signal-to-noise ratio conditions.

[0074] The technical solution of the present invention solves the technical problem of high-precision microseismic reverse time positioning when shale oil and gas exploration is carried out in areas with drastic terrain fluctuations in central and western my country.

[0075] my country's shale oil and gas resources are mainly distributed in the central and western regions where the terrain changes dramatically and the elevation difference is huge. The dramatic terrain fluctuations will inevitably affect the accuracy of the earthquake positioning results. How to efficiently eliminate the influence of terrain fluctuations in the process of earthquake source reverse time positioning is also a technical problem that needs to be solved urgently; at the same time, the central and western regions are also prone to geological disasters. The complex geological environment will further reduce the data quality of microseismic data collected in the region, making the current earthquake source reverse time imaging technology face the problem of imaging resolution and noise resistance needing to be improved, and there are many imaging illusions. The field of earthquake source reverse time imaging also needs to further develop high-precision earthquake source reverse time imaging methods that can adapt to complex undulating surfaces and complex geological environments.

[0076] The present invention combines the Poynting vector and polarization vector hybrid imaging condition (PPMIC) with the arbitrary curve grid finite difference algorithm, the DRP / opt MacCormack format for spatial differential solution and the fourth-order Runge-Kutta format for time differential solution, automatically considers the undulating terrain in the wave field back-propagation process, and effectively eliminates the influence of the violently undulating terrain on the microseismic reverse time imaging; at the same time, PPMIC can adapt to the data noise caused by complex geological conditions and effectively suppress the imaging illusion caused by data noise. Therefore, the present invention can well solve the technical problem of efficient and accurate positioning of low signal-to-noise ratio microseismic data when conducting shale oil and gas exploration in the central and western regions of my country with violently undulating terrain.

[0077] Third, in industrial applications, the microseismic reverse time positioning method of the present invention proposes an innovative solution to the shortcomings of the existing technology in terms of microseismic positioning accuracy and adaptability to complex environments, and achieves significant technical progress in terms of accuracy and efficiency. The details are as follows:

[0078] 1) Solved existing technical problems.

[0079] Low positioning accuracy: Traditional microseismic imaging methods usually use reflection wave method or simple superposition of seismic waveforms, which makes it difficult to achieve high-precision microseismic source positioning, especially in complex geological environments. The present invention uses a hybrid imaging method of Poynting vector and polarization vector to achieve consistency recognition of wave field energy concentration area and polarization direction through vector dot product conditions, greatly improving the resolution and accuracy of source imaging.

[0080] Poor adaptability to complex environments: Traditional methods are difficult to accurately simulate wave field propagation under irregular or complex geological conditions, resulting in large errors in microseismic source location. The present invention uses a finite difference format of an arbitrary curve grid to solve the wave equation, which can accurately adapt to different geological structures, reduce the impact of geological conditions on imaging results, and thus enhance the reliability of source location in complex environments.

[0081] Low imaging efficiency: Since the traditional method mainly relies on point-by-point scanning, it leads to large amount of calculation and low efficiency. The present invention uses a four-dimensional search method in the global spatial dimension and time dimension to quickly locate the energy concentration area after imaging, greatly improving the speed of earthquake source location.

[0082] 2) Significant technological progress has been achieved.

[0083] Accurate source location: Through the mixed imaging conditions of Poynting vector and polarization vector, the present invention can achieve high-precision location of microseismic sources. Compared with traditional technologies, the present invention can more accurately identify the source area where energy is concentrated, reduce positioning errors, and is particularly suitable for microseismic monitoring in shale gas extraction, oil and gas reservoir monitoring, and geothermal development.

[0084] Improved adaptability to complex geological conditions: The use of arbitrary curve grid finite difference format enables this method to accurately solve the wave equation in complex geological structures, reduce errors caused by irregular geological structures, and thus improve the quality of microseismic imaging. This innovation broadens the application scenarios of the method, enabling it to perform well in complex environments such as mines, oil fields, shale gas wells, and underground reservoirs.

[0085] High-efficiency earthquake source location speed: The four-dimensional space and time dimension search method significantly shortens the location time. By quickly locating the energy concentration area, the present invention maintains a balance between imaging accuracy and computational efficiency in big data processing, effectively reduces the computational cost in industrial applications, and improves the real-time nature of earthquake source location.

[0086] Enhanced real-time monitoring and early warning capabilities: This technical solution can monitor microseismic events in real time with high precision and efficiency, and is suitable for real-time early warning of geological changes in industrial scenarios such as oil and gas fields and mining areas. This capability provides a real-time feedback mechanism for industrial applications, helps to respond effectively before geological disasters or abnormal geological activities, and improves safety.

