Prediction method and application of adsorption behavior of underground hydrogen in pore scale of impurity-containing and water-containing clay minerals

Abstract

The application relates to a prediction method and application of underground hydrogen adsorption behavior in a pore scale of a clay mineral containing impurities and water, and belongs to the technical field of underground hydrogen energy storage and unconventional energy development. The key points are as follows: an initial pore model of the clay mineral containing impurities and water is subjected to energy minimization and pre-equilibrium through a molecular dynamics method to obtain a stable pore model of the clay mineral containing impurities and water; based on the stable pore model of the clay mineral containing impurities and water, hydrogen fugacity is calculated through an SRK-EOS state equation, the corresponding relationship between the hydrogen fugacity and pressure is calibrated, and an initial hydrogen adsorption simulation model is obtained; based on the initial hydrogen adsorption simulation model, hydrogen molecules are introduced into the pore through a grand canonical Monte Carlo method with temperature and fugacity as input parameters, hydrogen insertion and deletion simulation is carried out, and a hydrogen adsorption model is obtained; and the hydrogen adsorption characteristics are calculated according to the hydrogen adsorption model, so that the prediction of the hydrogen adsorption behavior in the pore scale of an underground reservoir is realized.

Description

Technical Field

[0001] This invention belongs to the field of underground hydrogen energy storage and unconventional gas reservoir behavior prediction technology. Specifically, it discloses a molecular-scale simulation method for simulating and predicting the adsorption behavior of hydrogen in the pores of impure and hydrous clay minerals. This method is applicable to the study of hydrogen adsorption behavior in natural hydrogen reservoirs, underground hydrogen storage facilities, shale-clay capping systems, and geological bodies with clay minerals as the main porous medium. It provides a theoretical basis and microscopic mechanism support for the safety assessment of underground hydrogen storage and the prediction of hydrogen retention behavior. Background Technology

[0002] The mass migration and redistribution of hydrogen underground is a crucial factor affecting the effective exploration and exploitation of hydrogen resources. However, hydrogen inevitably suffers losses in various forms during this process, including adsorption loss, diffusion loss, and migration obstruction due to interactions with associated gases or the aqueous phase. Natural reservoirs typically consist of various geological components such as sandstone, carbonate rocks, clay minerals, and organic matter. Clay minerals are widely distributed in both reservoirs and caprocks, serving as important microscopic media influencing hydrogen storage and containment capabilities. Under actual underground conditions, clay pores not only generally contain aqueous phases of varying saturation but also frequently contain formation gases such as methane, carbon dioxide, and nitrogen. In artificial underground hydrogen storage, methane or carbon dioxide may be artificially injected as buffer gases to maintain reservoir pressure stability. The coexistence of aqueous phases and buffer gases facilitates the formation of water films, water bridges, and multi-component competitive adsorption phenomena within the pore structure. These effects significantly influence the adsorption capacity, mobility, and redistribution behavior of hydrogen within the reservoir. However, a systematic, quantitative, and predictable research method is still lacking regarding the adsorption behavior of hydrogen in the pores of impure and hydrous clay. Therefore, in-depth research on the adsorption behavior of hydrogen in impure and hydrous clay minerals is of great significance for understanding the mass migration mechanism of underground hydrogen and the changes in its recoverable quantity.

[0003] While the adsorption behavior of hydrogen in clay pores has garnered some attention, systematic, quantitative, and predictive research methods remain lacking. Particularly under conditions of buffer gases such as methane and carbon dioxide, and different water saturation levels, the microscopic mechanisms influencing hydrogen adsorption site occupancy, interfacial potential redistribution, and changes in adsorption selectivity remain unclear. Existing studies largely rely on laboratory adsorption experiments and macroscopic thermodynamic models, but these models are often based on idealized pore assumptions and primarily focus on dry or buffer-free systems. They struggle to describe the water-gas-mineral multiphase interface effects in nanopores and fail to reveal the coupling mechanism between water saturation changes and multi-component competitive adsorption. Furthermore, the hydrogen adsorption process is influenced by multiple factors, including temperature, pressure, pore water salinity, and the proportion of buffer gases, resulting in significant diversity and nonlinear characteristics under complex geological conditions. Since traditional methods are insufficient to deeply reveal these microscopic phenomena, constructing a research system capable of characterizing the pore structure of hydrated clay at the molecular level, considering the competitive effects of buffer gases, and accurately simulating hydrogen adsorption is crucial. Therefore, there is an urgent need for a molecular simulation method that can simultaneously consider water saturation, buffer gas composition, and real clay pore structure to reveal the adsorption mechanism of hydrogen in underground reservoirs at the nanoscale, and to provide a scientific basis for underground hydrogen storage safety assessment, injection and production capacity prediction, buffer gas optimization configuration, and long-term stability study of caprock. Summary of the Invention

[0004] The purpose of this invention is to propose a method for predicting the adsorption behavior of underground hydrogen in the pore scale of impure and hydrated clay minerals. By constructing a pore model of impure and hydrated clay minerals and combining large canonical Monte Carlo and molecular dynamics simulation methods, the adsorption behavior of hydrogen is quantified under different buffer gas ratios, water saturation, temperature, pressure and salinity conditions, revealing the interaction mechanism of the hydrogen-water-clay interface, thereby providing microscopic mechanism support for the safety assessment of underground hydrogen storage and the prediction of reservoir adsorption capacity.

