A molecular simulation method for quantifying the extent of hysteresis in shale gas adsorption-desorption processes

Abstract

The application discloses a molecular simulation method for quantifying the hysteresis degree of a shale gas adsorption-desorption process, and belongs to the technical field of shale gas exploration and development. The method comprises the following steps: S1, constructing a kerogen matrix pore model; S2, obtaining initial structure parameters of the matrix pore model; S3, calibrating a conversion relationship between fugacity and pressure; S4, carrying out shale gas adsorption process simulation; S5, carrying out shale gas desorption process simulation; and S6, quantitatively analyzing the hysteresis degree of the adsorption-desorption process. The application realizes the construction of a real shale kerogen pore structure, and combines the proposed GCMC+MD simulation method to restore the adsorption-desorption process of shale gas in the shale kerogen pore structure at a molecular scale, while the deformation characteristics of the kerogen are considered, so that the microscopic mechanism explanation and quantitative characterization of the adsorption-desorption hysteresis phenomenon are realized, and then theoretical guidance is provided for shale gas production capacity prediction and the selection of production-increasing measures.

Description

Technical Field

[0001] This invention belongs to the field of shale gas exploration and development technology, specifically relating to a molecular simulation method for quantifying the degree of lag in the adsorption-desorption process of shale gas. Background Technology

[0002] Against the backdrop of ever-increasing global energy demand and the gradual depletion of traditional fossil fuels, the development and utilization of unconventional natural gas resources have attracted widespread attention from the international community. Shale gas, as a key component of unconventional natural gas resources, has significant strategic importance for optimizing the energy structure and ensuring energy security through its effective development. Shale gas is mainly distributed in organic-rich shale reservoirs. Due to its extremely low porosity and permeability, its extraction technologies are more complex and challenging than those for conventional natural gas.

[0003] Shale gas development involves multiple technical fields, including geological exploration, reservoir stimulation, and production enhancement measures. Molecular simulation technology plays a crucial role in shale gas development. This technology allows researchers to gain a deep understanding of the adsorption and desorption behavior of shale gas in kerogen pores at the microscopic level and assess the specific impact of these behaviors on gas production capacity. However, the adsorption and desorption behavior of shale gas is influenced by various factors, including kerogen type, pore structure, pressure, and temperature. In actual shale gas development, the desorption process often exhibits a significant hysteresis, i.e., the irreversibility of adsorption and desorption processes, which has a profound impact on shale gas production capacity assessment and the formulation of production enhancement strategies. Summary of the Invention

[0004] The purpose of this invention is to propose a molecular simulation method for quantifying the lag degree of shale gas adsorption-desorption process. This method can reproduce the adsorption and desorption behavior of shale gas in the pore structure of shale kerogen at the molecular level, and fully consider the deformation effect of kerogen, thereby revealing the microscopic coupling mechanism between the degree of adsorption-desorption lag and pore deformation.

[0005] The technical solution adopted in this invention is:

[0006] A molecular simulation method for quantifying the hysteresis of shale gas adsorption-desorption processes includes the following steps:

[0007] S1. Construct a kerogen matrix pore model;

[0008] S2. Obtain the initial structural parameters of the kerogen matrix pore model;

[0009] S3. Calibrate the conversion relationship between fugacity and pressure;

[0010] S4. Conduct simulations of shale gas adsorption processes;

[0011] Using the S1-constructed kerogen matrix pore model with temperature and fugacity as input parameters, the gas molecule adsorption process of the kerogen matrix pore model under a certain pressure condition was first simulated using the giant canonical Monte Carlo method to obtain the adsorption configuration under that pressure condition. Then, molecular dynamics simulation was performed to obtain the equilibrium configuration after deformation. Subsequently, the adsorbed gas molecules in the pores were deleted to obtain the structural parameters of the kerogen matrix pore model under that pressure condition, which was used as the initial system configuration for the next pressure point. The above simulation process was repeated, and the simulation pressure was gradually increased to obtain the isothermal adsorption curve and the structural parameters of the kerogen matrix pore model under different pressures during the adsorption process.

[0012] S5. Conduct simulations of shale gas desorption processes;

[0013] The pore equilibrium state at the maximum pressure point in the S4 shale gas adsorption process simulation was used as the initial configuration for shale gas desorption process simulation. The simulation pressure was gradually reduced, and the adsorption amount and equilibrium configuration after kerogen matrix deformation under different pressure conditions were obtained using the simulation process in S4. For each pressure point, the pore model structure parameters of the kerogen matrix under that pressure condition were obtained and used as the initial system configuration for the next pressure point. Through the above process, isothermal desorption curves and pore model structure parameters of the kerogen matrix under different pressures during the desorption process were obtained.