[0087] In summary, the technical solution of the present invention solves the existing technical problems such as insufficient microseismic imaging accuracy, poor adaptability to complex geology and low positioning efficiency, achieves significant technological progress, and provides an efficient and reliable source positioning solution for industries such as energy, geological exploration and underground engineering, which has great industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 It is a flow chart of a Poynting vector and polarization vector hybrid imaging method for reverse time positioning of microseismic earthquakes provided by an embodiment of the present invention.

[0089] Figure 2 It is a structural block diagram of a Poynting vector and polarization vector hybrid imaging system for microseismic reverse time positioning provided by an embodiment of the present invention.

[0090] Figure 3 It is a schematic diagram of the technical route provided by an embodiment of the present invention.

[0091] Figure 4 It is a real three-dimensional Marmousi longitudinal wave model (including undulating terrain) for forward simulation provided by an embodiment of the present invention ( Figure 4 (a) in the figure); Smoothed 3D Marmousi P-wave model (including undulating terrain) for reverse time propagation and positioning ( Figure 4 (b) in the figure); the black five-pointed star indicates the true location of the epicenter, i.e. (22 km, 18 km, -7.6 km); surface topography data ( Figure 4 (c) in the figure), where 441 conventional stations with a spacing of 1.6 km are deployed (the data of stations 148 to 231 represented by the red triangles are prepared for display in the sub-figure below); the noise-free Z component data recorded by stations 148 to 231 ( Figure 4 (d) in the figure); Z component data with strong random noise (SNR = 0.192) recorded by stations 148 to 231 ( Figure 4 (e) in the figure).

[0092] Figure 5 It is a comparison diagram of the time-reverse imaging results of the earthquake source of the three-dimensional Marmousi model (including undulating terrain) using synthetic data with a signal-to-noise ratio of 0.192 provided by an embodiment of the present invention.

[0093] Figure 6 This is a synthetic Z component data diagram of the three-dimensional Marmousi model multi-source simulation along stations No. 148 to No. 231 provided by an embodiment of the present invention.

[0094] Figure 7 This is a diagram of the imaging result (signal-to-noise ratio = 0.494) of the Poynting vector and polarization vector hybrid imaging condition (PPMIC) of the three-dimensional Marmousi model multi-source synthetic data provided by an embodiment of the present invention.

[0095] Figure 8It is a comparison chart of computing resources consumed by the Poynting vector and polarization vector hybrid imaging condition (PPMIC) and the traditional polarity-corrected scalar imaging condition (SCCIC) provided in an embodiment of the present invention.

[0096] Fig. 9 The imaging effect of the PPMIC proposed in the embodiment of the present invention is far better than that of the traditional imaging conditions, and can adapt to the situation of drastic terrain fluctuations. DETAILED DESCRIPTION

[0097] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0098] like Figure 1 As shown, the Poynting vector and polarization vector hybrid imaging method for microseismic reverse time positioning provided by an embodiment of the present invention includes the following steps:

[0099] S101, time-reverse propagation of teleseismic wave fields;

[0100] Taking advantage of the time symmetry and consistency of the wave field in forward and reverse propagation, the first step of source reverse time imaging is to load the seismic data as boundary conditions into the elastic wave equation in the form of a force source; then the wave field is reversely propagated to reconstruct the reverse time wave field.

[0101] S102, curved grid finite difference scheme for solving wave equations;

[0102] The above equation is discretized using arbitrary curve grid finite difference scheme to solve the wave equation.

[0103] S103, performing imaging using a mixed imaging condition of a Poynting vector and a polarization vector;

[0104] For elastic wave fields, the direction of the wave field vector itself represents their polarization direction, and the propagation direction of the wave field can be represented by the Poynting vector. By performing a dot product of the solved wave field polarization vector and the Poynting vector, the imaging of the microseismic source can be achieved.

[0105] S104, four-dimensional search and positioning of the maximum energy of microseismic imaging;

[0106] After imaging using the mixed imaging conditions of Poynting vector and polarization vector, a four-dimensional search for the maximum imaging energy is performed in the global spatial dimension and time dimension of imaging to determine the final spatial position and occurrence time of the microearthquake.

[0107] The hybrid imaging method of Poynting vector and polarization vector for reverse time positioning of microseismic events of the present invention realizes high-precision imaging and positioning of the microseismic source position through a series of sophisticated wave field processing steps. The specific principles are as follows:

[0108] 1. Time-reverse propagation of teleseismic wave fields.

[0109] First, in step S101, the teleseismic wave field of the microseism is reconstructed by reverse time propagation technology. The seismic data is loaded into the elastic wave equation in the form of a force source as a reverse time boundary condition. Using the time symmetry of the forward and reverse propagation of the wave field, the seismic wave field is back-propagated back to time zero to reconstruct the initial wave field of the source. This process can effectively restore the wave field distribution when the microseismic occurs, laying the foundation for subsequent precise imaging.