[0005] The method for predicting the adsorption behavior of underground hydrogen in the pore scale of impure and hydrous clay minerals according to some embodiments of this application includes the following steps:

[0006] Based on the given surface hydroxyl distribution and force field charge distribution of clay mineral crystal structure parameters, the pore layer spacing is determined. Water molecules, salt ions and buffer gas are filled into the pores according to the target water saturation, salinity and buffer gas ratio to obtain the initial pore model of impurity-containing and water-containing clay minerals under different water saturation, salinity and buffer gas conditions.

[0007] The initial pore model of impurity-containing hydrous clay minerals was minimized and pre-equilibrium was obtained by using molecular dynamics methods to obtain a stable pore model of impurity-containing hydrous clay minerals.

[0008] Based on the pore stability model of impure and hydrated clay minerals, hydrogen fugacity was calculated using the SRK-EOS equation of state, the correspondence between hydrogen fugacity and pressure was calibrated, and an initial model for hydrogen adsorption simulation was obtained.

[0009] Based on the initial model of hydrogen adsorption simulation, with temperature and fugacity as input parameters, hydrogen molecules are introduced into the pores through the large canonical Monte Carlo method to simulate hydrogen insertion and deletion, and thus obtain the hydrogen adsorption model.

[0010] Adsorption characteristics were calculated based on a hydrogen adsorption model.

[0011] According to the prediction method for the adsorption behavior of underground hydrogen in the pore scale of impure and hydrated clay minerals in some embodiments of this application, the clay minerals include kaolinite.

[0012] The unit cell parameters of the kaolinite model are a = 5.149 Å, b = 8.934 Å, c = 7.384 Å, α = 91.93°, β = 105.042°, and γ = 89.7910°; where a represents the unit vector length along the x-axis, b represents the unit vector length along the y-axis, and c represents the unit vector length along the z-axis. This represents the angle between the b-axis and the c-axis. This represents the angle between the a-axis and the c-axis. This represents the angle between the a-axis and the b-axis;

[0013] In MaterialsStudio software, the kaolinite model was hydrogenated, with three hydroxyl groups facing the aluminum oxide outer surface and the fourth hydroxyl group facing the siloxane surface, forming a surface hydroxyl distribution. Force field parameters and charge parameters were assigned, and nano-slit pores were constructed by cutting along the (001) crystal plane, where the (001) crystal plane is a set of planes parallel to the clay mineral structure layer plane. A vacuum layer was set and 8×4×2 cell expansion was performed to create two clay mineral substrates, with a given pore size of 50 Å, forming an upper and lower symmetrical wall model with x, y, and z direction dimensions of 41.192 Å, 35.736 Å, and 81.536 Å, respectively.

[0014] According to the prediction method for the adsorption behavior of underground hydrogen in the pore scale of impure and hydrated clay minerals in some embodiments of this application, water molecules, salt ions, and buffer gases are filled into the pores based on target water saturation, salinity, and buffer gas ratio, including...

[0015] Based on the target water saturation, the number of water molecules at different water saturations is calculated using the water molecule density.

[0016] Calculate the number of NaCl ions based on the target salinity;

[0017] The number of CH4 buffer gases was calculated based on the volume occupied by the buffer gas. Water molecules, salt ions and buffer gases under different water saturation, salinity and buffer gas conditions were added into the pores of kaolinite to obtain an initial model of the pores of impurity-containing and water-bearing clay minerals under different water saturation, salinity and buffer gas conditions.

[0018] Among them, the number of water molecules The calculation formula is as follows:

[0019]

[0020] In the formula, The density of water molecules; This represents the molar mass of a water molecule. The pore surface area; The aperture size; It is Avogadro's constant;

[0021] Among them, the number of methane molecules in the buffer gas The calculation formula is as follows:

[0022]

[0023] In the formula, ' is the density of the buffer gas; ' is the molar mass of the buffer gas; The pore surface area; The aperture size; It is Avogadro's constant;

[0024] The salt ion number is obtained based on the following calculation: the volume of 1 mol of water is calculated to be 18 ml / mol, and the volume of 1 water molecule is 3 × 10⁻⁶. -26 L is determined by the number of water molecules and salinity, which in turn determines the number of NaCl molecules.