[0014] S6. Quantitative analysis of the hysteresis degree in the adsorption-desorption process;

[0015] Based on the isothermal adsorption curve obtained from S4 simulation and the isothermal desorption curve obtained from S5 simulation, the degree of lag in the shale gas adsorption-desorption process is quantified.

[0016] The beneficial technical effects of the present invention are as follows:

[0017] This invention constructs a kerogen matrix pore model to obtain its initial structural parameters and establishes the correspondence between gas fugacity and pressure. Then, it employs a grand canonical Monte Carlo-Molecular Dynamics (GCMC+MD) simulation method to simulate the adsorption and desorption processes of shale gas. This method can reproduce the adsorption and desorption behavior of shale gas in the pore structure of shale kerogen at the molecular level, fully considering the deformation effect of kerogen, thereby quantifying the degree of lag in the shale gas adsorption-desorption process and revealing the microscopic coupling mechanism between the degree of adsorption-desorption lag and pore deformation. This provides important theoretical guidance and scientific basis for a deeper understanding of the adsorption behavior and desorption lag of supercritical gases in the pores of shale organic matter, and thus for predicting shale gas production capacity and optimizing production enhancement measures. Attached Figure Description

[0018] Figure 1This is a flowchart of the molecular simulation method for quantifying the hysteresis of the shale gas adsorption-desorption process according to the present invention;

[0019] Figure 2 This is a schematic diagram of the hysteresis curve for shale gas desorption.

[0020] Figure 3 This is a schematic diagram of the initial equilibrium configuration of the kerogen matrix;

[0021] Figure 4 This is a diagram showing the initial pore size distribution of the kerogen matrix.

[0022] Figure 5 The graph shows the fugacity-pressure relationship of methane at 353.15 K.

[0023] Figure 6 The isothermal adsorption / desorption curves of methane in kerogen at 353.15 K are shown.

[0024] Figure 7 This is a schematic diagram showing the change in the volumetric strain of kerogen with pressure.

[0025] Figure 8 This is a schematic diagram showing the changes in kerogen pore volume and porosity with pressure. Detailed Implementation

[0026] This invention provides a molecular simulation method for quantifying the lag in shale gas adsorption-desorption processes within the nanopores of shale organic matter. The method includes the following steps: S1. Constructing a kerogen matrix pore model; S2. Obtaining initial structural parameters (pore volume and porosity) of the kerogen matrix pore model; S3. Calibrating the relationship between fugacity and pressure conversion; S4. Simulating the shale gas adsorption process; S5. Simulating the shale gas desorption process; S6. Quantitatively analyzing the lag in the adsorption-desorption process. This invention achieves the construction of a realistic shale kerogen pore structure and, combined with the proposed GCMC+MD simulation method, reconstructs the adsorption-desorption process of shale gas in the shale kerogen pore structure at the molecular scale. It also considers the deformation characteristics of kerogen, thus realizing the microscopic mechanism explanation and quantitative characterization of the adsorption-desorption lag phenomenon. The methodological approach provided by this invention is beneficial for understanding the adsorption behavior and desorption lag mechanism of supercritical gases in the pores of shale organic matter, thereby providing theoretical guidance for shale gas production prediction and the selection of production enhancement measures.

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0028] like Figure 1 As shown, a molecular simulation method for quantifying the hysteresis of shale gas adsorption-desorption processes includes the following steps:

[0029] S1. Construct a kerogen matrix pore model;

[0030] This invention employs the kerogen molecular model proposed by Ungerer et al., and performs a series of geometric optimizations and annealing processes to ensure a stable configuration with the lowest energy. Subsequently, an appropriate amount of kerogen molecules are randomly arranged in the initial configuration of the simulation box according to a predetermined density. Under NVT ensemble conditions, a high-temperature relaxation process is used to promote the full expansion of the kerogen molecules to simulate their natural state. Finally, the final equilibrium state of the kerogen matrix is ​​obtained by performing NPT ensemble simulations under real formation temperature and pressure conditions.

