Method and device for predicting in-situ stress of shale reservoir

Abstract

The application discloses a shale reservoir ground stress prediction method and device, and belongs to the technical field of geophysical exploration. The method comprises the following steps: performing prestack seismic inversion based on seismic data to obtain a plurality of perturbation elastic impedance data bodies, wherein the values of the angles and / or the azimuths of any two perturbation elastic impedance data bodies are different; obtaining a perturbation elastic impedance equation by eliminating the influence of isotropic media according to an elastic impedance equation based on an orthogonal anisotropic medium; substituting the plurality of perturbation elastic impedance data bodies into the perturbation elastic impedance equation to calculate anisotropy parameters; and calculating shale reservoir ground stress according to the anisotropy parameters. The method establishes the connection between the perturbation elastic impedance and the anisotropy parameters, realizes targeted inversion, can calculate the shale reservoir ground stress, and has good inversion stability and high inversion precision.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of geophysical exploration technology, in particular to a shale reservoir geostress prediction method and device. BACKGROUND

[0002] Geostress is a characteristic response of elastic deformation caused by the action of geological structure movement, gravity of the earth and additional power of underground engineering on the internal unit of medium. The accurate prediction of geostress is of great significance to shale gas exploration and development.

[0003] Nowadays, geostress prediction technology has made great progress in many fields. For example, using logging data to calculate geostress, geomechanics numerical simulation of geostress, and the rising of prestack seismic inversion based geostress prediction in recent years. The current geostress prediction method based on prestack seismic inversion mainly assumes that the bottom model is a horizontal transverse isotropy (HTI) or vertical transverse isotropy (VTI) medium model, and estimates the formation geostress size by calculating the difference ratio of maximum horizontal stress and minimum horizontal stress. This method uses the reflection coefficient approximation equation proposed by Ruger or Bachrach, and extracts the weak anisotropy parameters proposed by Thomsen based on prestack seismic inversion to calculate the geostress. Since only anisotropy parameters are needed to calculate the geostress, this method directly inverts all parameters in the approximation equation, which lacks pertinence, and thus has the problems of low inversion accuracy and poor predictability. SUMMARY

[0004] In view of this, the present application provides a shale reservoir geostress prediction method and device, which solves the problems of low inversion accuracy and poor predictability in predicting geostress.

[0005] Specifically, the technical scheme comprises the following:

[0006] On the one hand, the present application provides a shale reservoir geostress prediction method, which comprises:

[0007] Performing prestack seismic inversion based on seismic data to obtain a plurality of perturbed elastic impedance data bodies, wherein the values of the angle and / or azimuth of any two perturbed elastic impedance data bodies are different;

[0008] Dividing the elastic impedance equation of the orthotropic anisotropic medium by the isotropic elastic impedance equation of the longitudinal and transverse wave velocity and density to obtain a perturbed elastic impedance equation;

[0009] According to the plurality of perturbation elastic impedance data bodies, the anisotropy parameters are calculated by substituting the perturbation elastic impedance equation.

[0010] According to the anisotropy parameters, the in-situ stress of the shale reservoir is calculated.

[0011] In some embodiments, before the pre-stack seismic inversion based on the seismic data, the method further comprises:

[0012] The seismic data is obtained, wherein the seismic data comprises partial incidence angle and azimuth stack seismic data.

[0013] In some embodiments, the perturbation elastic impedance equation is obtained by dividing the elastic impedance equation based on the orthotropic anisotropic medium by the isotropic elastic impedance approximation equation of the longitudinal and transverse wave velocity and density.

[0014] The elastic impedance equation based on the orthotropic anisotropic medium is obtained, wherein the calculation formula of the elastic impedance equation based on the orthotropic anisotropic medium is:

[0015]

[0016] The calculation formula of the isotropic elastic impedance approximation equation of the longitudinal and transverse wave velocity and density is:

[0017] EI iso (θ)=α0ρ0(α) a(θ) (β) b(θ) (ρ) c(θ) ;

[0018] The perturbation elastic impedance equation is obtained by dividing the elastic impedance equation based on the orthotropic anisotropic medium by the isotropic elastic impedance approximation equation of the longitudinal and transverse wave velocity and density, wherein the calculation formula of the perturbation elastic impedance equation is:

[0019]

[0020] In the above formulae, α represents the longitudinal wave velocity; β represents the transverse wave velocity; ρ represents the density; θ represents the incidence angle; and φ represents the azimuth angle. b(θ)=-8g sin 2 θ, c(θ)=1-4g sin 2 θ, Г x represents the anisotropy gradient in the X direction, and Г y represents the anisotropy gradient in the Y direction.