[0025] Based on the prediction method for the adsorption behavior of underground hydrogen in the pore scale of impure and hydrated clay minerals in some embodiments of this application, the initial pore model of impure and hydrated clay minerals is minimized and pre-equilibriumed using molecular dynamics methods to obtain a stable pore model of impure and hydrated clay minerals. This model includes a CLAYFF force field for clay minerals, an SPC / E model for water molecules, a COMPASS force field for methane, and a Michels unit point model for hydrogen. The unit system is set to real, periodic boundary conditions are set in the x, y, and z directions, the atomic style is set to full, the time step is set to 1.0 fs, the running time is 1 ns, the mineral substrate is set to rigid, and the bonds and bond angles of water molecules and methane molecules are set to rigid. The stable pore model of impure and hydrated clay minerals is obtained by simulation in the large-scale atomic and molecular parallel simulator LAMMPS while keeping the number of particles N, volume V, and temperature T constant.

[0026] According to the prediction method for the adsorption behavior of underground hydrogen in the pore scale of impure and hydrated clay minerals in some embodiments of this application, the potential energy function of the initial pore model of impure and hydrated clay minerals consists of bond stretching energy, bond angle energy, van der Waals potential energy, and Coulomb potential energy, and the total potential energy E is shown in the following formula:

[0027]

[0028] In the formula, Represents total energy. Indicates the bonding energy. Representing nonbonds and energy

[0029] Among them, bonds and energy It is expressed as follows:

[0030]

[0031] In the formula, The bond stretching force constant; This is the actual bond length; Standard bond length;

[0032] Among them, nonbonds and energy It is expressed as follows:

[0033]

[0034] Among them, van der Waals can It is expressed as follows:

[0035]

[0036] In the formula, and For different particles, For particles and particles Between potential well depths, For the same particles Between potential well depths, For the same particles Between potential well depths, For particles and particles Collision distance between them For the same particles Collision distance between them For the same particles The collision distance between particles and the LJ parameters between different particles are calculated using the Lorentz-Berthelot mixing rule, where... , , For particles and particles The distance between them;

[0037] Among them, Coulomb potential energy It is expressed as follows:

[0038]

[0039] In the formula, Where is the dielectric constant. and It is a particle and particles The charge, For particles and particles Distance between

[0040] Among them, bond angle energy It is expressed as follows:

[0041]

[0042] In the formula, The constant of the key angle bending force; This refers to the actual bond angle; This is the standard bond angle.

[0043] Based on the prediction method for the adsorption behavior of underground hydrogen in the pore scale of impure and hydrated clay minerals in some embodiments of this application, the hydrogen fugacity is calculated using the SRK-EOS equation of state, the correspondence between hydrogen fugacity and pressure is calibrated, and an initial model for hydrogen adsorption simulation is obtained, as follows:

[0044]

[0045]

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055] In the formula, For pressure, The gas constant is Thermodynamic temperature For specific volume, The critical temperature. The critical pressure. As the compression factor, The fugacity coefficient. For the degree of fugacity.

[0056] Based on the prediction method for the adsorption behavior of underground hydrogen in the pore scale of impure and hydrated clay minerals in some embodiments of this application, and using an initial model for hydrogen adsorption simulation as input parameters, hydrogen molecules are introduced into the pores through the large canonical Monte Carlo method to simulate hydrogen insertion and deletion, thereby obtaining a hydrogen adsorption model, including...

[0057] Given a temperature and fugacity of 300-420 K and a pressure of 50-250 atm, the hydrogen fugacity is obtained by correcting the pressure based on the relationship between hydrogen fugacity and pressure. The GCMC simulation adsorption settings are as follows: the time step is set to 1.0 fs, the run time is 1 ns, and a GCMC cycle is executed every 100 time steps. Each GCMC cycle contains 100 attempts to insert or remove particles, and the proposed changes are accepted according to the Metropolis criteria to obtain the hydrogen adsorption model.

[0058] According to the method for predicting the adsorption behavior of underground hydrogen in the pore scale of impure and hydrous clay minerals in some embodiments of this application, the adsorption characteristics include at least one of the following adsorption amounts:

[0059] Total adsorption amount :

[0060]

[0061] In the formula, The density of hydrogen gas, The pore surface area;

[0062] Absolute adsorption capacity :

[0063]

[0064] Excess adsorption amount :

[0065]

[0066] In the formula, and These represent the lower and upper limits of the pore size in the Z direction of the adsorption region. and The value of the pore size in the Z direction at the first adsorption valley;

[0067] This indicates the Z-direction range of the adsorption region. Indicates the Z-direction range of the main region;

[0068] and The density is located in the adsorption region and the bulk region. This represents the total number of adsorbate molecules in the mineral slit. Let Avogadro's constant be 1. and The surface area of ​​the slit and the effective adsorption volume of hydrogen are given.

[0069] The method for predicting the adsorption behavior of underground hydrogen in the pore scale of impure and hydrated clay minerals according to some embodiments of this application further includes calculating the hydrogen density distribution and / or interaction energy to predict the adsorption mechanism of hydrogen in underground reservoir pores.

[0070] The hydrogen density distribution was output using the LAMMPS software's built-in command computechunk / atom, combined with the fixave / chunk command.

[0071] The interaction energy is output using the LAMMPS software's built-in command computegroup / group, combined with the fixave / time command.

