Coal reservoir earthquake rock physical modeling method and system
By obtaining the microstructure and elastic parameters of directional core samples, and combining CT scanning and modeling methods, the problem that existing models cannot accurately characterize coal reservoirs has been solved, and precise modeling and high-precision seismic prediction of coal reservoirs have been achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-09
- Publication Date
- 2026-04-03
AI Technical Summary
Existing rock physics models are insufficient to accurately characterize the adsorbed state occurrence, micro-component elastic differences, and orthogonal fracture systems of coal reservoirs, thus limiting the reliability and effectiveness of seismic exploration for coalbed methane.
By obtaining the volumetric composition and elastic parameters of directional core samples, and using CT scans to obtain porosity and fracture morphology, a three-phase coupled VTI model and an orthogonal anisotropic equivalent medium model of the coal reservoir are constructed by combining the Voigt-Reuss-Hill average model and nonlinear programming method, thus achieving accurate modeling of the coal reservoir.
It significantly improves the accuracy of seismic prediction for coalbed methane reservoirs and enables quantitative characterization of the adsorbed gas effect and orthogonal anisotropy of coal reservoirs.
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Abstract
Description
Technical Field
[0001] This application relates to the field of seismic rock modeling technology, and in particular to a method and system for seismic rock physical modeling of coal reservoirs. Background Technology
[0002] Seismic rock physics modeling, as a crucial bridge connecting the physical properties of subsurface rocks with seismic response, is a research hotspot in the field of seismic exploration. Based on seismic rock physics theories and methods, we can establish a more scientific and quantitative interpretive framework, thereby more accurately revealing the intrinsic correspondence between reservoir physical parameters and seismic attributes. This process not only deepens our understanding of reservoir characteristics but also significantly improves the predictive accuracy and application value of seismic exploration in coalbed methane development. Establishing accurate rock physics models, by changing reservoir physical parameters, and conducting rock physics analysis and forward modeling, can effectively simulate the underground occurrence state of reservoirs, obtain the changing patterns of their seismic response, and thus determine effective information such as reservoir development status and gas-bearing enrichment areas. However, previous rock physics theories have specific applicable conditions. Coalbed methane reservoirs differ fundamentally from other conventional rocks in terms of pore and fracture structure and fluid properties, making it difficult to simulate coal and rock using the properties of conventional reservoirs.
[0003] Existing rock physics models mainly focus on sandstone, mudstone, and carbonate reservoirs. Conventional sandstone reservoirs are dominated by free gas, while coalbed methane (CBM) exists in an adsorbed state on the coal matrix surface for over 90%. Micropores and natural fractures coexist in the matrix. Furthermore, coal has low mechanical strength, with a uniaxial compressive strength typically less than 20 MPa and a high brittleness index, making it susceptible to plastic deformation or fracture due to mining disturbances. Traditional rock physics models based on the properties of conventional sandstone and mudstone reservoirs struggle to characterize these coupled processes. Moreover, the characterization of fractures in coal reservoirs often employs isotropic assumptions, failing to reflect the anisotropic elastic response induced by orthogonal fractures in coal reservoirs.
[0004] In addition to the above, current research in academia and industry on the organic microscopic components of coal (mainly including vitrinite, chalcanthite, and inertinite) focuses primarily on the mechanical properties of each component at the microscale (such as hardness, brittleness, and compressive strength) and their control mechanisms on the development of macroscopic fractures in coal and rock. This research aims to reveal how different microscopic components affect the fracture behavior of coal. However, the fundamental elastic moduli of each microscopic component in coal (such as Young's modulus, shear modulus, and bulk modulus) are also important components related to coal reservoir characteristics, but research and systematic discussion on these moduli are extremely limited. This results in models lacking a physical basis from the microscopic to the macroscopic level, thus limiting their predictive capabilities. Therefore, there is an urgent need for a novel seismic petrophysical modeling method for coal reservoirs that can start from microscopic mechanisms and comprehensively consider the adsorbed gas effect, multi-scale pore structure, elasticity of microscopic components, and orthogonal anisotropy, in order to improve the reliability and effectiveness of coalbed methane seismic exploration. Summary of the Invention
[0005] This application provides a method and system for seismic rock physics modeling of coal reservoirs, which at least solves the technical problem of inaccurate characterization caused by existing conventional rock physics models that do not consider the adsorbed state occurrence, elastic differences of micro-components, and orthogonal fracture systems in coal reservoirs.