[0021] ​In some embodiments, the anisotropy parameter includes an anisotropy gradient Γ of the X direction x and an anisotropy gradient Γ of the Y direction y .

[0022] In some embodiments, the formula for calculating the geostress of the shale reservoir is:

[0023] Geostress = Γ x Γ y ,

[0024] In the formula, Geostress represents the geostress index of the shale reservoir.

[0025] In some embodiments, the calculation of the anisotropy parameter according to the substitution of the plurality of perturbed elastic impedance data bodies into the perturbed elastic impedance equation includes:

[0026] Substituting the plurality of perturbed elastic impedance data bodies into the perturbed elastic impedance equation to obtain a plurality of perturbed elastic impedance equations to be operated;

[0027] Using the least square method to calculate the plurality of perturbed elastic impedance equations to be operated to obtain the anisotropy parameter.

[0028] In some embodiments, the pre-stack seismic inversion has an objective function, and the formula for calculating the objective function is:

[0029]

[0030] In the formula, m represents the model parameter; d represents the observed seismic data with noise; G represents the wavelet matrix represents the variance of the noise; represents the variance of the model parameter;

[0031] α EI represents the constraint coefficient.

[0032] In some embodiments, before the pre-stack seismic inversion based on the seismic data to obtain the plurality of perturbed elastic impedance data bodies, the method further includes:

[0033] Obtaining reservoir characteristic information of the shale;

[0034] Substituting the reservoir characteristic information of the shale into the post-stack inversion software to perform well-seismic calibration, wavelet extraction, and low-frequency model establishment.

[0035] In some embodiments, the pre-stack seismic inversion based on the seismic data to obtain the plurality of perturbed elastic impedance data bodies includes:

[0036] Performing prestack seismic inversion under the low frequency model constraint to obtain multiple perturbation elastic impedance data bodies.

[0037] In another aspect, the embodiment of the present application also provides a shale reservoir geostress prediction device, which comprises:

[0038] The data body acquisition module is configured to perform prestack seismic inversion based on seismic data to obtain multiple perturbation elastic impedance data bodies, wherein any two of the perturbation elastic impedance data bodies are different in angle and / or azimuth value.

[0039] The equation obtaining module is configured to obtain a perturbation elastic impedance equation by dividing an elastic impedance equation based on an orthotropic anisotropic medium by an isotropic elastic impedance equation facing a longitudinal wave, a transverse wave and density.

[0040] The parameter obtaining module is configured to calculate an anisotropic parameter by substituting the multiple perturbation elastic impedance data bodies into the perturbation elastic impedance equation.

[0041] The geostress calculation module is configured to calculate a shale reservoir geostress based on the anisotropic parameter.

[0042] The technical scheme provided by the embodiment of the present application has at least the following beneficial effects:

[0043] The shale reservoir geostress prediction method provided by the embodiment of the present application uses a perturbation elastic impedance equation obtained by dividing an elastic impedance equation based on an orthotropic anisotropic medium by an isotropic elastic impedance approximate equation facing a longitudinal wave velocity, a transverse wave velocity and density to establish a connection between the perturbation elastic impedance and the anisotropic parameter, realizes targeted inversion, and then calculates a shale reservoir geostress through the anisotropic parameter. Since the perturbation elastic impedance equation eliminates the influence of the isotropic part on the seismic reflection coefficient, the change of the perturbation elastic impedance is entirely from the anisotropic part, so that the inversion stability is good and the inversion precision is high. BRIEF DESCRIPTION OF DRAWINGS

[0044] In order to more clearly illustrate the technical scheme in the embodiment of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0045] Figure 1 The method flowchart of the shale reservoir geostress prediction method of the embodiment of the present application;

