1. A Kraukls wave simulation method excited by hydraulic fracturing is applied to monitoring artificial fractures under the hydraulic fracturing method, and is characterized by comprising the following steps:

s1), acquiring a crack model of the artificial crack, and performing discretization processing on the crack model according to a preset subdivision rule to obtain a grid cell model;

s2), scanning all grid cells, screening out the grid cells relevant to the crack openings, and determining the attribute parameters of the grid cells relevant to the crack openings;

s3) calculating the displacement load of the crack openings corresponding to the grid cells related to the crack openings one by one according to the attribute parameters of the grid cells related to the crack openings and a preset displacement load calculation formula;

s4) carrying out displacement load assembly on all grid units according to the displacement load calculation result, and adding the assembled displacement load to the displacement item of the conventional finite element to obtain a final finite element equation;

s5) solving the finite element equation, and obtaining and outputting a simulation result.

2. The Kraukls wave simulation method excited by hydraulic fracturing as claimed in claim 1, wherein in step S1), the obtaining of the fracture model of the artificial fracture and the discretization of the fracture model according to the preset subdivision rule to obtain the grid cell model comprises:

obtaining model parameters of a crack model;

and fitting the shape of each crack by using the Delaunay isoparametric triangular grid unit model and the model parameters to obtain a grid unit model.

3. The method for Kraukls wave simulation of hydraulic fracture stimulation of claim 2, wherein the model parameters include:

the spatial position of the crack, the pore diameter of the crack, the smoothness of the crack surface and the trend of the crack.

4. The Kraukls wave simulation method of hydraulic fracture stimulation according to claim 2, wherein the fitting of each fracture shape using the Delaunay et al triangular mesh unit model and the model parameters comprises:

at each crack opening position, the corresponding grid unit has one edge which is superposed with the crack opening.

5. The Kraukls wave simulation method of claim 4, wherein the property parameters of the grid cells related to the fracture openings in step S2) include:

the number of the grid cell nodes on the edge corresponding to the crack opening vector is the same as the number of the grid cell nodes on the edge corresponding to the crack opening vector.

6. The Kraukls wave simulation method for hydraulic fracturing stimulation according to claim 5, wherein in step S3), the step of calculating the displacement load at the fracture openings corresponding to each grid cell associated with the fracture openings one by one according to the attribute parameters of the grid cells associated with the fracture openings and a preset displacement load calculation formula comprises:

selecting a grid unit related to the crack opening each time, and determining the number and the coordinates of grid unit nodes on the edge, which is coincident with the crack opening vector, in the grid unit related to the crack opening;

calculating the displacement load of the current grid unit node coordinate to represent the displacement load at the current crack opening;

obtaining a displacement load method equation according to a preset space scale function and a preset time and wavelet function, wherein the expression relation is as follows:

F_time＝F_space·F_time

wherein, F_spaceIs a preset spatial scale function;

F_timeis a predetermined time and wavelet function.

7. The Kraukls wave simulation method of hydraulic fracture stimulation of claim 6, wherein the preset spatial scale function expression is:

wherein the content of the first and second substances,the position vector of the node at the opening relative to the central point of the crack is obtained;

is a vector characterizing the fracture opening;

the expression of the function of the preset time and the wavelet is as follows:

wherein A is₀Is the amplitude coefficient;

tau is a time scale factor of the wavelet function;

t₀is the central time of the wavelet function;

t is a time series.

8. The Kraukls wave simulation method for hydraulic fracture stimulation according to claim 1, wherein the step S4) of assembling displacement loads of all grid cells according to the displacement load calculation result comprises:

obtaining the displacement load calculation results of unit nodes of all grid units related to the crack openings;

performing displacement load assembly on unit nodes of all grid units related to the crack openings according to a displacement load assembly calculation formula to obtain a final displacement load matrix; wherein the displacement load assembly calculation formula is as follows:

wherein F is a final displacement load matrix;

N_openingthe number of nodes falling at the crack opening is shown;

C_ia number position vector for describing the ith node falling at the crack opening;

F_ithe displacement load of the ith node at the crack opening is shown.