[0006] The first aspect of this application proposes a method for seismic rock physics modeling of coal reservoirs, the method comprising: A set of oriented core samples representing the anisotropic characteristics of the target coal reservoir were obtained, and the volume content and elastic parameters of the micro-components of the core samples were measured. Then, the porosity, fracture morphology and number of each core sample were obtained by CT scanning. Based on the volume content of the micro-components, the micro-elastic modulus of the micro-components was calculated by inversion using the Voigt-Reuss-Hill average model and nonlinear programming method. A matrix model was constructed based on the elastic parameters and microelastic moduli of the core samples. A three-phase coupled VTI model is constructed based on the porosity and the matrix model; Based on the fracture morphology and number, and the three-phase coupled VTI model, an orthogonal anisotropic equivalent medium model of the seismic rock in the coal reservoir is constructed.
[0007] Preferably, the microscopic components include: vitrinite, chitinite, inertinite, clay minerals, and carbonate minerals; The elastic parameters include: Young's modulus, Poisson's ratio, shear modulus, and bulk modulus.
[0008] Furthermore, the process of obtaining the elastic parameters of the core sample includes: The ultrasonic longitudinal wave velocity, ultrasonic transverse wave velocity, density, Poisson's ratio of ultrasonic longitudinal wave velocity, and Poisson's ratio of ultrasonic transverse wave velocity of the core sample were obtained. The longitudinal wave conversion coefficient is determined based on the Poisson's ratio of the ultrasonic longitudinal wave velocity, and the transverse wave conversion coefficient is determined based on the Poisson's ratio of the ultrasonic transverse wave velocity. The seismic P-wave velocity of the core sample is determined based on the P-wave conversion coefficient and the ultrasonic P-wave velocity, and the seismic S-wave velocity of the core sample is determined based on the S-wave conversion coefficient and the ultrasonic S-wave velocity. The elastic parameters of the core sample are determined based on the longitudinal wave velocity, the transverse wave velocity, and the density of the seismic wave.
[0009] Furthermore, the calculation of the microscopic elastic modulus of the microscopic component based on its volume content using the Voigt-Reuss-Hill average model and nonlinear programming method includes: Using the macroscopic elastic modulus of the coal sample as the constraint objective, and the bulk modulus, shear modulus, and volume percentage of each micro-component as variables, the solution is obtained... , The system of equations achieves inversion; Wherein, the macroscopic elastic modulus of the coal sample is the bulk modulus and shear modulus of the coal sample. It is the bulk modulus in the macroscopic elastic modulus. This refers to the shear modulus within the macroscopic elastic modulus. Let be the bulk modulus of the i-th microstructure. Let N be the volume content of the i-th microscopic component, and N be the total number of microscopic components. Let be the shear modulus of the i-th micro-component.
[0010] Furthermore, the construction of the three-phase coupled VTI model based on the porosity and the matrix model includes: Based on the porosity and the matrix model, and using the self-compatible approximate equivalent medium theory, a three-phase coupling model of coal matrix-adsorbed gas-pores is constructed. A three-phase coupled VTI model was established by mixing single-layer coal samples at various locations and directions using the Backus averaging method.
[0011] Furthermore, the construction of the orthogonal anisotropic equivalent medium model of the coal reservoir seismic rock based on the fracture morphology and number and the three-phase coupled VTI model includes: Invert the stiffness matrix corresponding to the three-phase coupled VTI model to obtain the compliance matrix of the background medium; Based on the crack density, aspect ratio, and filling material parameters determined by the crack morphology and number, the additional compliance tensor caused by a set of vertically oriented cracks is calculated using the Hudson model and linear slip theory. The compliance moment of the background medium is linearly superimposed with the additional compliance tensor to obtain the total compliance matrix of the fractured coal reservoir. The stiffness matrix of the orthogonal anisotropic coal reservoir rock physics model under dry conditions is obtained by inverting the total compliance matrix. Based on the stiffness matrix, porosity, and fluid parameters within the fractures of the orthotropic coal reservoir rock physics model under dry conditions, the orthotropic equivalent elastic stiffness matrix of the coal reservoir under saturated fluid conditions is calculated using the anisotropic fluid substitution theory. This orthotropic equivalent elastic stiffness matrix of the coal reservoir under saturated fluid conditions is then used as the orthotropic equivalent medium model for the seismic rock of the coal reservoir.
