Molecular simulation method for representing double electric layers on surface of tight reservoir after carbon dioxide injection

Abstract

The invention provides a molecular simulation method for representing double electric layers on the surface of a tight reservoir after carbon dioxide injection. The method comprises the following steps: constructing a tight reservoir rock pore surface model, a crude oil system model, an original environment formation water system model and a CO2 environment formation water system model, and further constructing to obtain an original environment tight reservoir surface system model and a CO2 environment tight reservoir surface system model; performing NVT ensemble lower equilibrium molecular dynamics simulation on the original environment tight reservoir surface system model and the CO2 environment tight reservoir surface system model to enable the models to reach a thermodynamic equilibrium state, and then performing NPT ensemble lower dynamics simulation to balance the temperature and pressure of each model to the actual temperature and pressure of the tight reservoir; and on the basis of a dynamic simulation result under the NPT ensemble, performing tight reservoir surface double-electric-layer characterization after carbon dioxide injection.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas field development, and particularly relates to a molecular simulation method for characterizing the electric double layer on the surface of a tight reservoir after carbon dioxide injection. Background Art

[0002] CO injection 2 has become a key technology for the efficient development of tight oil reservoirs. It can not only achieve the efficient utilization of CO 2 , but also minimize carbon emissions to the greatest extent, having both economic and environmental benefits and playing an important strategic role in oil and gas field development. The complex microporous structure of tight reservoirs determines the significant influence of the electric double layer at the microscale, which in turn affects the wettability of the reservoir surface. The interfacial phenomena caused by CO 2 injection have an impact on the electric double layer on the surface of tight reservoirs. The interaction between supercritical CO 2 and the surface of tight reservoirs cannot be ignored in terms of its influence on wettability, which is of great significance for the development of the microtheory of tight reservoirs. At present, the research on the influence of the electric double layer on the surface of tight reservoirs and the method of improving oil recovery by CO 2 injection on microscale wettability still remains at the stage of qualitative speculation and experiments. Due to the limitations of macroscopic scale conditions, it is difficult to obtain the microscopic influence mechanism of the electric double layer on wettability after CO 2 injection. Therefore, it is necessary to study the interaction of the electric double layer on the surface of tight reservoirs from a microscopic perspective to provide microscopic theoretical support for the method of improving oil recovery in tight reservoirs. Molecular simulation can accurately describe the solid-liquid interface structure, control environmental conditions, and obtain microscopic information that cannot be accessed by experiments, making it a powerful tool for studying the characteristics of the electric double layer. However, the influence mechanism of the electric double layer structure on the micro-nano pore surface of tight reservoirs after CO 2 injection on interfacial interaction is still unclear. Accurately describing the particle distribution near the interface of tight reservoirs is of great significance for studying the electric double layer on the surface of tight reservoirs and microscale wettability.

[0003] In summary, there is still a need to study a molecular simulation method that can accurately characterize the characteristics of the electric double layer on the surface of tight reservoirs after carbon dioxide injection. Summary of the Invention

[0004] The purpose of the present invention is to provide a molecular simulation method that can accurately characterize the characteristics of the electric double layer on the surface of tight reservoirs after carbon dioxide injection.

[0005] To achieve the above purpose, the present invention provides a molecular simulation method for characterizing the electric double layer on the surface of a tight reservoir (a reservoir with a matrix permeability less than 0.1×10 -3 μm 2 ), wherein the method includes:

[0006] Construct a pore surface model of tight reservoir rock, a crude oil system model, an original environmental formation water system model, and a CO 2 environmental formation water system model;

[0007] Combine the pore surface model of tight reservoir rock, the crude oil system model, and the original environmental formation water system model, and then perform energy minimization and relaxation processing to obtain the original environmental tight reservoir surface system model; combine the pore surface model of tight reservoir rock, the crude oil system model, and the CO 2 environmental formation water system model, and then perform energy minimization and relaxation processing to obtain the CO 2 environmental tight reservoir surface system model;

[0008] Perform equilibrium molecular dynamics simulations on the original environmental tight reservoir surface system model and the CO 2 environmental tight reservoir surface system model under the NVT ensemble to bring the models to a thermodynamic equilibrium state, and then perform kinetic simulations under the NPT ensemble to balance the temperature and pressure of each model to the actual temperature and pressure of the tight reservoir;

[0009] Based on the results of the kinetic simulations under the NPT ensemble, perform double-layer characterization on the tight reservoir surface after CO injection.

[0010] According to the preferred embodiment of the above method, constructing a pore surface model of tight reservoir rock includes: constructing an initial model of the pore surface of tight reservoir rock, and then performing energy minimization and relaxation processing to obtain the pore surface model of tight reservoir rock;

[0011] Furthermore, constructing the initial model of the pore surface of tight reservoir rock includes: using Materials Studio software to export the rock unit cell in the crystal library that can simulate the actual tight reservoir rock, then cutting the rock unit cell through the Surfaces module to obtain the cut surface of the rock unit cell, and then expanding the cut surface of the rock unit cell through the Supercell module to obtain the supercell surface, modifying the supercell surface, and assembling two modified supercell surfaces into a rock nanopore to obtain the initial model of the pore surface of tight reservoir rock;

[0012] Furthermore, the energy minimization and relaxation processing are performed using the Smart algorithm.

[0013] According to the preferred embodiment of the above method, constructing a crude oil system model includes: constructing an initial model of the crude oil system, and then performing energy minimization and relaxation processing to obtain the crude oil system model;

[0014] Furthermore, constructing the initial model of the crude oil system includes: establishing the initial model of the crude oil system using the AC module in Materials Studio software according to the components of the crude oil and the crude oil density in the actual tight reservoir;

[0015] Furthermore, energy minimization and relaxation processing are performed using the Smart algorithm.

[0016] According to the preferred embodiment of the above method, constructing the original environmental formation water system model includes: constructing the initial model of the original environmental formation water system, and then performing energy minimization and relaxation processing to obtain the original environmental formation water system model;

[0017] Furthermore, constructing the initial model of the original environmental formation water system includes: establishing the initial model of the original environmental formation water system using the AC module in Materials Studio software according to the types of formation water ions, the concentration of various ions, and the formation water density in the actual tight reservoir;

[0018] Furthermore, energy minimization and relaxation processing are performed using the Smart algorithm.

[0019] According to the preferred embodiment of the above method, constructing the CO 2 environmental formation water system model includes: constructing the initial model of the CO 2 environmental formation water system, and then performing energy minimization and relaxation processing to obtain the CO 2 environmental formation water system model;

[0020] Furthermore, constructing the initial model of the CO 2 environmental formation water system includes: setting the solubility of CO 2 according to the solubility thermodynamics model, setting the density of the CO 2 environmental formation water according to the temperature and pressure conditions of the actual tight reservoir, and constructing a certain number of CO 2 molecules and the ions generated after CO 2 dissolution on the basis of the initial model of the original environmental formation water system using the AC module in MaterialsStudio software to form the initial model of the CO 2 environmental formation water system; 2 2

[0021] Furthermore, energy minimization and relaxation processing are performed using the Smart algorithm.

[0022] According to the preferred embodiment of the above method, the dimensions of the original environmental formation water system model and the CO 2 environmental formation water system model are the same in the x, y, and z coordinate axes directions; wherein, the x, y, and z coordinate axes directions are the three coordinate axes directions of the 3D space of the model.

[0023] According to the preferred embodiment of the above method, wherein, the pore surface model of the tight reservoir rock, the crude oil system model, the original environmental formation water system model, and CO 2 The sizes of the environmental formation water system model in the x and y coordinate axes are the same; wherein, the plane formed by the x and y coordinate axes is parallel to the upper tight reservoir rock surface or the lower tight reservoir rock surface in contact with the pores in the pore surface model of the tight reservoir rock.

[0024] According to the preferred embodiment of the above method, wherein, the pore surface model of the tight reservoir rock, the crude oil system model, and the original environmental formation water system model are combined, and then energy minimization and relaxation processing are performed to obtain the original environmental tight reservoir surface system model, including:

[0025] Using the Build Layers function of Materials Studio software to combine the pore surface model of the tight reservoir rock, the crude oil system model, and the original environmental formation water system model, placing the crude oil system model and the original environmental formation water system model into the pores in the pore surface model of the tight reservoir rock, setting them in the order from bottom to top as the lower tight reservoir rock surface, the original environmental formation water system, the crude oil system, and the upper tight reservoir rock surface, setting the periodic boundary conditions in the x, y, and z coordinate axes directions, and using the Constraints function to fix the top rock unit cell of the upper tight reservoir rock surface and the bottom rock unit cell of the lower tight reservoir rock surface that are not in contact with the pores in the pore surface model of the tight reservoir rock, and building the initial model of the original environmental tight reservoir surface system;

[0026] Performing energy minimization and relaxation processing on the initial model of the original environmental tight reservoir surface system to obtain the original environmental tight reservoir surface system model;

[0027] Furthermore, the energy minimization and relaxation processing are performed using the Smart algorithm.

[0028] According to the preferred embodiment of the above method, wherein, the pore surface model of the tight reservoir rock, the crude oil system model, and the CO 2 environmental formation water system model are combined, and then energy minimization and relaxation processing are performed to obtain the CO 2 environmental tight reservoir surface system model, including:

[0029] Using the Build Layers function of Materials Studio software to combine the pore surface model of the tight reservoir rock, the crude oil system model, and the CO 2 environmental formation water system model, and the crude oil system model, CO 2The environmental formation water system model is placed inside the pores of the pore surface model of the tight reservoir rock. From bottom to top, it is set as the lower tight reservoir rock surface, CO 2 the environmental formation water system, the crude oil system, and the upper tight reservoir rock surface. Periodic boundary conditions in the x, y, and z coordinate axis directions are set, and the top rock unit cell of the upper tight reservoir rock surface and the bottom rock unit cell of the lower tight reservoir rock surface that do not contact the pores in the tight reservoir rock pore surface model are fixed using the Constraints function to construct the initial model of the CO 2 environmental tight reservoir surface system;

[0030] For the CO 2 initial model of the environmental tight reservoir surface system, energy minimization and relaxation processing are performed to obtain the CO 2 model of the environmental tight reservoir surface system;

[0031] Furthermore, the energy minimization and relaxation processing are carried out using the Smart algorithm.