9. A hydraulic fracture stimulation Kraukls wave simulation system for artificial fracture monitoring under a hydraulic fracturing method, the system comprising:

the acquisition unit is used for acquiring a crack model of the artificial crack;

a processing unit to:

carrying out discretization treatment on the crack model according to a preset subdivision rule to obtain a grid unit model;

scanning all grid cells, screening out the grid cells related to the crack openings, and determining the attribute parameters of the grid cells related to the crack openings;

calculating the displacement load of the grid units related to the crack openings at the corresponding crack openings one by one according to the attribute parameters of the grid units related to the crack openings and a preset displacement load calculation formula;

performing displacement load assembly on all grid units according to the displacement load calculation result, and adding the assembled displacement load to a displacement item of a conventional finite element to obtain a final finite element equation;

and the output unit is used for solving the finite element equation to obtain and output a simulation result.

10. A computer-readable storage medium having instructions stored thereon, which when executed on a computer, cause the computer to perform the hydraulic fracture stimulation Kraukls wave simulation method of any one of claims 1 to 8.

Background

Hydraulic fracturing is a well stimulation tool with wide application prospect, and is the main mode for exploiting natural gas at present, and requires that water with a large amount of doped chemical substances is filled into a shale layer to carry out hydraulic fracture so as to release natural gas. Therefore, the hydraulic fracturing is a widely applied reservoir transformation means, and particularly aims at compact reservoirs such as shale, carbonate and the like. When the reservoir stratum is reformed through water conservancy fracturing, earthquake waves can be excited when rock stratum cracks crack. The Krauklis wave is a guided wave excited in the process, the guided wave propagates along the crack spreading direction, and the propagation characteristic of the guided wave is closely related to the development degree and the geometrical shape of the crack. In order to effectively locate the micro-seismic event caused by hydraulic fracturing and depict the fracture generated by fracturing so as to facilitate the preparation of accident potential or the location fracture for storage, the Krauklis wave generated by excitation in the fracture process has great value. But due to the characteristic of strong randomness of cracking cracks, the generation and propagation of Krauklis waves are also perceived to have strong randomness. Therefore, no method for effectively and accurately performing Krauklis wave simulation exists at present. Aiming at the problem that the current Krauklis wave simulation excited by hydraulic fracturing is difficult, a Kraukls wave simulation method excited by hydraulic fracturing needs to be created.

Disclosure of Invention

The invention aims to provide a method for simulating Kraukls wave excited by hydraulic fracturing, which at least solves the problem that the current Krauklis wave excited by hydraulic fracturing is difficult to simulate.

In order to achieve the above object, a first aspect of the present invention provides a hydraulic fracturing stimulation Kraukls wave simulation method for monitoring artificial fractures under a hydraulic fracturing method, the method including: s1), acquiring a crack model of the artificial crack, and performing discretization processing on the crack model according to a preset subdivision rule to obtain a grid cell model; s2), scanning all grid cells, screening out the grid cells relevant to the crack openings, and determining the attribute parameters of the grid cells relevant to the crack openings; s3) calculating the displacement load of the crack openings corresponding to the grid cells related to the crack openings one by one according to the attribute parameters of the grid cells related to the crack openings and a preset displacement load calculation formula; s4) carrying out displacement load assembly on all grid units according to the displacement load calculation result, and adding the assembled displacement load to the displacement item of the conventional finite element to obtain a final finite element equation; s5) solving the finite element equation, and obtaining and outputting a simulation result.

Optionally, in step S1), the obtaining of the fracture model of the artificial fracture and the discretization of the fracture model according to the preset splitting rule to obtain the grid cell model include: obtaining model parameters of a crack model; and fitting the shape of each crack by using the Delaunay isoparametric triangular grid unit model and the model parameters to obtain a grid unit model.

Optionally, the model parameters include: the spatial position of the crack, the pore diameter of the crack, the smoothness of the crack surface and the trend of the crack.

Optionally, the fitting of the shape of each crack by using the Delaunay isoparametric triangular mesh unit model and the model parameters includes: at each crack opening position, the corresponding grid unit has one edge which is superposed with the crack opening.

Optionally, in step S2), the attribute parameters of the grid cells related to the crack openings include: the number of the grid cell nodes on the edge corresponding to the crack opening vector is the same as the number of the grid cell nodes on the edge corresponding to the crack opening vector.

Optionally, in step S3), the step of calculating the displacement load of the crack opening corresponding to each grid cell associated with the crack opening one by one according to the attribute parameters of the grid cell associated with the crack opening and a preset displacement load calculation formula includes: selecting a grid unit related to the crack opening each time, and determining the number and the coordinates of grid unit nodes on the edge, which is coincident with the crack opening vector, in the grid unit related to the crack opening; calculating the displacement load of the current grid unit node coordinate to represent the displacement load at the current crack opening; obtaining a displacement load method equation according to a preset space scale function and a preset time and wavelet function, wherein the expression relation is as follows:

F_time＝F_space·F_time

wherein, F_spaceIs a preset spatial scale function; f_timeIs a predetermined time and wavelet function.