[0046] Figure 2A method flowchart of another shale reservoir stress prediction method of the embodiment of the present application;

[0047] Figure 3 A target parameter logging curve in the embodiment of the present application;

[0048] Figure 4 An inversion result in the case of no noise in the embodiment of the present application;

[0049] Figure 5 An inversion result in the case of a signal-to-noise ratio of 10 in the embodiment of the present application;

[0050] Figure 6 An inversion result in the case of a signal-to-noise ratio of 5 in the embodiment of the present application;

[0051] Figure 7 A structural block diagram of a shale reservoir stress prediction device of the embodiment of the present application. DETAILED DESCRIPTION

[0052] In order to make the technical solutions and advantages of the present application clearer, the embodiments of the present application will be further described in detail below with reference to the drawings.

[0053] The embodiment of the present application provides a shale reservoir stress prediction method, and a method flowchart thereof is as shown in Figure 1 The method comprises the following steps.

[0054] Step 101, prestack seismic inversion is performed based on seismic data to obtain a plurality of perturbation elastic impedance data bodies, wherein the values of the angle and / or the azimuth of any two perturbation elastic impedance data bodies are different.

[0055] Step 102, a perturbation elastic impedance equation is obtained according to an elastic impedance equation based on an orthotropic anisotropic medium divided by an isotropic elastic impedance approximate equation facing the longitudinal and transverse wave velocities and the density.

[0056] Step 103, an anisotropic parameter is calculated by substituting the plurality of perturbation elastic impedance data bodies into the perturbation elastic impedance equation.

[0057] Step 104, shale reservoir stress is calculated according to the anisotropic parameter.

[0058] In some embodiments, before the prestack seismic inversion based on the seismic data, the method provided by the embodiment of the present application further comprises: obtaining seismic data, wherein the seismic data comprises partial incidence angle and azimuth stacking seismic data.

[0059] In some embodiments, the perturbation elastic impedance equation obtained according to the elastic impedance equation based on the orthotropic anisotropic medium divided by the isotropic elastic impedance approximate equation facing the longitudinal and transverse wave velocities and the density comprises:

[0060] An elastic impedance equation based on orthotropic medium is obtained, and a calculation formula of the elastic impedance equation based on orthotropic medium is as follows:

[0061]

[0062] A calculation formula of an isotropic elastic impedance approximation equation for P-and S-wave velocities and density is as follows:

[0063] EI iso (θ)=α0ρ0(α) a(θ) (β) b(θ) (ρ) c(θ) ;

[0064] The elastic impedance equation based on orthotropic medium is divided by the isotropic elastic impedance approximation equation for P-and S-wave velocities and density to obtain a perturbation elastic impedance equation, and a calculation formula of the perturbation elastic impedance equation is as follows:

[0065]

[0066] In the above formulas, α represents a P-wave velocity; β represents an S-wave velocity; ρ represents a density; θ represents an incident angle; represents a azimuth angle; represents an anisotropy gradient in an X direction; and represents an anisotropy gradient in a Y direction. α(θ)=sec 2 θ, b(θ)=-8g sin 2 θ, c(θ)=1-4g sin 2 θ, Г x represents an anisotropy gradient in an X direction; and represents an anisotropy gradient in a Y direction. y

[0067] In some embodiments, the anisotropy parameters include an anisotropy gradient in an X direction and an anisotropy gradient in a Y direction. x y

[0068] In some embodiments, a calculation formula of a shale reservoir geostress is as follows:

[0069] Geostress=Γ x Γ y ,

[0070] In the formula, Geostress represents a shale reservoir geostress index.

[0071] In some embodiments, the anisotropy parameters are calculated according to a plurality of perturbation elastic impedance data bodies and the perturbation elastic impedance equation. ​​​​

[0072] Substitute the plurality of perturbation elastic impedance data bodies into the perturbation elastic impedance equation to obtain a plurality of perturbation elastic impedance equations to be operated;

[0073] Calculate the plurality of perturbation elastic impedance equations to be operated by using the least square method to obtain the anisotropic parameters.