[0110] 2. Solution using the finite difference method on curved grids.

[0111] In S102, the finite difference format of arbitrary curved grid is used to solve the wave equation, so as to more accurately simulate the wave field propagation process in complex geological environment. This method allows numerical calculation in irregular curved grids, improves the accuracy of solving the wave equation, enables the wave field propagation process to adapt to the complexity of geological structure, and provides a basis for accurate inversion of seismic source location.

[0112] 3. Poynting vector and polarization vector hybrid imaging.

[0113] In step S103, microseismic source imaging is achieved by combining the Poynting vector and the polarization vector. The Poynting vector represents the energy flow direction of the wave field, while the polarization vector represents the vibration direction of the wave field. The dot product of the two is calculated as a hybrid imaging condition. This can not only highlight the energy concentration area of ​​the wave field, but also emphasize the source position where the polarization direction is consistent with the wave propagation direction, thereby improving the clarity and accuracy of the imaging.

[0114] 4. Four-dimensional search and positioning of maximum imaging energy.

[0115] After the imaging is completed, a four-dimensional search for the maximum imaging energy is performed in the spatial and temporal dimensions through step S104. The maximum imaging energy, i.e., the location of the earthquake source and its time of occurrence, is found by searching and locating in the global spatial dimensions (X, Y, and Z directions) and the temporal dimensions. This method achieves accurate positioning of microseismic events, solves the problem of low positioning accuracy of traditional imaging methods in complex environments, and improves the reliability and accuracy of microseismic imaging and positioning.

[0116] The time-reverse propagation of the teleseismic wave field provided by the embodiment of the present invention:

[0117] Back propagation of the wavefield to reconstruct the reverse time wavefield is expressed by the following formula:

[0118] (1)

[0119] in represents the time-reverse reconstruction of the wave field, From the station location To any point in space The Green function of It is the station data transmitted in reverse time. It's time. is the total time length of the data, Represents the convolution operator.

[0120] In the Cartesian coordinate system, the first-order velocity-stress elastic wave equation of an isotropic medium expressed in the form of tensor components can be expressed as:

[0121] (2)

[0122] in, It is the velocity wave field No. i Quantity, is the stress component, and the time derivative is represented by the subscript t express, λ and μ is the Lamé constant, ρ is the medium density, is the Kronecker symbol. Note that the above expressions all omit the physical terms (source terms) and use the Einstein summation convention.

[0123] The curved grid finite difference format provided in the embodiment of the present invention solves the wave equation:

[0124] Assume that the grid points in the computational domain are , the corresponding physical grid point is , the mapping relationship between the two can be expressed as:

[0125] (3)

[0126] According to the above mapping relationship, the coordinate transformation coefficient can be calculated as follows:

[0127] (4)

[0128] in represents a linear difference operator and can be computed using the same difference scheme used to solve the governing equations.

[0129] by For example, the control equation in the curvilinear coordinate system can be written as:

[0130] (5)

[0131] in, , , , , , , , , The spatial differential term in the above equation is solved using the DRP / opt MacCormack format with a collocated grid, and the temporal differential term is solved using the fourth-order Runge-Kutta format.

[0132] The embodiment of the present invention provides imaging using mixed imaging conditions of Poynting vector and polarization vector:

[0133] The Poynting vector of the wave field before decoupling can be expressed as:

[0134] (6)

[0135] in Poynting vector representing the wavefield before decoupling No. Quantity, are the components of the stress tensor, is the component of the velocity vector. For formula (6), since the P wave and S wave are not decoupled in the wave field, the calculated Poynting vector includes the contribution of both the P wave and the S wave, corresponding to the propagation directions of the P wave and the S wave in the entire velocity wave field, respectively.

[0136] The specific formula for imaging conditions can be written as:

[0137] (7)

[0138] in, In this hybrid imaging condition, the present invention directly calculates the polarization velocity of the original wave field. and Poynting vector The dot product of is taken and the square is used as the imaging value.

[0139] By converting the velocity wave field Expressed as , and the Poynting vector Expressed as , the formula (7) for the mixed imaging condition of the Poynting vector and the polarization vector can be decomposed into four parts:

[0140] (8)

[0141] Since the polarization direction of the S wave at the earthquake source is approximately orthogonal to the propagation direction of the P wave and the S wave, and The term can be ignored. Therefore, the mixed imaging condition of Poynting vector and polarization vector can be simplified as:

[0142] (9).

[0143] The four-dimensional search and positioning of the maximum energy of microseismic imaging provided by the embodiment of the present invention:

[0144] The first step is to, at each moment after the wave field is reversed and the imaging condition is applied, for each fixed time , find the image body at The maximum value in space and its corresponding spatial coordinates:

[0145] (10)

[0146] here, Indicates at time Moment, imaging body The spatial coordinate corresponding to the maximum value of .