Optionally, the preset spatial scale function expression is as follows:

wherein the content of the first and second substances,the position vector of the node at the opening relative to the central point of the crack is obtained;is a vector characterizing the fracture opening; the expression of the function of the preset time and the wavelet is as follows:

wherein A is₀Is the amplitude coefficient; tau is a time scale factor of the wavelet function; t is t₀Is the central time of the wavelet function; t is a time series.

Optionally, in step S4), the assembling the displacement load of all the grid cells according to the calculation result of the displacement load includes: obtaining the displacement load calculation results of unit nodes of all grid units related to the crack openings; performing displacement load assembly on unit nodes of all grid units related to the crack openings according to a displacement load assembly calculation formula to obtain a final displacement load matrix; wherein the displacement load assembly calculation formula is as follows:

wherein F is a final displacement load matrix; n is a radical of_openingThe number of nodes falling at the crack opening is shown; c_iA number position vector for describing the ith node falling at the crack opening; f_iThe displacement load of the ith node at the crack opening is shown.

The invention provides a hydraulic fracturing excited Kraukls wave simulation system, which is used for monitoring artificial fractures under a hydraulic fracturing method and comprises the following components: the acquisition unit is used for acquiring a crack model of the artificial crack; a processing unit to: carrying out discretization treatment on the crack model according to a preset subdivision rule to obtain a grid unit model; scanning all grid cells, screening out the grid cells related to the crack openings, and determining the attribute parameters of the grid cells related to the crack openings; calculating the displacement load of the grid units related to the crack openings at the corresponding crack openings one by one according to the attribute parameters of the grid units related to the crack openings and a preset displacement load calculation formula; performing displacement load assembly on all grid units according to the displacement load calculation result, and adding the assembled displacement load to a displacement item of a conventional finite element to obtain a final finite element equation; and the output unit is used for solving the finite element equation to obtain and output a simulation result.

In another aspect, the present invention provides a computer-readable storage medium having instructions stored thereon, which when executed on a computer, cause the computer to perform the above-described hydraulic fracture stimulation Kraukls wave simulation method.

Through the technical scheme, the randomized crack model is triangulated, so that the shape of the crack is changed into a regular and recyclable triangular combination to form a grid unit model. Then, grid units related to crack openings are screened out from the grid unit model, displacement load calculation is carried out, and the calculated displacement loads are assembled into the grid units correspondingly. The assembled grid unit model is fitted with the actual displacement load condition of the crack opening, the displacement load condition represents the displacement condition of the crack, and the displacement item is used as known data to carry out finite element equation solution, so that the simulation result of the Kraukls wave can be obtained. The method is used for coping with the random property generated by fracturing, realizing the accurate simulation of the Kraukls wave excited by hydraulic fracturing, and solving the problem of difficult simulation of the Krauklis wave excited by hydraulic fracturing at present.

Additional features and advantages of embodiments of the invention will be set forth in the detailed description which follows.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the embodiments of the invention without limiting the embodiments of the invention. In the drawings:

FIG. 1 is a flow chart of the steps of a method for simulating Kraukls wave stimulated by hydraulic fracturing provided by one embodiment of the present invention;

fig. 2 is a system configuration diagram of a hydraulic fracture stimulation Kraukls wave simulation system according to an embodiment of the present invention.

Description of the reference numerals

10-an acquisition unit; 20-a processing unit; 30-output unit.

Detailed Description

The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

Fig. 2 is a system configuration diagram of a hydraulic fracture stimulation Kraukls wave simulation system according to an embodiment of the present invention. As shown in fig. 2, an embodiment of the present invention provides a hydraulic fracture stimulation Kraukls wave simulation system, which includes: the acquisition unit 10 is used for acquiring a crack model of the artificial crack; a processing unit 20 for: carrying out discretization treatment on the crack model according to a preset subdivision rule to obtain a grid unit model; scanning all grid cells, screening out the grid cells related to the crack openings, and determining the attribute parameters of the grid cells related to the crack openings; calculating the displacement load of the grid units related to the crack openings at the corresponding crack openings one by one according to the attribute parameters of the grid units related to the crack openings and a preset displacement load calculation formula; performing displacement load assembly on all grid units according to the displacement load calculation result, and adding the assembled displacement load to a displacement item of a conventional finite element to obtain a final finite element equation; and the output unit 30 is used for solving the finite element equation, and obtaining and outputting a simulation result.

