Analysis method for rock core occurrence state in oil displacement process of oil reservoir

Abstract

The invention provides a method for analyzing the occurrence state of a rock core in the oil displacement process of an oil reservoir. The analysis method comprises the following steps: analyzing the occurrence state of the rock core in different oil displacement stages of the oil reservoir by utilizing Material Studio software and LAMMPS software; the rock core occurrence state comprises a combination of at least two of an oil phase occurrence state, a water phase occurrence state and a gas phase occurrence state in the rock core. According to the analysis method provided by the invention, the occurrence state of oil / gas / water in each stage in the CO2 oil displacement process can be clearly and intuitively displayed; change of reservoir conditions such as temperature, pressure intensity and a gap structure can be further explored, and the influence rule of environmental factors and pore type differences on the occurrence state of the core in the micro-nano-scale oil reservoir can be explored.

Description

Technical Field

[0001] The invention belongs to the technical field of shale oil development and production in oil and gas fields, and relates to a method for analyzing the occurrence state of a core during oil reservoir displacement, and specifically to a method for analyzing the occurrence state of oil / water / gas during oil reservoir displacement. Background Art

[0002] As the "blood of industry", oil is closely related to economic development, social progress and energy security. With the development of social economy, human dependence on coal and oil is still increasing. However, the oil reserves in existing oil fields are decreasing. Therefore, more research is needed to improve the recovery rate of oil in oil reservoirs.

[0003] At present, the remaining reserves of conventional oil and gas resources are decreasing day by day, and the exploitation of unconventional oil and gas resources such as tight oil and shale oil with huge reserves has begun to become the focus of scholars and oilfield production. Shale is not suitable for water flooding due to its characteristics such as the development of micro-nano pores, extremely low permeability and porosity. CO2 can reduce the viscosity and interfacial tension of crude oil, which is an effective way to improve the recovery rate of unconventional shale reservoirs. At the same time, the impact of CO2 as a greenhouse gas on the environment is becoming increasingly significant. Injecting CO2 into oil and gas reservoirs can not only effectively improve the recovery rate of crude oil but also achieve emission reduction effects. It is a win-win project for economic and social benefits.

[0004] With the continuous deepening of CO2 oil recovery, the distribution and phase characteristics of oil, gas and water in the pore space of the reservoir have changed accordingly. The occurrence state of oil, gas and water has become more complicated and has affected the oil recovery efficiency to a certain extent. Therefore, the study of the occurrence state is the basis for clarifying the characteristics of micro-nanoscale reservoirs and developing targeted gas injection strategies to increase oil production.

[0005] In recent years, nuclear magnetic resonance experiments have shown the state of fluid in pore throats: large pores are mainly filled with free flow and bound flow in capillaries, medium pores are mainly occupied by bound flow with a small amount of free flow and electrochemical bound flow, and micropores are mainly electrochemical bound flow, which provides support for a clear understanding of the state of crude oil in micro-nano pores. However, shale oil exists in nano-scale pores in tight reservoirs, and traditional experimental methods are difficult to accurately analyze at the nanoscale level. Molecular dynamics (MD) simulation method is an effective means to study the behavior of fluid-solid interfaces. It can observe microscopic phenomena at the molecular scale and avoid multi-factor problems in the experimental process.

[0006] Therefore, it is necessary to propose an analysis method, using the molecular dynamics simulation method to explore the influence of the storage and displacement environment on oil and gas displacement from a microscopic perspective, and by changing reservoir conditions such as temperature, pressure, and pore structure, the oil / gas / water storage state of CO2 in the process of oil displacement in micro-nano reservoirs is analyzed and summarized from the perspectives of density distribution and adsorption characteristics. Summary of the invention

[0007] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for analyzing the occurrence state of cores in the process of oil recovery. The analysis method can clearly and intuitively display the occurrence state of oil / gas / water at each stage in the CO2 recovery process; and can further explore the influence of environmental factors and pore type differences on the occurrence state of cores in micro-nano scale oil reservoirs by changing reservoir conditions such as temperature, pressure, and pore structure.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for analyzing the occurrence state of a core during oil recovery in an oil reservoir, the method comprising:

[0010] Material Studio and LAMMPS software were used to analyze the occurrence state of cores in different reservoir flooding stages;

[0011] The core occurrence state includes a combination of at least two of the oil phase occurrence state, water phase occurrence state or gas phase occurrence state in the core, and a typical but non-limiting combination includes a combination of the oil phase occurrence state and the gas phase occurrence state, or a combination of the oil phase occurrence state, the water phase occurrence state and the gas phase occurrence state.