[0147] The second step is to In the first step, compare the maximum values ​​of each moment and find the global maximum value and its corresponding time. .

[0148] Further, the (11)

[0149] At the same time, the final spatial coordinates are obtained:

[0150] (12)

[0151] but It is the time when the micro-earthquake occurs. It is the three-dimensional spatial coordinate of the microearthquake.

[0152] like Figure 2 As shown, a Poynting vector and polarization vector hybrid imaging system for microseismic reverse time positioning provided by an embodiment of the present invention includes:

[0153] The reverse time propagation module is used to utilize the time symmetry and consistency of the forward and reverse propagation of the wave field. The first step of reverse time imaging of the source is to load the seismic data as boundary conditions into the elastic wave equation in the form of a force source; then the wave field is reversely propagated to reconstruct the reverse time wave field.

[0154] The solution module is used to solve the wave equation using the curved grid finite difference format; the above equation is discretized using the arbitrary curved grid finite difference format.

[0155] The imaging module is used to perform imaging using mixed imaging conditions of Poynting vector and polarization vector. For elastic wave fields, the directions of the wave field vectors themselves represent their polarization directions, while the propagation direction of the wave field can be represented by the Poynting vector.

[0156] The search and positioning module is used for the four-dimensional search and positioning of the maximum energy of microseismic imaging. After imaging using the mixed imaging conditions of Poynting vector and polarization vector, a four-dimensional search for the maximum imaging energy is performed in the global spatial dimension and time dimension of the imaging to determine the final spatial position and occurrence time of the microseism.

[0157] Another object of the present invention is to provide a computer device, which includes a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the Poynting vector and polarization vector hybrid imaging method for microseismic reverse time positioning.

[0158] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, enables the processor to execute the steps of the Poynting vector and polarization vector hybrid imaging method for microseismic reverse time positioning.

[0159] Another object of the present invention is to provide an information data processing terminal, which is used to implement the Poynting vector and polarization vector hybrid imaging system for microseismic reverse time positioning.

[0160] The present invention is specifically implemented:

[0161] The present invention can be implemented by the following technical measures, and the specific steps are as follows:

[0162] 1. Time-reverse propagation of teleseismic wave fields.

[0163] Source time-reversal imaging (TRI) is a method used in seismology to accurately locate the source of earthquakes or microseismic events. It mainly uses the time symmetry and consistency of the forward and reverse propagation of the wave field. The first step of source time-reversal imaging is to load the seismic data as boundary conditions into the elastic wave equation in the form of a force source. The wave field is then back-propagated to reconstruct the reverse wave field (Zhou et al., 2022). This process can be expressed by the following formula:

[0164] (1)

[0165] in represents the time-reverse reconstruction of the wave field, From the station location To any point in space The Green function of It is the station data transmitted in reverse time. It's time. is the total time length of the data, Represents the convolution operator. The process of reverse time propagation of the wave field is controlled by the elastic wave equation. There are many mathematical equivalent forms of the wave equation, including the second-order displacement form, the first-order velocity-stress form, etc. Among them, in the finite difference numerical solution, the second-order displacement equation has spatial derivative terms of the medium parameters. When the medium changes drastically, the finite difference solution of the equation will have a relatively large numerical dispersion, and the solution process is prone to instability. Therefore, the present invention mainly solves the first-order velocity-stress equation. In the Cartesian coordinate system, the first-order velocity-stress elastic wave equation of the isotropic medium expressed in the form of tensor components can be expressed as:

[0166] (2)

[0167] in, It is the velocity wave field No. i Quantity, is the stress component, and the time derivative is represented by the subscript t express, λ and μ is the Lamé constant, ρ is the medium density, is the Kronecker symbol. Note that the above expressions all omit the physical terms (source terms) and use the Einstein summation convention.

[0168] 2. The curved grid finite difference format is used to solve the wave equation.

[0169] In order to adapt to the time-reverse imaging of earthquake sources with undulating terrain, the present invention discretizes the above formula using the arbitrary curve grid finite difference format. Assume that the grid points in the calculation area are , the corresponding physical grid point is , the mapping relationship between the two can be expressed as:

[0170] (3)

[0171] According to the above mapping relationship, the coordinate transformation coefficient can be calculated as follows:

[0172] (4)

[0173] in represents a linear difference operator and can be computed using the same difference scheme used to solve the governing equations.

[0174] by For example, the control equation in the curvilinear coordinate system can be written as:

[0175] (5).

[0176] in, , , , , , , , , The spatial differential term in the above equation is solved using the DRP / opt MacCormack format with a collocated grid, and the temporal differential term is solved using the fourth-order Runge-Kutta format.

