Seismic response simulation test method for shale with different water saturations

Abstract

The invention discloses a seismic response simulation test method for shale with different water saturations, which comprises the following steps of: simulating an equivalent stiffness coefficient matrix based on a rock physical model of an anisotropic inclusion so as to obtain an elastic stiffness tensor of transverse isotropic medium shale; the method comprises the following steps: simulating the influence of a pore fluid on shale based on an anisotropic Gassmann-Biot model, and calculating the bulk modulus of a mixed fluid by adopting a Wood model for simulating an equivalent flexibility tensor; establishing a shale rock physical model by combining the rock physical model of the anisotropic inclusion and the anisotropic Gassmann-Biot model, and simulating an equivalent stiffness coefficient matrix; setting an elastic modulus of an isotropic shale matrix, and simulating anisotropic parameters of the fluid-containing shale and seismic longitudinal wave and transverse wave velocities of the fluid-containing shale; and analyzing the influence on the shale seismic longitudinal wave and transverse wave velocity under the conditions of different pore types, porosities and water saturation.

Description

Technical Field

[0001] The invention belongs to the technical field of anisotropic shale seismic simulation, and in particular relates to a seismic response simulation test method for shales with different water saturations. Background Art

[0002] The simulation test of seismic response of shale with different water saturation is an important technology for the response of shale to seismic waves under different water conditions. On this basis, we can analyze the influence of saturation on seismic wave propagation, the change of shale dynamic characteristics with saturation, the mechanism of water content on the interaction between seismic waves and shale, and the stability of shale with different saturations in geological engineering and earthquake disaster research, which is helpful to understand the rock dynamic characteristics of fluid-containing shale and provide an important scientific basis for earthquake risk assessment and geological engineering design.

[0003] Rock physics modeling methods are crucial when conducting seismic response simulation tests on shales with different water saturations. The physical model of shale provides a theoretical basis for quantitatively predicting shale elasticity and anisotropy parameters. However, shales usually develop complex pore structures, in which isolated and connected pores / fractures may coexist, which restricts the simulation accuracy of shale reservoirs by conventional shale physical modeling methods. Therefore, for shale rocks with complex pore structures, how to propose an effective shale physical model and conduct seismic response simulation tests of shales with different saturations based on it is of great significance to improve shale geological evaluation. Summary of the invention

[0004] The purpose of the present invention is to solve the problems existing in the prior art and to provide a seismic response simulation test method for shales with different water saturations.

[0005] In order to achieve the above-mentioned invention object, the present invention specifically adopts the following technical solutions:

[0006] A method for simulating the seismic response of shales with different water saturations comprises the following steps:

[0007] S1. Based on the rock physics model of anisotropic inclusions, the equivalent stiffness coefficient matrix of the shale matrix is ​​simulated, and the pore type is used to characterize the geometric shapes of pores and fractures to obtain the elastic stiffness tensor of the transversely isotropic medium shale;

[0008] S2. Based on the anisotropic Gassmann-Biot model, the effect of porous fluid on shale is simulated, and the bulk modulus of the mixed fluid is calculated using the Wood model to simulate the equivalent flexibility tensor of shale containing porous fluid;

[0009] S3. The rock physics model of anisotropic inclusions and the anisotropic Gassmann-Biot model are combined to construct a shale rock physics model, and the shale rock physics model is used to simulate the equivalent stiffness coefficient matrix of fluid-containing shale;

[0010] S4. Based on the constructed shale rock physics model, the elastic modulus of the isotropic shale matrix is ​​set, and the anisotropic parameters of the fluid-containing shale and the seismic P-wave and S-wave velocities of the fluid-containing shale are simulated based on the equivalent stiffness coefficient matrix of the fluid-containing shale;

[0011] S5. Based on the shale rock physics model, calculate the P-wave and S-wave anisotropy parameter values ​​of gas-bearing shale under different pore types and the P-wave and S-wave anisotropy parameter values ​​of formation water-bearing shale under different pore types;

[0012] S6. Based on the shale rock physics model, calculate the P-wave and S-wave anisotropy parameter values ​​of gas-bearing shale at different porosities and the P-wave and S-wave anisotropy parameter values ​​of formation water-bearing shale at different porosities;

[0013] S7. Based on the shale rock physics model, the P-wave and S-wave anisotropy parameter values ​​of gas-bearing shale under different pore types, porosities and water saturations, as well as the P-wave and S-wave anisotropy parameter values ​​of formation water-bearing shale under different pore types, porosities and water saturations are calculated.