[0032] According to the preferred implementation of the above method, among them, the original environmental tight reservoir surface system model and the CO 2 model of the environmental tight reservoir surface system are respectively subjected to equilibrium molecular dynamics simulation (EMD) under the NVT ensemble to make the model reach the thermodynamic equilibrium state, and then kinetic simulation under the NPT ensemble is carried out to balance the temperature and pressure of each model to the actual temperature and pressure of the tight reservoir, including:

[0033] Using the Dynamics function of the Forcite module of Materials Studio software, perform equilibrium molecular dynamics simulation (EMD) under the NVT ensemble on the original environmental tight reservoir surface system model to make the original environmental tight reservoir surface system model reach the thermodynamic equilibrium state to obtain the thermodynamically stable configuration of the original environmental tight reservoir surface system model; furthermore, use the NVT structure file obtained by performing equilibrium molecular dynamics simulation (EMD) on the original environmental tight reservoir surface system model under the NVT ensemble as the input file, and use the Dynamics function of the Forcite module of Materials Studio software to perform kinetic simulation under the NPT ensemble. Through the Nose-Hoover temperature control method and the Berendsen pressure control method, balance the temperature and pressure of the original environmental tight reservoir surface system model to the actual temperature and pressure of the tight reservoir to obtain the equilibrium configuration of the original environmental tight reservoir surface system model;

[0034] Using the Dynamics function of the Forcite module of Materials Studio software, for the CO 2The surface system model of the environmental tight reservoir is subjected to equilibrium molecular dynamics simulation (EMD) in the NVT ensemble to make CO 2 The surface system model of the environmental tight reservoir reaches the thermodynamic equilibrium state to obtain CO 2 The thermodynamic stable configuration of the surface system model of the environmental tight reservoir; and then CO 2 The NVT structure file obtained by subjecting the surface system model of the environmental tight reservoir to equilibrium molecular dynamics simulation (EMD) in the NVT ensemble is used as the input file, and the Dynamics function of the Forcite module of Materials Studio software is used to perform kinetic simulation in the NPT ensemble. The temperature and pressure of the surface system model of the environmental tight reservoir are balanced to the actual temperature and pressure of the tight reservoir by the Nose-Hoover temperature control method and the Berendsen pressure control method to obtain CO 2 The equilibrium configuration of the surface system model of the environmental tight reservoir; 2 The equilibrium configuration of the surface system model of the environmental tight reservoir;

[0035] Furthermore, during the kinetic simulation in the NPT ensemble, the COMPASS force field is selected;

[0036] Furthermore, during the kinetic simulation in the NPT ensemble, the Ewald summation method is used for the electrostatic potential of the system;

[0037] Furthermore, during the kinetic simulation in the NPT ensemble, the AtomBased summation method is used for the van der Waals potential of the system;

[0038] Furthermore, during the kinetic simulation in the NPT ensemble, the cutoff radius is less than half of the minimum side length of the model.

[0039] According to the preferred implementation manner of the above method, wherein, based on the results of the kinetic simulation in the NPT ensemble, the characterization of the electric double layer on the surface of the tight reservoir after injecting carbon dioxide includes:

[0040] Based on the results of the kinetic simulation in the NPT ensemble of the original surface system model of the environmental tight reservoir, the ion diffusion coefficient and the ion density distribution along the z-axis direction of the electric double layer in the formation water under the original environment are determined to characterize the ion distribution characteristics of the electric double layer at the solid-liquid interface under the original environment; wherein, the z-axis direction is perpendicular to the upper tight reservoir rock surface and the lower tight reservoir rock surface in contact with the pores in the tight reservoir rock pore surface model.

[0041] Furthermore, based on the results of the kinetic simulation in the NPT ensemble of the original surface system model of the environmental tight reservoir, determining the ion diffusion coefficient and the ion density distribution along the z-axis direction of the electric double layer in the formation water under the original environment includes:

[0042] Based on the NPT structure file obtained from the kinetic simulation of the surface system model of the tight reservoir in the original environment under the NPT ensemble, use the Mean square displacement function of the Forcite Analysis module in Materials Studio software to obtain the ionic mean square displacement curve of the electric double layer in the formation water system under the original environment, and use the Concentration profile function to obtain the relative ionic density distribution of the electric double layer in the formation water system under the original environment along the z-axis direction;

[0043] Based on the obtained ionic mean square displacement curve of the electric double layer in the formation water system under the original environment, determine the ionic diffusion coefficient of the electric double layer in the formation water under the original environment;

[0044] Based on the obtained relative ionic density distribution of the electric double layer in the formation water system under the original environment along the z-axis direction, determine the ionic density distribution of the electric double layer in the formation water under the original environment along the z-axis direction;

[0045] Furthermore, the ionic diffusion coefficient is 1 / 6 of the slope of the ionic mean square displacement curve and is determined using the following formula:

[0046]

[0047] In the formula, D is the ionic diffusion coefficient, with the unit 10 -4 cm 2 / s; MSD is the ionic mean square displacement, with the unit cm 2 ; t is the simulation duration, with the unit s;

[0048] Furthermore, the ionic density is determined using the following formula:

[0049] ρ i =ρ rel，i ·ρ bulk

[0050] In the formula, ρ i is the density of ion i, with the unit g / cm 3 ; ρ rel，i is the relative density of ion i, with the unit dimensionless; ρ bulk is the ionic density of the formation water system under the original environment, with the unit g / cm 3 .

[0051] According to the preferred implementation of the above method, among them, based on the results of the kinetic simulation under the NPT ensemble, the characterization of the electric double layer on the surface of the tight reservoir after injecting carbon dioxide includes:

[0052] Based on CO 2Results of kinetic simulations of the environmental tight reservoir surface system model under the NPT ensemble to determine the ion diffusion coefficient of the electric double layer in formation water and the supercritical CO 2 molecular density distribution along the z-axis in the environment, to characterize the properties of the electric double layer on the surface of the tight reservoir after CO injection; where the z-axis is perpendicular to the upper tight reservoir rock surface and the lower tight reservoir rock surface in contact with the pores in the tight reservoir rock pore surface model; 2

[0053] Furthermore, based on the results of kinetic simulations of the environmental tight reservoir surface system model under the NPT ensemble, determine the CO 2 ion diffusion coefficient of the electric double layer in formation water and the supercritical CO 2 molecular density distribution along the z-axis in the environment, including: 2

[0054] Based on the NPT structure file obtained from kinetic simulations of the environmental tight reservoir surface system model under the NPT ensemble, use the Mean square displacement function of the Forcite Analysis module in Materials Studio software to obtain the mean square displacement curve of ions in the electric double layer in the formation water system under the CO 2 environment, and use the Concentration profile function to obtain the relative density distribution of supercritical CO 2 molecules along the z-axis in the formation water system under the CO 2 environment; 2

[0055] Based on the obtained mean square displacement curve of ions in the electric double layer in the formation water system under the CO 2 environment, determine the ion diffusion coefficient of the electric double layer in formation water under the CO 2 environment;

[0056] Based on the obtained relative density distribution of supercritical CO 2 molecules along the z-axis in the formation water system under the CO 2 environment, determine the supercritical CO 2 molecular density distribution along the z-axis in formation water under the CO 2 environment;

[0057] Furthermore, the ion diffusion coefficient is 1 / 6 of the slope of the mean square displacement curve of ions, and is determined using the following formula:

[0058]

[0059] In the formula, D is the ion diffusion coefficient, with the unit of 10 -4 cm​​​2 / s; The MSD is the mean square displacement of ions, with the unit of cm 2 ; t is the simulation duration, with the unit of s;

[0060] Furthermore, the supercritical CO 2 molecular density is determined using the following formula:

[0061] In the formula, is the supercritical CO 2 molecular density, with the unit of g / cm 3 ; is the relative density of supercritical CO 2 molecules, with the unit of dimensionless; is CO 2 in the formation water system under CO 2 molecular density, g / cm 3 ;

[0062] Furthermore, based on the results of the kinetic simulation under the NPT ensemble, the characterization of the electric double layer on the surface of the tight reservoir after CO2 injection includes:

[0063] Based on the supercritical CO 2 molecular density distribution along the z-axis in the formation water under CO 2 environment, determine the adsorption peak value and adsorption layer number of supercritical CO 2 molecules at the solid-liquid interface to characterize the electric double layer characteristics on the surface of the tight reservoir after CO2 injection.

[0064] According to the preferred implementation mode of the above method, among them, based on the results of the kinetic simulation under the NPT ensemble, the characterization of the electric double layer on the surface of the tight reservoir after CO2 injection includes:

[0065] Based on the results of the kinetic simulation of the surface system model of the tight reservoir under the NPT ensemble in the CO 2 environment, obtain the hydrogen bonds between CO 2 molecules and the rock surface to characterize the action mechanism of supercritical CO 2 at the solid-liquid interface and its influence on wettability;

[0066] Furthermore, based on the results of the kinetic simulation of the surface system model of the tight reservoir under the NPT ensemble in the CO 2 environment, obtain the hydrogen bonds between CO 2 molecules and the rock surface, including:

[0067] Based on the pair of CO 2The NPT structure file obtained from the kinetic simulation of the environmental tight reservoir surface system model under the NPT ensemble is used to obtain the hydrogen bonds between CO molecules and the rock surface by using the Calculate Hydrogen Bonds function in the Forcite Analysis module of Materials Studio software. 2 Obtaining hydrogen bonds between molecules and the rock surface.

[0068] According to the preferred embodiment of the above method, wherein, based on the results of the kinetic simulation under the NPT ensemble, the characterization of the electric double layer on the tight reservoir surface after carbon dioxide injection includes:

[0069] Based on the CO 2 The results of the kinetic simulation of the environmental tight reservoir surface system model under the NPT ensemble, determine the CO 2 Under the environmental conditions, the radial distribution function between crude oil and CO 2 molecules is used to characterize the mass transfer of supercritical CO in the tight reservoir after carbon dioxide injection; 2 in the oil-water system.

[0070] Furthermore, based on the results of the kinetic simulation of the environmental tight reservoir surface system model under the NPT ensemble, determine the CO 2 The results of the kinetic simulation of the environmental tight reservoir surface system model under the NPT ensemble, determine the CO 2 Under the environmental conditions, the radial distribution function between crude oil and CO 2 includes:

[0071] Based on the CO 2 The NPT structure file obtained from the kinetic simulation of the environmental tight reservoir surface system model under the NPT ensemble is used to capture the model snapshots at different times by using the Animation Options function in the Forcite Analysis module of Materials Studio software.

