A method for determining fluid-solid coupling thermal stress of shale gas reservoir considering heterogeneity

Abstract

This invention discloses a method for determining fluid-structure interaction thermal stress in shale gas reservoirs considering heterogeneity, comprising the following steps: S1, performing on-site core sampling of the shale gas field; S2, grinding the core into powder and performing X-ray diffraction composition analysis to calculate the bulk modulus v of different mineral components. k S3. Measure the elastic modulus E, Poisson's ratio μ, and linear expansion coefficient α of different minerals from the core samples obtained through rock mechanics experiments. k S4. Using the bulk modulus v of different mineral components k Elastic modulus E, Poisson's ratio μ, and linear expansion coefficient α of different minerals k This invention calculates the thermal stress in heterogeneous shale. It establishes a method for determining the thermal stress of shale reservoirs considering their heterogeneity. Furthermore, it proposes the influence of thermal stress on the displacement and seepage fields, deriving a thermal-fluid-structure interaction equilibrium equation for shale reservoirs considering heterogeneity. This provides a more accurate basis for studying the thermal-fluid-structure interaction effect during shale gas development.

Description

Technical Field

[0001] This invention relates to the field of shale gas technology, and more specifically to a method for determining the fluid-structure interaction thermal stress of shale gas reservoirs that takes into account heterogeneity. Background Technology

[0002] In the development of shale gas reservoirs, there is a significant coupling relationship between the thermal field, stress field, and seepage field. The accuracy of numerical simulation calculations of fluid-structure interaction directly affects the accuracy of calculations of the entire flow field, stress field, and temperature field. Therefore, it is necessary to establish a mathematical model that truly reflects the thermal-fluid-structure interaction process.

[0003] Currently, in fluid-structure-thermal coupling mathematical models, the thermal stress expression reflects the influence of the temperature field on the stress field of the solid. However, the constitutive relation of the current thermal stress equation is based on the traditional solid mechanics assumption of an equivalent continuous medium, which makes it difficult to reflect the true thermal stress characteristics of non-homogeneous materials such as shale. Shale is composed of various minerals, including brittle minerals such as quartz and feldspar, as well as clay minerals such as montmorillonite and kaolinite. Its thermodynamic properties are a comprehensive reflection of the characteristics of these various minerals.

[0004] Therefore, existing technologies have obvious technical defects, and there is an urgent need for a method that can reflect the thermal stress characteristics of heterogeneous shale reservoirs. Summary of the Invention

[0005] To address the aforementioned shortcomings in existing technologies, this invention provides a fluid-structure interaction thermal stress determination method for shale gas reservoirs that considers heterogeneity, solving the problem that existing thermal stress equations are unable to reflect the true thermal stress characteristics of non-homogeneous materials such as shale.

[0006] To achieve the aforementioned objectives, the present invention employs the following technical solution: a method for determining the fluid-structure interaction thermal stress of shale gas reservoirs considering heterogeneity, characterized by comprising the following steps:

[0007] S1. Conduct on-site core sampling for shale gas fields;

[0008] S2. Grind the core into powder and perform X-ray diffraction compositional analysis to calculate the bulk modulus v of different mineral components. k ;

[0009] S3. Measure the elastic modulus E, Poisson's ratio μ, and linear expansion coefficient α of different minerals from the core samples obtained through rock mechanics experiments. k ;

[0010] S4. Using the bulk modulus v of different mineral components k Elastic modulus E, Poisson's ratio μ, and linear expansion coefficient α of different minerals k Calculate the thermal stress of heterogeneous shale.

[0011] Furthermore, minerals with a content of less than 1% are not included in the calculation of the bulk modulus of the different mineral components.

[0012] Furthermore, the elastic modulus E and Poisson's ratio μ are obtained by uniaxial compression tests on rocks, and the expansion coefficient is obtained by a high-temperature rock expansion coefficient testing device.

[0013] Further: The formula for calculating the thermal stress of heterogeneous shale in step S4 is:

[0014]

[0015] In the above formula, σ T The value represents the thermal stress of heterogeneous shale, ΔT represents the calculation time, and max and min represent the maximum and minimum values ​​of the thermal expansion coefficient, respectively.

[0016] Furthermore, after step S4, the following steps are also included:

[0017] S5. Substituting the thermal stress of heterogeneous shale into the stress field equation, we can obtain the thermo-solid coupling relationship considering thermal stress balance.

[0018] S6. Substituting the thermo-solid coupling equation into the expression for the effect of thermal stress on the seepage field, we can obtain the permeability correction formula.