[0031] S2. Obtain the initial structural parameters of the kerogen matrix pore model;

[0032] Using the Atom Volumes & Surfaces module in Materials Studio simulation software, the pore volume and surface area of ​​the matrix model were accurately calculated first using the helium molecular dynamics diameter (0.26 nm) as a baseline and the spherical probe method. Based on this, a series of decreasing free pore volume data were obtained by progressively increasing the diameter of the virtual probe molecules (0-0.5 nm). By differentiating the free pore volumes corresponding to probe molecules of different sizes, the pore size distribution curves of the organic matter pore model were obtained, thus providing initial pore structure information for subsequent molecular simulation studies of adsorption and desorption processes.

[0033] S3. Calibrate the relationship between fugacity and pressure conversion;

[0034] In a blank simulation chamber without kerogen matrix, the adsorption behavior of methane under different fugacity conditions was simulated using the GCMC method. By analyzing the number of adsorbed molecules, the corresponding system density was obtained and compared with pressure data at the same density in the NIST database. This established the conversion relationship between gas fugacity and pressure at a specific temperature, providing necessary input parameters for subsequent molecular simulation studies of adsorption and desorption processes under specific pressure conditions.

[0035] S4. Conduct simulations of shale gas adsorption processes;

[0036] Using the final equilibrium configuration obtained in step S1, with temperature and fugacity as input parameters, the adsorption process of the kerogen pore model under a relatively low pressure condition was first simulated using the GCMC method to obtain the adsorption configuration at that pressure. Based on this, MD simulation was performed on the kerogen pore model. First, kinetic relaxation was performed for 100 ps under the NVT ensemble; then, NPT simulation was performed for 4000 ps under zero effective stress to fully reflect the deformation characteristics of the kerogen pore model due to gas adsorption under specific pressure conditions; finally, kinetic relaxation was performed for 2000 ps under the NVT ensemble to obtain the adsorption equilibrium configuration after deformation. Subsequently, adsorbed gas molecules in the pores were removed, and the pore structure parameters of the kerogen matrix under this pressure condition were obtained using the method described in step S2, and this was used as the initial system configuration for the next pressure point. Through the above GCMC+MD simulation process, the simulation pressure was gradually increased to obtain isothermal adsorption curves under specific temperature conditions and pore structure parameters under different pressures during the adsorption process.

[0037] S5. Conduct simulations of shale gas desorption processes;

[0038] The pore equilibrium state at the maximum pressure point of the adsorption process in step S4 is used as the initial configuration for simulating the desorption process. The simulation pressure is gradually decreased, and the adsorption capacity and the equilibrium configuration after deformation of the kerogen matrix under different pressure conditions are obtained using the GCMC+MD method described in step S4. For each pressure point, the pore structure parameters of the kerogen matrix under that condition are obtained using the method described in step S2, and this is used as the initial system configuration for the next pressure point. Through the above process, isothermal desorption curves under specific temperature conditions and pore structure parameters under different pressures during the desorption process are obtained.

[0039] S6. Quantitative analysis of the hysteresis degree in the adsorption-desorption process;

[0040] Based on the isothermal adsorption and desorption curves obtained from steps S4 and S5, the degree of lag in the shale gas adsorption-desorption process is quantified using the hysteresis index (HI). Simultaneously, by combining the pore structure parameters at different pressure points during the adsorption-desorption process, the volumetric strain characteristics of kerogen are analyzed, revealing the microscopic coupling mechanism between kerogen matrix deformation and shale gas desorption lag.

[0041] The lag factor can be calculated using the following formula:

[0042]

[0043] In the formula: A hys It is the area of ​​the hysteresis loop ( Figure 2 (the red shaded area in the middle), A des It is the area corresponding to the desorption curve ( Figure 2 (The red and black shaded areas), A ads It is the area corresponding to the adsorption curve ( Figure 2 (The black shaded area in the middle); p max It is the maximum adsorption pressure; V i des V i ads The pressure is p i The amount of adsorption corresponding to the desorption and adsorption processes.

[0044] The degree of volumetric strain is calculated using the following formula:

[0045]

[0046] In the formula: Vε is the volumetric strain (dimensionless), and V and V0 are the total volumes of the adsorption deformation model and the initial kerogen model, respectively.

[0047] In step S1 above, the construction process of the kerogen matrix pore model can be roughly divided into the following steps:

[0048] S11. Import kerogen molecular units and perform geometry optimization and annealing simulation processes to finally obtain the stable structure with the lowest energy.

[0049] S12. Determine the dimensions (X, Y, Z) of the periodic unit cell and randomly place a certain number of kerogen molecules into the unit cell at a predetermined density.