[0072] Based on the captured model snapshots at different times, use the Radial distribution function function in the Forcite Analysis module of Materials Studio software to statistically analyze the radial distribution function between crude oil and CO 2 molecules at each time.

[0073] According to the preferred embodiment of the above method, wherein, based on the results of the kinetic simulation under the NPT ensemble, the characterization of the electric double layer on the tight reservoir surface after carbon dioxide injection includes:

[0074] Based on the results of the kinetic simulation of the original environmental tight reservoir surface system model under the NPT ensemble, determine the radial distribution function between the ions in the electric double layer in formation water and the hydrogen and oxygen atoms in water under the original environmental conditions; based on the CO 2Results of kinetic simulations of the environmental tight reservoir surface system model under the NPT ensemble to determine CO 2 The radial distribution functions of the ions in the electric double layer and the hydrogen and oxygen atoms in water in formation water under the CO 2 environment; The hydration intensity of the ions in the electric double layer on the tight reservoir surface after CO injection is characterized by the radial distribution functions of the ions in the electric double layer and the hydrogen and oxygen atoms in water in formation water under the original environment and the CO

[0075] Furthermore, based on the results of kinetic simulations of the original environmental tight reservoir surface system model under the NPT ensemble, determining the radial distribution functions of the ions in the electric double layer and the hydrogen and oxygen atoms in water in formation water under the original environment includes:

[0076] Based on the NPT structure file obtained from the kinetic simulation of the original environmental tight reservoir surface system model under the NPT ensemble, the radial distribution functions of the ions in the electric double layer and the hydrogen and oxygen atoms in water in formation water under the original environment are statistically analyzed using the Radial distributionfunction function of the Forcite Analysis module of Materials Studio software;

[0077] Furthermore, based on the results of kinetic simulations of the CO 2 environmental tight reservoir surface system model under the NPT ensemble, determining the radial distribution functions of the ions in the electric double layer and the hydrogen and oxygen atoms in water in formation water under the CO 2 environment includes:

[0078] Based on the NPT structure file obtained from the kinetic simulation of the CO 2 environmental tight reservoir surface system model under the NPT ensemble, the radial distribution functions of the ions in the electric double layer and the hydrogen and oxygen atoms in water in formation water under the CO 2 environment are statistically analyzed using the Radial distributionfunction function of the Forcite Analysis module of Materials Studio software.

[0079] The technical solution provided by the present invention can accurately characterize the electric double layer characteristics on the tight reservoir surface after CO injection, which helps to explore the influence mechanism on the electric double layer and wettability after CO 2 injection. The technical solution provided by the present invention is based on the DLVO theory, and a molecular dynamics simulation is used to obtain an electric double layer model on the tight reservoir surface under reservoir conditions. Specifically, according to the actual temperature, pressure conditions of the tight reservoir, the crude oil components in the tight oil reservoir, and the ion types and concentrations in the formation water with a certain salinity, and by changing the formation water environment, CO 2Environmental formation water, molecular simulation of the double electric layer characteristics on the surface of tight reservoirs is carried out to obtain the double electric layer model on the surface of tight reservoirs under reservoir conditions. Using the molecular simulation results, the molecular dynamics related parameters that can accurately characterize the double electric layer can be obtained, and the injection of CO 2 After supercritical CO 2 The mechanism of action at the water-rock interface and the mass transfer in the oil-water system are studied, and then the evaluation of the injection of CO from the perspective of the microscopic double electric layer is realized 2 The influence mechanism on the wettability of the tight reservoir surface, making up for the deficiencies of limited indoor experimental conditions, provides a microscopic theoretical reference for the study of the mechanism of enhanced oil recovery in tight reservoirs. Brief Description of the Drawings

[0080] Figure 1 It is a flowchart of the molecular simulation method for characterizing the double electric layer on the surface of a tight reservoir after injecting carbon dioxide provided in Embodiment 1 of the present invention.

[0081] Figure 2A It is a rock unit cell diagram.

[0082] Figure 2B It is a supercell surface diagram.

[0083] Figure 2C It is an initial model diagram of the pore surface of tight reservoir rock.

[0084] Figure 3A It is an initial model diagram of the crude oil system.

[0085] Figure 3B It is an initial model diagram of the original environmental formation water system.

[0086] Figure 3C It is for CO 2 Initial model diagram of the environmental formation water system.

[0087] Figure 4A It is an initial model diagram of the original environmental tight reservoir surface system.

[0088] Figure 4B It is for CO 2 Initial model diagram of the environmental tight reservoir surface system.

[0089] Figure 5 It is a curve graph of the ion density distribution of the double electric layer along the z-axis in the formation water system under the original environment.

[0090] Figure 6 It is for CO 2 In the formation water system under the CO 2 Molecular density distribution curve graph along the z-axis.

[0091] Figure 7 It is for supercritical CO 2Snapshot diagram of the microscopic dynamic process model of molecules gradually adsorbing on the rock surface.

[0092] Figure 8 For CO 2 Hydrogen bond diagram between the molecule and the rock surface.

[0093] Figure 9 For the radial distribution function curves between crude oil and CO 2 molecules at each moment.

[0094] Figure 10A For the radial distribution function curves between the Cl - ions in the electric double layer of formation water in the original environment and the hydrogen and oxygen atoms in water.

[0095] Figure 10B For the radial distribution function curves between the Na + ions in the electric double layer of formation water in the original environment and the hydrogen and oxygen atoms in water.

[0096] Figure 10C For CO 2 For the radial distribution function curves between the Cl - ions in the electric double layer of formation water in the CO

[0097] Figure 10D For CO 2 For the radial distribution function curves between the Na + ions in the electric double layer of formation water in the CO Detailed implementation manner

[0098] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0099] The embodiments of the present invention provide a molecular simulation method for characterizing the electric double layer on the surface of a tight reservoir after carbon dioxide injection. Among them, the method includes:

[0100] Step S1: Construct a pore surface model of the tight reservoir rock, a crude oil system model, an original environment formation water system model, and a CO 2 environment formation water system model;

[0101] Step S2: Combine the pore surface model of the tight reservoir rock, the crude oil system model, and the original environmental formation water system model, and then perform energy minimization and relaxation processing to obtain the original environmental tight reservoir surface system model; Combine the pore surface model of the tight reservoir rock, the crude oil system model, and the CO 2 environmental formation water system model, and then perform energy minimization and relaxation processing to obtain the CO 2 environmental tight reservoir surface system model;

[0102] Step S3: Perform equilibrium molecular dynamics simulation (EMD) on the original environmental tight reservoir surface system model and the CO 2 environmental tight reservoir surface system model under the NVT ensemble to make the model reach the thermodynamic equilibrium state, and then perform kinetic simulation under the NPT ensemble to balance the temperature and pressure of each model to the actual temperature and pressure of the tight reservoir;

[0103] Step S4: Based on the results of the kinetic simulation under the NPT ensemble, perform double-layer characterization on the surface of the tight reservoir after injecting carbon dioxide.

[0104] In some embodiments, Step S1 includes:

[0105] Step S11: Construct an initial model of the pore surface of the tight reservoir rock, and then perform energy minimization and relaxation processing to obtain the pore surface model of the tight reservoir rock;

[0106] Step S12: Construct an initial model of the crude oil system, and then perform energy minimization and relaxation processing to obtain the crude oil system model;

[0107] Step S13: Construct an initial model of the original environmental formation water system, and then perform energy minimization and relaxation processing to obtain the original environmental formation water system model;

[0108] Step S14: Construct an initial model of the CO 2 environmental formation water system, and then perform energy minimization and relaxation processing to obtain the CO 2 environmental formation water system model.

[0109] In some embodiments, in Step S11, constructing the initial model of the pore surface of the tight reservoir rock includes: Exporting the rock unit cell in the crystal library that can simulate the actual tight reservoir rock using Materials Studio software, then obtaining the cut surface of the rock unit cell through the Surfaces module, then expanding the cut surface of the rock unit cell through the Supercell module to obtain the supercell surface, modifying the supercell surface, and assembling two modified supercell surfaces into a rock nanopore to obtain the initial model of the pore surface of the tight reservoir rock.

[0110] In some embodiments, in step S12, constructing the initial model of the crude oil system includes: establishing the initial model of the crude oil system using the AC module in Materials Studio software according to the components and density of the crude oil in the actual tight reservoir.

[0111] In some embodiments, in step S13, constructing the initial model of the original environmental formation water system includes: establishing the initial model of the original environmental formation water system using the AC module in Materials Studio software according to the types of formation water ions, the concentration of various ions, and the density of the formation water in the actual tight reservoir.

[0112] In some embodiments, in step S14, constructing the initial model of the CO 2 environmental formation water system includes: setting the solubility of CO 2 according to the solubility thermodynamic model of CO 2 and setting the density of the CO 2 environmental formation water according to the temperature and pressure conditions of the actual tight reservoir. Then, on the basis of the initial model of the original environmental formation water system, a certain number of CO 2 molecules and the ions generated after the dissolution of CO 2 are used to construct the initial model of the CO 2 environmental formation water system using the AC module in Materials Studio software.

[0113] In some embodiments, in steps S11, S12, S13, and S14, energy minimization and relaxation processing are performed using the Smart algorithm.

[0114] In some embodiments, in step S1, the sizes of the constructed initial models of the original environmental formation water system and the CO 2 environmental formation water system in the x, y, and z coordinate axes directions are the same; where the x, y, and z coordinate axes directions are the three coordinate axes directions of the 3D space of the model.

[0115] In some embodiments, in step S1, the sizes of the constructed tight reservoir rock pore surface model, crude oil system model, original environmental formation water system model, and CO 2 environmental formation water system model in the x and y coordinate axes directions are the same; where the plane formed by the x and y coordinate axes directions is parallel to the upper tight reservoir rock surface or the lower tight reservoir rock surface in contact with the pores in the tight reservoir rock pore surface model.