[0012] The LAMMPS software described in the present invention is Large-scale Atomic / Molecular Massively ParallelSimulator software.

[0013] As a preferred technical solution of the present invention, the analysis method comprises the following steps:

[0014] (1) Use Materials Studio software to construct a reservoir shale pore structure model;

[0015] (2) performing equilibrium molecular dynamics (EMD) simulation on the micro-nano reservoir shale pore structure model obtained in step (1) to obtain the micro-nano reservoir shale pore structure with oil / gas / water three-phase steady-state distribution;

[0016] (3) performing non-equilibrium molecular dynamics (NEMD) simulation based on step (2) to simulate the CO2 flooding process;

[0017] (4) Analyze the occurrence state of the core obtained during the CO2 oil recovery process in step (3).

[0018] The present invention constructs the shale pore structure by using Material Studio software, and then simulates the specific process of CO2 oil displacement by equilibrium molecular dynamics (EMD) simulation and non-equilibrium molecular dynamics (NEMD) simulation methods. Those skilled in the art can analyze the occurrence states of oil, gas, and water phases at each stage or even at each moment according to the oil displacement process presented by the software. The gas phase occurrence state of the present invention is the occurrence state of CO2, and the oil phase occurrence state is the occurrence state of alkane organic compounds, which is specifically divided into adsorbed state and free state.

[0019] As a preferred technical solution of the present invention, the construction in step (1) includes:

[0020] Material Studio software was used to construct and optimize the molecular structures of silicon dioxide, water, CO2, and oil phases, and the α-quartz crystal planes were aligned along the The crystallographic direction is cut, and the silica molecular structure is subjected to hydrophilic manipulation to obtain a hydrophilic reservoir shale pore model.

[0021] It is worth noting that the present invention selects silicon dioxide as a typical mineral component and constructs a reservoir shale pore model based on the silicon dioxide structure. More specifically, the present invention selects the silicon dioxide surface structure as a benchmark for simulation analysis.

[0022] Preferably, the oil phase molecules include alkane organic compounds.

[0023] Preferably, the alkane organic compound comprises any one of hexane, octane, decane or pentadecane or a combination of at least two thereof, and typical but non-limiting combinations include a combination of octane and decane, a combination of octane and hexane, a combination of octane, decane and hexane, or a combination of octane, decane, hexane and pentadecane.

[0024] Preferably, the reservoir shale pore structure model in step (1) includes a micro-nano reservoir shale pore structure model.

[0025] As a preferred technical solution of the present invention, the hydrophilic operation includes: connecting a hydrogen atom to each oxygen atom on the silicon dioxide molecular structure to achieve surface hydroxylation.

[0026] The present invention realizes the hydrophilicity of the reservoir shale pore model by hydroxylation of the silicon dioxide surface, so that the constructed wall surface is more consistent with the shale characteristics in actual conditions.

[0027] As a preferred technical solution of the present invention, the equilibrium molecular dynamics (EMD) simulation in step (2) is performed using LAMMPS.

[0028] Preferably, the NVT ensemble is used in the equilibrium molecular dynamics (EMD) simulation in step (2).

[0029] Preferably, the temperature of the Nosé-Hoover thermostat in the NVT ensemble is set to 320-350K, for example, it can be 320K, 325K, 330K, 335K, 340K, 345K or 350K, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the pressure of the Nosé-Hoover thermostat in the NVT ensemble is set at 15 to 25 MPa, for example, 15 MPa, 17 MPa, 19 MPa, 21 MPa, 23 MPa or 25 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] As a preferred technical solution of the present invention, the end point of the equilibrium molecular dynamics (EMD) simulation is: energy minimization of the oil phase, the water phase and the gas phase respectively.

[0032] The present invention uses equilibrium molecular dynamics (EMD) simulation to optimize the initial states of oil and water phases in shale pores, minimizes the energy of the oil phase, water phase and gas phase respectively, and obtains the basic environment for CO2 flooding.

[0033] As a preferred technical solution of the present invention, the non-equilibrium molecular dynamics (NEMD) simulation in step (3) is performed using LAMMPS software.