[0072] The method for predicting the adsorption behavior of underground hydrogen in the pore scale of impure and hydrated clay minerals according to some embodiments of this application is used to identify the nonlinear characteristics of excessive adsorption, adsorption inflection points, or abrupt changes in adsorption layer structure caused by changes in buffer gas, water saturation, temperature, pressure, and salinity.

[0073] Beneficial Effects: The method for predicting the adsorption behavior of underground hydrogen in the pore scale of impure and hydrated clay minerals proposed in this invention can accurately predict the hydrogen storage capacity in underground clay pores based on the changes in hydrogen adsorption and interfacial structure under different buffer gas ratios, water saturation, temperature, pressure, and salinity conditions. Compared with existing technologies, this invention constructs a molecular-scale simulation system that can characterize the microenvironment of real hydrated clay pores and fully considers the adsorption behavior characteristics of hydrogen under the combined effects of buffer gas, water film structure, interfacial charge distribution, and mineral surface potential energy, thus more realistically reflecting the adsorption mechanism of hydrogen in complex pore structures in underground reservoirs. The method of this invention can effectively identify nonlinear responses, adsorption site rearrangements, and changes in interfacial water structure during hydrogen adsorption, significantly improving the accuracy of pore-scale hydrogen adsorption prediction. In addition, this invention can be adapted and extended for different buffer gas and water saturation levels and different underground operating conditions, and has wide applicability, providing an effective methodological basis for solving key technical problems such as adsorption uncertainty assessment, reservoir capacity prediction, and caprock safety analysis in underground hydrogen storage. Attached Figure Description

[0074] Figure 1 This is a flowchart illustrating the method for predicting the adsorption behavior of underground hydrogen in the pore scale of impurity-containing and water-bearing clay minerals in the embodiments.

[0075] Figure 2 The following are initial models of the pore size of impure and hydrated clay minerals: (a) is a schematic diagram of the initial model of the pore size of impure and hydrated clay minerals under dry conditions in the embodiment; (b) is a schematic diagram of the initial model of the pore size of impure and hydrated clay minerals under 0.3 water saturation conditions in the embodiment; and (c) is a schematic diagram of the initial model of the pore size of impure and hydrated clay minerals under 0.7 water saturation conditions in the embodiment.

[0076] Figure 3 This is a schematic diagram showing the number of hydrogen molecules calculated at different water saturation levels in the examples.

[0077] Figure 4 This is a schematic diagram showing the excess hydrogen adsorption amount calculated under different water saturation levels in the examples.

[0078] Figure 5 This is a schematic diagram of the hydrogen density distribution at different water saturation levels calculated in the example.

[0079] Figure 6 This is a schematic diagram illustrating the interaction energies between hydrogen, water, and salt ions and the kaolinite surface at different water saturations, calculated in the examples. Detailed Implementation

[0080] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0081] Example: This example provides a method for predicting the adsorption behavior of underground hydrogen in the pore scale of impurity-containing hydrous clay minerals, including the following steps:

[0082] S1. Constructing an initial pore model for impurity-containing hydrous clay minerals: Based on the crystal structure parameters of the clay minerals, given the surface hydroxyl distribution and force field charge distribution, and given the interlayer spacing of the pores, water molecules, salt ions, and buffer gas are filled into the pores according to the target water saturation, salinity, and buffer gas ratio to obtain an initial pore model for impurity-containing hydrous clay minerals under different water saturation, salinity, and buffer gas conditions. Specifically, step S1 includes the following steps:

[0083] S101. Kaolinite was selected as the representative mineral. The unit cell parameters were obtained from the Inorganic Crystal Structure Database (ICSD) to ensure high accuracy of the constructed model. The individual unit cell parameters are a = 5.149 Å, b = 8.934 Å, c = 7.384 Å, α = 91.93°, β = 105.042°, and γ = 89.7910°; where a represents the unit vector length along the x-axis, b represents the unit vector length along the y-axis, and c represents the unit vector length along the z-axis. This represents the angle between the b-axis and the c-axis. This represents the angle between the a-axis and the c-axis. This represents the angle between the a-axis and the b-axis.

[0084] S102. In MaterialsStudio software, the kaolinite model is hydrogenated, with three hydroxyl groups facing the aluminum oxide outer surface and the fourth hydroxyl group facing the siloxane surface to form a surface hydroxyl distribution. Force field parameters and charge parameters are assigned, and nano-slit pores are constructed by cutting along the (001) crystal plane. The (001) crystal plane is a set of planes parallel to the clay mineral structure layer plane. A vacuum layer is set and 8×4×2 cell expansion is performed. Then, two clay mineral substrates are created, with a given pore size of 50 Å, thus forming an upper and lower symmetrical wall model with x, y, and z direction dimensions of 41.192 Å, 35.736 Å, and 81.536 Å, respectively.