[0116] In some embodiments, in step S2, combining the tight reservoir rock pore surface model, crude oil system model, and original environmental formation water system model, and then performing energy minimization and relaxation processing to obtain the original environmental tight reservoir surface system model, including:

[0117] Step S21: Use the Build Layers function of Materials Studio software to combine the pore surface model of tight reservoir rock, the crude oil system model, and the original environmental formation water system model. Place the crude oil system model and the original environmental formation water system model into the pores in the pore surface model of tight reservoir rock. Set them in the order from bottom to top as the lower tight reservoir rock surface, the original environmental formation water system, the crude oil system, and the upper tight reservoir rock surface. Set the periodic boundary conditions in the x, y, and z coordinate axes directions, and use the Constraints function to fix the top rock unit cell of the upper tight reservoir rock surface and the bottom rock unit cell of the lower tight reservoir rock surface that do not contact the pores in the pore surface model of tight reservoir rock, and build the initial model of the original environmental tight reservoir surface system;

[0118] Step S22: Perform energy minimization and relaxation processing on the initial model of the original environmental tight reservoir surface system to obtain the model of the original environmental tight reservoir surface system.

[0119] In some embodiments, in step S2, combine the pore surface model of tight reservoir rock, the crude oil system model, and the CO 2 environmental formation water system model, and then perform energy minimization and relaxation processing to obtain the CO 2 environmental tight reservoir surface system model, including:

[0120] Step S23: Use the Build Layers function of Materials Studio software to combine the pore surface model of tight reservoir rock, the crude oil system model, and the CO 2 environmental formation water system model. Place the crude oil system model and the CO 2 environmental formation water system model into the pores in the pore surface model of tight reservoir rock. Set them in the order from bottom to top as the lower tight reservoir rock surface, the CO 2 environmental formation water system, the crude oil system, and the upper tight reservoir rock surface. Set the periodic boundary conditions in the x, y, and z coordinate axes directions, and use the Constraints function to fix the top rock unit cell of the upper tight reservoir rock surface and the bottom rock unit cell of the lower tight reservoir rock surface that do not contact the pores in the pore surface model of tight reservoir rock, and build the initial model of the CO 2 environmental tight reservoir surface system;

[0121] Step S24: Perform energy minimization and relaxation processing on the initial model of the CO 2 environmental tight reservoir surface system to obtain the CO 2 environmental tight reservoir surface system model.

[0122] In some embodiments, in steps S22 and S24, the energy minimization and relaxation processes are performed using the Smart algorithm.

[0123] In some embodiments, step S3 includes:

[0124] Step S31: Using the Dynamics function of the Forcite module in Materials Studio software, perform equilibrium molecular dynamics simulation (EMD) on the original environmental tight reservoir surface system model under the NVT ensemble to bring the original environmental tight reservoir surface system model to a thermodynamic equilibrium state to obtain the thermodynamic stable configuration of the original environmental tight reservoir surface system model; furthermore, use the NVT structure file obtained from performing equilibrium molecular dynamics simulation (EMD) on the original environmental tight reservoir surface system model under the NVT ensemble as the input file, and perform dynamics simulation under the NPT ensemble using the Dynamics function of the Forcite module in Materials Studio software. By means of the Nose-Hoover temperature control method and the Berendsen pressure control method, balance the temperature and pressure of the original environmental tight reservoir surface system model to the actual temperature and pressure of the tight reservoir to obtain the equilibrium configuration of the original environmental tight reservoir surface system model;

[0125] Step S32: Using the Dynamics function of the Forcite module in Materials Studio software, perform equilibrium molecular dynamics simulation (EMD) on the CO 2 environmental tight reservoir surface system model to bring the CO 2 environmental tight reservoir surface system model to a thermodynamic equilibrium state to obtain the thermodynamic stable configuration of the CO 2 environmental tight reservoir surface system model; furthermore, use the NVT structure file obtained from performing equilibrium molecular dynamics simulation (EMD) on the CO 2 environmental tight reservoir surface system model under the NVT ensemble as the input file, and perform dynamics simulation under the NPT ensemble using the Dynamics function of the Forcite module in Materials Studio software. By means of the Nose-Hoover temperature control method and the Berendsen pressure control method, balance the temperature and pressure of the CO 2 environmental tight reservoir surface system model to the actual temperature and pressure of the tight reservoir to obtain the equilibrium configuration of the CO 2 environmental tight reservoir surface system model.

[0126] In some embodiments, in steps S31 and S32, during the kinetic simulation under the NPT ensemble, the COMPASS force field is selected for the force field, the Ewald summation method is used for the electrostatic potential of the system, and the Atom Based summation method is used for the van der Waals potential of the system. The cut-off radius is less than half of the minimum side length of the model.

[0127] In some embodiments, step S4 includes:

[0128] Step S41: Based on the results of the kinetic simulation of the original environment dense reservoir surface system model under the NPT ensemble, determine the ionic diffusion coefficient of the electric double layer in formation water and the ionic density distribution along the z-axis coordinate direction under the original environment, so as to characterize the ionic distribution characteristics of the electric double layer at the solid-liquid interface under the original environment;

[0129] Among them, the z-axis coordinate direction is perpendicular to the upper dense reservoir rock surface and the lower dense reservoir rock surface in contact with the pores in the dense reservoir rock pore surface model.

[0130] In some embodiments, in step S41, based on the results of the kinetic simulation of the original environment dense reservoir surface system model under the NPT ensemble, determining the ionic diffusion coefficient of the electric double layer in formation water and the ionic density distribution along the z-axis coordinate direction includes:

[0131] Based on the NPT structure file obtained from the kinetic simulation of the original environment dense reservoir surface system model under the NPT ensemble, use the Mean square displacement function of the Forcite Analysis module in Materials Studio software to obtain the mean square displacement curve of the ions in the electric double layer in the formation water system under the original environment, and use the Concentration profile function to obtain the relative ionic density distribution along the z-axis coordinate direction of the electric double layer in the formation water system under the original environment;

[0132] Based on the obtained mean square displacement curve of the ions in the electric double layer in the formation water system under the original environment, determine the ionic diffusion coefficient of the electric double layer in formation water under the original environment;

[0133] Based on the obtained relative ionic density distribution along the z-axis coordinate direction of the electric double layer in the formation water system under the original environment, determine the ionic density distribution along the z-axis coordinate direction of the electric double layer in formation water under the original environment;

[0134] Among them, the ionic diffusion coefficient is preferably 1 / 6 of the slope of the mean square displacement curve of the ions, and is determined using the following formula:

[0135]

[0136] In the formula, D is the ionic diffusion coefficient, and the unit is 10-4 cm 2 / s; The MSD is the mean square displacement of ions, with the unit of cm 2 ; T is the simulation duration, with the unit of s;

[0137] Among them, the ion density is preferably determined using the following formula:

[0138] ρ i = ρ rel，i ·ρ bulk

[0139] In the formula, ρ i is the density of ion i, with the unit of g / cm 3 ; ρ rel，i is the relative density of ion i, with the unit of dimensionless; ρ bulk is the ion density of the formation water system in the original environment, with the unit of g / cm 3 .

[0140] In some embodiments, step S4 includes:

[0141] Step S42: Based on the results of the kinetic simulation of the CO 2 environment dense reservoir surface system model under the NPT ensemble, determine the ion diffusion coefficient of the electric double layer in the formation water and the supercritical CO 2 molecular density distribution along the z-axis direction in the environment, so as to characterize the characteristics of the electric double layer on the surface of the dense reservoir after injecting carbon dioxide; 2 Among them, the z-axis direction is perpendicular to the upper dense reservoir rock surface and the lower dense reservoir rock surface in contact with the pores in the dense reservoir rock pore surface model.

[0142] In some embodiments, in step S42, based on the results of the kinetic simulation of the CO

[0143] environment dense reservoir surface system model under the NPT ensemble, determine the ion diffusion coefficient of the electric double layer in the formation water and the supercritical CO 2 molecular density distribution along the z-axis direction in the environment includes: 2 2 2 Based on the NPT structure file obtained by performing kinetic simulation on the CO

[0144] environment dense reservoir surface system model under the NPT ensemble, use the Mean square displacement function of the Forcite Analysis module of Materials Studio software to obtain the ion mean square displacement curve of the electric double layer in the formation water system in the CO 2 environment, and use the Concentration profile function to obtain the CO 2 environment, and use the Concentration profile function to obtain the CO 2Supercritical CO in the formation water system along the z-axis direction under the 2 relative molecular density distribution;

[0145] Based on the obtained mean square displacement curve of ions in the electric double layer in the formation water system under the CO 2 environment, determine the ion diffusion coefficient of the electric double layer in the formation water under the CO 2 environment;

[0146] Based on the obtained supercritical CO in the formation water system along the z-axis direction under the CO 2 environment 2 relative molecular density distribution, determine the supercritical CO 2 in the formation water along the z-axis direction under the CO 2 molecular density distribution;

[0147] Among them, the ion diffusion coefficient is preferably 1 / 6 of the slope of the mean square displacement curve of ions, and is determined by the following formula:

[0148]

[0149] In the formula, D is the ion diffusion coefficient, with the unit of 10 -4 cm 2 / s; MSD is the mean square displacement of ions, with the unit of cm 2 ; t is the simulation duration, with the unit of s;

[0150] Among them, the supercritical CO 2 molecular density is preferably determined by the following formula:

[0151]

[0152] In the formula, is the supercritical CO 2 molecular density, with the unit of g / cm 3 ; is the supercritical CO 2 relative molecular density, with the unit of dimensionless; is the CO 2 in the formation water system under the CO 2 molecular density, g / cm 3 .

[0153] In some embodiments, step S42 further includes:

[0154] Based on the supercritical CO molecular density distribution in the formation water along the z-axis direction under the CO 2 environment, determine the supercritical CO 2 2 ​The adsorption peak and adsorption layer number of molecules at the solid-liquid interface are used to characterize the double electric layer characteristics of the surface of the tight reservoir after CO₂ injection.

[0155] In some embodiments, step S4 includes:

[0156] Step S43: Based on the results of the kinetic simulation of the surface system model of the tight reservoir under the NPT ensemble in the CO₂ environment, obtain the hydrogen bonds between CO₂ molecules and the rock surface to characterize the action mechanism of supercritical CO₂ at the solid-liquid interface of the water-rock interface and its influence on wettability. 2 In the results of the kinetic simulation of the surface system model of the tight reservoir under the NPT ensemble in the CO₂ environment, obtain the hydrogen bonds between CO₂ molecules and the rock surface. 2 To characterize the action mechanism of supercritical CO₂ at the solid-liquid interface of the water-rock interface and its influence on wettability. 2 At the solid-liquid interface of the water-rock interface and its influence on wettability.