[0034] As a preferred technical solution of the present invention, the CO2 displacement pressure in the CO2 oil recovery process in step (3) is 10 to 35 MPa, for example, it can be 10 MPa, 13 MPa, 16 MPa, 19 MPa, 22 MPa, 25 MPa, 28 MPa, 31 MPa or 34 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] Preferably, the CO2 displacement temperature during the CO2 oil recovery process in step (3) is 320-350K, for example, it can be 320K, 325K, 330K, 335K, 340K, 345K or 350K, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] Preferably, the water content in the reservoir during the CO2 flooding process in step (3) is 0-80%, for example, it can be 0%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] It is worth noting that the present invention simulates the shale reservoir in the unconventional oil reservoir. The special properties of shale rock, its porosity and permeability are very low, which makes it difficult for water to flow in the reservoir. Therefore, the water content in the shale reservoir is relatively low. Normally, the water content of unconventional shale reservoirs can be as low as 5% or lower. And there is a water-free production period in the reservoir, and the water content at this time is less than 2%, which can be regarded as 0% water-free. When the water content is low, the influence of water can be ignored during the simulation, and only the occurrence state of crude oil is explored. The high water content in the present invention is to simulate the large amount of water in the reservoir after hydraulic fracturing.

[0038] As a preferred technical solution of the present invention, the occurrence state analysis in step (4) includes: analyzing the occurrence state of the core using parameters at each displacement period during the CO2 flooding process.

[0039] As a preferred technical solution of the present invention, the parameters include any one of density, interaction energy or residence time, or a combination of at least two of them. Typical but non-limiting combinations include a combination of density and interaction energy, a combination of density and residence time, a combination of interaction energy and residence time, or a combination of density, interaction energy and residence time.

[0040] Preferably, the residence time is the residence time of the oil phase molecules in the adsorption layer.

[0041] It is worth mentioning that for conventional fracture pores, the existence form of each phase in the pore is mainly clarified through parameters such as molecular density distribution, interaction energy, and molecular residence time in the adsorption layer; for irregular pore structures such as wedge-shaped and connected pores, the molecular density image cannot intuitively display the adsorption layers such as oil film and water film formed by oil and water molecules near the wall. Therefore, a two-dimensional density map is drawn to more intuitively observe the adsorption state and occurrence state of each phase.

[0042] As a preferred technical solution of the present invention, the method for analyzing the core occurrence state during oil reservoir displacement comprises the following steps:

[0043] (1) Use Material Studio software to construct a reservoir shale pore structure model;

[0044] Material Studio software was used to construct and optimize the molecular structures of silicon dioxide, water, CO2, and octane, and the α-quartz crystal plane was parallel to the Crystallographically oriented cutting, surface hydroxylation is achieved by connecting hydrogen atoms to every oxygen atom on the surface, and a hydrophilic micro-nano reservoir shale pore model is established;

[0045] (2) performing equilibrium molecular dynamics (EMD) simulation on the micro-nano reservoir shale pore structure model obtained in step (1), optimizing the initial states of the oil and water phases in the pores, minimizing the energy of oil, water and CO2 respectively, and obtaining the micro-nano reservoir shale pore structure with a steady-state distribution of oil / gas / water three phases;

[0046] The EMD simulation was performed using LAMMPS software, using the NVT ensemble, and setting the temperature of the Nosé-Hoover thermostat to 320-350K and the pressure to 15-25MPa;

[0047] (3) Based on step (2), non-equilibrium molecular dynamics (NEMD) simulation is performed, and the CO2 flooding process is simulated using LAMMPS software;

[0048] Among them, during the CO2 flooding process, the CO2 displacement pressure is 10-35MPa, the temperature is 320-350K, and the water content in the reservoir is 0%-80%;

[0049] (4) analyzing the occurrence state of the core obtained in the CO2 flooding process in step (3);

[0050] Wherein, the occurrence state analysis is: analyzing the parameters of each displacement period in the CO2 flooding process; the parameters include any one of density, interaction energy or residence time, or a combination of at least two of them.