[0074] In some embodiments, the pre-stack seismic inversion has an objective function, and the calculation formula of the objective function is:

[0075]

[0076] In the formula, m represents a model parameter, d represents observed seismic data with noise, G represents a wavelet matrix, and represents a variance of noise. In the formula, m represents a model parameter, d represents observed seismic data with noise, G represents a wavelet matrix, and represents a variance of noise. In the formula, m represents a model parameter, d represents observed seismic data with noise, G represents a wavelet matrix, and represents a variance of noise.

[0077] α EI represents a constraint coefficient.

[0078] In some embodiments, before the pre-stack seismic inversion based on the seismic data is performed to obtain the plurality of perturbation elastic impedance data bodies, the prediction method provided by the embodiments of the present application further comprises:

[0079] Obtaining reservoir characteristic information of the shale;

[0080] Substituting the reservoir characteristic information of the shale into post-stack inversion software to perform well-seismic calibration, wavelet extraction, and establishment of a low-frequency model.

[0081] In some embodiments, the pre-stack seismic inversion based on the seismic data to obtain the plurality of perturbation elastic impedance data bodies comprises:

[0082] Performing pre-stack seismic inversion under the constraint of the low-frequency model to obtain the plurality of perturbation elastic impedance data bodies.

[0083] Therefore, the prediction method of the shale reservoir ground stress provided by the embodiments of the present application uses the elastic impedance equation based on the orthogonal anisotropic medium to divide the isotropic elastic impedance approximation equation facing the longitudinal and transverse wave velocities and the density to obtain the perturbation elastic impedance equation, to establish the relationship between the perturbation elastic impedance and the anisotropic parameters, to realize the targeted inversion, and then through the anisotropic parameters, the shale reservoir ground stress can be calculated. Since the perturbation elastic impedance equation eliminates the influence of the isotropic part on the seismic reflection coefficient, for the perturbation elastic impedance, its change is entirely from the anisotropic part, and thus the inversion stability is good and the inversion precision is high.

[0084] The embodiments of the present application also provide a prediction method of shale reservoir ground stress, and a method flowchart thereof is as followsFigure 2 The method comprises the following steps:

[0085] In step 201, reservoir characteristic information of the shale is obtained.

[0086] The reservoir characteristic information comprises P-wave velocity, S-wave velocity, density, Lame constant, shear modulus, Young's modulus and Poisson's ratio.

[0087] The reservoir characteristic information is obtained to prepare data for subsequent establishment of a low-frequency model.

[0088] In step 202, the reservoir characteristic information of the shale is substituted into post-stack inversion software to perform well-seismic calibration, wavelet extraction and establishment of a low-frequency model.

[0089] In some embodiments, the post-stack inversion software of FUGRO JASON can be used to perform well-seismic calibration, wavelet extraction and establishment of a low-frequency model.

[0090] The post-stack inversion software is a relatively mature software, and the low-frequency model required can be directly obtained by substituting the reservoir characteristic information.

[0091] In this step, the purpose of establishing the low-frequency model is to subsequently perform pre-stack seismic inversion under the constraint of the low-frequency model to obtain a plurality of perturbed elastic impedance data bodies.

[0092] In step 203, seismic data is obtained.

[0093] The seismic data comprises seismic data of partial incidence angles and azimuthal stacking.

[0094] It can be understood that the seismic data includes but is not limited to azimuth and incidence angle, for example, can also include azimuthal pre-stack gather, seismic interpretation horizon, etc.

[0095] The purpose of this step is to prepare data for subsequent pre-stack seismic inversion.

[0096] In step 204, pre-stack seismic inversion is performed based on the seismic data to obtain a plurality of perturbed elastic impedance data bodies, wherein the values of the angle and / or azimuth of any two perturbed elastic impedance data bodies are different.

[0097] By performing twice different pre-stack seismic inversion on the seismic data, isotropic impedance data bodies and elastic impedance data bodies can be obtained to prepare for subsequent solution of anisotropic parameters.