[0014] Based on the above scheme, each step can be implemented in the following preferred specific manner.

[0015] Preferably, in step S1, the rock physics model of the anisotropic inclusion and the equivalent stiffness coefficient matrix of the shale matrix are It is expressed as:

[0016]

[0017] Where N is the number of inclusions; is the equivalent stiffness coefficient matrix of the nth inclusion, v is the volume percentage, I is the fourth-order unit tensor, is the Eshelby tensor related to the pore geometry of the inclusion, is the equivalent stiffness coefficient of the inclusion; the subscript n of each parameter symbol indicates that the parameter symbol corresponds to the nth inclusion, and the subscripts ijkl, ikjl, and jkil indicate that the parameter symbol satisfies the Einstein summation convention;

[0018] When shale behaves as a transversely isotropic medium, assuming that the z-axis is the symmetry axis in the rectangular coordinate system, the elastic stiffness tensor of the transversely isotropic shale is expressed as:

[0019]

[0020] In the formula, C 11 , C 12 , C 13 , C 33 , C 44 , C 66 All are elements in the equivalent stiffness coefficient matrix of fluid-bearing shale; is the elastic stiffness tensor of the transversely isotropic shale medium.

[0021] Preferably, in step S2, the equivalent flexibility tensor of the shale containing porous fluid is It is expressed as:

[0022]

[0023] K f =S w ×K w +(1-S w )×K g

[0024] In the formula, is the equivalent flexibility tensor of fluid-containing shale; is the equivalent flexibility tensor of dry shale, which is obtained through the equivalent stiffness coefficient matrix of shale matrix calculate; is the equivalent flexibility tensor of shale minerals; β m is the compression coefficient of the rock skeleton; β f is the compressibility coefficient of pore fluid; φ is the porosity; K f is the bulk modulus of the mixed fluid of gas and water; S w is water saturation; K w is the bulk modulus of water; K g is the bulk modulus of the gas; the four-letter subscripts appearing in the above parameter symbols all indicate that the corresponding parameter symbols satisfy the Einstein summation convention.

[0025] Preferably, in step S3, the rock physics model of anisotropic inclusions is used to calculate the elastic stiffness tensors of dry shale and fluid-containing shale considering isolated pores, and the anisotropic Gassmann-Biot model is used to calculate the equivalent flexibility tensor of fluid-containing shale considering connected pores. The influence of connected pores and non-connected pores is considered, and the rock physics model of anisotropic inclusions and the anisotropic Gassmann-Biot model are combined to construct a shale rock physics model. Then, the equivalent stiffness coefficient matrix C of the fluid-containing shale is shale It is expressed as:

[0026]

[0027] In the formula, represents the pore type balance parameter; is the equivalent flexibility tensor of fluid-containing shale.

[0028] Preferably, in step S4, the anisotropic parameter of the fluid-containing shale is expressed as:

[0029]

[0030] The seismic P-wave and S-wave velocities of fluid-containing shale are expressed as:

[0031]

[0032] Among them, ε is the anisotropy parameter of longitudinal wave, γ is the anisotropy parameter of transverse wave; V S V represents the seismic shear wave velocity of fluid-bearing shale; P It represents the seismic P-wave velocity of fluid-containing shale; ρ is the shale density.