[0157] In some embodiments, in step S43, based on the results of the kinetic simulation of the surface system model of the tight reservoir under the NPT ensemble in the CO₂ environment, obtain the hydrogen bonds between CO₂ molecules and the rock surface. 2 In the results of the kinetic simulation of the surface system model of the tight reservoir under the NPT ensemble in the CO₂ environment, obtain the hydrogen bonds between CO₂ molecules and the rock surface. 2 The hydrogen bonds between CO₂ molecules and the rock surface include:

[0158] Based on the NPT structure file obtained by performing kinetic simulation on the surface system model of the tight reservoir under the NPT ensemble in the CO₂ environment, use the Calculate Hydrogen Bonds function of the Forcite Analysis module of Materials Studio software to obtain the hydrogen bonds between CO₂ molecules and the rock surface. 2 For the surface system model of the tight reservoir under the NPT ensemble in the CO₂ environment, use the Calculate Hydrogen Bonds function of the Forcite Analysis module of Materials Studio software to obtain the hydrogen bonds between CO₂ molecules and the rock surface. 2 Obtain the hydrogen bonds between CO₂ molecules and the rock surface.

[0159] In some embodiments, step S4 includes:

[0160] Step S44: Based on the results of the kinetic simulation of the surface system model of the tight reservoir under the NPT ensemble in the CO₂ environment, determine the radial distribution function between crude oil and CO₂ molecules in the CO₂ environment to characterize the mass transfer of supercritical CO₂ in the oil-water system in the tight reservoir after CO₂ injection. 2 In the results of the kinetic simulation of the surface system model of the tight reservoir under the NPT ensemble in the CO₂ environment, determine the radial distribution function between crude oil and CO₂ molecules in the CO₂ environment. 2 In the CO₂ environment, between crude oil and CO₂ molecules. 2 The radial distribution function between crude oil and CO₂ molecules in the CO₂ environment is used to characterize the mass transfer of supercritical CO₂ in the oil-water system in the tight reservoir after CO₂ injection. 2 In the oil-water system.

[0161] In some embodiments, in step S44, based on the results of the kinetic simulation of the surface system model of the tight reservoir under the NPT ensemble in the CO₂ environment, determine the radial distribution function between crude oil and CO₂ molecules in the CO₂ environment. 2 In the results of the kinetic simulation of the surface system model of the tight reservoir under the NPT ensemble in the CO₂ environment, determine the radial distribution function between crude oil and CO₂ molecules in the CO₂ environment. 2 In the CO₂ environment, between crude oil and CO₂ molecules. 2 The radial distribution function between them includes:

[0162] Based on the CO₂ 2The NPT structure file obtained from the kinetic simulation of the environmental tight reservoir surface system model under the NPT ensemble is used to intercept model snapshots at different times by using the Animation Options function in the Forcite Analysis module of Materials Studio software;

[0163] Based on the intercepted model snapshots at different times, the radial distribution function between crude oil and CO 2 molecules at each time is statistically analyzed by using the Radial distribution function function in the Forcite Analysis module of Materials Studio software.

[0164] In some embodiments, step S4 includes:

[0165] Step S45: Based on the results of the kinetic simulation of the original environmental tight reservoir surface system model under the NPT ensemble, determine the radial distribution function between the double-layer ions in formation water and the hydrogen and oxygen atoms in water in the original environment; based on the CO 2 results of the kinetic simulation of the environmental tight reservoir surface system model under the NPT ensemble, determine the radial distribution function between the double-layer ions in formation water and the hydrogen and oxygen atoms in water in the CO 2 environment; use the radial distribution functions between the double-layer ions in formation water and the hydrogen and oxygen atoms in water in the original environment and the CO 2 environment to characterize the hydration intensity of the double-layer ions on the tight reservoir surface after CO injection.

[0166] In some embodiments, in step S45, based on the results of the kinetic simulation of the original environmental tight reservoir surface system model under the NPT ensemble, determining the radial distribution function between the double-layer ions in formation water and the hydrogen and oxygen atoms in water in the original environment includes:

[0167] Based on the NPT structure file obtained from the kinetic simulation of the original environmental tight reservoir surface system model under the NPT ensemble, use the Radial distributionfunction function in the Forcite Analysis module of Materials Studio software to statistically analyze the radial distribution function between the double-layer ions in formation water and the hydrogen and oxygen atoms in water in the original environment;

[0168] Furthermore, based on the CO 2 results of the kinetic simulation of the environmental tight reservoir surface system model under the NPT ensemble, determining the radial distribution function between the double-layer ions in formation water and the hydrogen and oxygen atoms in water in the CO 2 environment includes:

[0169] Based on the CO 2The NPT structure file obtained from the kinetic simulation of the environmental tight reservoir surface system model under the NPT ensemble is used to statistically analyze the radial distribution function of the double-layer ions in formation water and the hydrogen and oxygen atoms in water under the CO 2 environment by using the Radial distribution function function in the Forcite Analysis module of Materials Studio software.

[0170] Example 1

[0171] This example provides a molecular simulation method for characterizing the double electric layer on the surface of a tight reservoir after CO injection.

[0172] As Figure 1 shown, the method specifically includes:

[0173] Step 1: Construct a tight reservoir rock pore surface model, a crude oil system model, an original environmental formation water system model, and a CO 2 environmental formation water system model; specifically including:

[0174] Use Materials Studio software to export the rock cell quartz cell in the crystal library that can simulate the actual tight reservoir rock (as Figure 2A shown), cut the (001) plane of the quartz cell through the Surfaces module to obtain the rock cell cut surface, and then expand the cut surface of the rock cell through the Supercell module to obtain the (001) supercell surface (as Figure 2B shown), perform hydrogenation treatment on the supercell surface to construct a fully hydroxylated quartz surface, and assemble two modified supercell surfaces into a quartz nanopore to obtain the initial model of the tight reservoir rock pore surface, as Figure 2C shown.

[0175] According to the crude oil components and crude oil density in the actual tight reservoir, select n-heptane (C 7 H 16 ) and n-decane (C 10 H 22 ) as crude oil components, set the molar ratio of the two to 1:1, and the density of crude oil under reservoir conditions (313.15K, 20MPa) is 0.85 g / cm 3 . Use the AC module (i.e., Amorphous Cell module) in Materials Studio software to establish an initial model of the crude oil system with dimensions of 4.2548 nm, 3.9304 nm, and 1.5 nm in the x, y, and z axis directions, as Figure 3A shown; among them, the quantity of each component in the initial model of the crude oil system is shown in Table 1.

[0176] According to the types of formation water ions, the concentrations of various ions, and the density of formation water in the actual tight reservoir, the main ions of the saturated formation water solution are set as Na + 、Cl - , the ionic molar concentration is 1.7 mol / L, and the density of sodium chloride aqueous solution under reservoir conditions (313.15 K, 20 MPa) is 1.05 g / cm 3 , and the molar ratio of water molecules, Na + and Cl - is calculated to be 31:1:1. Use the AC module (i.e., the Amorphous Cell module) in the Materials Studio software to establish an initial model of the original environmental formation water system with the same dimensions in the x and y coordinate directions as those of the initial model of the crude oil system, as shown in Figure 3B ; among them, the number of each particle in the initial model of the original environmental formation water system is shown in Table 1.

[0177] CO 2 exists in a supercritical form. By configuring a certain number of CO 2 molecules and the ions generated after the dissolution of CO 2 in the formation water, the formation water environment is changed, so that a certain amount of CO 2 is dissolved on the basis of the original salinity. According to the thermodynamic model of CO 2 solubility, set the CO 2 solubility to 1.2 mol / kg. Use the AC module (i.e., the AmorphousCell module) in the Materials Studio software to configure a certain number of CO 2 molecules and the ions generated after the dissolution of CO 2 on the basis of the initial model of the original environmental formation water system to form an initial model of the CO 2 environmental formation water system. Set the density of the CO 2 environmental formation water to 1.36 g / cm 3 . Use the AC module (i.e., the Amorphous Cell module) in the Materials Studio software to establish a CO 2 composed of H 2 O molecules, CO + molecules, Na - 、Cl 3 2- 、HCO 3- 、H 3 O + -constituted CO 2 environmental formation water system, in which the H 2 O molecules, CO 2Molecules, Na + , Cl - , CO 3 2- , HCO 3- , H 3 O + The molar ratio of is 300:100:12:12:2.5:1:6 to ensure the electroneutrality of the whole system. CO 2 The dimensions of the initial model of the environmental formation water system in the x, y, and z-axis directions are exactly the same as those of the initial model of the original environmental formation water system in the x, y, and z-axis directions, as Figure 3C shown; among them, CO 2 The number of each particle in the initial model of the environmental formation water system is shown in Table 1.

[0178] Among them, the plane formed by the x and y axes is parallel to the upper or lower tight reservoir rock surface in contact with the pores in the tight reservoir rock pore surface model, and the z-axis direction is perpendicular to the upper and lower tight reservoir rock surfaces in contact with the pores in the tight reservoir rock pore surface model.

[0179] Table 1

[0180]

[0181] Using the Geometry Optimization function of Materials Studio software, geometric optimizations (specifically energy minimization and relaxation processing) are performed on the initial model of the tight reservoir rock pore surface, the initial model of the crude oil system, the initial model of the original environmental formation water system, and the CO 2 initial model of the environmental formation water system to obtain the tight reservoir rock pore surface model, the crude oil system model, the original environmental formation water system model, and the CO 2 environmental formation water system model; specifically: select the Smart algorithm for geometric optimization to find the optimal structure; set the convergence thresholds for energy, external force, internal stress, and displacement to 2×10 -5 kcal / mol, 1×10 -2 kcal / mol / nm, 1×10 -3 GPa, and 1×10 -6 nm; select the COMPASS force field, the Ewald summation method for electrostatic interactions, and the Atom based summation method for van der Waals interactions, and set the cut-off radius to

[0182] Step 2: Construct the original environmental tight reservoir surface system model and the CO 2 environmental tight reservoir surface system model; specifically including:

[0183] Using the Build Layers function of Materials Studio software, the pore surface model of tight reservoir rock, the crude oil system model, and the original environmental formation water system model are combined. The crude oil system model and the original environmental formation water system model are placed in the pores of the pore surface model of tight reservoir rock. Settings are made in the order from bottom to top as the lower tight reservoir rock surface, the original environmental formation water system, the crude oil system, and the upper tight reservoir rock surface. Periodic boundary conditions in the x, y, and z directions are set, and the Constraints function is used to fix the bottom quartz unit cells of the upper and lower tight reservoir rock surfaces that do not contact the pores in the pore surface model of tight reservoir rock, thus building the initial model of the original environmental tight reservoir surface system, as Figure 4A shown.