[0098] In some embodiments, this step includes inverting multiple perturbation elastic impedance data volumes superimposed at different angles and orientations under low-frequency model constraints. In this embodiment of the invention, since the target parameter has two anisotropic gradients, at least two perturbation elastic impedance data volumes in different orientations are obtained through inversion, and the pre-stack seismic inversion has an objective function.

[0099] The objective function is calculated using the following formula:

[0100]

[0101] In the formula: m represents the model parameters; d represents the observed seismic data under noisy conditions; G represents the wavelet matrix; This represents the variance of the noise; This represents the variance of the model parameters;

[0102] α EI This represents the constraint coefficient.

[0103] Understandably, the objective function requires substituting the superimposed angle data for each azimuth, the corresponding seismic wavelet, and the azimuth elastic impedance to obtain the disturbance elastic impedance data volume that best matches reality. Therefore, the above steps are repeated, substituting the superimposed angle disturbance elastic impedance data volumes for different incident angles and azimuths to obtain the disturbance elastic impedance data volumes for different angles and azimuths in the actual work area.

[0104] Unlike isotropic elastic impedance inversion, seismic information needs to include both incident angle and azimuth information due to the addition of an anisotropic component.

[0105] Step 205: Divide the elastic impedance equation based on the orthogonal anisotropic medium by the isotropic elastic impedance approximation equation for the longitudinal and transverse wave velocities and densities to obtain the perturbation elastic impedance equation.

[0106] Since the elastic impedance equation based on orthogonal anisotropic media divided by the isotropic elastic impedance approximation equation facing the longitudinal and transverse wave velocities and densities are both existing equations, the perturbation elastic impedance equation can be derived based on the above two existing equations, and then the anisotropic parameters can be obtained by solving the perturbation elastic impedance equation.

[0107] This step specifically includes: obtaining the elastic impedance equation based on orthotropic media, wherein the calculation formula for the elastic impedance equation based on orthotropic media is:

[0108]

[0109] An isotropic elastic impedance approximation equation for P-and S-wave velocity and density is obtained, and a calculation formula of the isotropic elastic impedance approximation equation for P-and S-wave velocity and density is as follows:

[0110] EI iso (θ)=α0ρ0(α) a(θ) (β) b(θ) (ρ) c(θ) ;

[0111] The elastic impedance equation based on the orthotropic medium is divided by the isotropic elastic impedance approximation equation for P-and S-wave velocity and density to obtain a perturbation elastic impedance equation, and a calculation formula of the perturbation elastic impedance equation is as follows:

[0112]

[0113] In the above formulas, α represents P-wave velocity; β represents S-wave velocity; ρ represents density; θ represents an incident angle; represents an azimuth angle; α(θ)=sec 2 θ, b(θ)=-8g sin 2 θ, c(θ)=1-4g sin 2 θ, Г x represents an anisotropy gradient in the X direction, and Г y represents an anisotropy gradient in the Y direction.

[0114] In step 206, the anisotropy parameters are calculated by substituting the multiple perturbation elastic impedance data bodies into the perturbation elastic impedance equation.

[0115] The anisotropy parameters can be calculated by substituting the multiple perturbation elastic impedance data bodies into the perturbation elastic impedance equation, and the shale reservoir in-situ stress can be calculated by using the anisotropy parameters.

[0116] This step specifically includes: extracting the anisotropy parameters in the perturbation elastic impedance equation by using the inversion obtained perturbation elastic impedance data body; since the parameters in the perturbation elastic impedance equation present a nonlinear relationship, which is not conducive to calculation and is not conducive to the stability of inversion, the perturbation elastic impedance equation is linearly changed to obtain:

[0117]

[0118] The multiple obtained perturbation elastic impedance data bodies are substituted to construct an equation between the elastic impedance and the anisotropy parameters.

[0119] Optionally, taking the substitution of two volumes of perturbed elastic impedance data as an example, the system of equations between the elastic impedance and the anisotropy parameters is as follows:

[0120]

[0121] Rewritten in matrix form, it is:

[0122]

[0123] Finally, by substituting the perturbation elastic impedance data into the data volume, the anisotropic parameters can be extracted.

[0124] Step 207: Calculate the in-situ stress of the shale reservoir based on the anisotropy parameters.