[0033] Preferably, in step S5, based on the shale rock physics model, when calculating the longitudinal and transverse wave anisotropy parameter values ​​of gas-containing shale or formation water-containing shale in different pore types, the pore type balance parameter varies in the range of 0.01 to 0.99 with an interval of 0.01, the water saturation is set to 0, and the porosity is set to 0.1.

[0034] Preferably, in step S6, based on the shale rock physics model, when calculating the longitudinal and transverse wave anisotropy parameter values ​​of gas-containing shale or formation water-containing shale under different porosities, the porosity varies in the range of 0.01 to 0.15 with an interval of 0.005, the water saturation is set to 1, and the porosity is set to 0.3.

[0035] Preferably, in step S7, based on the shale rock physics model, when calculating the longitudinal and transverse wave anisotropy parameter values ​​of gas-containing shale or formation water-containing shale under different pore types, porosities and water saturations, the pore type balance parameter varies in the range of 0.01 to 0.99 at intervals of 0.01, the porosity varies in the range of 0.01 to 0.15 at intervals of 0.005, and the water saturation varies in the range of 0 to 1 at intervals of 0.2.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. Rock physics modeling combines the rock physics model of anisotropic inclusions and the anisotropic Gassmann-Biot model, taking into account the comprehensive influence of different pore types in shale and improving the accuracy of seismic simulation of shale;

[0038] 2. A calculation method is proposed to simulate the elastic and seismic response of shale under different pore aspect ratios, porosity and water saturation, which can effectively reveal the elastic and seismic response laws of shale under the influence of different pore parameters and water saturation. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of a flow chart of a simulation test method for rock seismic response with different water saturations according to the present invention;

[0040] Figure 2 This is a schematic diagram of the shale seismic rock physics modeling process in an embodiment of the present invention;

[0041] Figure 3 : is the variation of shale anisotropy parameters with pore aspect ratio in the embodiment of the present invention; wherein a is the longitudinal wave anisotropy parameter ε, b is the oblique wave anisotropy parameter δ, and c is the transverse wave anisotropy parameter γ;

[0042] Figure 4 : is the variation of shale anisotropy parameters with porosity in the embodiment of the present invention; wherein a is the longitudinal wave anisotropy parameter ε, b is the oblique wave anisotropy parameter δ, and c is the transverse wave anisotropy parameter γ;

[0043] Figure 5 : is the variation of shale anisotropy parameters with water saturation in the embodiment of the present invention; wherein a is the longitudinal wave anisotropy parameter ε, b is the oblique wave anisotropy parameter δ, and c is the transverse wave anisotropy parameter γ;

[0044] Figure 6 1 and 2 show the changes of shale elastic parameters with water saturation, pore aspect ratio and porosity in the embodiments of the present invention; wherein a is the influence of water saturation and porosity on P-wave velocity, b is the influence of water saturation and porosity on S-wave velocity, c is the influence of water saturation and pore aspect ratio on P-wave velocity, and d is the influence of water saturation and pore aspect ratio on S-wave velocity. DETAILED DESCRIPTION

[0045] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, the specific implementation mode of the present invention is described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0046] In a preferred embodiment of the present invention, a method for simulating the seismic response of shales with different water saturations is proposed, the purpose of which is to solve the problems existing in the prior art that conventional rock physics models are difficult to apply and cannot effectively describe the complex pore structure of shales, and to improve the accuracy of seismic response simulation of shales with different water saturations. Figure 1 As shown, the above-mentioned seismic response simulation test method of shale with different water saturation includes the following steps S1 to S7. The specific implementation process is described in detail below.

[0047] S1. Based on the rock physics model of anisotropic inclusions, the equivalent stiffness coefficient matrix of the shale matrix is ​​simulated, and the pore type is used to characterize the geometric shapes of pores and fractures to obtain the elastic stiffness tensor of the transversely isotropic medium shale.

