A Dynamic Assessment Method for CO2 Sequestration Potential in Basin-Level Marine Areas Based on Multi-Field Coupling

Abstract

This invention relates to the field of marine carbon dioxide geological sequestration, specifically a dynamic assessment method for the CO2 sequestration potential of basin-level marine areas based on multi-field coupling. The method includes: establishing a dynamic assessment equation for carbon dioxide sequestration potential; constructing a three-dimensional geological model of the actual reservoir based on geological data and importing it into numerical simulation software; applying multi-physics field coupling constraints to the three-dimensional geological model; combining initial formation parameters and the carbon dioxide gas equation of state, and through multi-physics field coupling calculations, obtaining dynamic parameters of reservoir porosity, reservoir CO2 saturation, and CO2 density evolving over time; and substituting these dynamic parameters into the dynamic assessment equation for carbon dioxide sequestration potential to calculate the CO2 sequestration potential. This invention, by constructing a dynamic assessment equation for carbon dioxide sequestration potential and combining it with multi-physics field coupling calculations to obtain the required dynamic parameters, achieves high-precision, full-process dynamic assessment of CO2 sequestration potential, significantly improving the accuracy and practicality of the assessment.

Description

Technical Field

[0001] This invention relates to the field of marine carbon dioxide geological sequestration, specifically a dynamic assessment method for the CO2 sequestration potential of basin-level marine areas based on multi-field coupling. Background Technology

[0002] Carbon capture, utilization, and storage (CCUS) technology is considered one of the key technologies for reducing carbon dioxide (CO2) emissions. Among them, deep saline aquifers are widely recognized as the most promising storage sites due to their wide distribution and huge storage potential. "Storage potential" is a core indicator for evaluating whether an area is suitable for CO2 storage and for determining its storage scale. It is a prerequisite for project site selection, design, and economic evaluation.

[0003] Currently, various methods for assessing CO2 geological storage potential have been developed globally, broadly categorized into two main types: the "volume method," aimed at rapid macroscopic estimation, and the "mechanistic method," centered on detailed process simulation. The volume method is the most classic and widely used, primarily for preliminary potential estimation at the regional and basin levels. Its core idea is to estimate storage potential by calculating the effective pore space volume available for CO2 storage underground; that is, the amount of storage mainly depends on the effective pore volume of the reservoir. The mechanistic method, based on the CO2 storage mechanism in saline aquifers, divides the storage process into four main modes: tectonic storage, bound storage, dissolution storage, and mineralization storage. By calculating the carbon storage amount for each storage mode separately, the storage potential of the entire reservoir can be obtained.

[0004] However, both existing methods have significant limitations: while the volumetric method is computationally simple and requires few parameters, it relies heavily on initial static reservoir data, leading to low accuracy in assessing CO2 storage potential; the mechanistic method, although capable of coupling multiple storage mechanisms, is difficult to apply to marine basins with low exploration levels due to complex parameters and high data requirements. Furthermore, neither method considers the dynamic evolution of reservoir properties during CO2 injection, limiting the accuracy and reliability of the assessment results.

[0005] CO2 sequestration in saline aquifers is a long-term, dynamic geological process. First, injected CO2 cannot completely occupy the entire reservoir pore space. Second, reservoir parameters dynamically change due to the geomechanical response caused by CO2 injection; continuing to use initial formation parameters for calculations in this state will lead to significant errors in the assessment of sequestration potential. Furthermore, due to its unique gaseous properties, CO2 typically undergoes phase transitions during injection and sequestration, causing changes in parameters such as gas density. Therefore, existing sequestration potential assessment methods struggle to accurately depict the total dynamic sequestration of CO2 throughout the injection process, necessitating the development of innovative theories and methods to shift the evaluation paradigm from static estimation to dynamic simulation. Summary of the Invention

[0006] To address the aforementioned technical issues, this invention proposes a dynamic assessment method for CO2 storage potential in basin-level marine areas based on multi-field coupling. This method aims to overcome the limitations of existing volumetric methods, which rely on initial static reservoir parameters, resulting in low assessment accuracy, and mechanistic methods, which are difficult to apply to low-exploration marine basins due to complex parameters and high data requirements. Furthermore, it effectively compensates for the assessment bias caused by the failure of both methods to consider the dynamic evolution of reservoir parameters during CO2 injection, thereby improving the accuracy and reliability of storage potential assessment.