[0012] A second aspect of this application provides a coal reservoir seismic rock physics modeling system, comprising: The acquisition module is used to acquire a set of oriented core samples representing the anisotropic characteristics of the target coal reservoir, and to measure the volume content and elastic parameters of the micro-components of the core samples. Then, the porosity, fracture morphology and number of each core sample are acquired by CT scanning. The calculation module is used to calculate the microscopic elastic modulus of the microscopic component based on the volume content of the microscopic component by using the Voigt-Reuss-Hill average model and nonlinear programming method. The first construction module is used to construct a matrix model based on the elastic parameters and microelastic modulus of the microstructure of the core sample. The second construction module is used to construct a three-phase coupled VTI model based on the porosity and the matrix model; The third construction module is used to construct an orthogonal anisotropic equivalent medium model of the seismic rock in the coal reservoir based on the fracture morphology and number and the three-phase coupled VTI model.
[0013] Preferably, the microscopic components include: vitrinite, chitinite, inertinite, clay minerals, and carbonate minerals; The elastic parameters include: Young's modulus, Poisson's ratio, shear modulus, and bulk modulus.
[0014] A third aspect of this application provides an electronic device, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, it implements the method described in the first aspect embodiment.
[0015] A fourth aspect of this application provides a computer-readable storage medium having a computer program stored thereon that, when executed by a processor, implements the method described in the first aspect.
[0016] The technical solutions provided by the embodiments of this application bring at least the following beneficial effects: This application proposes a method and system for seismic rock physics modeling of coal reservoirs. The method includes: acquiring a set of oriented core samples representing the anisotropic characteristics of a target coal reservoir, measuring the volume content and elastic parameters of the micro-components in the core samples, and then obtaining the porosity, fracture morphology, and number of each core sample through CT scanning; calculating the micro-elastic modulus of the micro-components based on the volume content of the micro-components using a Voigt-Reuss-Hill average model and a nonlinear programming method; constructing a matrix model based on the elastic parameters of the core samples and the micro-elastic modulus of the micro-components; constructing a three-phase coupled VTI model based on the porosity and the matrix model; and constructing an orthogonal anisotropic equivalent medium model of the seismic rock of the coal reservoir based on the fracture morphology and number and the three-phase coupled VTI model. The technical solution proposed in this application, for the first time, starts from the elasticity of micro-components and achieves quantitative characterization of the adsorbed gas effect and orthogonal anisotropy of coal reservoirs, significantly improving the accuracy of seismic prediction of coalbed methane reservoirs.
[0017] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description
[0018] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a flowchart illustrating a method for seismic rock physics modeling of coal reservoirs according to an embodiment of this application; Figure 2 This is a schematic diagram illustrating the construction process of an orthogonal anisotropic coal reservoir fracture equivalent medium model according to an embodiment of this application; Figure 3 This is a structural diagram of a coal reservoir seismic rock physics modeling system provided according to an embodiment of this application. Detailed Implementation
[0019] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.
[0020] This application proposes a method and system for seismic rock physics modeling of coal reservoirs. The method includes: acquiring a set of oriented core samples representing the anisotropic characteristics of a target coal reservoir, measuring the volume content and elastic parameters of the micro-components in the core samples, and then obtaining the porosity, fracture morphology, and number of each core sample through CT scanning; calculating the micro-elastic modulus of the micro-components based on the volume content of the micro-components using a Voigt-Reuss-Hill average model and a nonlinear programming method; constructing a matrix model based on the elastic parameters of the core samples and the micro-elastic modulus of the micro-components; constructing a three-phase coupled VTI model based on the porosity and the matrix model; and constructing an orthogonal anisotropic equivalent medium model of the seismic rock of the coal reservoir based on the fracture morphology and number and the three-phase coupled VTI model. The technical solution proposed in this application, for the first time, starts from the elasticity of micro-components and achieves quantitative characterization of the adsorbed gas effect and orthogonal anisotropy of coal reservoirs, significantly improving the accuracy of seismic prediction of coalbed methane reservoirs.
[0021] The following description, with reference to the accompanying drawings, illustrates a method and system for seismic rock physics modeling of coal reservoirs according to embodiments of this application.
[0022] Example 1 Figure 1 This is a flowchart illustrating a method for seismic rock physics modeling of coal reservoirs according to an embodiment of this application, as shown below. Figure 1 As shown, the method includes: Step 1: Obtain a set of oriented core samples representing the anisotropic characteristics of the target coal reservoir, and measure the volume content and elastic parameters of the micro-components of the core samples. Then, obtain the porosity, fracture morphology and number of each core sample by CT scanning. In this embodiment of the disclosure, the microscopic components include: vitrinite, chitinite, inertinite, clay minerals, and carbonate minerals; The elastic parameters include: Young's modulus, Poisson's ratio, shear modulus, and bulk modulus.