[0048] It should be noted that in step S1 of the present invention, the rock physics model of the anisotropic inclusion and the equivalent stiffness coefficient matrix of the shale matrix are It can be expressed as:

[0049]

[0050] Where N is the number of inclusions; is the equivalent stiffness coefficient matrix of the nth inclusion, v is the volume percentage, I is the fourth-order unit tensor, is the Eshelby tensor related to the pore geometry of the inclusion, is the equivalent stiffness coefficient of the inclusion; the subscript n of each parameter symbol indicates that the parameter symbol corresponds to the nth inclusion, and the subscripts ijkl, ikjl, and jkil indicate that the parameter symbol satisfies the Einstein summation convention;

[0051] When shale behaves as a transversely isotropic medium, assuming that the z-axis is the symmetry axis in the rectangular coordinate system, the elastic stiffness tensor of the transversely isotropic shale can be expressed as:

[0052]

[0053] In the formula, C 11 , C 12 , C 13 , C 33 , C 44 , C 66 All are elements in the equivalent stiffness coefficient matrix of fluid-bearing shale; is the elastic stiffness tensor of the transversely isotropic shale medium.

[0054] S2. Based on the anisotropic Gassmann-Biot model, the effect of porous fluid on shale is simulated, and the bulk modulus of the mixed fluid is calculated using the Wood model to simulate the equivalent flexibility tensor of shale containing porous fluid.

[0055] It should be noted that in step S2 of the present invention, the equivalent flexibility tensor of the shale containing porous fluid is It can be expressed as:

[0056]

[0057] K f =S w ×K w +(1-S w )×K g

[0058] In the formula, is the equivalent flexibility tensor of fluid-containing shale; is the equivalent flexibility tensor of dry shale, which is obtained through the equivalent stiffness coefficient matrix of shale matrix calculate; is the equivalent flexibility tensor of shale minerals; β m is the compression coefficient of the rock skeleton; β f is the compressibility coefficient of pore fluid; φ is the porosity; K f is the bulk modulus of the mixed fluid of gas and water; S w is water saturation; K w is the bulk modulus of water; K g is the bulk modulus of the gas; the four-letter subscripts appearing in the above parameter symbols all indicate that the corresponding parameter symbols satisfy the Einstein summation convention.

[0059] S3. The rock physics model of anisotropic inclusions and the anisotropic Gassmann-Biot model are combined to construct a shale rock physics model, and the shale rock physics model is used to simulate the equivalent stiffness coefficient matrix of fluid-containing shale.

[0060] It should be noted that in step S3 of the present invention, the rock physics model of anisotropic inclusions is used to calculate the elastic stiffness tensors of dry shale and fluid-containing shale considering isolated pores, and the anisotropic Gassmann-Biot model is used to calculate the equivalent flexibility tensor of fluid-containing shale considering connected pores. The influence of connected pores and non-connected pores is considered, and the rock physics model of anisotropic inclusions and the anisotropic Gassmann-Biot model are combined to construct a shale rock physics model. Then, the equivalent stiffness coefficient matrix C of fluid-containing shale is shale It can be expressed as:

[0061]

[0062] In the formula, represents the pore type balance parameter; is the equivalent flexibility tensor of fluid-containing shale.

[0063] S4. Based on the constructed shale rock physics model, the elastic modulus of the isotropic shale matrix is ​​set, and the anisotropic parameters of the fluid-containing shale and the seismic longitudinal and transverse wave velocities of the fluid-containing shale are simulated based on the equivalent stiffness coefficient matrix of the fluid-containing shale.

[0064] It should be noted that, in step S4 of the present invention, the anisotropic parameters of the simulation and experimental observation are compared to obtain the pore type balance parameters that satisfy the minimum error between the two; according to the obtained pore type balance parameters, the equivalent stiffness coefficient matrix Cshale of the fluid-containing shale is calculated, and the anisotropic parameters of the fluid-containing shale can be expressed as:

[0065]

[0066] The seismic P-wave and S-wave velocities of fluid-containing shale can be expressed as:

[0067]

[0068] Among them, ε is the anisotropy parameter of longitudinal wave, γ is the anisotropy parameter of transverse wave; V S V represents the seismic shear wave velocity of fluid-bearing shale; P It represents the seismic P-wave velocity of fluid-containing shale; ρ is the shale density.