[0125] This step specifically includes: The formula for calculating the in-situ stress in shale reservoirs is as follows:

[0126] Geostress=Γ x Γ y ,

[0127] In the formula: Geostress represents the geostress index of shale reservoirs.

[0128] To verify the feasibility of the shale reservoir in-situ stress prediction method provided in this embodiment of the invention, a well in an actual work area can be selected as a model for verification. After calculation, the target parameter logging curve is as follows: Figure 3 As shown, the anisotropic gradient parameters are inverted using the equation proposed in this embodiment of the invention. Parameter extraction is performed under three conditions: no noise, signal-to-noise ratio (SNR) of 10, and SNR of 5. The results are as follows: Figure 4 , Figure 5 and Figure 6 As shown.

[0129] The data in the figure show that the inversion results are in good agreement with the actual data. Even with added noise, the perturbation elastic impedance equation still has good stability and accuracy, which verifies the applicability of the method.

[0130] Therefore, the method for predicting shale reservoir in-situ stress provided in this embodiment of the invention establishes the relationship between anisotropy and reflection coefficient. The target parameters can be obtained through pre-stack seismic inversion. The calibration factor calibrates the dimensions of the equation onto the acoustic impedance, thereby improving the stability of the equation.

[0131] This invention also provides a device for predicting in-situ stress in shale reservoirs, the structural block diagram of which is shown below. Figure 7 As shown, the device includes: a data acquisition module 1001, an equation generation module 1002, a parameter generation module 1003, and a geostress calculation module 1004.

[0132] The data body obtaining module 1001 is configured to perform pre-stack seismic inversion based on seismic data to obtain a plurality of perturbed elastic impedance data bodies, wherein any two of the perturbed elastic impedance data bodies are different in angle and / or azimuth.

[0133] The equation obtaining module 1002 is configured to obtain a perturbed elastic impedance equation by dividing an elastic impedance equation based on an orthotropic anisotropic medium by an isotropic elastic impedance approximation equation for longitudinal and transverse wave velocities and density.

[0134] The parameter obtaining module 1003 is configured to calculate an anisotropic parameter by substituting the plurality of perturbed elastic impedance data bodies into the perturbed elastic impedance equation.

[0135] The in-situ stress calculation module 1004 is configured to calculate a shale reservoir in-situ stress based on the anisotropic parameter.

[0136] In some embodiments, the prediction device provided by the present embodiment further comprises:

[0137] The seismic data obtaining module is configured to obtain seismic data, wherein the seismic data comprises partial angle and azimuth stacked seismic data.

[0138] In some embodiments, the equation obtaining module 1002 specifically comprises:

[0139] The perturbed elastic impedance equation obtaining submodule is configured to obtain an elastic impedance equation based on an orthotropic anisotropic medium, wherein the elastic impedance equation based on the orthotropic anisotropic medium has a calculation formula as follows:

[0140]

[0141] The isotropic elastic impedance approximation equation for longitudinal and transverse wave velocities and density has a calculation formula as follows:

[0142] EI iso (θ)=α0ρ0(α) a(θ) (β) b(θ) (ρ) c(θ) ;

[0143] The perturbed elastic impedance equation obtaining submodule is configured to obtain a perturbed elastic impedance equation by dividing the elastic impedance equation based on the orthotropic anisotropic medium by the isotropic elastic impedance approximation equation for longitudinal and transverse wave velocities and density, wherein the perturbed elastic impedance equation has a calculation formula as follows:

[0144]

[0145] In the above formulas, α represents the longitudinal wave velocity, β represents the transverse wave velocity, ρ represents the density, and θ represents the incident angle. represents the azimuth angle; a (θ) = sec 2 θ, b (θ) = -8g sin 2 θ, c (θ) = 1-4g sin 2 θ, Г x represents the anisotropy gradient in the X direction, Г y represents the anisotropy gradient in the Y direction.

[0146] In some embodiments, the anisotropy parameters include an anisotropy gradient in the X direction Г x and an anisotropy gradient in the Y direction Г y .