[0177] 3. Use the mixed imaging conditions of Poynting vector and polarization vector for imaging.

[0178] For elastic wave fields, the direction of the wave field vector itself represents their polarization direction, and the propagation direction of the wave field can be represented by the Poynting vector. According to previous research results, the Poynting vector of the wave field before decoupling can be expressed as:

[0179] (6)

[0180] in Poynting vector representing the wavefield before decoupling No. Quantity, are the components of the stress tensor, is the component of the velocity vector. For formula (6), since the P wave and S wave are not decoupled in the wave field, the calculated Poynting vector includes the contribution of both the P wave and the S wave, corresponding to the propagation directions of the P wave and the S wave in the entire velocity wave field, respectively.

[0181] With the Poynting vector representing the wave field propagation direction, combined with the velocity wave field representing the wave field polarization direction obtained by solving the wave equation, the hybrid imaging condition of the Poynting vector and the polarization vector proposed in the present invention can be used to image microseismic events during the wave field back propagation process. The specific formula of the imaging condition can be written as:

[0182] (7)

[0183] in, In this hybrid imaging condition, the present invention directly calculates the polarization velocity of the original wave field. and Poynting vector The dot product of is obtained and the square of it is used as the imaging value. The calculation process is simple and clear, but it can simultaneously utilize the information of the wave field propagation direction and the polarization direction to suppress the imaging illusion that does not conform to the physical laws of imaging. The suppression mechanism of the imaging conditions of the present invention on the imaging illusion will be introduced below.

[0184] By converting the velocity wave field Expressed as , and the Poynting vector Expressed as , the formula (7) for the mixed imaging condition of the Poynting vector and the polarization vector can be decomposed into four parts:

[0185] (8)

[0186] Since the polarization direction of the S wave at the earthquake source is approximately orthogonal to the propagation direction of the P wave and the S wave, and The term can be ignored. Therefore, the mixed imaging condition of Poynting vector and polarization vector can be simplified as:

[0187] (9).

[0188] At any position in the imaging space, and are approximately parallel, so their dot product can take normal values ​​at the real source location or the imaging illusion, and cannot suppress the imaging illusion; but near the source point, and Approximately parallel, dot product calculation can achieve maximum imaging energy. On the contrary, when far away from the source point, and It is difficult to meet the parallel condition, and the direct dot product will cause the imaging energy of this area to be weakened. Therefore, the dot product of this part can increase the energy of the real source position, while suppressing the imaging artifacts caused by the dot product of the wave field where the propagation direction of the P wave field and the polarization direction of the S wave are not parallel. It should be noted that formula (9) is to explain the principle of suppressing imaging artifacts by the mixed imaging conditions of the Poynting vector and the polarization vector. In actual application, it is not necessary to decouple the P wave and the S wave, and the formula of the imaging condition can still use formula (7).

[0189] 4. Four-dimensional search and positioning of the maximum energy of microseismic imaging.

[0190] After imaging using the hybrid imaging conditions of the Poynting vector and polarization vector proposed in the present invention, a four-dimensional search for the maximum imaging energy is required in the global spatial dimension and time dimension of the imaging to determine the final spatial position and time of the microseismic event. In order to avoid storing a large amount of four-dimensional data bodies of imaging results during the search process, the present invention intends to locate the final source position and time of the event through the following two steps:

[0191] The first step is to, at each moment after the wave field is reversed and the imaging condition is applied, for each fixed time , find the image body at The maximum value in space and its corresponding spatial coordinates:

[0192] (10)

[0193] here, Indicates at time Moment, imaging body The spatial coordinate corresponding to the maximum value of .

[0194] The second step is to In the first step, compare the maximum values ​​of each moment and find the global maximum value and its corresponding time. :

[0195] (11)

[0196] At the same time, the final spatial coordinates are obtained:

[0197] (12)

[0198] but It is the time when the micro-earthquake occurs. It is the three-dimensional spatial coordinates of micro-earthquakes. In this process, there is no need to store the imaging data body, only the coordinate information at each moment needs to be output. Basically, there is no requirement for computer storage, which can save a lot of computer resources and make real-time monitoring of micro-earthquakes feasible.

[0199] Figure 3 Schematic diagram of the technical route.

[0200] Figure 4 (a) is the real 3D Marmousi P-wave model (including undulating terrain) used for forward modeling. Figure 4 (b) Smoothed 3D Marmousi P-wave model (including undulating terrain) for reverse time propagation and positioning. The black five-pointed star indicates the true location of the earthquake source, i.e. (22 km, 18 km, -7.6 km). Figure 4 (c) is the surface terrain data; 441 conventional stations with an interval of 1.6 km are deployed here (the data of stations No. 148 to 231 represented by the red triangles are to be shown in the sub-figure below). Figure 4 (d) in the figure is the noise-free Z component data recorded by stations 148 to 231. Figure 4 (e) in the figure shows the Z component data recorded by stations 148 to 231, which contains strong random noise (S / N ratio = 0.192).