[0050] S13. A series of geometric optimizations were performed on the unit cell to reduce the system energy: First, high-temperature relaxation was performed under the NVT ensemble; second, molecular dynamics simulations were performed under the NPT ensemble with the temperature decreasing by a certain gradient; finally, sufficient relaxation was performed under certain reservoir temperature and pressure conditions to obtain the final stable configuration.

[0051] The GCMC+MD method used in steps S4 and S5 above is further explained as follows: Within the pore structure of kerogen, this method employs Grand Canonical Monte Carlo (GCMC) technology, based on the Metropolis sampling algorithm, to simulate the insertion, removal, and migration of shale gas molecules; and employs Molecular Dynamics (MD) technology, based on Newton's laws of motion, to simulate the dynamic diffusion of shale gas molecules within the pores, while simultaneously revealing the deformation of the kerogen framework under specific temperature and pressure conditions, including the generation of new pores, the expansion of existing pores, and the collapse of some original pores. These phenomena are the result of the combined effects of the expansion effect caused by gas adsorption and the compression effect caused by external pressure, and will change with variations in simulation conditions. In the simulation system, the pore free volume is the key target region determining the gas adsorption capacity, and also the core of revealing the microscopic coupling mechanism between the degree of adsorption-desorption hysteresis and pore deformation. Since each GCMC+MD operation causes a change in the pore volume of the kerogen matrix, in order to ensure the continuity of the adsorption and desorption processes, the equilibrium configuration at each pressure point is used as the initial state for the simulation of the next pressure point, thereby ensuring the accuracy and reliability of the simulation process.

[0052] This invention combines cutting-edge Monte Carlo and molecular dynamics simulations to reveal the physical adsorption and desorption processes of shale gas in the pore structure of real kerogen under different temperature and pressure conditions. This method not only successfully reproduces the adsorption-desorption hysteresis phenomenon of supercritical shale gas observed in experiments, but also deeply analyzes the underlying microscopic mechanisms and influencing factors, thus providing important theoretical guidance and scientific basis for shale gas production prediction and the selection of optimal production enhancement measures.

[0053] The present invention will be further illustrated by taking the adsorption and desorption process of methane in the pores of shale type IIIA kerogen matrix as an example.

[0054] Specifically, the following steps are included:

[0055] S1. Construct a kerogen matrix pore model;

[0056] This invention is based on the type IIIA kerogen molecular model (C 233 H 204 N4O 27 The energy was reduced through geometry optimization, and 10 annealing cycles were performed, with the temperature gradually increased from 300K to 800K and then decreased back to 300K to obtain the molecular configuration with the lowest energy. Subsequently, a molecular configuration with a size of [missing information] was constructed. A blank simulation box was prepared, and 0.1 g / cm³ was added to it. 3Ten optimized kerogen molecules were randomly placed at a preset density. At 800 K, the simulation system was first subjected to a 1000 ps high-temperature relaxation in the NVT ensemble to ensure the kerogen molecules fully expanded and evenly filled the entire simulation chamber. Next, under a pressure of 30 MPa, the simulation temperature was gradually decreased, and NPT ensemble simulations were performed at 800 K, 600 K, 400 K, and 300 K, with a simulation time of 500 ps at each temperature. During the simulation, the energy and density changes of the system were continuously monitored to ensure sufficient simulation time and convergence of results. Finally, the above kerogen matrix model was further relaxed for 2000 ps at 353.15 K and 30 MPa to obtain a stable structure reflecting the actual formation temperature and pressure conditions, such as... Figure 3 As shown.

[0057] The specific simulation process for constructing the shale kerogen matrix model is shown in Table 1.

[0058] Table 1

[0059] step Series Temperature (K) Pressure (MPa) Simulated time (ps) 1 NVT 800 30 1000 2 NPT 800 30 500 3 NPT 600 30 500 4 NPT 400 30 500 5 NPT 300 30 500 6 NPT 353.15 30 2000

[0060] S2. Obtain the initial structural parameters of the matrix pore model;

[0061] Using the Atom Volumes & Surfaces module in Materials Studio software, and taking a spherical probe with a helium molecular dynamics diameter (0.26 nm) as the standard, the initial free pore volume and porosity of the kerogen matrix model constructed in step S1 were calculated. Based on this, a series of progressively decreasing free pore volumes were obtained by gradually increasing the diameter of the virtual probe molecules (0-0.5 nm), and the pore size distribution of the initial kerogen model was calculated by differentiating the free pore volumes under different probe molecule diameters. Figure 4 As shown.

[0062] Table 2 shows the structural parameters of the initial pore model.