[0023] In this embodiment of the disclosure, the process of obtaining the elastic parameters of the core sample includes: The ultrasonic longitudinal wave velocity, ultrasonic transverse wave velocity, density, Poisson's ratio of ultrasonic longitudinal wave velocity, and Poisson's ratio of ultrasonic transverse wave velocity of the core sample were obtained. The longitudinal wave conversion coefficient is determined based on the Poisson's ratio of the ultrasonic longitudinal wave velocity, and the transverse wave conversion coefficient is determined based on the Poisson's ratio of the ultrasonic transverse wave velocity. The seismic P-wave velocity of the core sample is determined based on the P-wave conversion coefficient and the ultrasonic P-wave velocity, and the seismic S-wave velocity of the core sample is determined based on the S-wave conversion coefficient and the ultrasonic S-wave velocity. The elastic parameters of the core sample are determined based on the longitudinal wave velocity, the transverse wave velocity, and the density of the seismic wave.
[0024] It should be noted that the purpose is to obtain representative directional core samples and key physical properties, elasticity, and microstructure parameters of coal reservoirs to provide experimental constraints for modeling.
[0025] (1) Preparation of core samples: To obtain representative oriented cores of coal reservoirs (including high-rank coal, medium-rank coal, and low-rank coal), it is necessary to take cores oriented along the coal reservoir bedding direction and two orthogonal directions perpendicular to the bedding (for anisotropy testing), and measure key physical property parameters (density, porosity) to provide sample support for inversion parameters; (2) Quantitative analysis of microstructures: including the volume percentage of vitrinite, chitinite, inertinite, clay minerals, and carbonate minerals (mainly calcite) in coal core samples from each direction; (3) Elastic parameter testing: mainly includes ultrasonic velocity testing to obtain the elastic modulus parameters (Young's modulus, Poisson's ratio, shear modulus, bulk modulus, etc.) of coal and rock samples in different directions. The formula for cross-scale conversion of ultrasonic velocity is: In the formula, V ps For seismic wave velocity, V pu For ultrasonic testing speed, C For conversion factors, ν Poisson's ratio calculated for ultrasonic velocity.
[0026] The formulas for calculating its elastic modulus parameters are as follows: a. Young's modulus : ; b. Poisson's ratio : ; c. Shear modulus : ; d. Bulk modulus : ; In the formula, V P The longitudinal wave velocity is (m / s). V S The transverse wave velocity is (m / s). ρ Density (g / cm³) 3 ).
[0027] Step 2: Based on the volume content of the micro-component, the micro-elastic modulus of the micro-component is calculated by inversion using the Voigt-Reuss-Hill average model and nonlinear programming method. In this embodiment of the disclosure, the step of calculating the microscopic elastic modulus of the microscopic component based on its volume content using the Voigt-Reuss-Hill average model and nonlinear programming method includes: Using the macroscopic elastic modulus of the coal sample as the constraint objective, and the bulk modulus, shear modulus, and volume percentage of each micro-component as variables, the solution is obtained... , The system of equations achieves inversion; Wherein, the macroscopic elastic modulus of the coal sample is the bulk modulus and shear modulus of the coal sample. It is the bulk modulus in the macroscopic elastic modulus. This refers to the shear modulus within the macroscopic elastic modulus. Let be the bulk modulus of the i-th microstructure. Let N be the volume content of the i-th microscopic component, and N be the total number of microscopic components. Let be the shear modulus of the i-th micro-component.
[0028] It should be noted that determining the elastic modulus of key components such as the vitrinite, inertinite, and chitinite provides microscopic parameter support for matrix modeling.
[0029] Based on the collected data, the Voigt-Ruess-Hill inversion method based on nonlinear programming was used, combined with the macroscopic elastic modulus (bulk modulus) of the coal sample. K shear modulus μ The elastic parameters of each micro-component are derived by inversion, and constraints are set. The formula is as follows: , In the formula, N The total number of microscopic components and inorganic minerals that make up the coal matrix. K i , μ i , f i These represent the bulk modulus, shear modulus, and volume percentage of a certain mineral that constitutes the rock matrix.
[0030] Step 3: Construct a matrix model based on the elastic parameters and microelastic moduli of the core sample; Step 4: Construct a three-phase coupled VTI model based on the porosity and the matrix model; In this embodiment of the disclosure, step 4 specifically includes: Based on the porosity and the matrix model, and using the self-compatible approximate equivalent medium theory, a three-phase coupling model of coal matrix-adsorbed gas-pores is constructed. A three-phase coupled VTI model was established by mixing single-layer coal samples at various locations and directions using the Backus averaging method.