[0085] S103. Based on the target water saturation, calculate the number of water molecules at different water saturation levels using water molecule density; calculate the number of NaCl ions based on the target salinity; calculate the number of CH4 molecules in the buffer gas based on the volume occupied by the buffer gas; and add water molecules, salt ions, and buffer gas under different water saturation, salinity, and buffer gas conditions into the kaolinite pores to obtain initial pore models under different water saturation, salinity, and buffer gas conditions. The formulas for calculating the number of water molecules and buffer gas methane molecules are as follows:

[0086]

[0087] in, This is the density of water molecules or buffer gas; detailed values ​​can be found in the NIST database. The molar mass of a water molecule or buffer gas; The pore surface area; The aperture size; This is Avogadro's constant. For example, there are 992 water molecules at a water saturation level of 0.4 and 1984 water molecules at a water saturation level of 0.8. Under 10% buffer gas conditions, there are 44 methane molecules.

[0088] The determination of the number of salt ions is based on the following assumptions: the volume of the solution is approximately the volume of water; the density of water is 1 g / cm³. 3 The molar mass of a water molecule is 18 g / mol; Avogadro's constant N A ≈6×10 23 / mol; the volume of 1 mol of water is calculated to be 18 ml / mol, and the volume of 1 water molecule is 3 × 10⁻⁶. -26 L is then used to determine the number of NaCl molecules based on the number of water molecules and the salinity. For example, at a water saturation of 0.3 and a salinity of 3M, the number of NaCl molecules is 40, and at a water saturation of 0.7 and a salinity of 3M, the number of NaCl molecules is 93.

[0089] S2. Obtain a stable pore model for impure and hydrated clay minerals. Use molecular dynamics simulation to minimize the energy and pre-equilibrium the initial pore model of impure and hydrated clay minerals from step S1. This includes setting and selecting appropriate force fields, unit systems, boundary conditions, atomic patterns, time steps, running times, water molecule and mineral treatments, and isothermal-volume (NVT) relaxation adjustment to obtain a stable pore model for impure and hydrated clay minerals. Specifically, the settings include: based on the initial model of the pore size of the impurity-containing and water-bearing clay minerals obtained in step S1, the clay mineral force field is selected as the CLAYFF force field, the water molecules adopt the SPC / E model compatible with the CLAYFF force field, the methane adopts the COMPASS force field, the hydrogen adopts Michels' unit point model, the unit system is set to real, periodic boundary conditions are set in all three directions, the atom style is set to full, the time step is set to 1.0fs, the running time is 1ns, the mineral substrate is kept as rigid, and the bonds and bond angles of water molecules and methane molecules are kept as rigid. The simulation is carried out in the large-scale atomic and molecular parallel simulator LAMMPS while keeping the number of particles N, volume V and temperature T constant.

[0090] The potential energy function of the initial pore model of impurity-containing hydrous clay minerals consists of bond stretching energy, bond angle energy, van der Waals potential energy, and Coulomb potential energy. The total potential energy E is shown in the following equation:

[0091]

[0092] Represents total energy. Indicates the bonding energy. Represents nonbonds and energy.

[0093] Among them, bonds and energy It is expressed as follows:

[0094]

[0095] in, The bond stretching force constant is expressed in units of 1 / 3. ; For actual bond length, in units ; Standard bond length, unit .

[0096] Among them, nonbonds and energy It is expressed as follows:

[0097]

[0098] Among them, van der Waals can It is expressed as follows:

[0099]

[0100] in, and For different particles, For particles and particles Between potential well depths, For the same particles Between potential well depths, For the same particles Between potential well depths, For particles and particles Collision distance between them For the same particles Collision distance between them For the same particles The collision distance between particles and the LJ parameters between different particles are calculated using the Lorentz-Berthelot mixing rule, i.e. , , For particles and particles The distance between them.

[0101] Among them, Coulomb potential energy It is expressed as follows:

[0102]

[0103] in, Where is the dielectric constant. and It is a particle and particles The charge, For particles and particles The distance between them.

[0104] Among them, bond angle energy It is expressed as follows:

[0105]

[0106] in, The key angle bending force constant, in units of ; Actual bond angle, unit ; Standard bond angle, unit .

[0107] S3. Establish the conversion relationship between hydrogen fugacity and pressure. Using the pore stability model of the impurity-containing, water-bearing clay minerals obtained in step S2 as the initial configuration for hydrogen adsorption, calculate the hydrogen fugacity using the SRK-EOS equation of state, calibrate the correspondence between hydrogen fugacity and pressure, obtain the fugacity, and thus obtain the initial model for hydrogen adsorption simulation. Specifically, the settings include: Fugacity f is calculated using the SRK-EOS equation as follows:

[0108]

[0109]

[0110]

[0111]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[0118]

[0119] in, For pressure, The gas constant is Thermodynamic temperature For specific volume, The critical temperature. The critical pressure. As the compression factor, The fugacity coefficient. The fugacity of . Among them, the eccentricity factor of hydrogen. Critical pressure and critical temperature The values ​​are -0.216, 1.28 MPa, and 33.2 K, respectively.