[0147] In some embodiments, the calculation formula of the shale reservoir geostress is:

[0148] Geostress = Γ x Γ y ,

[0149] In the formula, Geostress represents the shale reservoir geostress index.

[0150] In some embodiments, the parameter obtaining module 1003 specifically includes:

[0151] A data substitution sub-module, configured to substitute a plurality of perturbed elastic impedance data bodies into a perturbed elastic impedance equation to obtain a plurality of perturbed elastic impedance equations to be operated;

[0152] An equation calculation sub-module, configured to calculate the plurality of perturbed elastic impedance equations to be operated by using a least square method to obtain anisotropy parameters.

[0153] In some embodiments, the pre-stack seismic inversion has an objective function, and the calculation formula of the objective function is:

[0154]

[0155] In the formula, m represents a model parameter; d represents observed seismic data under a noise condition; G represents a wavelet matrix; represents the variance of the noise; represents the variance of the model parameter; α EI represents a constraint coefficient.

[0156] In some embodiments, the device provided by the embodiments of the present application further includes:

[0157] A reservoir characteristic information obtaining module, configured to obtain reservoir characteristic information of the shale;

[0158] The reservoir characteristic information substitution module substitutes the reservoir characteristic information of the shale into the post-stack inversion software to perform well-seismic calibration, wavelet extraction and low-frequency model establishment.

[0159] In some embodiments, the obtaining a plurality of perturbed elastic impedance data volumes based on seismic data comprises:

[0160] The elastic data volume obtaining submodule obtains a plurality of perturbed elastic impedance data volumes by performing pre-stack seismic inversion under the constraint of the low-frequency model.

[0161] Therefore, the shale reservoir geostress prediction device provided by the embodiments of the present application uses the perturbed elastic impedance equation obtained by dividing the elastic impedance equation based on the orthotropic medium by the isotropic elastic impedance equation facing the longitudinal and transverse wave velocities and density to establish the relationship between the perturbed elastic impedance and the anisotropic parameters, realizes targeted inversion, and then calculates the shale reservoir geostress through the anisotropic parameters. Since the perturbed elastic impedance equation eliminates the influence of the isotropic part on the seismic reflection coefficient, the change of the perturbed elastic impedance is entirely from the anisotropic part, so that the inversion stability is good and the inversion precision is high.

[0162] In the present application, the terms "first" and "second" are used only for descriptive purposes and should not be construed as indicating or implying relative importance. The term "a plurality of" refers to two or more, unless otherwise expressly limited.

[0163] Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples given are considered exemplary only, and the scope of the application is not to be limited.

[0164] The above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for predicting in-situ stress in shale reservoirs, characterized in that, The method includes: The reservoir characteristic information of shale is obtained, wherein the reservoir characteristic information includes: P-wave velocity, S-wave velocity, density, Lamé constant, shear modulus, Young's modulus and Poisson's ratio; The reservoir characteristic information is substituted into the post-stack inversion software to perform well-seismic calibration, wavelet extraction, and low-frequency model establishment. Under the constraints of the low-frequency model, pre-stack seismic inversion is performed based on seismic data to obtain multiple perturbation elastic impedance data volumes, wherein the angle and / or azimuth values ​​of any two perturbation elastic impedance data volumes are different; the perturbation elastic impedance equation is obtained by dividing the elastic impedance equation of the orthogonal anisotropic medium by the isotropic elastic impedance approximation equation facing the P-wave and S-wave velocity and density. Substituting the multiple perturbation elastic impedance data volumes into the perturbation elastic impedance equation, the anisotropy parameters are calculated; the anisotropy parameters include the anisotropy gradient Γ in the X direction. x and the anisotropic gradient Γ in the Y direction y ; Based on the anisotropy parameters, the in-situ stress of the shale reservoir is calculated; The process of obtaining the perturbation elastic impedance equation by dividing the elastic impedance equation based on orthogonal anisotropic media by the isotropic elastic impedance approximation equations for longitudinal and transverse wave velocities and densities includes: The elastic impedance equation based on orthotropic media is obtained, wherein the calculation formula for the elastic impedance equation based on orthotropic media is as follows: ； The calculation formula for the approximate equations of isotropic elastic impedance facing the longitudinal and transverse wave velocities and densities is as follows: ； Dividing the elastic impedance equation based on orthogonal anisotropic media by the isotropic elastic impedance approximation equation for longitudinal and transverse wave velocities and densities yields the perturbed elastic impedance equation, wherein the calculation formula for the perturbed elastic impedance equation is: ； In the above formulas: This represents the longitudinal wave velocity; This represents the transverse wave velocity; This represents density; θ It represents the angle of incidence; φ This indicates the azimuth angle; , , , , , Г x This represents the anisotropic gradient in the X direction, Γ. y This represents the anisotropic gradient in the Y direction.