[0184] Using the Build Layers function of Materials Studio software, the pore surface model of tight reservoir rock, the crude oil system model, and the CO 2 environmental formation water system model are combined. The crude oil system model and the CO 2 environmental formation water system model are placed in the pores of the pore surface model of tight reservoir rock. Settings are made in the order from bottom to top as the lower tight reservoir rock surface, the CO 2 environmental formation water system, the crude oil system, and the upper tight reservoir rock surface. Periodic boundary conditions in the x, y, and z coordinate directions are set, and the Constraints function is used to fix the top rock unit cells of the upper tight reservoir rock surface and the bottom rock unit cells of the lower tight reservoir rock surface that do not contact the pores in the pore surface model of tight reservoir rock, thus building the initial model of the CO 2 environmental tight reservoir surface system, as Figure 4B shown.

[0185] Using the Geometry Optimization function of Materials Studio software, geometric optimizations (specifically energy minimization and relaxation processing) are performed on the initial model of the original environmental tight reservoir surface system and the initial model of the CO 2 environmental tight reservoir surface system respectively, to obtain the model of the original environmental tight reservoir surface system and the model of the CO 2 environmental tight reservoir surface system; specifically: The Smart algorithm is selected for geometric optimization to find the optimal structure; the convergence thresholds for energy, external force, internal stress, and displacement are set to 2×10 -5 kcal / mol, 1×10 -2 kcal / mol / nm, 1×10 -3 GPa, and 1×10 -6nm; Select the COMPASS force field, the Ewald summation method for electrostatic interactions, and the Atom based summation method for van der Waals interactions, with the cut-off radius set to

[0186] Step 3: Perform molecular dynamics simulations on the original environmental tight reservoir surface system model and the CO 2 environmental tight reservoir surface system model respectively; specifically including:

[0187] Using the Dynamics function of the Forcite module in Materials Studio software, perform a 2-ns equilibrium molecular dynamics simulation of the original environmental tight reservoir surface system model under the NVT ensemble to bring the original environmental tight reservoir surface system model to a thermodynamic equilibrium state to obtain the thermodynamic stable configuration of the original environmental tight reservoir surface system model. Among them, the temperature is controlled at 313.15 K through the Nose-Hoover thermostat, the time step is set to 1 fs, the trajectory dynamic interval is 0.5 ps, and the total simulation time is 2 ns; then use the NVT structure file obtained from the equilibrium molecular dynamics simulation of the original environmental tight reservoir surface system model under the NVT ensemble as the input file, and use the Dynamics function of the Forcite module in Materials Studio software to perform a 1-ns dynamics simulation under the NPT ensemble. Through the Nose-Hoover temperature control method and the Berendsen pressure control method, balance the temperature and pressure of the original environmental tight reservoir surface system model to the actual temperature and pressure of the tight reservoir (313.15 K and 20 MPa) to obtain the equilibrium configuration of the original environmental tight reservoir surface system model. Among them, the force field selects the COMPASS force field, the electrostatic potential of the system adopts the Ewald summation method, the van der Waals potential adopts the Atom Based summation method, and the cut-off radius is

[0188] Using the Dynamics function of the Forcite module in Materials Studio software, for the CO 2 environmental tight reservoir surface system model, perform a 2-ns equilibrium molecular dynamics simulation under the NVT ensemble to bring the CO 2 environmental tight reservoir surface system model to a thermodynamic equilibrium state to obtain the thermodynamic stable configuration of the CO 2 environmental tight reservoir surface system model. Among them, the temperature is controlled at 313.15 K through the Nose-Hoover thermostat, the time step is set to 1 fs, the trajectory dynamic interval is 0.5 ps, and the total simulation time is 2 ns; then 2The NVT structure file obtained from the equilibrium molecular dynamics simulation of the environmental tight reservoir surface system model under the NVT ensemble is used as the input file. The Dynamics function of the Forcite module in Materials Studio software is used to perform a 1 ns dynamics simulation under the NPT ensemble. The temperature and pressure of the CO 2 The temperature and pressure of the environmental tight reservoir surface system model are balanced to the actual temperature and pressure of the tight reservoir (313.15 K and 20 MPa) to obtain the CO 2 Equilibrium configuration of the environmental tight reservoir surface system model. The COMPASS force field is selected for the force field. The Ewald summation method is used for the electrostatic potential of the system, and the Atom Based summation method is used for the van der Waals potential. The cut-off radius is

[0189] Step 4: Based on the results of the molecular dynamics simulation, conduct the characterization of the electric double layer on the surface of the tight reservoir after injecting carbon dioxide; specifically including:

[0190] Step 4.1: Determine the ion diffusion coefficient and the ion density distribution along the z-axis direction of the electric double layer in the formation water under the original environment to characterize the ion distribution characteristics of the electric double layer at the solid-liquid interface under the original environment; specifically including:

[0191] Based on the NPT structure file obtained from the dynamics simulation of the environmental tight reservoir surface system model under the NPT ensemble, use the Mean square displacement function of the Forcite Analysis module in Materials Studio software to obtain the ion mean square displacement curve of the electric double layer in the formation water system under the original environment, and the Concentration profile function to obtain the relative ion density distribution along the z-axis direction of the electric double layer in the formation water system under the original environment.

[0192] Based on the obtained ion mean square displacement curve of the electric double layer in the formation water system under the original environment, combined with the fact that the ion diffusion coefficient is 1 / 6 of the slope of the ion mean square displacement curve, use the formula To determine the ion diffusion coefficient of the electric double layer in the formation water under the original environment; in the formula, D is the ion diffusion coefficient, with the unit of 10 -4 cm 2 / s; MSD is the ion mean square displacement, with the unit of cm 2 ; t is the simulation duration, with the unit of s; in this embodiment, the Na + ion diffusion coefficient of the electric double layer in the formation water under the original environment is 0.3310×10 -4 cm 2 / s, Cl -The ion diffusion coefficient is 0.3914×10 -4 cm 2 / s.

[0193] Based on the relative ion density distribution of the double electric layer along the z-axis in the formation water system under the original environment, the formula ρ i =ρ rel，i ·ρ bulk Determine the ion density distribution of the double layer in the formation water in the original environment along the z-axis direction; where ρ i is the density of ion i, in g / cm 3 ρ rel，i is the relative density of ion i, unit is dimensionless; ρ bulk is the ion density of the formation water system in the original environment, in g / cm 3 In this embodiment, ρ bulk 0.09936 g / cm 3 , the ion density distribution curve of the double electric layer in the formation water in the original environment along the z-axis direction is obtained, as shown in Figure 5 shown.

[0194] Step 4.2: Determine CO 2 The ionic diffusion coefficient of the double layer in formation water and the supercritical CO along the z-axis 2 Molecular density distribution is used to characterize the double electrical layer characteristics of the surface of the dense reservoir after CO2 injection; determine the supercritical CO 2 The adsorption peak and number of adsorption layers of molecules at the solid-liquid interface are used to characterize the double electrical layer characteristics of the surface of the dense reservoir after carbon dioxide injection; specifically including:

[0195] Based on CO 2 The NPT structure file obtained by dynamic simulation of the NPT ensemble under the surface system model of the environmental tight reservoir is used to obtain the CO 2 The mean square displacement curve of the ions in the double electric layer of the formation water system under the environment, and the concentration profile function obtains CO 2 Supercritical CO along the z-axis in the formation water system under ambient conditions 2 Relative molecular density distribution.

[0196] Based on the obtained CO 2 The ion mean square displacement curve of the double electric layer in the formation water system under the environment, combined with the ion diffusion coefficient as 1 / 6 of the slope of the ion mean square displacement curve, is used by the formula Determine CO 2Ionic diffusion coefficient of the electric double layer in formation water under the -4 cm 2 / s; MSD is the mean square displacement of ions, in cm 2 ; t is the simulation duration, in s; in this embodiment, CO 2 Under the environment, the Na + ionic diffusion coefficient of the electric double layer in formation water is 0.3650×10 -4 cm 2 / s, and the Cl - ionic diffusion coefficient is 0.4294×10 -4 cm 2 / s.

[0197] Based on the obtained relative density distribution of supercritical CO 2 molecules along the z-axis direction in the formation water system under the 2 environment, use the formula to determine the density distribution of supercritical CO 2 molecules along the z-axis direction in the formation water under the 2 environment; where is the density of supercritical CO 2 molecules, in g / cm 3 ; is the relative density of supercritical CO 2 molecules, dimensionless; is the density of CO 2 molecules in the formation water system under the 2 environment, in g / cm 3 ; in this embodiment, is 0.0216 g / cm 3 , and the determined density distribution curve of supercritical CO 2 molecules along the z-axis direction in the formation water under the 2 environment is as Figure 6 shown.

[0198] Based on the density distribution of supercritical CO 2 molecules along the z-axis direction in the formation water under the 2 environment, determine the adsorption peak value and adsorption layer number of supercritical CO 2 molecules at the solid-liquid interface: in this embodiment, supercritical CO 2 molecules have two adsorption layers at the solid-liquid interface (i.e., the water-rock interface), and the maximum peak density is 1.02 g / cm 3 ; there is a relatively thick adsorption layer at the oil-water interface, and the peak density is 0.5 g / cm 3 .