[0201] Figure 5 Using synthetic data with a signal-to-noise ratio of 0.192 ( Figure 4 (e) compares the time-reversal imaging results of the earthquake source in the three-dimensional Marmousi model (including undulating terrain). Figure 5 (a) The imaging result of the Poynting vector and polarization vector hybrid imaging condition (PPMIC) proposed in the present invention. The left image shows the combined image of the x, y, and z slices through the positioning point, and the right image is a separate enlarged image of the same area, highlighting the relationship between the positioning result (five-pointed star) and the true position (circle). The consistency between the positioning result and the true position indicates accurate positioning. Figure 5 (b) The imaging result of the conventional polarity-corrected scalar imaging condition (SCCIC), where the imaging artifact causes the positioning point (pentagram) to be far away from the true position (circle), indicating inaccurate positioning. Figure 5 (c) The maximum imaging value in the whole space changes with time. In this test, the detected earthquake time PPMIC is 0.9 seconds and SCCIC is 11.8 seconds. The source time of the real earthquake is 1.0 seconds. This shows that the PPMIC earthquake time is correct, and the SCCIC is quite different from the real result. PPMIC can better suppress imaging artifacts than traditional SCCIC.

[0202] Figure 6 Synthetic Z-component data of three-dimensional Marmousi model multi-source simulation along stations 148 to 231. Figure 6 (a) Noise-free data; Figure 6 (b) Data with a signal-to-noise ratio of 0.494.

[0203] Figure 7 The Poynting vector and polarization vector hybrid imaging condition (PPMIC) imaging results of the three-dimensional Marmousi model multi-source synthetic data (signal-to-noise ratio = 0.494). Figure 7 (a) The variation of the maximum imaging value in the whole space with time. Six microseismic events were detected, with the occurrence times of 4.16 seconds, 8.58 seconds, 13.48 seconds, 18.08 seconds, 23.12 seconds and 24.88 seconds respectively. Figure 7 (b) Comparison of the spatial positions of the located microseismic events and the real event positions. The positioning results are basically consistent with the real results, indicating that PPMIC can also correctly locate multiple earthquake sources.

[0204] Figure 8 Comparison of computational resources consumed by Poynting vector and polarization vector hybrid imaging condition (PPMIC) and traditional polarity-corrected scalar imaging condition (SCCIC). Figure 8 (a) Computation time comparison. Figure 8 (b) shows the GPU memory usage. For the traditional SCCIC, the average time consumed for each imaging is 34.81 seconds. In contrast, PPMIC does not need to solve the decoupled P-wave and S-wave equations, and the time consumed is only 28.01 seconds, accounting for 80.44% of the SCCIC calculation time. Similarly, since PPMIC does not need to store the decoupled P-wave and S-wave arrays, the memory consumption for each imaging is 847 MB, which is only 71.96% of the 1177 MB required by SCCIC.

[0205] 1. Specific application fields or related products of the present invention.

[0206] The microseismic reverse time imaging based on the Poynting vector and polarization vector hybrid imaging condition (PPMIC) proposed in the present invention can be applied to the following fields: (1) Unconventional energy development, such as shale gas, tight gas and coalbed methane exploitation. The microseismic reverse time imaging technology proposed in the present invention can monitor the microseismic activity generated during hydraulic fracturing, optimize the fracture network design, and improve resource recovery efficiency. (2) Geothermal resource development. The microseismic reverse time imaging technology proposed in the present invention can track the seepage path and reservoir structure after water injection to ensure the sustainable use of thermal energy. (3) Carbon capture and storage (CCS) field. The microseismic reverse time imaging technology proposed in the present invention can monitor the microseismic activity during the storage process to ensure the success of the storage. (4) In the field of mining and tailings dam monitoring, the microseismic reverse time imaging technology proposed in the present invention can be used to evaluate the stability of the goaf and dam structure and reduce the risk of geological disasters; (5) In the field of groundwater monitoring and environmental protection, the microseismic reverse time imaging technology proposed in the present invention can be used to track the dynamic changes of groundwater and prevent ground subsidence and resource depletion; (6) In the field of earthquake science research, the microseismic reverse time imaging technology proposed in the present invention can be used to analyze microseismic events in fault systems, reveal changes in crustal stress, and provide a basis for earthquake early warning; (7) In the field of large-scale engineering construction, the microseismic reverse time imaging technology proposed in the present invention can be used to monitor blasting in tunnel, subway and bridge construction to ensure the safe progress of the project.

[0207] 2. Relevant evidence of the technical effects obtained by the embodiments of the present invention.