[0019] Furthermore: the thermo-mechanical coupling relationship considering thermal stress balance in step S5 is as follows:

[0020]

[0021] In the above formula, G is the shear modulus, and F is the elastic modulus. i Let u be the volume force in the direction i, including gravity, electromagnetic force, and inertial force. i Let be the displacement in the i-direction.

[0022] Furthermore: the expression for the influence of thermal stress on the seepage field is:

[0023]

[0024] In the above formula, k represents the effect of thermal stress on the seepage field, k0 represents the initial permeability of the formation, φ0 represents the initial porosity of the formation, and ε v Let α be the volumetric strain and α be the coefficient of linear expansion.

[0025] Further: The permeability correction formula in step S6 is:

[0026]

[0027] In the above formula, k represents the effect of thermal stress on the seepage field, k0 represents the initial permeability of the formation, φ0 represents the initial porosity of the formation, and F represents the initial porosity of the formation.x For the horizontal principal stress of the formation, F z This represents the vertical principal stress of the formation.

[0028] The beneficial effects of this invention are as follows: This invention addresses the different mineral compositions and varying thermal expansion properties of heterogeneous shale reservoirs, which lead to internal material interactions and thus influence the overall thermal stress. A method for determining the thermal stress of shale reservoirs considering their heterogeneity is established. Furthermore, the influence of thermal stress on the displacement and seepage fields is proposed, resulting in a thermal-fluid-structure interaction equilibrium equation for shale reservoirs considering heterogeneity. This provides a more precise basis for studying the thermal-fluid-structure interaction effect during shale gas development. Attached Figure Description

[0029] Figure 1 This is a flowchart of the present invention;

[0030] Figure 2 This is a diagram showing the results of an X-ray diffraction experiment on a shale core. Detailed Implementation

[0031] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0032] like Figure 1 As shown, a method for determining the fluid-structure interaction thermal stress of a shale gas reservoir considering heterogeneity includes the following steps:

[0033] S1. Conduct on-site core sampling for shale gas fields;

[0034] S2. Grind the core into powder and perform X-ray diffraction compositional analysis to calculate the bulk modulus v of different mineral components. k Minerals with a content of less than 1% are not included in the calculation.

[0035] S3. Measure the elastic modulus E, Poisson's ratio μ, and linear expansion coefficient α of different minerals from the core samples obtained through rock mechanics experiments. k Among them, the elastic model and Poisson's ratio were obtained by uniaxial compression test of rock; the linear expansion coefficient was obtained by high-temperature rock thermal expansion coefficient test device;

[0036] S4. Using the bulk modulus v of different mineral components k Elastic modulus E, Poisson's ratio μ, and linear expansion coefficient α of different minerals kCalculate the thermal stress of heterogeneous shale; this formula takes into account the thermal stress caused by the large differences in the thermal expansion coefficients of different minerals in the shale itself.

[0037]

[0038] In the above formula, σ T The value represents the thermal stress of heterogeneous shale, ΔT represents the calculation time, and max and min represent the maximum and minimum values ​​of the thermal expansion coefficient, respectively.

[0039] S5. Substituting the thermal stress of heterogeneous shale into the stress field equation, we can obtain the thermo-solid coupling relationship considering thermal stress balance.

[0040]

[0041] In the above formula, G is the shear modulus, and F is the elastic modulus. i Let u be the volume force in the direction i, including gravity, electromagnetic force, and inertial force. i Let be the displacement in the i-direction.

[0042] S6. Substituting the thermo-solid coupling equation into the expression for the effect of thermal stress on the seepage field, we can obtain the permeability correction formula.

[0043] The effect of thermal stress on the seepage field is reflected in the effect of the thermal stress field on permeability.

[0044]

[0045] In the above formula, k represents the effect of thermal stress on the seepage field, k0 represents the initial permeability of the formation, φ0 represents the initial porosity of the formation, and ε v Let α be the volumetric strain and α be the coefficient of linear expansion.

[0046] The volumetric strain ε can be obtained from the thermo-mechanical coupling equation. v Substituting the formula into the above equation yields the permeability correction formula:

[0047]

[0048] In the above formula, k represents the effect of thermal stress on the seepage field, k0 represents the initial permeability of the formation, φ0 represents the initial porosity of the formation, and F represents the initial porosity of the formation. x For the horizontal principal stress of the formation, F z This represents the vertical principal stress of the formation.