[0120] S4. Based on the initial hydrogen adsorption simulation model from step S3, conduct hydrogen adsorption simulations. Using temperature and fugacity as input parameters, employ the large canonical Monte Carlo method to introduce hydrogen molecules into the pores, performing hydrogen insertion and deletion simulations to obtain the hydrogen adsorption configuration. Based on the adsorption configuration, calculate the excess hydrogen adsorption, density distribution, and interaction energy. Specifically, the settings are as follows: Based on the initial hydrogen adsorption simulation model from step S3, perform large canonical Monte Carlo (GCMC) simulations at given temperature and fugacity. Set the temperature to 300-420 K and the pressure to 50-250 atm, correcting for pressure using fugacity. The GCMC simulation adsorption settings are as follows: time step is set to 1.0 fs, runtime is 1 ns, one GCMC cycle is executed every 100 time steps, and each GCMC cycle contains 100 attempts to insert or remove particles. The acceptance of proposed changes is determined according to the Metropolis criteria.

[0121] The adsorption capacity is divided into total adsorption capacity, absolute adsorption capacity, and excess adsorption capacity. Total adsorption capacity is the adsorption capacity of all gases in the pores, absolute adsorption capacity is the adsorption capacity of gases only in the adsorption zone, and excess adsorption capacity is the adsorption capacity of gases in the adsorption zone minus the adsorption capacity assuming that the gases in this zone are at the same density as those in the bulk section.

[0122] The total adsorption capacity is calculated using the following formula:

[0123]

[0124] The absolute adsorption capacity is calculated using the following formula:

[0125]

[0126] The excess adsorption amount is calculated using the following formula:

[0127]

[0128] in, and These represent the lower and upper limits of the pore size in the Z direction of the adsorption region, respectively. and These represent the Z-direction values ​​of the pore size at the first adsorption valley. This indicates the Z-direction range of the adsorption region. Indicates the Z-direction range of the main region. and These represent the densities in the adsorption region and the main region, respectively. This represents the total number of adsorbate molecules in the mineral slits; Avogadro's constant ; and The surface area of ​​the slits Effective adsorption volume of hydrogen ; Characterized the molar density of adsorbate molecules in the bulk phase .

[0129] In this embodiment, , , , and , All of these can be obtained through density distribution curves. For example, under conditions of zero water saturation (i.e., dry conditions), a temperature of 300 K, and a pressure of 200 atm, the calculated excess hydrogen adsorption capacity is... At a water saturation level of 0.3, a temperature of 300 K, and a pressure of 250 atm, the calculated excess hydrogen adsorption capacity is: .

[0130] According to a method for predicting the pore-scale diffusion behavior of underground hydrogen according to some embodiments of this application, in step S4, the hydrogen density distribution and interaction energy are further output to predict the adsorption mechanism of hydrogen in the pores of underground reservoirs. Specifically, the density distribution is output using the LAMMPS software's built-in command `computetechunk / atom` combined with the `fixave / chunk` command. The interaction energy is output using the LAMMPS software's built-in command `computegroup / group` combined with the `fixave / time` command, and then subjected to time averaging.

[0131] The computechunk / atom command is set to one-dimensional Z-axis, calculating once every 1 Å starting from the bottom of the model in the Z-axis. The fixave / chunk command is set to save the average value every 100,000 steps. Based on 100,000, a sample is taken every 100 steps, for a total of 1,000 samples. Then, only the data from the last 500,000 steps is selected for statistical averaging to obtain the hydrogen density distribution along the Z-axis of the pores. The energy is output once every 100 steps, calculated 100 times, and then averaged once. Then, only the data from the last 500,000 steps is selected for statistical averaging to obtain the interaction energy between hydrogen, water, salt ions and the kaolinite surface.

[0132] In this embodiment, Figure 3 This is a schematic diagram showing the number of hydrogen molecules calculated at different water saturations in the example. Figure 4 This is a schematic diagram showing the excess hydrogen adsorption amount calculated at different water saturations in the examples; Figure 5 This is a schematic diagram showing the density distribution of hydrogen gas at different water saturations calculated in the example; as shown. Figures 3-5As shown, in the aqueous state, the number of hydrogen molecules and the amount of excess adsorption in the pores are greatly reduced. When the water saturation exceeds 0.4, there is no adsorbed hydrogen. A water film is formed at low to medium water saturation (0.1-0.6), and a water bridge is formed at high water saturation (0.7-0.9). Figure 6 This is a schematic diagram of the interaction energies between hydrogen, water, and salt ions and the kaolinite surface at different water saturations, calculated in Example 2 of the present invention; it effectively characterizes the hydrogen adsorption behavior.