[0208] The microseismic time-reverse imaging based on the Poynting vector and polarization vector hybrid imaging condition (PPMIC) proposed in the present invention has been successfully applied to the source imaging of the continuous microseismic data set monitored in the shale gas field in the southern Sichuan Basin of my country.

[0209] like Fig. 9As shown, in order to verify the actual application effect of the present invention in reverse time positioning of microseismic data, the inventor's team successfully deployed 251 Zland 3C 5 Hz nodes in the shale gas field in the southern Sichuan Basin of my country, and carried out microseismic data collection and monitoring for 35 days. The collection area is about 7000 meters in the east-west direction and about 6000 meters in the north-south direction. The continuous microseismic data set of the work area is imaged in reverse time using the hybrid imaging conditions of the Poynting vector and polarization vector proposed in the present invention, and the imaging results with higher resolution and fewer artifacts are obtained than the traditional methods. At the same time, considering the terrain undulation problem commonly faced by the exploration of unconventional oil and gas resources in the central and western regions of my country, the curve grid finite difference algorithm is used to solve the wave equation in the process of reverse time propagation of the wave field, thereby eliminating the influence of elevation differences in the observation system on the imaging results and avoiding complex data static correction problems. The proposal and application of the present invention are of great significance to improving the applicability and accuracy of microseismic monitoring, guiding hydraulic fracturing operations, and ensuring my country's energy security. Application effect diagram of the embodiment of the present invention: Imaging effect of the PPMIC proposed by the present invention ( Fig. 9 (c) is much better than the imaging effect of traditional imaging conditions ( Fig. 9 (d) in the figure), and can adapt to conditions with drastic terrain fluctuations.

[0210] It should be noted that the embodiments of the present invention can be implemented by hardware, software, or a combination of software and hardware. The hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated design hardware. It can be understood by a person of ordinary skill in the art that the above-mentioned devices and methods can be implemented using computer executable instructions and / or contained in a processor control code, such as a carrier medium such as a disk, CD or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. Such code is provided on the carrier medium. The device and its modules of the present invention can be implemented by hardware circuits such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., can also be implemented by software executed by various types of processors, and can also be implemented by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0211] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modification, equivalent substitution and improvement made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A hybrid imaging method of Poynting vector and polarization vector for microseismic reverse time positioning, characterized in that: The following steps are involved: Step 1, time-reverse propagation of the teleseismic wave field; Using the time symmetry and consistency of the wave field in forward and reverse propagation, the first step of source reverse imaging is to load the seismic data as boundary conditions into the elastic wave equation in the form of force source; then the wave field is reversely propagated to reconstruct the reverse wave field; Step 2, solving the wave equation using a curved grid finite difference format; Discretize the wave equation using arbitrary curvilinear grid finite difference scheme; Step 3, applying the mixed imaging condition of Poynting vector and polarization vector to perform imaging; For elastic wave fields, the direction of the wave field vectors themselves represents their polarization direction, while the propagation direction of the wave field is represented by the Poynting vector; Step 4: Four-dimensional search and positioning of the maximum energy of microseismic imaging; After imaging using the mixed imaging conditions of Poynting vector and polarization vector, a four-dimensional search for the maximum imaging energy is performed in the global spatial dimension and time dimension of the imaging to determine the final spatial position and time of the microearthquake. The imaging is performed by applying the mixed imaging conditions of Poynting vector and polarization vector: The Poynting vector of the wave field before decoupling is expressed as: (1) in i and j They refer to the direction components (x, y, z) of the three-dimensional space respectively. E i Poynting vector representing the wavefield before decoupling E No. i Quantity, is the stress tensor i The amount in j Direction projection, is the velocity vector j components; for formula (1), since the P wave and S wave are not decoupled in the wave field, the calculated Poynting vector includes the contribution of both the P wave and the S wave, which correspond to the propagation directions of the P wave and the S wave in the entire velocity wave field respectively; The specific formula of imaging conditions is written as: l(x) =[v(x)·E(x)] 2 (2) in, I The imaging results are shown in Figure 2. Under this hybrid imaging condition, the polarization velocity v and Poynting vector of the original wave field are directly calculated. The dot product of , and taking the square of it as the imaging value; By converting the velocity wave field Expressed as , and the Poynting vector Expressed as , the formula (2) of the mixed imaging condition of Poynting vector and polarization vector is decomposed into four parts: l(x) =[v P (x)·E P (x) +v P (x)·E S (x) +v S (x)·E P (x) +v S (x)·E S (x)] 2 (3) Since the polarization direction of the S wave at the earthquake source is approximately orthogonal to the propagation direction of the P wave and the S wave, v S (x)·E P (x) and v S (x)·E S (x) is ignored; therefore, the mixed imaging condition of Poynting vector and polarization vector is simplified to: l(x) =[v P (x)·E P (x) +v P (x)·E S (x) ] 2 (4)。 2. The Poynting vector and polarization vector hybrid imaging method for microseismic reverse time positioning according to claim 1, characterized in that: The time-reverse propagation of the teleseismic wave field is: Back propagation of the wavefield to reconstruct the reverse time wavefield is expressed by the following formula: (5) in In the middle, it indicates a station. represents the direction component of the source point, represents the directional component of the observation point, represents the time-reversal reconstruction of the wave field, From the station location To any point in space The Green function of It is the station data transmitted in reverse time. It's time. is the total time length of the data, represents the convolution operator; In the Cartesian coordinate system, the first-order velocity-stress elastic wave equation of an isotropic medium expressed in the form of tensor components is expressed as: (6) in i , j and k They refer to the direction components (x, y, z) of the three-dimensional space respectively. v i It is the velocity wave field No. i Quantity, , and The velocity components are , and In space j , i , k Directional derivatives; , is the stress tensor i The amount in j Direction projection, yes In space j Directional derivatives; time derivatives use subscripts t express, λ and μ is the Lamé constant, ρ is the medium density, is the Kronecker symbol; note that the above expressions all omit the physical terms and use the Einstein summation convention.