[0199] Step 4.3: Obtain CO2 Hydrogen bonds between molecules and the rock surface are used to characterize supercritical CO 2 The mechanism of action at the water-rock interface and its influence on wettability; specifically including:

[0200] Based on the NPT structure file obtained from the kinetic simulation of the CO 2 environmental dense reservoir surface system model under the NPT ensemble, the Calculate Hydrogen Bonds function of the Forcite Analysis module in Materials Studio software is used to determine the CO 2 Hydrogen bonds between molecules and the rock surface are obtained, and the results are as Figure 8 shown; from Figure 8 it can be seen that the van der Waals force is the main force between the rock and the formation water under CO 2 environment.

[0201] Step 4.4: Determine the radial distribution function between crude oil and CO 2 molecules under CO 2 environment, which is used to characterize the mass transfer of supercritical CO 2 in the oil-water system; specifically including:

[0202] Based on the NPT structure file obtained from the kinetic simulation of the CO 2 environmental dense reservoir surface system model under the NPT ensemble, the model snapshots at 250 ps, 500 ps, 750 ps, and 1000 ps are intercepted using the Animation Options function of the Forcite Analysis module in Materials Studio software, as Figure 7 shown, Figure 7 where (a) is the model snapshot at 250 ps, (b) is the model snapshot at 500 ps, and (c) is the model snapshot at 1000 ps.

[0203] Based on the intercepted model snapshots at 250 ps, 500 ps, 750 ps, and 1000 ps, the Radial distribution function function of the Forcite Analysis module in MaterialsStudio software is used to statistically analyze the radial distribution function between crude oil and CO 2 molecules (C(C 7 H 16 \C 10 H 22 ))-C(CO 2 )) at each moment, as Figure 9 shown, indicating that supercritical CO 2Gradually enter the oil phase to reduce the viscosity of crude oil.

[0204] Step 4.5: Determine the radial distribution functions of the ions in the electric double layer in formation water with hydrogen and oxygen atoms in water under the original environment and CO 2 The radial distribution functions of the ions in the electric double layer in formation water with hydrogen and oxygen atoms in water under the CO

[0205] Based on the NPT structure file obtained from the kinetic simulation of the surface system model of the tight reservoir in the original environment under the NPT ensemble, use the Radial distributionfunction function in the Forcite Analysis module of Materials Studio software to statistically analyze the radial distribution functions of the ions in the electric double layer in formation water with hydrogen and oxygen atoms in water under the original environment. The results are as Figure 10A 、 Figure 10B shown;

[0206] Based on the NPT structure file obtained from the kinetic simulation of the surface system model of the tight reservoir in the CO 2 environment under the NPT ensemble, use the Radial distributionfunction function in the Forcite Analysis module of Materials Studio software to statistically analyze the radial distribution functions of the ions in the electric double layer in formation water with hydrogen and oxygen atoms in water under the CO 2 environment. The results are as Figure 10C 、 Figure 10D shown.

[0207] From Figure 10A 、 Figure 10B 、 Figure 10C 、 Figure 10D it can be seen that after injecting carbon dioxide, the hydration of the ions in the electric double layer on the surface of the tight reservoir is enhanced, the stable distribution of ions in the electric double layer is enhanced, and the water wettability of the rock surface is enhanced.

[0208] From the above embodiments, it can be seen that the molecular simulation method provided in this specification for characterizing the electric double layer on the surface of the tight reservoir after injecting carbon dioxide breaks through the limitations of experimental objective conditions and can evaluate the enhanced oil recovery method from a microscopic perspective; it realizes the accurate simulation of the interfacial characteristics of the tight reservoir after injecting CO 2 After that, according to the on-site geological data, the crude oil components and formation water components that meet the on-site conditions can be screened in step 1. Constructing different crude oil systems can be achieved by mixing the screened crude oil components in specific proportions according to the geological data; constructing different formation water systems with different compositions and salinities can be achieved by mixing the screened ions in the electric double layer in specific proportions according to the geological data. After injecting CO 2 According to different solubilities, screen CO2 Environmental formation water ions are used to characterize the electric double layer of tight reservoirs under different environmental conditions.

[0209] The preferred embodiments of the present invention have been described above. Many features and advantages of these embodiments are apparent from the detailed description, and the claims are intended to cover all such features and advantages that fall within the true spirit and scope of these embodiments. In addition, since many modifications and changes are readily envisioned by those skilled in the art, the embodiments of the present invention are not to be limited to the exact structures and operations illustrated and described, but may cover all suitable modifications and equivalents that fall within their scope.

Claims

1. A molecular simulation method for characterizing the double electrical layer on the surface of a tight reservoir after CO2 injection, wherein: The method includes: Construct tight reservoir rock pore surface model, crude oil system model, original environment formation water system model and CO2 environment formation water system model; The tight reservoir rock pore surface model, crude oil system model, and original environment formation water system model are combined, and then energy minimization and relaxation treatment are performed to obtain the original environment tight reservoir surface system model; the tight reservoir rock pore surface model, crude oil system model, and CO2 environment formation water system model are combined, and then energy minimization and relaxation treatment are performed to obtain the CO2 environment tight reservoir surface system model; The surface system model of the tight reservoir in the original environment and the surface system model of the tight reservoir in the CO2 environment were respectively subjected to equilibrium molecular dynamics simulation under the NVT ensemble to make the model reach the thermodynamic equilibrium state, and then the dynamic simulation under the NPT ensemble was performed to balance the temperature and pressure of each model to the actual temperature and pressure of the tight reservoir. Based on the results of kinetic simulation under the NPT ensemble, the double electrical layer on the surface of the tight reservoir after carbon dioxide injection was characterized.

2. The method according to claim 1, wherein: The construction of tight reservoir rock pore surface model, crude oil system model, original environment formation water system model and CO2 environment formation water system model includes: Construct an initial model of the pore surface of tight reservoir rocks, and then perform energy minimization and relaxation processing to obtain a pore surface model of tight reservoir rocks; Construct an initial model of the crude oil system, and then perform energy minimization and relaxation processing to obtain a crude oil system model; Construct an initial model of the original environmental formation water system, and then perform energy minimization and relaxation processing to obtain the original environmental formation water system model; Construct an initial model of the formation water system in a CO2 environment, and then perform energy minimization and relaxation processing to obtain a model of the formation water system in a CO2 environment; Preferably, constructing an initial model of the pore surface of a tight reservoir rock includes: The rock unit cell that can simulate the actual tight reservoir rock is exported from the crystal library using Materials Studio software. The rock unit cell is then sectioned using the Surfaces module to obtain the rock unit cell cutting surface. The rock unit cell cutting surface is then expanded using the Supercell module to obtain the supercell surface. The supercell surface is modified, and two modified supercell surfaces are assembled into rock nanopores to obtain the initial model of the tight reservoir rock pore surface. Preferably, constructing the initial model of the crude oil system includes: According to the composition and density of crude oil in the actual tight reservoir, the AC module in Materials Studio software was used to establish the initial model of the crude oil system. Preferably, constructing an initial model of the original environmental formation water system includes: According to the types of formation water ions, concentrations of various ions and density of formation water in actual tight reservoirs, the AC module in MaterialsStudio software was used to establish the initial model of the original environmental formation water system. Preferably, constructing an initial model of a formation water system in a CO2 environment includes: The solubility of CO2 is set according to the CO2 solubility thermodynamic model, the density of CO2 environmental formation water is set according to the actual temperature and pressure conditions of the tight reservoir, and a certain number of CO2 molecules and ions generated by the dissolution of CO2 are constructed on the basis of the initial model of the original environmental formation water system using the AC module in the Materials Studio software to form the initial model of the CO2 environmental formation water system; Preferably, energy minimization and relaxation processing are performed using the Smart algorithm.

3. The method according to claim 1 or 2, wherein: The original environment formation water system model and the CO2 environment formation water system model have the same size in the x, y, and z coordinate axis directions; wherein the x, y, and z coordinate axis directions are the three coordinate axis directions of the model 3D space; The tight reservoir rock pore surface model, crude oil system model, original environment formation water system model and CO2 environment formation water system model have the same dimensions in the x and y coordinate axis directions; wherein, the plane formed by the x and y coordinate axis directions is parallel to the upper tight reservoir rock surface or the lower tight reservoir rock surface in contact with the pores in the tight reservoir rock pore surface model.

4. The method according to claim 3, wherein: The tight reservoir rock pore surface model, crude oil system model, and original environment formation water system model are combined, and then energy minimization and relaxation processing are performed to obtain the original environment tight reservoir surface system model including: The Build Layers function of Materials Studio software is used to combine the tight reservoir rock pore surface model, crude oil system model, and original environment formation water system model. The crude oil system model and the original environment formation water system model are placed in the pores of the tight reservoir rock pore surface model. The lower tight reservoir rock surface, the original environment formation water system, the crude oil system, and the upper tight reservoir rock surface are set from bottom to top, and periodic boundary conditions in the x, y, and z coordinate axis directions are set. The top rock unit cell of the upper tight reservoir rock surface that is not in contact with the pores and the bottom rock unit cell of the lower tight reservoir rock surface in the tight reservoir rock pore surface model are fixed by the Constraints function to build the initial model of the original environment tight reservoir surface system. Performing energy minimization and relaxation processing on the initial model of the original environment tight reservoir surface system, and obtaining the original environment tight reservoir surface system model; The tight reservoir rock pore surface model, crude oil system model, and CO2 environment formation water system model are combined, and then energy minimization and relaxation treatment are performed to obtain the CO2 environment tight reservoir surface system model including: The Build Layers function of Materials Studio software is used to combine the tight reservoir rock pore surface model, crude oil system model, and CO2 environment formation water system model. The crude oil system model and CO2 environment formation water system model are placed in the pores of the tight reservoir rock pore surface model. The lower tight reservoir rock surface, CO2 environment formation water system, crude oil system, and upper tight reservoir rock surface are set from bottom to top, and periodic boundary conditions in the x, y, and z coordinate axis directions are set. The top rock unit cell of the upper tight reservoir rock surface that is not in contact with the pores and the bottom rock unit cell of the lower tight reservoir rock surface in the tight reservoir rock pore surface model are fixed by the Constraints function to obtain the initial model of the CO2 environment tight reservoir surface system. The initial model of the surface system of the tight reservoir in the CO2 environment is subjected to energy minimization and relaxation treatment to obtain the surface system model of the tight reservoir in the CO2 environment.