[0007] To achieve the above objectives, the present invention provides a dynamic assessment method for CO2 sequestration potential in basin-level sea areas based on multi-field coupling, which specifically includes the following steps:

[0008] (1) Establish a dynamic evaluation equation for carbon dioxide storage potential;

[0009] (2) Establish a three-dimensional geological model of the real reservoir based on geological data and import it into numerical simulation software;

[0010] (3) Apply multiphysics coupling constraints to the above three-dimensional geological model;

[0011] (4) Combining the initial formation parameters and the carbon dioxide gas equation of state, the dynamic parameters of reservoir porosity, reservoir CO2 saturation and CO2 density evolution over time are obtained through multi-physics field coupling calculation;

[0012] (5) Substitute the above dynamic parameters into the dynamic evaluation equation of carbon dioxide sequestration potential to calculate the CO2 sequestration potential of the marine basin.

[0013] This invention constructs a dynamic evaluation equation for carbon dioxide sequestration potential and obtains the required dynamic parameters by combining multi-physics field coupling calculations, thereby achieving high-precision, full-process dynamic evaluation of CO2 sequestration potential and significantly improving the accuracy and practicality of the evaluation.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] This invention proposes a dynamic assessment method for CO2 sequestration potential in basin-level sea areas based on multi-field coupling. This method dynamically calculates the potential of the entire basin based on model volume. Compared with the traditional volume method, it abandons the highly uncertain "effective sequestration coefficient" and adopts time-varying dynamic parameters obtained by multi-physics field coupling simulation. This makes the parameter selection more scientific and reasonable, effectively overcoming the problem that the traditional volume method relies too much on static parameters, which leads to overly idealized assessment results. This further improves the authenticity and accuracy of the evaluation results.

[0016] This invention establishes a reservoir geological model based on geological data, taking into account the complex underground geological dynamics and fluid interactions. It calculates the CO2 saline water layer sequestration process by coupling multiphysics field control equations, thus avoiding the problems of oversimplification of the model and empirical evaluation parameters. Attached Figure Description

[0017] Figure 1 This is a technical roadmap of the present invention;

[0018] Figure 2 The revised formula for calculating the potential sequestration of this invention and the corresponding model diagram;

[0019] Figure 3 This is a schematic diagram of the multiphysics coupling relationship of the present invention;

[0020] Figure 4 This is a schematic diagram illustrating the change of CO2 density with temperature and pressure according to the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0022] like Figure 1 As shown, a dynamic assessment method for CO2 sequestration potential in basin-level sea areas based on multi-field coupling includes the following specific implementation steps:

[0023] S1: Modify the volumetric potential evaluation equation and establish a dynamic evaluation formula.

[0024] like Figure 2 As shown, the static volumetric method calculation formula is transformed into a dynamic calculation formula. The volumetric method is a static estimation method based on the effective pore volume of underground reservoirs. Its basic principle is to estimate all pore spaces in the geological body that can be used for CO2 geological storage and convert them into storage potential under corresponding storage conditions. Its core parameters include reservoir distribution area, average reservoir thickness, average reservoir porosity, CO2 density, and effective storage coefficient. The calculation formula is as follows:

[0025] ,

[0026] in, CO2 sequestration potential, in kg; The reservoir area is expressed in m². 2 ; The average reservoir thickness is expressed in meters (m). The average porosity of the reservoir is expressed as % (%). This refers to the density of CO2, expressed in kg / m³. 3 ; The effective sealing coefficient is dimensionless.

[0027] As can be seen from the above equation, the reservoir's storage potential depends entirely on the reservoir's average size, porosity, CO2 density, and effective storage coefficient. The selection of these parameters can lead to significant errors in the potential assessment results. The dynamic assessment method, however, no longer calculates a single total quantity. Instead, it simulates the spatiotemporal evolution of CO2 saturation, pressure, and concentration by solving the governing equations, and then obtains the time-varying storage capacity through integration. The calculation equation can be rewritten as:

[0028] ,

[0029] in, The reservoir volume is expressed in meters (m³). 3 ; The dynamic porosity of the reservoir is expressed in % (%). The dynamic saturation of CO2 is dimensionless. CO2 dynamic density, in kg / m³ 3 ; The spatial location of the reservoir is dimensionless. For time, the unit is days (d).