Fig. 1 is a flow chart of a method for simulating Kraukls waves by hydraulic fracturing stimulation according to an embodiment of the present invention. As shown in fig. 1, an embodiment of the present invention provides a hydraulic fracture stimulation Kraukls wave simulation method, including:

step S10: and acquiring a crack model of the artificial crack, and performing discretization treatment on the crack model according to a preset subdivision rule to obtain a grid unit model.

Specifically, the acquisition unit 10 acquires an artificial fracture model generated after hydraulic fracturing, including the spatial shape and the projection shape of the artificial fracture. Because the space distribution of the cracks has complexity, and subsequent simulation can not be directly carried out by using the shape model, a grid unit model is required to be used for carrying out artificial crack shape fitting so as to ensure the simplicity of subsequent moving load calculation and assembly and improve the simulation efficiency of Kraukls wave. Preferably, the triangular mesh generation is carried out on discrete points in the artificial crack model, and the crack shape with a complex and irregular shape is fitted into a plurality of connected triangles, so that the shape analysis of the crack is convenient to carry out subsequently. Whether the result generated by one triangular meshing is optimal or not is judged, and generally, the more slender and sharp triangles in the triangles obtained after the triangular meshing are better, and the more equilateral triangles and acute triangles are similar, the better. The Delaunay isoparametric triangular mesh unit model has the characteristics of a hollow circle and a maximized minimum angle, so that the generation of a long and narrow triangle is avoided, and the Delaunay isoparametric triangular mesh unit model is preferably selected to perform artificial crack original shape fitting in the invention. The size of the grid can be flexibly changed along with the size of the fitting area, and a biquadratic interpolation function can be provided, so that the numerical solution to be solved has biquadratic accuracy. Mesh units are obtained through the Delaunay isoparametric triangular mesh unit model subdivision, each mesh unit comprises 6 nodes, wherein 3 corner nodes correspond to three vertexes of a triangle; the other 3 are edge nodes corresponding to the midpoints of the three edges of the triangle. In the mesh generation process, the processing unit 20 performs real-time scanning of the spatial morphology of the artificial crack acquired by the acquisition unit 10, including the spatial position of the crack, the pore diameter of the crack, the smoothness of the crack surface, and the crack orientation. The spatial position of the crack is used for confirming the position of the grid unit in the space, and the aperture of the crack and the smoothness degree of the surface of the crack are used for determining the size of the grid unit. The smaller the aperture of the crack and the larger the roughness of the crack surface, the finer the size requirement of the grid. The orientation of the slit is used to confirm the angular distribution of the triangular interior angle.

Step S20: scanning all grid cells, screening out grid cells related to crack openings, and determining attribute parameters of the grid cells related to the crack openings.

Specifically, the processing unit 20 obtains a grid cell model formed by combining all the divided grid cells, then performs grid cell model screening to filter out grid cells far away from the crack opening, and only keeps the grid cells related to the crack opening. Then, the attribute parameter acquisition of the grid cells related to the crack openings is carried out. In step S10, when performing triangular mesh splitting, in order to avoid interference, when obtaining the mesh cells related to the crack opening, it is necessary to ensure that there is one edge and only one edge of the mesh cells related to the crack opening coincides with the crack opening, so as to load a displacement load at the crack opening subsequently. The processing unit 20 integrates the screened grid cells related to the crack openings, and then obtains one edge of the grid cells coinciding with the crack openings one by one to obtain the serial numbers and coordinates of all the grid cell nodes on the edge. When the parameters are obtained for displacement load calculation, vector determination is required to be carried out according to the coordinate position so as to ensure accurate displacement load calculation.

Step S30: and calculating the displacement load of the crack openings corresponding to the grid units related to the crack openings one by one according to the attribute parameters of the grid units related to the crack openings and a preset displacement load calculation formula.