[0031] Step 5: Construct an orthogonal anisotropic equivalent medium model of the seismic rock in the coal reservoir based on the fracture morphology and number and the three-phase coupled VTI model.
[0032] In this embodiment of the disclosure, step 5 specifically includes: Invert the stiffness matrix corresponding to the three-phase coupled VTI model to obtain the compliance matrix of the background medium; Based on the crack density, aspect ratio, and filling material parameters determined by the crack morphology and number, the additional compliance tensor caused by a set of vertically oriented cracks is calculated using the Hudson model and linear slip theory. The compliance moment of the background medium is linearly superimposed with the additional compliance tensor to obtain the total compliance matrix of the fractured coal reservoir. The stiffness matrix of the orthogonal anisotropic coal reservoir rock physics model under dry conditions is obtained by inverting the total compliance matrix. Based on the stiffness matrix, porosity, and fluid parameters within the fractures of the orthotropic coal reservoir rock physics model under dry conditions, the orthotropic equivalent elastic stiffness matrix of the coal reservoir under saturated fluid conditions is calculated using the anisotropic fluid substitution theory. This orthotropic equivalent elastic stiffness matrix of the coal reservoir under saturated fluid conditions is then used as the orthotropic equivalent medium model for the seismic rock of the coal reservoir.
[0033] It should be noted that, as Figure 2 As shown, (1) matrix construction First, using the Voigt-Reuss-Hill multiphase media elastic modulus average model, the equivalent mixed elastic modulus of organic components (vitrinite, inertinite, and crustalinite) and inorganic components (clay minerals and calcite) of multiple coal core samples cut along different directions was systematically calculated. The results can be represented as an isotropic medium described by two independent non-zero elements corresponding to the rock symmetry. The elastic parameter matrix of the isotropic medium is shown below:
[0034] (2) Construct a three-phase coupled VTI model of "coal matrix-adsorbed gas-pores". Based on the aforementioned steps, CT scans reveal the morphology of pores and fractures. Coal reservoirs exhibit the characteristic of coexisting adsorbed and free gas. Adsorbed gas, which does not undergo seepage, constitutes over 90% of coalbed methane and is adsorbed onto the surface of matrix pores. Calculating its equivalent elastic parameters using fluid substitution is inaccurate. Therefore, considering adsorbed gas as part of the coal matrix is more consistent with model accuracy. Thus, the coal-rock system can be viewed as a heterogeneous mixture composed of spherical coal particles, adsorbed gas, and pores. Based on the self-compatible approximation (SCA) equivalent medium theory, a three-phase coupled model of "coal matrix-adsorbed gas-pores" is constructed, introducing equivalent pore parameters to quantitatively characterize the pore structure. The formula is as follows:
[0035] in, i It refers to the first i Phase medium, x i This corresponds to the volume percentage. P , Q For a given coefficient of a spherical inclusion, their superscripts *i This means that the given coefficient is for a self-consistent equivalent modulus. K*SC and μ*SC Background medium includes materials i .
[0036] Using the Backus averaging method, single-layer coal samples from different locations and orientations are mixed to construct a layered background medium with VTI properties, composed of multiple layers of transversely isotropic material. The equivalent model can then be represented by five independent transversely isotropic parameters:
[0037] (3) Orthogonal anisotropic crack coupling (VTI+HTI) A method combining linear slip theory and the Hudson model is used to calculate the compliance of vertical fractures, thereby obtaining a pore fracture skeleton model. The effective elastic compliance matrix of the formation can be represented by the compliance of the background medium. S b and the change in flexibility caused by cracks ΔS The linear sum: ; The above-obtained stiffness matrix describes the stiffness of fracture-free coal and rock with VTI properties. It needs to be inverted and transformed into the compliance matrix of the background medium. S b , represented as:
[0038] When a crack with weak HTI properties is added, the crack compliance changes, and this change can be expressed by the following formula:
[0039] in, B N It reflects the compressibility enhancement effect caused by the change in crack aperture under normal stress, and represents the normal crack compliance when perpendicular to the crack direction. B V and B H The increment of shear deformation capacity under vertical (V direction) and horizontal (H direction) tangential stress in the crack plane can represent the two tangential crack compliances.