[0030] To calculate the above integrals, it is necessary to characterize the dynamic evolution of reservoir porosity, reservoir CO2 saturation, and CO2 density. At this point, it is necessary to establish a multiphysics coupling model suitable for CO2 saline water layer storage and calculate the spatiotemporal variations of the above parameters.

[0031] S2: Establish a multiphysics coupling model

[0032] Thermo-fluid-structure interaction (TFS) constraint establishes a multi-physics coupling model by combining the governing equations of the temperature field, seepage field, and stress field. The various physical fields are mutually constrained, and their coupling relationships are as follows: Figure 3 As shown.

[0033] The model is input into numerical simulation software for coupled calculation. The model uses the stress field control equation and the reservoir porosity dynamic evolution equation to calculate the reservoir porosity; uses the seepage field control equation to solve for the reservoir CO2 saturation and reservoir pressure changes; uses the temperature field control equation to obtain the reservoir temperature changes; and combines the CO2 gas state equation to solve for the CO2 density.

[0034] The expression for the stress field governing equation is:

[0035] ,

[0036] in, It is the shear modulus (Pa). It is Poisson's ratio. , It is a tensor representation of displacement. The Biot coefficient of the reservoir matrix. This is the tensor expression for fluid pressure within the reservoir. Bulk modulus The coefficient of thermal expansion of the rock. and These represent the reservoir temperature component and the volume force component in the i-direction, respectively.

[0037] The dynamic evolution equation of reservoir porosity is:

[0038] ,

[0039] ,

[0040] ,

[0041] in, The initial porosity of the matrix, and These are the effective strain and the initial effective strain, respectively. and These are the matrix volumetric strain and the initial volumetric strain of the matrix, respectively. and These represent the fluid pressure in the matrix pores and the initial fluid pressure, respectively. and These are the substrate temperature and the initial substrate temperature, respectively. The bulk modulus of the matrix particles. The coefficient of thermal expansion of the rock. is the Biot coefficient of the reservoir matrix.

[0042] The governing equation for the seepage field is expressed as follows:

[0043] ,

[0044] in, For reservoir porosity, For formation water saturation, and These are CO2 and formation water density, respectively. and These represent the relative permeability of reservoir CO2 and formation water, respectively. and These are CO2 and formation water viscosity, respectively. For reservoir permeability, For reservoir capillary pressure, It is the acceleration due to gravity. and These are CO2 and formation water source sinks, respectively.

[0045] The expression for the temperature field control equation is:

[0046] ,

[0047] in, The specific heat capacity of the equivalent unit cell. For reservoir temperature, Bulk modulus The coefficient of thermal expansion of the rock. For volumetric strain, and These represent the thermal conductivity and thermal convection coefficients of the equivalent unit cell, respectively. This indicates the heat source term.

[0048] S3: Dynamic Simulation and Parameter Evolution of Reservoir Multiphysics Coupling

[0049] A three-dimensional geological model of the actual reservoir was established based on geological data and imported into numerical simulation software. By inputting the governing equations for stress, temperature, and seepage fields, a thermo-fluid-solid multiphysics coupling constraint was applied to the three-dimensional geological model. Combined with initial formation parameters and the carbon dioxide gas equation of state, multiphysics coupling calculations were performed to obtain the dynamic response of parameters such as reservoir temperature, reservoir pressure, reservoir porosity, and reservoir CO2 saturation over time. Furthermore, based on the obtained temperature and pressure data, the classical PR equation of state was used to characterize the CO2 density change.

[0050] ,

[0051] in, To balance the pressure, To balance the temperature, is the ideal gas constant, with a value of 8.314472. , For molar volume, and The coefficients of the state equation can be expressed by the following formula:

[0052]

[0053] ,

[0054] in, Let be the ideal gas constant. The critical pressure of the gas. The critical temperature of the gas. Relative temperature ( ), As the eccentricity factor, These are the coefficients of the state equation.