[0069] S5. Based on the shale rock physics model, the P-wave and S-wave anisotropy parameter values ​​of gas-bearing shale in different pore types and the P-wave and S-wave anisotropy parameter values ​​of formation water-bearing shale in different pore types are calculated.

[0070] It should be noted that in step S5 of the present invention, based on the shale rock physics model, when calculating the longitudinal and transverse wave anisotropy parameter values ​​of gas-containing shale or formation water-containing shale in different pore types, the pore type balance parameter varies in the range of 0.01 to 0.99 with an interval of 0.01, the water saturation is set to 0, and the porosity is set to 0.1.

[0071] In step S5 of this embodiment, based on the constructed shale rock physics model, the shale anisotropy parameters are calculated for pores filled with gas and water, respectively. Under different fluid filling conditions, the pore type balance parameter varies from 0.01 to 0.99, and the shear wave anisotropy parameter values ​​of gas-containing and water-containing shales are compared. The longitudinal and shear wave anisotropy parameter value trends of gas-containing and water-containing shales with different pore types are compared. The specific steps are as follows: In step S5, based on the shale rock physics model, when calculating the longitudinal and shear wave anisotropy parameter values ​​of gas-containing shale or formation water-containing shale with different pore types, the pore type balance parameter varies within the range of 0.01 to 0.99 with an interval of 0.01, the water saturation is set to 0, and the porosity is set to 0.1.

[0072] S6. Based on the shale rock physics model, the P-wave and S-wave anisotropy parameter values ​​of gas-bearing shale at different porosities and the P-wave and S-wave anisotropy parameter values ​​of formation water-bearing shale at different porosities are calculated.

[0073] It should be noted that in step S6 of the present invention, based on the shale rock physics model, when calculating the longitudinal and transverse wave anisotropy parameter values ​​of gas-containing shale or formation water-containing shale under different porosities, the porosity varies in the range of 0.01 to 0.15 with an interval of 0.005, the water saturation is set to 1, and the porosity is set to 0.3.

[0074] In step S6 of this embodiment, based on the constructed shale rock physics model, the shale anisotropy parameters under the conditions of pore filling gas and water are calculated respectively. Under different porosities, the porosity varies from 0.01 to 0.15, and the shear wave anisotropy parameter values ​​of gas-containing and water-containing shales are compared. The change trends of the longitudinal and shear wave anisotropy parameter values ​​of gas-containing and water-containing shales under different porosities are compared. The specific steps are as follows: In step S6, based on the shale rock physics model, when calculating the longitudinal and shear wave anisotropy parameter values ​​of gas-containing shale or formation water-containing shale under different porosities, the porosity varies within the range of 0.01 to 0.15 with an interval of 0.005, the water saturation is set to 1, and the porosity is set to 0.3.

[0075] S7. Based on the shale rock physics model, the P-wave and S-wave anisotropy parameter values ​​of gas-bearing shale under different pore types, porosities and water saturations, as well as the P-wave and S-wave anisotropy parameter values ​​of formation water-bearing shale under different pore types, porosities and water saturations are calculated.

[0076] It should be noted that in step S7 of the present invention, based on the shale rock physics model, when calculating the longitudinal and transverse wave anisotropy parameter values ​​of gas-containing shale or formation water-containing shale under different pore types, porosities and water saturations, the pore type balance parameter varies in the range of 0.01 to 0.99 at intervals of 0.01, the porosity varies in the range of 0.01 to 0.15 at intervals of 0.005, and the water saturation varies in the range of 0 to 1 at intervals of 0.2.

[0077] In step S7 of the present embodiment, based on the shale rock physics model, the seismic P-wave and S-wave velocity values ​​of the fluid-containing shale under different pore types, porosities and water saturations are calculated respectively, wherein the pore type balance parameter varies in the range of 0.01 to 0.99 at intervals of 0.01, the porosity varies in the range of 0.01 to 0.15 at intervals of 0.005, and the water saturation varies in the range of 0 to 1 at intervals of 0.2.