[0040] in:
[0041] In the formula, g It is the square of the ratio of the transverse wave velocity to the longitudinal wave velocity. K h , μ h These represent the bulk modulus and shear modulus of the fluid filling the crack, respectively. Both are assigned a value of 0 when the crack needs to be dried. a Where is the crack radius. C 33 , C 44 These represent the longitudinal wave modulus and shear modulus within the stiffness matrix of the coal and rock skeleton model, respectively. e Crack density can be expressed as the number of cracks per unit volume or porosity. Compared with the aspect ratio of cracks α calculate: ; The above results in the flexibility tensor matrix of a coal reservoir rock physics model containing a set of perfectly vertically arranged fractures. The result needs to be inverted and converted into the stiffness tensor matrix of an orthogonal anisotropic coal reservoir rock physics model under dry conditions.
[0042] (4) Construction of anisotropic fluid replacement and saturation model The Wood formula is used to calculate the fluid parameters within the fracture, and the equivalent mixed fluid bulk modulus, which mainly includes water and free coalbed methane. The formula is as follows:
[0043] in, K f This represents the bulk modulus parameter of the mixed fluid. K w The parameter representing the bulk modulus of water. K gThis represents the bulk modulus parameter of free coalbed methane. f w and f g These represent the volume percentages of water and free coalbed methane in the mixed fluid, respectively.
[0044] After obtaining the mixed fluid parameters, the mixed fluid was added to the pore fracture skeleton model using the anisotropic Brown and Korringa saturated rock equivalent model based on the Gassmann equation, resulting in an anisotropic coal reservoir rock physics model filled with saturated fluid. The calculation method is as follows:
[0045] In the formula, For the effective elastic flexibility tensor of the rock skeleton, The effective elastic flexibility tensor of rock saturated with pore fluid. To form the effective elastic flexibility tensor of the mineral, To represent the compressibility of pore fluids, For the compressibility of minerals, Porosity, where the subscripts represent rows and columns.
[0046] The above describes the entire process of constructing the equivalent medium model of fractures in orthogonal anisotropic coal reservoirs.
[0047] The modeling method proposed in this embodiment has the following advantages: 1. A systematic model of the equivalent medium of fractures in orthogonal anisotropic coal reservoirs was constructed, enabling characterization from microscopic composition to macroscopic elastic response; 2. It can reveal the correlation between fracture parameters and elastic anisotropy in coal reservoirs; 3. It can effectively simulate parameters of coalbed methane reservoirs.
[0048] In summary, the seismic rock physics modeling method for coal reservoirs proposed in this embodiment is the first to achieve quantitative characterization of the adsorbed gas effect and orthogonal anisotropy of coal reservoirs from the perspective of microscopic component elasticity, which significantly improves the accuracy of seismic prediction of coalbed methane reservoirs.
[0049] Example 2 Figure 3 This is a structural diagram of a coal reservoir seismic rock physics modeling system according to an embodiment of this application, as shown below. Figure 3 As shown, the system includes: The acquisition module 100 is used to acquire a set of oriented core samples representing the anisotropic characteristics of the target coal reservoir, and to measure the volume content and elastic parameters of the micro-components of the core samples. Then, the porosity, fracture morphology and number of each core sample are acquired by CT scanning. It should be noted that the microscopic components include: vitrinite, chitinite, inertinite, clay minerals, and carbonate minerals; The elastic parameters include: Young's modulus, Poisson's ratio, shear modulus, and bulk modulus.
[0050] The calculation module 200 is used to calculate the microscopic elastic modulus of the microscopic component based on the volume content of the microscopic component by using the Voigt-Reuss-Hill average model and nonlinear programming method. The first construction module 300 is used to construct a matrix model based on the elastic parameters and microelastic modulus of the micro-components of the core sample. The second construction module 400 is used to construct a three-phase coupled VTI model based on the porosity and the matrix model; The third construction module 500 is used to construct an orthogonal anisotropic equivalent medium model of the seismic rock in the coal reservoir based on the fracture morphology and number and the three-phase coupled VTI model.
[0051] In this embodiment of the disclosure, the acquisition module 100 is further configured to: The ultrasonic longitudinal wave velocity, ultrasonic transverse wave velocity, density, Poisson's ratio of ultrasonic longitudinal wave velocity, and Poisson's ratio of ultrasonic transverse wave velocity of the core sample were obtained. The longitudinal wave conversion coefficient is determined based on the Poisson's ratio of the ultrasonic longitudinal wave velocity, and the transverse wave conversion coefficient is determined based on the Poisson's ratio of the ultrasonic transverse wave velocity. The seismic P-wave velocity of the core sample is determined based on the P-wave conversion coefficient and the ultrasonic P-wave velocity, and the seismic S-wave velocity of the core sample is determined based on the S-wave conversion coefficient and the ultrasonic S-wave velocity. The elastic parameters of the core sample are determined based on the longitudinal wave velocity, the transverse wave velocity, and the density of the seismic wave.