[0063] Table 2

[0064]

[0065] S3. Calibration of fugacity and pressure conversion relationship:

[0066] Methane adsorption was simulated in a blank simulation chamber without kerogen matrix at 353.15 K using the GCMC method. The fugacity input in the simulation was calculated based on the Peng-Robinson equation of state. Based on the number of methane molecules obtained from the adsorption simulation and the volume of the blank simulation chamber, the average bulk density of methane within the chamber under specific fugacity conditions could be calculated. Furthermore, the calculated density was compared with density-pressure curves retrieved from the NIST database at the same temperature to establish the conversion relationship between methane fugacity and pressure at that temperature. Figure 5 As shown.

[0067] S4. Conduct simulations of shale gas adsorption processes;

[0068] Using the final equilibrium configuration obtained in step S1, and with temperature and fugacity as input parameters, the adsorption process of the kerogen pore model was first simulated under low-pressure conditions (1 MPa) using the GCMC method to obtain the methane adsorption capacity under these conditions. The number of equilibrium steps and production steps were both set to 2 × 10⁻⁶. 7 Based on this, MD simulations were performed on the adsorption configuration. First, kinetic relaxation was performed for 100 ps under the NVT ensemble; then, NPT ensemble simulation was performed for 4000 ps under zero effective stress, allowing the kerogen pores to fully deform under these adsorption conditions; finally, kinetic equilibrium was achieved on the deformed kerogen matrix under the NVT ensemble for 2000 ps. Subsequently, adsorbed gas molecules in the pores were removed, and the pore structure parameters of the kerogen matrix under this pressure condition were obtained using the method described in step S2, and this was used as the initial system configuration for the next pressure point. Through the above GCMC+MD simulation process, the simulation pressure was gradually increased to 30 MPa to obtain the isothermal adsorption curves under this temperature condition (e.g., ...). Figure 6 (as shown) and pore structure parameters under different pressure conditions.

[0069] S5. Conduct simulations of shale gas desorption processes;

[0070] The pore equilibrium state at the maximum pressure point (30 MPa) of the adsorption process in step S4 was used as the initial configuration for simulating the desorption process. The simulation pressure was gradually decreased. For each pressure point, the adsorption configuration under that condition was first obtained using GCMC simulation. Then, the system underwent 100 ps of NVT ensemble relaxation to reach equilibrium. Next, the system was simulated for 4000 ps under the NPT ensemble, during which the kerogen underwent expansion and compression until equilibrium was reached. Finally, the system was further equilibrated using the NVT ensemble for 2000 ps, ​​and the final pore configuration was obtained after removing the adsorbed gas molecules. For each pressure point, the pore structure parameters of the kerogen matrix under that condition were obtained using the method described in step S2, and this was used as the initial system configuration for the next pressure point. Through the above process, the isothermal desorption curve under this temperature condition was obtained (e.g., ...). Figure 6 (as shown) and pore structure parameters under different pressure conditions.

[0071] S6. Quantitative analysis of the hysteresis degree in the adsorption-desorption process;

[0072] Based on the isothermal adsorption and desorption curves obtained from the simulation processes in steps S4 and S5, and using formulas (1) and (2), the desorption hysteresis coefficient HI = 0.129 can be calculated. This allows for the quantification of the hysteresis degree of the adsorption-desorption process of shale gas (methane) in the pores of type IIIA kerogen under the pressure range of 0-30 MPa at 353.15 K. Figure 7 The volumetric strain of type IIIA kerogen during the adsorption-desorption process is shown. Figure 8 The changes in pore volume and porosity during adsorption and desorption processes follow a pattern similar to that of volumetric strain. Therefore, the formation of the hysteresis loop in this application example is mainly due to the irreversible deformation of the pore structure of kerogen after methane adsorption, leading to an increase in free pore volume during desorption compared to adsorption. This results in a greater adsorption capacity during desorption than during adsorption at the same pressure. Using a similar approach, the adsorption-desorption hysteresis of shale gas under different simulation conditions can be quantified, and the influence of different factors (such as temperature, maximum adsorption pressure, kerogen type, and kerogen moisture content) can be explored.