Specifically, the principle of loading the displacement load is that, in the same manner as the crack formation principle, the value of the displacement load decreases from the geometric center of the crack to the positions of the two side crack walls on the crack opening surface. To characterize this decreasing relationship, a spatial scale function needs to be defined in the load equation. The value of the spatial scale function reaches a peak value of 1 at the centre of the crack and is 0 at the location of the two side crack walls. At a location between the center of the fracture and the two side fracture walls, the scale function is symmetrically smooth handed off. The characteristic that the displacement load is decreased from the center of the crack to the two side crack walls is embodied through the establishment of a space scale function. Preferably, the spatial scale function relation established according to the rule of the present invention is:

wherein the content of the first and second substances,the position vector of the node at the opening relative to the central point of the crack is obtained;the vector characterizing the crack opening. Wherein the content of the first and second substances,the vector is defined as a vector pointing to the node from the center point of the crack, and the specific expression is as follows:

wherein (x)₀,y₀) The coordinates of the center store for the crack; (x)_node,y_node) The coordinates of the nodes falling at the crack opening.The vector representing the crack opening is derived from the starting point of the crack opening to the terminal point of the crack opening, and the expression is as follows:

wherein the content of the first and second substances,is the starting point of the crack opening in the anticlockwise direction;is the end point of the crack opening in the counterclockwise direction. In addition to the requirement of a spatial scale function, the generation and transmission of Krauklis waves need to be characterized by a time domain, and the nature and the characteristics of time series of the time domain are the theoretical basis of various mathematical filtering, so that the research on seismic exploration data in the time domain is of great significance in modern seismic exploration. The fracture excites seismic waves when it is cracked, and the Krauklis wave is a guided wave excited in the process. Therefore, a time and wavelet function needs to be defined, and preferably, the time domain wavelet function expression provided by the invention is as follows:

wherein A is₀Is the amplitude coefficient; tau is a time scale factor of the wavelet function; t is t₀Is the central time of the wavelet functionEngraving; t is a time series. The displacement load equation is obtained by multiplying a space scale function and a time domain wavelet function, so that the final displacement load equation is as follows: f_time＝F_space·F_timeNamely:

and calculating the displacement load on the opening line in each grid unit related to the crack opening one by one according to the relational expression.

Step S40: and assembling the displacement loads of all the grid units according to the displacement load calculation result, and adding the assembled displacement loads to the displacement items of the conventional finite element to obtain a final finite element equation.

Specifically, after the calculation of the displacement load of each grid cell associated with the fracture opening is completed, the displacement loads obtained through the calculation need to be assembled into the whole grid cell model, so that the displacement load of the complete artificial fracture is obtained. The finite element node assembly mode is to integrate and assemble the created finite element model to form a complete component or assembly body. Therefore, the invention selects a finite element node assembling mode to carry out displacement load assembling. The calculation formula is as follows:

wherein F is a final displacement load matrix; n is a radical of_openingThe number of nodes falling at the crack opening is shown; c_iA number position vector for describing the ith node falling at the crack opening; f_iThe displacement load of the ith node at the crack opening is shown. In one possible embodiment, the displacement loading is not limited to being performed only in the grid cells associated with the open fractures, but may be performed in all grid cells. And acquiring a complete grid cell model, wherein the grid cells related to the crack openings are subjected to assembly result calculation through the assembly formula. And identified by the processing unit 20 as having no crack openingThe result is directly defaulted to 0 for the grid cell off, and the final displacement load is obtained by integrating all the results together. After the displacement load assembly is completed, the final displacement load is directly added to the displacement term of the finite element equation to serve as the known condition of the finite element equation.

Step S50: and solving the finite element equation to obtain and output a simulation result.

Specifically, after the final displacement load is obtained, the displacement term becomes a known condition in the finite element equation. The output unit 30 directly puts the displacement load value obtained by assembly into a finite element equation to be solved, so as to obtain a solution result, wherein the current result is a simulation result of Kraukls waves.

Embodiments of the present invention also provide a computer-readable storage medium having instructions stored thereon, which when executed on a computer, cause the computer to perform the above-described hydraulic fracture stimulation Kraukls wave simulation method.

Those skilled in the art will appreciate that all or part of the steps in the method for implementing the above embodiments may be implemented by a program, which is stored in a storage medium and includes several instructions to enable a single chip, a chip, or a processor (processor) to execute all or part of the steps in the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.

While the embodiments of the present invention have been described in detail with reference to the accompanying drawings, the embodiments of the present invention are not limited to the details of the above embodiments, and various simple modifications can be made to the technical solution of the embodiments of the present invention within the technical idea of the embodiments of the present invention, and the simple modifications are within the scope of the embodiments of the present invention. It should be noted that the various features described in the above embodiments may be combined in any suitable manner without departing from the scope of the invention. In order to avoid unnecessary repetition, the embodiments of the present invention will not be described separately for the various possible combinations.

In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as disclosed in the embodiments of the present invention as long as it does not depart from the spirit of the embodiments of the present invention.