[0052] In this embodiment of the disclosure, the first construction module 300 is further configured to: Using the macroscopic elastic modulus of the coal sample as the constraint objective, and the bulk modulus, shear modulus, and volume percentage of each micro-component as variables, the solution is obtained... , The system of equations achieves inversion; Wherein, the macroscopic elastic modulus of the coal sample is the bulk modulus and shear modulus of the coal sample. It is the bulk modulus in the macroscopic elastic modulus. This refers to the shear modulus within the macroscopic elastic modulus. Let be the bulk modulus of the i-th microstructure. Let N be the volume content of the i-th microscopic component, and N be the total number of microscopic components. Let be the shear modulus of the i-th micro-component.
[0053] In this embodiment of the disclosure, the second construction module 400 is further configured to: Based on the porosity and the matrix model, and using the self-compatible approximate equivalent medium theory, a three-phase coupling model of coal matrix-adsorbed gas-pores is constructed. A three-phase coupled VTI model was established by mixing single-layer coal samples at various locations and directions using the Backus averaging method.
[0054] In this embodiment of the disclosure, the third construction module 500 is further configured to: Invert the stiffness matrix corresponding to the three-phase coupled VTI model to obtain the compliance matrix of the background medium; Based on the crack density, aspect ratio, and filling material parameters determined by the crack morphology and number, the additional compliance tensor caused by a set of vertically oriented cracks is calculated using the Hudson model and linear slip theory. The compliance moment of the background medium is linearly superimposed with the additional compliance tensor to obtain the total compliance matrix of the fractured coal reservoir. The stiffness matrix of the orthogonal anisotropic coal reservoir rock physics model under dry conditions is obtained by inverting the total compliance matrix. Based on the stiffness matrix, porosity, and fluid parameters within the fractures of the orthotropic coal reservoir rock physics model under dry conditions, the orthotropic equivalent elastic stiffness matrix of the coal reservoir under saturated fluid conditions is calculated using the anisotropic fluid substitution theory. This orthotropic equivalent elastic stiffness matrix of the coal reservoir under saturated fluid conditions is then used as the orthotropic equivalent medium model for the seismic rock of the coal reservoir.
[0055] In summary, the coal reservoir seismic rock physics modeling system proposed in this embodiment is the first to achieve quantitative characterization of the adsorbed gas effect and orthogonal anisotropy of coal reservoirs from the perspective of microscopic component elasticity, which significantly improves the accuracy of seismic prediction of coalbed methane reservoirs.
[0056] Example 3 To implement the above embodiments, this disclosure also proposes an electronic device, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, it implements the method described in Embodiment 1.
[0057] Example 4 To implement the above embodiments, this disclosure also proposes a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method described in Embodiment 1.
[0058] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.
[0059] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing custom logic functions or processes, and the scope of the preferred embodiments of this application includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as should be understood by those skilled in the art to which embodiments of this application pertain.
[0060] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.
Claims
1. A method for seismic rock physics modeling of coal reservoirs, characterized in that, The method includes: A set of oriented core samples representing the anisotropic characteristics of the target coal reservoir were obtained, and the volume content and elastic parameters of the micro-components of the core samples were measured. Then, the porosity, fracture morphology and number of each core sample were obtained by CT scanning. Based on the volume content of the micro-components, the micro-elastic modulus of the micro-components was calculated by inversion using the Voigt-Reuss-Hill average model and nonlinear programming method. A matrix model was constructed based on the elastic parameters and microelastic moduli of the core samples. A three-phase coupled VTI model is constructed based on the porosity and the matrix model; Based on the fracture morphology and number, and the three-phase coupled VTI model, an orthogonal anisotropic equivalent medium model of the seismic rock in the coal reservoir is constructed.
2. The method as described in claim 1, characterized in that, The microscopic components include: vitrinite, chitinite, inertinite, clay minerals, and carbonate minerals; The elastic parameters include: Young's modulus, Poisson's ratio, shear modulus, and bulk modulus.