Claims

1. A molecular simulation method for quantifying the hysteresis degree of shale gas adsorption-desorption process, characterized in that... Includes the following steps: S1. Construct a kerogen matrix pore model; S2. Obtain the initial structural parameters of the kerogen matrix pore model; S3. Calibrate the conversion relationship between fugacity and pressure; S4. Conduct simulations of shale gas adsorption processes; Using the S1 model of kerogen matrix pores with temperature and fugacity as input parameters, the gas molecule adsorption process of the kerogen matrix pore model under a certain pressure condition was first simulated using the giant canonical Monte Carlo method to obtain the adsorption configuration under that pressure condition; then molecular dynamics simulation was performed to obtain the equilibrium configuration after deformation. Subsequently, the adsorbed gas molecules in the pores were removed, and the structural parameters of the kerogen matrix pore model under this pressure condition were obtained and used as the initial system configuration for the next pressure point. The above simulation process was repeated, and the simulation pressure was gradually increased to obtain the isothermal adsorption curve and the structural parameters of the kerogen matrix pore model under different pressures during the adsorption process. S5. Conduct simulations of shale gas desorption processes; The pore equilibrium state at the maximum pressure point in the S4 shale gas adsorption process simulation was used as the initial configuration for the shale gas desorption process simulation. The simulation pressure was gradually reduced, and the adsorption amount and equilibrium configuration after kerogen matrix deformation under different pressure conditions were obtained using the simulation process in S4. For each pressure point, the pore model structure parameters of the kerogen matrix under that pressure condition were obtained and used as the initial system configuration for the next pressure point. Through the above process, isothermal desorption curves and structural parameters of kerogen matrix pore model under different pressures during desorption are obtained. S6. Quantitative analysis of the hysteresis degree in the adsorption-desorption process; Based on the isothermal adsorption curve obtained from S4 simulation and the isothermal desorption curve obtained from S5 simulation, the degree of lag in the shale gas adsorption-desorption process is quantified.

2. The molecular simulation method for quantifying the hysteresis degree of shale gas adsorption-desorption process according to claim 1, characterized in that, S1 includes the following steps: S11. Introduce kerogen molecules and perform geometry optimization and annealing to obtain the stable configuration with the lowest energy. S12. Randomly place the kerogen molecules that have obtained a stable configuration in S11 into the simulation box at a predetermined density; S13. Process the simulation box to reduce system energy: First, perform high-temperature relaxation under the NVT ensemble; then perform NPT ensemble simulation to obtain the final equilibrium state of the kerogen matrix.

3. The molecular simulation method for quantifying the hysteresis degree of shale gas adsorption-desorption process according to claim 1, characterized in that, S2 includes the following steps: Using the helium molecule dynamics diameter as a benchmark, the free pore volume and surface area of ​​the kerogen matrix pore model were calculated using the spherical probe method. Then, by gradually increasing the diameter of the virtual probe molecules, a series of decreasing free pore volume data were obtained. By differentiating the free pore volumes corresponding to probe molecules of different sizes, the pore size distribution curve of the kerogen matrix pore model was obtained.

4. The molecular simulation method for quantifying the hysteresis degree of shale gas adsorption-desorption process according to claim 1, characterized in that, S3 includes the following steps: In a blank simulation box without kerogen matrix, the adsorption behavior of methane under different fugacity conditions was simulated using the giant canonical Monte Carlo method. The corresponding system density was obtained by analyzing the number of adsorbed molecules, and it was compared with the pressure data at the same density in the NIST database to establish the conversion relationship between gas fugacity and pressure at a specific temperature.

5. The molecular simulation method for quantifying the hysteresis degree of shale gas adsorption-desorption process according to claim 1, characterized in that, The molecular dynamics simulation process in S4 includes the following steps: First, kinetic relaxation is performed under the NVT ensemble; then, NPT ensemble simulation is performed under zero effective stress to fully reflect the deformation characteristics of the kerogen matrix pore model under specific pressure conditions due to gas adsorption; finally, kinetic relaxation is performed again under the NVT ensemble to obtain the adsorption equilibrium configuration after deformation.

6. The molecular simulation method for quantifying the hysteresis degree of shale gas adsorption-desorption process according to claim 1, characterized in that, In S6: The degree of lag in the shale gas adsorption-desorption process is quantified based on the desorption lag coefficient; A hys =A des -A ads (2) In the formula: HI is the desorption hysteresis coefficient, A hys It is the area of ​​the hysteresis loop, A des It is the area corresponding to the desorption curve, A ads It is the area corresponding to the adsorption curve.

7. The molecular simulation method for quantifying the hysteresis degree of shale gas adsorption-desorption process according to claim 1, characterized in that, It also includes the following steps: The degree of volumetric strain is calculated using the following formula: In the formula: Vε is the volumetric strain, and V and V0 are the total volumes of the pore models of the adsorption deformation and the initial kerogen matrix, respectively.

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