[0049] Example 1:

[0050] Three core samples from a shale gas field in Southwest China were ground into powder and subjected to X-ray diffraction composition analysis. The results are as follows: Figure 2 As shown;

[0051] After testing, the Young's moduli of the five shale core samples were 35.3, 32.7, and 39.5 GPa, respectively; the Poisson's ratios were 0.23, 0.25, and 0.22, respectively; and the coefficients of linear expansion were 1.23 × 10⁻⁶. -4 0.85×10 -4 0.93×10 -4 / K;

[0052] The test results of the thermal expansion coefficients of different mineral components are shown in Table 1.

[0053] Table 1. Test results of thermal expansion coefficients of different mineral components (1 / K×10⁻⁶) -4 )

[0054]

[0055]

[0056] The thermal expansion coefficient of shale core was calculated according to the formula; the results were compared with experimental test results, which are shown in Table 2.

[0057] Table 2. Coefficient of thermal expansion and experimental results (1 / K×10⁻⁶) -4 )

[0058] Core 1 1.23 1.25 1.16％ Core 2 0.85 0.85 0.3％ Core 3 0.93 0.94 1.07％

[0059] The interpretation results of the X-ray diffraction experiment on shale cores are shown in Table 3.

[0060] Table 3. Interpretation results of X-ray diffraction experiments on shale cores (%)

[0061] M1 12.5 17 21.5 37 9 M2 3 21.5 7.5 51 11 6 M3 6.5 30.5 3 45 10 3 2

[0062] This invention addresses the impact of heterogeneous shale reservoirs on overall thermal stress due to their varying mineral compositions and thermal expansion properties, which lead to internal material interactions. A method for determining thermal stress in shale reservoirs considering their heterogeneity is established. Furthermore, the influence of thermal stress on displacement and seepage fields is proposed, resulting in a thermo-fluid-structure interaction equilibrium equation for heterogeneous shale reservoirs. This provides a more precise basis for studying the thermo-fluid-structure interaction effect during shale gas development.

Claims

1. A method for determining the fluid-structure interaction thermal stress of a shale gas reservoir considering heterogeneity, characterized in that, Includes the following steps: S1. Conduct on-site core sampling for shale gas fields; S2. Grind the core into powder and perform X-ray diffraction compositional analysis to calculate the bulk modulus of different mineral components. ; S3. Measure the elastic modulus of the core samples obtained through rock mechanics experiments. E Poisson's ratio μ Coefficient of linear expansion of different minerals ; S4. Using the bulk modulus of different mineral components Elastic modulus E Poisson's ratio μ Coefficient of linear expansion of different minerals Calculate the thermal stress in heterogeneous shale; The formula for calculating the thermal stress of heterogeneous shale in step S4 is as follows: In the above formula, Thermal stress in heterogeneous shale, For the calculation time, max and min are the maximum and minimum values ​​of the coefficient of thermal expansion, respectively; Following step S4, the following steps are also included: S5. Substituting the thermal stress of heterogeneous shale into the stress field equation, we can obtain the thermo-solid coupling relationship considering thermal stress balance. S6. Substituting the thermo-mechanical coupling relationship into the expression for the influence of thermal stress on the seepage field, we can obtain the permeability correction formula. The thermo-mechanical coupling relationship considering thermal stress balance in step S5 is as follows: In the above formula, G is the shear modulus. Let i be the volume force in the direction i, which includes gravity, electromagnetic force, and inertial force. Let be the displacement in the i-th direction.

2. The method for determining the fluid-structure interaction thermal stress of shale gas reservoirs considering heterogeneity according to claim 1, characterized in that, Minerals with a content of less than 1% are not included in the calculation of the bulk modulus of different mineral components.

3. The method for determining the fluid-structure interaction thermal stress of shale gas reservoirs considering heterogeneity according to claim 1, characterized in that, The elastic modulus E Compared to Poisson μ The expansion coefficient was obtained by a uniaxial compression test of rock, and the expansion coefficient was obtained by a high-temperature rock expansion coefficient testing device.

4. The method for determining the fluid-structure interaction thermal stress of shale gas reservoirs considering heterogeneity according to claim 3, characterized in that, The expression for the influence of thermal stress on the seepage field is as follows: In the above formula, k The effect of thermal stress on the seepage field, The initial permeability of the formation. The initial porosity of the formation. For volumetric strain, is the coefficient of linear expansion.

5. The method for determining the fluid-structure interaction thermal stress of shale gas reservoirs considering heterogeneity according to claim 3, characterized in that, The permeability correction formula in step S6 is: In the above formula, k The effect of thermal stress on the seepage field, The initial permeability of the formation. The initial porosity of the formation. The horizontal principal stress of the formation, This represents the vertical principal stress of the formation.

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