[0051] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] (1) The method for analyzing the occurrence state of the core during oil recovery provided by the present invention can be analyzed at the nanoscale level which is difficult to analyze by traditional experimental methods, and the method provided by the present invention is applicable to various reservoir conditions;

[0054] (2) The method for analyzing the occurrence state of cores during oil recovery provided by the present invention can determine the influence of a single factor on the occurrence characteristics of oil / gas / water during oil recovery;

[0055] (3) The present invention can clarify the dynamic change process of the occurrence state of each phase, such as the accumulation and balance of each phase in the pores at each stage of the displacement through the change of the occurrence state of each phase at different stages of the CO2 flooding process;

[0056] (4) The method for analyzing the occurrence state of cores during oil recovery provided by the present invention is the basis for clarifying the characteristics of micro-nano-sized oil reservoirs and developing gas injection strategies for increased production. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 is a density distribution diagram provided by Example 1 of the present invention;

[0058] Figure 2 is the oil / gas density image provided by Example 1 of the present invention;

[0059] Figure 3 is a schematic diagram of the interaction between oil / gas / wall provided in Example 1 of the present invention;

[0060] Figure 4 This is a diagram of the wetting angle analysis in water-containing / ion-containing pores provided in Example 2 of the present invention;

[0061] Figure 5 A two-dimensional density map provided by Example 3 of the present invention;

[0062] Figure 6 This is a residence time analysis diagram provided for Example 3 of the present invention. DETAILED DESCRIPTION

[0063] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0064] Example 1

[0065] This embodiment provides a method for analyzing the occurrence state of a core during oil recovery in an oil reservoir, the method comprising the following steps:

[0066] (1) Use Material Studio software to construct a reservoir shale pore structure model;

[0067] Material Studio software was used to construct and optimize the molecular structures of silicon dioxide, CO2, and octane, and the α-quartz crystal plane was parallel to the Crystallographically oriented cutting, surface hydroxylation is achieved by connecting hydrogen atoms to every oxygen atom on the surface, and a hydrophilic micro-nano reservoir shale pore model is established;

[0068] The reservoir shale pore structure model is a single-pore shale fracture, and the shale pore length is 17nm and the width is 6nm;

[0069] (2) The micro-nano reservoir shale pore structure model obtained in step (1) is subjected to equilibrium molecular dynamics (EMD) simulation to optimize the initial state of the oil phase in the pores, and the energy of oil and CO2 is minimized to obtain the micro-nano reservoir shale pore structure with steady-state distribution of oil / gas phases, and the density distribution of oil in the optimized system is analyzed to obtain the following: Figure 1 The density distribution map shown;

[0070] The EMD simulation was performed using LAMMPS software, using the NVT ensemble, and setting the temperature of the Nosé-Hoover thermostat to 333 K and the pressure to 20 MPa;

[0071] (3) Based on step (2), non-equilibrium molecular dynamics (NEMD) simulation is performed, and the CO2 flooding process is simulated using LAMMPS software;

[0072] The CO2 displacement pressure during CO2 flooding is 25MPa and the temperature is 333K; the water content in the reservoir is 0%.

[0073] (4) analyzing the occurrence state of oil / gas / water in the CO2 flooding process obtained in step (3);

[0074] Wherein, the occurrence state analysis includes: drawing Figure 2 The oil / gas density image shown, Figure 3 Schematic diagram of the interaction between oil / gas / wall is shown, and Table 1 provides the CO2 / oil boundary layer thickness at different displacement times.

[0075] The micro-nano reservoir shale pore structure model simulated in this embodiment does not consider the water content, but only considers the oil phase. Figure 1 The distribution of various components in the initial stage of displacement and the state of oil phase in the pores can be clearly determined. It can be analyzed that three layers of orderly and dense oil film adsorption layers are formed near the wall, and the thickness of each adsorption layer on each side is about The middle is the free state;

[0076] This embodiment adopts Figure 2 The molecular distribution characteristics of oil / gas at different displacement periods can be analyzed. In the middle and late stages of displacement, the oil adsorption layer near the wall gradually decreases, the overall density of CO2 and the density peak near the wall gradually increase, and the oil molecules are stripped from the wall by CO2 and dissolved into CO2, and are no longer adsorbed on the wall.

[0077] This embodiment adopts Figure 3 As shown in Table 1, the changes in the adsorption layer during the CO2 displacement process can be analyzed. As the displacement process proceeds, E oil-CO2It gradually increases, providing a driving force for the diffusion of oil molecules. The thickness of the CO2 / oil boundary layer in the pores increases with the increase of Eoil-CO2, indicating that CO2 and oil are gradually miscible. oil-wall Gradually decrease, E CO2-wall It gradually increases, indicating that CO2 is adsorbed on the reservoir surface and oil molecules detach from the wall and enter the CO2 to be dissolved, and the adsorption layer is transformed from oil molecules to CO2 molecules.