[0133] This invention belongs to the field of underground hydrogen energy storage and unconventional energy development technology, proposing a method for predicting the adsorption behavior of underground hydrogen in the pore scale of impure and hydrated clay minerals. Based on the real mineral structure of the porous medium, the water-gas coexistence state at the pore scale, and the interaction characteristics between hydrogen, water, and minerals, a pore-scale hydrogen adsorption kinetic model is constructed. Based on statistical mechanics and molecular simulation theory, an isothermal adsorption model of hydrogen under different water saturation, buffer gas, temperature, pressure, and salinity conditions is established using the Grand Canonical Monte Carlo method (GCMC). This model obtains the hydrogen adsorption capacity, excess adsorption capacity, interfacial adsorption configuration, and their nonlinear evolution laws with changes in water saturation, buffer gas, and salinity. Based on the spatiotemporal distribution characteristics of the adsorption capacity, the prediction of hydrogen adsorption behavior at the pore scale of underground reservoirs is achieved. This invention can accurately capture key microscopic mechanisms such as changes in interfacial water film structure and water bridges, and adsorption inflection points, significantly improving the reliability of predicting underground hydrogen adsorption behavior under complex water-gas coexistence conditions.

[0134] The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A method for predicting the adsorption behavior of underground hydrogen in the pore scale of impure and hydrous clay minerals, characterized in that, Includes the following steps: Based on the given surface hydroxyl distribution and force field charge distribution of clay mineral crystal structure parameters, the pore layer spacing is determined. Water molecules, salt ions and buffer gas are filled into the pores according to the target water saturation, salinity and buffer gas ratio to obtain the initial pore model of impurity-containing and water-containing clay minerals under different water saturation, salinity and buffer gas conditions. The initial pore model of impurity-containing hydrous clay minerals was minimized and pre-equilibrium was obtained by using molecular dynamics methods to obtain a stable pore model of impurity-containing hydrous clay minerals. Based on the pore stability model of impure and hydrated clay minerals, hydrogen fugacity was calculated using the SRK-EOS equation of state, the correspondence between hydrogen fugacity and pressure was calibrated, and an initial model for hydrogen adsorption simulation was obtained. Based on the initial model of hydrogen adsorption simulation, with temperature and fugacity as input parameters, hydrogen molecules are introduced into the pores through the large canonical Monte Carlo method to simulate hydrogen insertion and deletion, and thus obtain the hydrogen adsorption model. Adsorption characteristics were calculated based on a hydrogen adsorption model.

2. The method for predicting the adsorption behavior of underground hydrogen in the pore scale of impurity-containing and water-bearing clay minerals according to claim 1, characterized in that, Clay minerals include kaolinite; The unit cell parameters of the kaolinite model are a = 5.149 Å, b = 8.934 Å, c = 7.384 Å, α = 91.93°, β = 105.042°, and γ = 89.7910°; where a represents the unit vector length along the x-axis, b represents the unit vector length along the y-axis, and c represents the unit vector length along the z-axis. This represents the angle between the b-axis and the c-axis. This represents the angle between the a-axis and the c-axis. This represents the angle between the a-axis and the b-axis; In Materials Studio software, the kaolinite model was hydrogenated, with three hydroxyl groups facing the aluminum oxide outer surface and the fourth hydroxyl group facing the siloxane surface, forming a surface hydroxyl distribution. Force field parameters and charge parameters were assigned, and nano-slit pores were constructed by cutting along the 001 crystal plane, where the 001 crystal plane is a set of planes parallel to the clay mineral structure layer plane. A vacuum layer was set and 8×4×2 cell expansion was performed to create two layers of clay mineral substrate. Given a pore size of 50 Å, a symmetrical upper and lower wall model with x, y, and z direction dimensions of 41.192 Å, 35.736 Å, and 81.536 Å, respectively, was formed.

3. The method for predicting the adsorption behavior of underground hydrogen in the pore scale of impurity-containing and water-bearing clay minerals according to claim 1, characterized in that, Based on the target water saturation, salinity, and buffer gas ratio, water molecules, salt ions, and buffer gas are filled into the pores, including... Based on the target water saturation, the number of water molecules at different water saturations is calculated using the water molecule density. Calculate the number of NaCl ions based on the target salinity; The number of CH4 buffer gases was calculated based on the volume occupied by the buffer gas. Water molecules, salt ions and buffer gases under different water saturation, salinity and buffer gas conditions were added into the pores of kaolinite to obtain an initial model of the pores of impurity-containing and water-bearing clay minerals under different water saturation, salinity and buffer gas conditions. Among them, the number of water molecules The calculation formula is as follows: In the formula, The density of water molecules; This represents the molar mass of a water molecule. The pore surface area; The aperture size; It is Avogadro's constant; Among them, the number of methane molecules in the buffer gas The calculation formula is as follows: In the formula, ' is the density of the buffer gas; ' is the molar mass of the buffer gas; The pore surface area; The aperture size; It is Avogadro's constant; The salt ion number is obtained based on the following calculation: the volume of 1 mol of water is calculated to be 18 ml / mol, and the volume of 1 water molecule is 3 × 10⁻⁶. -26 L is determined by the number of water molecules and salinity, which in turn determines the number of NaCl molecules.