3. The method as described in claim 2, characterized in that, The process of obtaining the elastic parameters of the core sample includes: The ultrasonic longitudinal wave velocity, ultrasonic transverse wave velocity, density, Poisson's ratio of ultrasonic longitudinal wave velocity, and Poisson's ratio of ultrasonic transverse wave velocity of the core sample were obtained. The longitudinal wave conversion coefficient is determined based on the Poisson's ratio of the ultrasonic longitudinal wave velocity, and the transverse wave conversion coefficient is determined based on the Poisson's ratio of the ultrasonic transverse wave velocity. The seismic P-wave velocity of the core sample is determined based on the P-wave conversion coefficient and the ultrasonic P-wave velocity, and the seismic S-wave velocity of the core sample is determined based on the S-wave conversion coefficient and the ultrasonic S-wave velocity. The elastic parameters of the core sample are determined based on the longitudinal wave velocity, the transverse wave velocity, and the density of the seismic wave.
4. The method as described in claim 3, characterized in that, The microscopic elastic modulus of the microscopic components is calculated by inversion using the Voigt-Reuss-Hill average model and nonlinear programming method based on the volume content of the microscopic components, including: Using the macroscopic elastic modulus of the coal sample as the constraint objective, and the bulk modulus, shear modulus, and volume percentage of each micro-component as variables, the solution is obtained... , The system of equations achieves inversion; Wherein, the macroscopic elastic modulus of the coal sample is the bulk modulus and shear modulus of the coal sample. It is the bulk modulus in the macroscopic elastic modulus. This refers to the shear modulus within the macroscopic elastic modulus. Let be the bulk modulus of the i-th microstructure. Let N be the volume content of the i-th microscopic component, and N be the total number of microscopic components. Let be the shear modulus of the i-th micro-component.
5. The method as described in claim 4, characterized in that, The construction of the three-phase coupled VTI model based on the porosity and the matrix model includes: Based on the porosity and the matrix model, and using the self-compatible approximate equivalent medium theory, a three-phase coupling model of coal matrix-adsorbed gas-pores is constructed. A three-phase coupled VTI model was established by mixing single-layer coal samples at various locations and directions using the Backus averaging method.
6. The method as described in claim 5, characterized in that, The construction of the orthogonal anisotropic equivalent medium model of the seismic rock in the coal reservoir based on the fracture morphology and number and the three-phase coupled VTI model includes: Invert the stiffness matrix corresponding to the three-phase coupled VTI model to obtain the compliance matrix of the background medium; Based on the crack density, aspect ratio, and filling material parameters determined by the crack morphology and number, the additional compliance tensor caused by a set of vertically oriented cracks is calculated using the Hudson model and linear slip theory. The compliance moment of the background medium is linearly superimposed with the additional compliance tensor to obtain the total compliance matrix of the fractured coal reservoir. The stiffness matrix of the orthogonal anisotropic coal reservoir rock physics model under dry conditions is obtained by inverting the total compliance matrix. Based on the stiffness matrix, porosity, and fluid parameters within the fractures of the orthotropic coal reservoir rock physics model under dry conditions, the orthotropic equivalent elastic stiffness matrix of the coal reservoir under saturated fluid conditions is calculated using the anisotropic fluid substitution theory. This orthotropic equivalent elastic stiffness matrix of the coal reservoir under saturated fluid conditions is then used as the orthotropic equivalent medium model for the seismic rock of the coal reservoir.
7. A seismic rock physics modeling system for coal reservoirs, characterized in that, The system includes: The acquisition module is used to acquire a set of oriented core samples representing the anisotropic characteristics of the target coal reservoir, and to measure the volume content and elastic parameters of the micro-components of the core samples. Then, the porosity, fracture morphology and number of each core sample are acquired by CT scanning. The calculation module is used to calculate the microscopic elastic modulus of the microscopic component based on the volume content of the microscopic component by using the Voigt-Reuss-Hill average model and nonlinear programming method. The first construction module is used to construct a matrix model based on the elastic parameters and microelastic modulus of the microstructure of the core sample. The second construction module is used to construct a three-phase coupled VTI model based on the porosity and the matrix model; The third construction module is used to construct an orthogonal anisotropic equivalent medium model of the seismic rock in the coal reservoir based on the fracture morphology and number and the three-phase coupled VTI model.
8. The system as described in claim 7, characterized in that, The microscopic components include: vitrinite, chitinite, inertinite, clay minerals, and carbonate minerals; The elastic parameters include: Young's modulus, Poisson's ratio, shear modulus, and bulk modulus.
9. An electronic device, characterized in that, include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the program, implements the method as described in any one of claims 1-6.
10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1-6.