3. The Poynting vector and polarization vector hybrid imaging method for microseismic reverse time positioning according to claim 1, characterized in that: The curved grid finite difference scheme solves the wave equation: Assume that the grid points in the computational domain are , the corresponding physical grid point is , the mapping relationship between the two is expressed as: (7) According to the above mapping relationship, the coordinate transformation coefficient is calculated in the following way: (8) Where D represents the linear difference operator, which is calculated using the same difference format as that used to solve the governing equations; by For example, the control equation in the curvilinear coordinate system is written as: (9) in, , , , , , , , , represents the coordinate conversion coefficient from Cartesian coordinates to curvilinear coordinates; the spatial differential term in the above formula is solved using the DRP / opt MacCormack format of the collocated grid, and the time differential term is solved using the fourth-order Runge-Kutta format.

4. The Poynting vector and polarization vector hybrid imaging method for microseismic reverse time positioning according to claim 1, characterized in that: The four-dimensional search and positioning of the maximum energy of microseismic imaging: The first step is to, at each moment after the wave field is reversed and the imaging condition is applied, for each fixed time , find the image body at The maximum value in space and its corresponding spatial coordinates: （10） here, Indicates at time Moment, imaging body The spatial coordinates corresponding to the maximum value of ; The second step is to In the first step, compare the maximum values ​​of each moment and find the global maximum value and its corresponding time. .

5. The Poynting vector and polarization vector hybrid imaging method for microseismic reverse time positioning according to claim 4, characterized in that: Said (11) At the same time, the final spatial coordinates are obtained: （12） but It is the time when the micro-earthquake occurs. It is the three-dimensional spatial coordinate of the microearthquake.

6. A Poynting vector and polarization vector hybrid imaging system for microseismic reverse time positioning, which implements the Poynting vector and polarization vector hybrid imaging method for microseismic reverse time positioning as described in any one of claims 1 to 5, characterized in that: The Poynting vector and polarization vector hybrid imaging system for microseismic reverse time positioning comprises: The reverse time propagation module is used to exploit the time symmetry and consistency of the wave field in forward and reverse propagation. The first step of reverse time imaging of the source is to load the seismic data as boundary conditions into the elastic wave equation in the form of a force source. The wave field is then propagated backward to reconstruct the reverse time wave field. Solving module, used for solving wave equations using a finite difference scheme on a curved grid; discretizing wave equations using a finite difference scheme on an arbitrary curved grid; An imaging module is used to perform imaging using mixed imaging conditions of Poynting vector and polarization vector. For elastic wave fields, the direction of the wave field vectors themselves represents their polarization direction, while the propagation direction of the wave field is represented by the Poynting vector. The search and positioning module is used for the four-dimensional search and positioning of the maximum energy of microseismic imaging. After imaging using the mixed imaging conditions of Poynting vector and polarization vector, a four-dimensional search for the maximum imaging energy is performed in the global spatial dimension and time dimension of the imaging to determine the final spatial position and occurrence time of the microseism.

7. A computer device, characterized in that: The computer device includes a memory and a processor, the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the Poynting vector and polarization vector hybrid imaging method for microseismic reverse time positioning as described in any one of claims 1-5.

8. A computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the processor executes the steps of the Poynting vector and polarization vector hybrid imaging method for reverse time positioning of microseismic according to any one of claims 1 to 5.

9. An information data processing terminal, characterized in that: The information data processing terminal is used to implement the Poynting vector and polarization vector hybrid imaging system for microseismic reverse time positioning as described in claim 6.

Images