[0078] In order to better demonstrate the specific implementation and technical effect of the present invention, a seismic response simulation test method for shales with different water saturations shown in steps S1 to S7 in the above preferred implementation is applied to a specific example.

[0079] Example

[0080] The specific implementation process of the seismic response simulation test method for shales with different water saturations used in this embodiment is as described above and will not be repeated here.

[0081] like Figure 2 As shown in the figure, the DEM and SCA models assume isolated pores and fracture spaces, and can predict the elastic response of rocks at relatively high frequencies. On the other hand, the Gassmann and Brown-Korringa models allow the pores to be fully connected, that is, the pore pressure is assumed to be balanced, which meets the conditions of low-frequency seismic simulation. Therefore, in order to consider the influence of connected and non-connected pores, the DEM-SCA and Brown-Korringa models are combined to construct a shale rock physics model.

[0082] Based on the seismic response simulation test method of shale with different water saturation constructed by the present invention, numerical analysis and testing are carried out to analyze the influence of rock physical parameters on the elastic properties of shale and the difference between isolated pores and connected pores. A simplified rock physical parameter is used for analysis, assuming that the elements in the equivalent stiffness coefficient matrix of fluid-containing shale are: C 11 =C 33 =86.5GPa,C 44 =C 66 =24.6GPa,C13 =21.1GPa. Anisotropic DEM models are used for dry shale and fluid-containing shale (considering isolated pores). Fluid-containing shale (considering connected pores) uses the Brown-Korringa equation to fill dry shale with fluid (gas, water and their mixtures). Among them, anisotropic parameters are used to quantify the elastic response characteristics of shale. In order to reveal the influence of fluid saturation on the seismic and elastic response of shale, this embodiment simulates and analyzes the influence of different pore aspect ratios, porosity and water saturation on the anisotropic parameters of shale.

[0083] Figure 3 The effect of pore aspect ratio α on shale anisotropy parameters was analyzed. The analysis is based on an anisotropic DEM model considering isolated pores. By adding gas / water inclusions to the shale matrix, shales under different fluid filling conditions are compared and analyzed. The pore aspect ratio ranges from thin flat cracks with α=0.01 to spherical pores with α=1 to describe the different pore shapes that may exist in shale. The analysis results show that shale has a higher ε (P-wave anisotropy), especially for gas-bearing shales and water-bearing shales with smaller aspect ratios. Compared with water-bearing shales, the ε and δ anisotropies of gas-bearing shales are significantly increased (e.g. Figure 3 a and Figure 3 b), the variation trend of γ (S-wave velocity anisotropy) is basically the same as that of ε, but the pore fluid (gas or water) has no obvious effect on it (as shown in Figure 3 c).

[0084] Figure 4 The effect of porosity φ on shale anisotropy parameters was analyzed, and the difference in elastic anisotropy of water-bearing shale predicted by anisotropic DEM and Brown-Korringa model was compared. This analysis compares the effects of isolated pores and connected pores on shale modeling and reveals the effect of porosity on the elastic response of shale. The results show that the anisotropic parameters ε and δ are more important when the shale porosity is large (greater than 0.04) (e.g. Figure 4 a and Figure 4 b), the predictions using DEM and Brown-Korringa model will show large differences, especially the prediction results of δ are relatively different, while γ is less affected by pore connectivity (as shown in Figure 4 c); in addition, the anisotropy parameters all show a trend of increasing with increasing porosity.

[0085] Figure 5 The influence of different water saturations on shale anisotropic parameters was analyzed. Assuming that the pore fluid of shale is a gas-water mixture (the bulk modulus of the mixed fluid is calculated using the Wood model), the water saturation S wFrom the changes in shale anisotropy parameters from 50% to 100%, we can see that with the increase of water saturation (i.e., the decrease of gas content), the anisotropy parameters all show a decreasing trend, among which the change trends of ε and δ are more obvious (e.g. Figure 5 a and Figure 5 b), while γ (S-wave velocity anisotropy) is less affected by pore fluid and its change trend is not obvious (as shown in Figure 5 c).