4. The method for predicting the adsorption behavior of underground hydrogen in the pore scale of impurity-containing and water-bearing clay minerals according to claim 1, characterized in that, The initial porosity model of the impure hydrous clay mineral was minimized and pre-equilibriumed using molecular dynamics methods to obtain a stable porosity model. This model included a CLAYFF force field for the clay mineral, an SPC / E model for the water molecule, a COMPASS force field for the methane, and a Michels unit point model for the hydrogen. The unit system was set to real, periodic boundary conditions were set in the x, y, and z directions, the atom pattern was set to full, the time step was set to 1.0 fs, the runtime was 1 ns, the mineral substrate was set to rigid, and the bonds and bond angles between the water and methane molecules were set to rigid. The stable porosity model of the impure hydrous clay mineral was obtained by simulation in the large-scale atomic and molecular parallel simulator LAMMPS while keeping the number of particles N, volume V, and temperature T constant.

5. The method for predicting the adsorption behavior of underground hydrogen in the pore scale of impurity-containing and water-bearing clay minerals according to claim 1, characterized in that, The potential energy function of the initial pore model of impurity-containing hydrous clay minerals consists of bond stretching energy, bond angle energy, van der Waals potential energy, and Coulomb potential energy. The total potential energy E is shown in the following equation: In the formula, Represents total energy. Indicates the bonding energy. Representing nonbonds and energy Among them, bonds and energy It is expressed as follows: In the formula, The bond stretching force constant; This is the actual bond length; Standard bond length; Among them, nonbonds and energy It is expressed as follows: Among them, van der Waals can It is expressed as follows: In the formula, and For different particles, For particles and particles Between potential well depths, For the same particles Between potential well depths, For the same particles Between potential well depths, For particles and particles Collision distance between them For the same particles Collision distance between them For the same particles The collision distance between particles and the LJ parameters between different particles are calculated using the Lorentz-Berthelot mixing rule, where... , , For particles and particles The distance between them; Among them, Coulomb potential energy It is expressed as follows: In the formula, Where is the dielectric constant. and It is a particle and particles The charge, For particles and particles Distance between Among them, bond angle energy It is expressed as follows: In the formula, The constant of the key angle bending force; This refers to the actual bond angle; This is the standard bond angle.

6. The method for predicting the adsorption behavior of underground hydrogen in the pore scale of impurity-containing hydrous clay minerals according to claim 1, characterized in that, Hydrogen fugacity was calculated using the SRK-EOS equation of state, and the relationship between hydrogen fugacity and pressure was calibrated to obtain an initial model for hydrogen adsorption simulation, as shown below: In the formula, For pressure, The gas constant is Thermodynamic temperature For specific volume, The critical temperature. The critical pressure. As the compression factor, The fugacity coefficient. For the degree of fugacity.

7. The method for predicting the adsorption behavior of underground hydrogen in the pore scale of impurity-containing and water-bearing clay minerals according to claim 1, characterized in that, Based on the initial model for hydrogen adsorption simulation, using temperature and fugacity as input parameters, hydrogen molecules were introduced into the pores using the large canonical Monte Carlo method to simulate hydrogen insertion and deletion, thus obtaining the hydrogen adsorption model, including... Given a temperature and fugacity of 300-420 K and a pressure of 50-250 atm, the hydrogen fugacity is obtained by correcting the pressure based on the relationship between hydrogen fugacity and pressure. The GCMC simulation adsorption settings are as follows: the time step is set to 1.0 fs, the run time is 1 ns, and a GCMC cycle is executed every 100 time steps. Each GCMC cycle contains 100 attempts to insert or remove particles, and the proposed changes are accepted according to the Metropolis criteria to obtain the hydrogen adsorption model.

8. The method for predicting the adsorption behavior of underground hydrogen in the pore scale of impurity-containing and water-bearing clay minerals according to claim 1, characterized in that, in, Adsorption characteristics include at least one of the following adsorption amounts: Total adsorption amount : In the formula, The density of hydrogen gas, The pore surface area; Absolute adsorption capacity : Excess adsorption amount : In the formula, and These represent the lower and upper limits of the pore size in the Z direction of the adsorption region. and The value of the pore size in the Z direction at the first adsorption valley; This indicates the Z-direction range of the adsorption region. Indicates the Z-direction range of the main region; and The density is located in the adsorption region and the bulk region. This represents the total number of adsorbate molecules in the mineral slit. Let Avogadro's constant be 1. and The surface area of ​​the slit and the effective adsorption volume of hydrogen are given.

9. The method for predicting the adsorption behavior of underground hydrogen in the pore scale of impurity-containing and water-bearing clay minerals according to claim 1, characterized in that, It also includes calculating hydrogen density distribution and / or interaction energy to predict the adsorption mechanism of hydrogen in underground reservoir pores; The hydrogen density distribution was output using the LAMMPS software's built-in command compute chunk / atom, combined with the fix ave / chunk command. The interaction energy is output using the LAMMPS software's built-in command compute group / group, combined with the fix ave / time command.

10. The method for predicting the adsorption behavior of underground hydrogen in the pore scale of impurity-containing and water-bearing clay minerals as described in claim 1, for the purpose of identifying the nonlinear characteristics of excess adsorption, adsorption inflection points, or abrupt changes in adsorption layer structure caused by changes in buffer gas, water saturation, temperature, pressure, and salinity.

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