2. The method for predicting in-situ stress in shale reservoirs according to claim 1, characterized in that, Before performing pre-stack seismic inversion based on seismic data, the method further includes: The earthquake data is acquired, wherein the earthquake data includes partial incident angle and azimuth angle superimposed earthquake data.

3. The method for predicting in-situ stress in shale reservoirs according to claim 1, characterized in that, The formula for calculating the in-situ stress in the shale reservoir is as follows: ， In the formula: This represents the geostress index of shale reservoirs.

4. The method for predicting in-situ stress in shale reservoirs according to claim 1, characterized in that, Substituting the multiple perturbation elastic impedance data volumes into the perturbation elastic impedance equation, the anisotropy parameters are calculated as follows: Substituting the multiple perturbation elastic impedance data volumes into the perturbation elastic impedance equations yields multiple perturbation elastic impedance equations to be calculated. The anisotropic parameters are obtained by calculating the multiple perturbation elastic impedance equations to be calculated using the least squares method.

5. The method for predicting in-situ stress in shale reservoirs according to claim 1, characterized in that, The pre-stack seismic inversion has an objective function, and the formula for calculating the objective function is as follows: ， In the formula: m This represents the model parameters; d This represents observed seismic data under noisy conditions; G This represents the wavelet matrix; This represents the variance of the noise; This represents the variance of the model parameters; ; ; This represents the constraint coefficient.

6. A device for predicting in-situ stress in shale reservoirs, characterized in that, The device includes: The data volume acquisition module is used to acquire reservoir characteristic information of shale, wherein the reservoir characteristic information includes: P-wave velocity, S-wave velocity, density, Lamé constant, shear modulus, Young's modulus, and Poisson's ratio; the reservoir characteristic information is substituted into the post-stack inversion software for well-seismic calibration, wavelet extraction, and establishment of a low-frequency model; under the constraints of the low-frequency model, pre-stack seismic inversion is performed based on seismic data to obtain multiple perturbed elastic impedance data volumes, wherein any two perturbed elastic impedance data volumes have different angle and / or azimuth values; The equations are obtained by dividing the elastic impedance equation based on orthogonal anisotropic media by the isotropic elastic impedance equations facing longitudinal, transverse, and density directions, to obtain the perturbation elastic impedance equation. The parameter acquisition module is used to calculate anisotropic parameters by substituting the multiple perturbed elastic impedance data volumes into the perturbed elastic impedance equation; the anisotropic parameters include the anisotropic gradient Γ in the X direction. x and the anisotropic gradient Γ in the Y direction y ; The geostress calculation module is used to calculate the geostress of the shale reservoir based on the anisotropy parameters. The equation yields a module used for: The elastic impedance equation based on orthotropic media is obtained, wherein the calculation formula for the elastic impedance equation based on orthotropic media is as follows: ； The calculation formula for the approximate equations of isotropic elastic impedance facing the longitudinal and transverse wave velocities and densities is as follows: ； Dividing the elastic impedance equation based on orthogonal anisotropic media by the isotropic elastic impedance approximation equation for longitudinal and transverse wave velocities and densities yields the perturbed elastic impedance equation, wherein the calculation formula for the perturbed elastic impedance equation is: ； In the above formulas: This represents the longitudinal wave velocity; This represents the transverse wave velocity; This represents density; θ It represents the angle of incidence; φ This indicates the azimuth angle; , , , , , Г x This represents the anisotropic gradient in the X direction, Γ. y This represents the anisotropic gradient in the Y direction.

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