[0086] In order to reveal the comprehensive effects of water saturation, pore aspect ratio and porosity on the seismic response of shale, Figure 6 The longitudinal wave (V P ), transverse wave (V S The analysis is based on the constructed shale rock physics model, which takes into account the influence of connected and non-connected pores.

[0087] The analysis results show that the seismic longitudinal wave velocity V of shale is P It decreases with increasing porosity and increases with increasing water saturation (e.g. Figure 6 a), for example, when φ = 0.05, when the water saturation increases from 50% to 100%, the seismic longitudinal wave velocity V P The increase is about 15% (from 2.8m / s to 3.2m / s). Since the shear wave velocity is insensitive to the change of pore fluid, the seismic shear wave velocity V of shale is S It is only affected by porosity and has little effect on saturation (e.g. Figure 6 b). The seismic longitudinal wave velocity V of shale P It increases with the increase of pore aspect ratio and water saturation (e.g. Figure 6 c), but when the aspect ratio is small (when the fracture is developed), it is more affected by the pore fluid; similarly, the shear wave velocity is not sensitive to the change of pore fluid. The seismic shear wave velocity V of shale is S Only affected by the pore aspect ratio (e.g. Figure 6 d).

[0088] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for simulating the seismic response of shales with different water saturations, characterized in that: The following steps are involved: S1. Based on the rock physics model of anisotropic inclusions, the equivalent stiffness coefficient matrix of the shale matrix is ​​simulated, and the pore type is used to characterize the geometric shapes of pores and fractures to obtain the elastic stiffness tensor of the transversely isotropic medium shale; S2. Based on the anisotropic Gassmann-Biot model, the effect of porous fluid on shale is simulated, and the bulk modulus of the mixed fluid is calculated using the Wood model to simulate the equivalent flexibility tensor of shale containing porous fluid; S3. The rock physics model of anisotropic inclusions and the anisotropic Gassmann-Biot model are combined to construct a shale rock physics model, and the shale rock physics model is used to simulate the equivalent stiffness coefficient matrix of fluid-containing shale; S4. Based on the constructed shale rock physics model, the elastic modulus of the isotropic shale matrix is ​​set, and the anisotropic parameters of the fluid-containing shale and the seismic P-wave and S-wave velocities of the fluid-containing shale are simulated based on the equivalent stiffness coefficient matrix of the fluid-containing shale; S5. Based on the shale rock physics model, calculate the P-wave and S-wave anisotropy parameter values ​​of gas-bearing shale under different pore types and the P-wave and S-wave anisotropy parameter values ​​of formation water-bearing shale under different pore types; S6. Based on the shale rock physics model, calculate the P-wave and S-wave anisotropy parameter values ​​of gas-bearing shale at different porosities and the P-wave and S-wave anisotropy parameter values ​​of formation water-bearing shale at different porosities; S7. Based on the shale rock physics model, the P-wave and S-wave anisotropy parameter values ​​of gas-bearing shale under different pore types, porosities and water saturations, as well as the P-wave and S-wave anisotropy parameter values ​​of formation water-bearing shale under different pore types, porosities and water saturations are calculated.

2. The seismic response simulation test method of shales with different water saturations according to claim 1 is characterized in that: In step S1, the rock physics model of anisotropic inclusions and the equivalent stiffness coefficient matrix of shale matrix are It is expressed as: Where N is the number of inclusions; is the equivalent stiffness coefficient matrix of the nth inclusion, v is the volume percentage, I is the fourth-order unit tensor, is the Eshelby tensor related to the pore geometry of the inclusion, is the equivalent stiffness coefficient of the inclusion; the subscript n of each parameter symbol indicates that the parameter symbol corresponds to the nth inclusion, and the subscripts ijkl, ikjl, and jkil indicate that the parameter symbol satisfies the Einstein summation convention; When shale behaves as a transversely isotropic medium, assuming that the z-axis is the symmetry axis in the rectangular coordinate system, the elastic stiffness tensor of the transversely isotropic shale is expressed as: In the formula, C 11 , C 12 , C 13 , C 33 , C 44 , C 66 All are elements in the equivalent stiffness coefficient matrix of fluid-bearing shale; is the elastic stiffness tensor of the transversely isotropic shale medium.