[0078] Table 1

[0079] Displacement time (ns) <![CDATA[Eoil-CO2(Kcal / mol)]]> <![CDATA[CO2 / oil boundary layer thickness (nm)]]> 0.45 1000 4.2 2.2 2000 7.3 3.3 3000 7.9

[0080] Example 2

[0081] This embodiment provides a method for analyzing the occurrence state of a core during oil recovery in an oil reservoir, the method comprising the following steps:

[0082] (1) Use Material Studio software to construct a reservoir shale pore structure model;

[0083] Material Studio software was used to construct and optimize the molecular structures of silicon dioxide, water, CO2, and octane, and the α-quartz crystal plane was parallel to the Crystallographically oriented cutting, surface hydroxylation is achieved by connecting hydrogen atoms to every oxygen atom on the surface, and a hydrophilic micro-nano reservoir shale pore model is established;

[0084] The reservoir shale pore structure model is specifically a high water-content oil reservoir, taking into account the influence of pore water content, salinity and ion type, and selecting Na + and Ca 2+ Calibration of mineralization;

[0085] (2) performing equilibrium molecular dynamics (EMD) simulation on the micro-nano reservoir shale pore structure model obtained in step (1), optimizing the initial states of the oil and water phases in the pores, minimizing the energy of oil, water and CO2 respectively, and obtaining the micro-nano reservoir shale pore structure with a steady-state distribution of oil / gas / water three phases;

[0086] The EMD simulation was performed using LAMMPS software, using the NVT ensemble, and setting the temperature of the Nosé-Hoover thermostat to 333K, the pressure to 20 MPa, and the water content to 60%;

[0087] (3) Based on step (2), non-equilibrium molecular dynamics (NEMD) simulation is performed, and the CO2 flooding process is simulated using LAMMPS software;

[0088] Among them, the CO2 displacement pressure during CO2 flooding is 25MPa and the temperature is 333K;

[0089] (4) analyzing the occurrence state of oil / gas / water in the CO2 flooding process obtained in step (3);

[0090] Wherein, the occurrence state analysis is: providing Figure 4 The wetting angle analysis diagram of water-containing / ion-containing pores shown in the figure shows that the presence of ions will slow down the change in the occurrence state of water clusters, while the presence of Ca 2+ When the valence state is higher, the cohesion of water clusters is stronger, and the dispersion of water clusters is stronger than that of Na + Time is slow.

[0091] This embodiment adopts Figure 4 The influence of water and salt on the properties of multiphase interfaces can be analyzed.

[0092] Compared with Example 1, water molecules are added to the pores of the shale in this example, and the water content is 60%. The analysis method in Example 1 can also be used for the oil / water / gas storage state in this example.

[0093] Example 3

[0094] This embodiment provides a method for analyzing the occurrence state of a core during oil recovery in an oil reservoir, the method comprising the following steps:

[0095] (1) Use Material Studio software to construct a reservoir shale pore structure model;

[0096] Material Studio software was used to construct and optimize the molecular structures of silicon dioxide, water, CO2, and octane, and the α-quartz crystal plane was parallel to the Crystallographically oriented cutting, surface hydroxylation is achieved by connecting hydrogen atoms to every oxygen atom on the surface, and a hydrophilic micro-nano reservoir shale pore model is established;

[0097] Wherein, the pore structure in the reservoir shale pore structure model is wedge-shaped pores;

[0098] (2) performing equilibrium molecular dynamics (EMD) simulation on the micro-nano reservoir shale pore structure model obtained in step (1), optimizing the initial states of the oil and water phases in the pores, minimizing the energy of oil, water and CO2 respectively, and obtaining the micro-nano reservoir shale pore structure with a steady-state distribution of oil / gas / water three phases;

[0099] The EMD simulation was performed using LAMMPS software, using the NVT ensemble, and setting the temperature of the Nosé-Hoover thermostat to 333 K and the pressure to 20 MPa;

[0100] (3) Based on step (2), non-equilibrium molecular dynamics (NEMD) simulation is performed, and the CO2 flooding process is simulated using LAMMPS software;

[0101] Among them, the CO2 displacement pressure during CO2 flooding is 25MPa and the temperature is 333K;

[0102] (4) analyzing the occurrence state of oil / gas / water in the CO2 flooding process obtained in step (3);

[0103] The occurrence state analysis is as follows: Figure 5 The two-dimensional density map shown in Figure 6 The residence time analysis graph is shown.