[0055] The relationship between CO2 density and temperature and pressure, calculated using the PR equation of state, is as follows: Figure 4 As shown, this reflects its dynamic evolution characteristics under different temperature and pressure conditions.

[0056] In summary, the dynamic evaluation method of this invention follows this process: The volumetric potential evaluation equation is modified to establish a dynamic evaluation formula; a three-dimensional geological model of the actual reservoir is established based on geological data and imported into numerical simulation software; the stress field, temperature field, and seepage field control equations are input to couple and constrain the model; combined with initial formation parameters and the gas state equation, the dynamic evolution of reservoir porosity, reservoir CO2 saturation, and CO2 density is calculated and obtained; these are then input into the dynamic potential evaluation equation to calculate the total storage potential. This invention has low computational complexity and high accuracy, enabling dynamic evaluation of the CO2 storage potential of large-scale saline aquifers in marine areas, and is easy to promote and apply.

[0057] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for dynamic assessment of CO2 sequestration potential in basin-level sea areas based on multi-field coupling, characterized in that, Includes the following steps: S1: Establish a dynamic evaluation equation for carbon dioxide sequestration potential; The dynamic evaluation equation for the carbon dioxide sequestration potential is as follows: ， in, The reservoir volume is expressed in meters (m³). 3 ; The dynamic porosity of the reservoir is expressed in % (%). The dynamic saturation of CO2 is dimensionless. CO2 dynamic density, in kg / m³ 3 ; The spatial location of the reservoir is dimensionless. Time, in days (d). S2: Establish a three-dimensional geological model of the real reservoir based on geological data and import it into numerical simulation software; S3: Apply multiphysics coupling constraints to the above three-dimensional geological model; S4: Combining initial formation parameters and the carbon dioxide gas equation of state, dynamic parameters of reservoir porosity, reservoir CO2 saturation and CO2 density evolution over time are obtained through multiphysics field coupling calculations. S5: Substitute the above dynamic parameters into the dynamic evaluation equation for carbon dioxide sequestration potential to calculate the CO2 sequestration potential of the marine basin.

2. The method for dynamic assessment of CO2 sequestration potential in basin-level sea areas based on multi-field coupling as described in claim 1, characterized in that, The multiphysics fields in S3 include: stress field, temperature field, and seepage field.

3. The method for dynamic assessment of CO2 sequestration potential in basin-level sea areas based on multi-field coupling as described in claim 1, characterized in that, The reservoir porosity in S4 is obtained by solving the stress field control equation and the reservoir porosity dynamic evolution equation; the stress field control equation is: ， in, It is the shear modulus. It is Poisson's ratio. , It is a tensor representation of displacement. The Biot coefficient of the reservoir matrix. This is the tensor expression for fluid pressure within the reservoir. Bulk modulus The coefficient of thermal expansion of the rock. and These represent the reservoir temperature component and the volume force component in the i-direction, respectively. The dynamic evolution equation for reservoir porosity is as follows: ， ， ， in, The initial porosity of the matrix, and These are the effective strain and the initial effective strain, respectively. and These are the matrix volumetric strain and the initial volumetric strain of the matrix, respectively. and These represent the fluid pressure in the matrix pores and the initial fluid pressure, respectively. and These are the substrate temperature and the initial substrate temperature, respectively. The bulk modulus of the matrix particles. The coefficient of thermal expansion of the rock. is the Biot coefficient of the reservoir matrix.

4. The method for dynamic assessment of CO2 sequestration potential in basin-level sea areas based on multi-field coupling as described in claim 1, characterized in that, The CO2 saturation of the reservoir in S4 is calculated by solving the control equations of the seepage field: ， in, For reservoir porosity, For formation water saturation, and These are CO2 and formation water density, respectively. and These represent the relative permeability of reservoir CO2 and formation water, respectively. and These are CO2 and formation water viscosity, respectively. For reservoir permeability, For reservoir capillary pressure, It is the acceleration due to gravity. and These are CO2 and formation water source sinks, respectively.

5. The method for dynamic assessment of CO2 sequestration potential in basin-level sea areas based on multi-field coupling as described in claim 1, characterized in that, The CO2 density in S4 is calculated using the gas law: ， in, To balance the pressure, To balance the temperature, Let be the ideal gas constant. For molar volume, and These are the coefficients of the state equation.

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