5. The method according to claim 1, wherein: The surface system model of the tight reservoir in the original environment and the surface system model of the tight reservoir in the CO2 environment were respectively subjected to equilibrium molecular dynamics simulation under the NVT ensemble to make the model reach the thermodynamic equilibrium state, and then the dynamic simulation under the NPT ensemble was performed to balance the temperature and pressure of each model to the actual temperature and pressure of the tight reservoir, including: The Dynamics function of the Forcite module of Materials Studio software is used to perform equilibrium molecular dynamics simulation under NVT ensemble on the surface system model of the original environment tight reservoir, so that the surface system model of the original environment tight reservoir reaches a thermodynamic equilibrium state to obtain the thermodynamically stable configuration of the surface system model of the original environment tight reservoir; then the NVT structure file obtained by the equilibrium molecular dynamics simulation of the surface system model of the original environment tight reservoir under NVT ensemble is used as an input file, and the Dynamics function of the Forcite module of Materials Studio software is used to perform dynamic simulation under NPT ensemble, and the temperature and pressure of the surface system model of the original environment tight reservoir are balanced to the actual temperature and pressure of the tight reservoir through the Nose-Hoover temperature control method and the Berendsen pressure control method to obtain the equilibrium configuration of the surface system model of the original environment tight reservoir; The Dynamics function of the Forcite module of Materials Studio software is used to perform equilibrium molecular dynamics simulation on the surface system model of the tight reservoir in the CO2 environment under the NVT ensemble, so that the surface system model of the tight reservoir in the CO2 environment reaches a thermodynamic equilibrium state to obtain the thermodynamically stable configuration of the surface system model of the tight reservoir in the CO2 environment; then the NVT structure file obtained by the equilibrium molecular dynamics simulation of the surface system model of the tight reservoir in the CO2 environment under the NVT ensemble is used as the input file, and the Dynamics function of the Forcite module of Materials Studio software is used to perform dynamic simulation under the NPT ensemble, and the temperature and pressure of the surface system model of the tight reservoir in the CO2 environment are balanced to the actual temperature and pressure of the tight reservoir through the Nose-Hoover temperature control method and the Berendsen pressure control method to obtain the equilibrium configuration of the surface system model of the tight reservoir in the CO2 environment; Preferably, during the dynamics simulation under the NPT ensemble, the force field is selected as COMPASS force field; Preferably, during the dynamic simulation under the NPT ensemble, the electrostatic potential of the system adopts the Ewald summation method; Preferably, during the dynamic simulation of the NPT ensemble, the van der Waals potential of the system adopts the Atom Based summation method; Preferably, during the dynamic simulation under the NPT ensemble, the cutoff radius is less than half of the minimum side length of the model.

6. The method according to claim 1, wherein: Based on the results of dynamic simulation under the NPT ensemble, the double electrical layer characterization of the surface of the tight reservoir after CO2 injection includes: Based on the results of dynamic simulation under the NPT ensemble of the surface system model of the pristine environment tight reservoir, the ion diffusion coefficient of the double electric layer in the formation water and the ion density distribution along the z-axis direction are determined to characterize the ion distribution characteristics of the double electric layer at the solid-liquid interface in the pristine environment. Wherein, the z coordinate axis direction is perpendicular to the upper tight reservoir rock surface and the lower tight reservoir rock surface in contact with the pores in the tight reservoir rock pore surface model; Preferably, based on the results of dynamic simulation under the NPT ensemble of the surface system model of the original environment tight reservoir, determining the ion diffusion coefficient of the double electric layer in the formation water in the original environment and the ion density distribution along the z-axis direction includes: Based on the NPT structure file obtained by the dynamic simulation of the surface system model of the dense reservoir in the original environment under the NPT ensemble, the Mean square displacement function of the Forcite Analysis module of the Materials Studio software is used to obtain the ion mean square displacement curve of the double electric layer in the formation water system under the original environment, and the Concentration profile function is used to obtain the ion relative density distribution of the double electric layer in the formation water system under the original environment along the z coordinate axis. Based on the obtained ion mean square displacement curve of the double electric layer in the formation water system under the original environment, the ion diffusion coefficient of the double electric layer in the formation water under the original environment is determined; Based on the obtained ion relative density distribution of the double electric layer in the formation water system under the original environment along the z-axis direction, the ion density distribution of the double electric layer in the formation water under the original environment along the z-axis direction is determined.

7. The method according to claim 1, wherein: Based on the results of dynamic simulation under the NPT ensemble, the double electrical layer characterization of the surface of the tight reservoir after CO2 injection includes: Based on the results of dynamic simulation of the surface system model of tight reservoirs in CO2 environment under NPT ensemble, the ion diffusion coefficient of the double layer in formation water and the supercritical CO2 molecular density distribution along the z-axis are determined to characterize the double layer characteristics of the surface of tight reservoirs after CO2 injection. Wherein, the z coordinate axis direction is perpendicular to the upper tight reservoir rock surface and the lower tight reservoir rock surface in contact with the pores in the tight reservoir rock pore surface model; Preferably, based on the results of kinetic simulation under the NPT ensemble of the CO2 environment tight reservoir surface system model, determining the ion diffusion coefficient of the double electric layer in the formation water in the CO2 environment and the supercritical CO2 molecular density distribution along the z-axis direction includes: Based on the NPT structure file obtained by the dynamic simulation of the surface system model of the tight reservoir in the CO2 environment under the NPT ensemble, the Mean square displacement function of the Forcite Analysis module of the Materials Studio software is used to obtain the ion mean square displacement curve of the double electric layer in the formation water system under the CO2 environment, and the Concentration profile function is used to obtain the relative density distribution of supercritical CO2 molecules along the z-axis direction in the formation water system under the CO2 environment; Based on the obtained ion mean square displacement curve of the double electric layer in the formation water system under the CO2 environment, the ion diffusion coefficient of the double electric layer in the formation water under the CO2 environment is determined; Based on the obtained supercritical CO2 molecule relative density distribution along the z-axis in the formation water system under the CO2 environment, the supercritical CO2 molecule density distribution along the z-axis in the formation water under the CO2 environment is determined; Preferably, based on the results of the kinetic simulation under the NPT ensemble, characterizing the double electrical layer on the surface of the tight reservoir after carbon dioxide injection includes: Based on the supercritical CO2 molecular density distribution along the z-axis in formation water under CO2 environment, the adsorption peak and adsorption layer number of supercritical CO2 molecules at the solid-liquid interface are determined to characterize the double electrical layer characteristics of the tight reservoir surface after CO2 injection.

8. The method according to claim 1, wherein: Based on the results of dynamic simulation under the NPT ensemble, the double electrical layer characterization of the surface of the tight reservoir after CO2 injection includes: Based on the results of dynamic simulation of the surface system model of tight reservoirs in CO2 environment under the NPT ensemble, the hydrogen bonds between CO2 molecules and rock surfaces are obtained to characterize the action mechanism of supercritical CO2 at the solid-liquid interface and its influence on wettability. Preferably, based on the results of kinetic simulation of the CO2 environment tight reservoir surface system model NPT ensemble, obtaining the hydrogen bond between the CO2 molecule and the rock surface includes: Based on the NPT structure file obtained by dynamic simulation of the surface system model of the tight reservoir in the CO2 environment under the NPT ensemble, the Calculate Hydrogen Bonds function of the Forcite Analysis module of the Materials Studio software was used to obtain the hydrogen bonds between the CO2 molecules and the rock surface.

9. The method according to claim 1, wherein: Based on the results of dynamic simulation under the NPT ensemble, the double electrical layer characterization of the surface of the tight reservoir after CO2 injection includes: Based on the results of dynamic simulation of the surface system model of tight reservoirs in CO2 environment under NPT ensemble, the radial distribution function between crude oil and CO2 molecules in CO2 environment is determined to characterize the mass transfer effect of supercritical CO2 in the oil-water system in tight reservoirs after CO2 injection. Preferably, based on the results of dynamic simulation of the surface system model of the tight reservoir in the CO2 environment under the NPT ensemble, determining the radial distribution function between crude oil and CO2 in the CO2 environment includes: Based on the NPT structure file obtained by the dynamic simulation of the surface system model of the CO2 tight reservoir under the NPT ensemble, the Animation Options function of the Forcite Analysis module of Materials Studio software was used to capture model snapshots at different times; Based on the snapshots of the model taken at different times, the radial distribution function of the Forcite Analysis module of Materials Studio software was used to calculate the radial distribution function between crude oil and CO2 molecules at each time.

10. The method according to claim 1, wherein: Based on the results of dynamic simulation under the NPT ensemble, the double electrical layer characterization of the surface of the tight reservoir after CO2 injection includes: Based on the results of dynamic simulation of the surface system model of the tight reservoir in the original environment under the NPT ensemble, the radial distribution function of the double-layer ions in the formation water and the hydrogen and oxygen atoms in the water in the original environment is determined; Based on the results of dynamic simulation of the surface system model of the tight reservoir in the CO2 environment under the NPT ensemble, the radial distribution function of the double-layer ions in the formation water and the hydrogen and oxygen atoms in the water in the CO2 environment is determined; The radial distribution function of the double-layer ions in the formation water and the hydrogen and oxygen atoms in the water in the original environment and the CO2 environment is used to characterize the intensity of the double-layer ion hydration on the surface of the tight reservoir after carbon dioxide injection; Preferably, based on the results of dynamic simulation under the NPT ensemble of the surface system model of the original environment tight reservoir, the radial distribution function of the double layer ions and the hydrogen and oxygen atoms in the formation water under the original environment is determined to include: Based on the NPT structure file obtained by dynamic simulation of the surface system model of the dense reservoir in the original environment under the NPT ensemble, the radial distribution function of the double-layer ions and hydrogen and oxygen atoms in the formation water in the original environment was statistically analyzed using the Radial distribution function of the Forcite Analysis module of Materials Studio software. Preferably, based on the results of dynamic simulation under the NPT ensemble of the CO2 environment tight reservoir surface system model, determining the radial distribution function of double-layer ions and hydrogen and oxygen atoms in formation water under the CO2 environment includes: Based on the NPT structure file obtained by dynamic simulation of the surface system model of the tight reservoir in the CO2 environment under the NPT ensemble, the radial distribution function of the double-layer ions and the hydrogen and oxygen atoms in the formation water under the CO2 environment was statistically analyzed using the Radial distribution function of the Forcite Analysis module of the Materials Studio software.

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