3. The seismic response simulation test method of shales with different water saturations according to claim 2 is characterized in that: In step S2, the equivalent flexibility tensor of shale containing pore fluid is It is expressed as: K f =S w ×K w +(1-S w )×K g In the formula, is the equivalent flexibility tensor of fluid-containing shale; is the equivalent flexibility tensor of dry shale, which is obtained through the equivalent stiffness coefficient matrix of shale matrix calculate; is the equivalent flexibility tensor of shale minerals; β m is the compression coefficient of the rock skeleton; β f is the compressibility coefficient of pore fluid; φ is the porosity; K f is the bulk modulus of the mixed fluid of gas and water; S w is water saturation; K w is the bulk modulus of water; K g is the bulk modulus of the gas; the four-letter subscripts appearing in the above parameter symbols all indicate that the corresponding parameter symbols satisfy the Einstein summation convention.

4. The seismic response simulation test method of shales with different water saturations according to claim 2 is characterized in that: In step S3, the rock physics model of anisotropic inclusions is used to calculate the elastic stiffness tensors of dry shale and fluid-containing shale considering isolated pores, and the anisotropic Gassmann-Biot model is used to calculate the equivalent flexibility tensor of fluid-containing shale considering connected pores. The influence of connected pores and non-connected pores is considered, and the rock physics model of anisotropic inclusions and the anisotropic Gassmann-Biot model are combined to construct a shale rock physics model. Then, the equivalent stiffness coefficient matrix C of fluid-containing shale is shale It is expressed as: In the formula, represents the pore type balance parameter; is the equivalent flexibility tensor of fluid-containing shale.

5. The seismic response simulation test method of shales with different water saturations according to claim 2 is characterized in that: In step S4, the anisotropic parameter of the fluid-containing shale is expressed as: The seismic P-wave and S-wave velocities of fluid-containing shale are expressed as: Among them, ε is the anisotropy parameter of longitudinal wave, γ is the anisotropy parameter of transverse wave; V S V represents the seismic shear wave velocity of fluid-bearing shale; P It represents the seismic P-wave velocity of fluid-containing shale; ρ is the shale density.

6. The seismic response simulation test method of shales with different water saturations according to claim 1 is characterized in that: In step S5, based on the shale rock physics model, when calculating the longitudinal and transverse wave anisotropy parameter values ​​of gas-containing shale or formation water-containing shale in different pore types, the pore type balance parameter varies in the range of 0.01 to 0.99 with an interval of 0.01, the water saturation is set to 0, and the porosity is set to 0.

1.

7. The method for simulating seismic response of shales with different water saturations according to claim 1, characterized in that: In step S6, based on the shale rock physics model, when calculating the longitudinal wave and transverse wave anisotropy parameter values ​​of gas-containing shale or formation water-containing shale under different porosities, the porosity varies in the range of 0.01 to 0.15 with an interval of 0.005, the water saturation is set to 1, and the porosity is set to 0.

3.

8. The method for simulating the seismic response of shales with different water saturations according to claim 1, characterized in that: In step S7, based on the shale rock physics model, when calculating the longitudinal and transverse wave anisotropy parameter values ​​of gas-containing shale or formation water-containing shale under different pore types, porosities and water saturations, the pore type balance parameter varies in the range of 0.01 to 0.99 at intervals of 0.01, the porosity varies in the range of 0.01 to 0.15 at intervals of 0.005, and the water saturation varies in the range of 0 to 1 at intervals of 0.2.

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