[0104] This embodiment adopts Figure 5 The adsorption and stripping process of oil / gas / water during displacement can be clearly observed; Figure 6 The ease of oil phase separation and the strength of adsorption performance can be obtained, further demonstrating the occurrence state of oil during the displacement process.

[0105] Example 4

[0106] This embodiment provides a method for analyzing the state of core occurrence during oil recovery in an oil reservoir. The difference between the analysis method and the embodiment 1 is that:

[0107] In this embodiment, the temperature of the Nosé-Hoover thermostat in step (2) is modified to 300K and the pressure to 10 MPa.

[0108] Example 5

[0109] This embodiment provides a method for analyzing the state of core occurrence during oil recovery in an oil reservoir. The difference between the analysis method and the embodiment 1 is that:

[0110] In this embodiment, the displacement pressure in the CO2 flooding process in step (3) is modified to 10 MPa.

[0111] Example 6

[0112] This embodiment provides a method for analyzing the state of core occurrence during oil recovery in an oil reservoir. The difference between the analysis method and the embodiment 1 is that:

[0113] In this embodiment, the displacement pressure in the CO2 flooding process in step (3) is modified to 40 MPa.

[0114] Example 1 of the present invention provides an analysis process for the oil / gas occurrence state during CO2 displacement in a single pore of a shale fracture, Example 2 provides an analysis process for the core occurrence state during CO2 displacement in a single pore containing water in a shale fracture, and Example 3 provides an analysis process for the core occurrence state during CO2 displacement in different reservoir environments; Examples 4-5 provide the effects of different oil displacement processes on the core occurrence state analysis. Under high temperature or low pressure environments, oil / gas molecules are more likely to enter a free state and be more easily displaced, whereas under low temperature or high pressure environments they can be more tightly adsorbed on the reservoir wall.

[0115] In summary, the analysis method provided by the present invention can clearly and intuitively display the occurrence status of oil / gas / water at each stage in the CO2 flooding process; and can further explore the influence of environmental factors and pore type differences on the occurrence status of cores in micro-nano scale reservoirs by changing reservoir conditions such as temperature, pressure, and pore structure.

[0116] The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed structural features, that is, it does not mean that the present invention must rely on the above-mentioned detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0117] The applicant declares that the present invention illustrates the detailed process flow of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed process flow, that is, it does not mean that the present invention must rely on the above-mentioned detailed process flow to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for analyzing the occurrence state of cores during oil recovery, characterized in that: The analysis method comprises: Material Studio and LAMMPS software were used to analyze the occurrence state of cores in different reservoir flooding stages; The core occurrence state includes a combination of at least two of the oil phase occurrence state, the water phase occurrence state or the gas phase occurrence state in the core.

2. The analysis method according to claim 1, characterized in that The analytical method comprises the following steps: (1) Use Material Studio software to construct a reservoir shale pore structure model; (2) performing equilibrium molecular dynamics (EMD) simulation on the micro-nano reservoir shale pore structure model obtained in step (1) to obtain the micro-nano reservoir shale pore structure with oil / gas / water three-phase steady-state distribution; (3) performing non-equilibrium molecular dynamics (NEMD) simulation based on step (2) to simulate the CO2 flooding process; (4) Analyze the occurrence state of the core obtained during the CO2 oil recovery process in step (3).

3. The analysis method according to claim 2, characterized in that The construction in step (1) includes: Material Studio software was used to construct and optimize the molecular structures of silicon dioxide, water, CO2, and oil phases, and the α-quartz crystal planes were aligned along the Cutting in the crystallographic direction and performing hydrophilic manipulation on the silica molecular structure to obtain a hydrophilic reservoir shale pore model; Preferably, the oil phase molecules include alkane organic compounds; Preferably, the alkane organic compound includes any one or a combination of at least two of hexane, octane, decane or pentadecane; Preferably, the reservoir shale pore structure model in step (1) includes a micro-nano reservoir shale pore structure model.

4. The analysis method according to claim 3, characterized in that The hydrophilic operation includes: connecting a hydrogen atom to each oxygen atom on the silicon dioxide molecular structure to achieve surface hydroxylation.

5. The analysis method according to claim 2, characterized in that The equilibrium molecular dynamics (EMD) simulation in step (2) is performed using LAMMPS software; Preferably, the NVT ensemble is used in the equilibrium molecular dynamics (EMD) simulation in step (2); Preferably, the temperature of the Nosé-Hoover thermostat in the NVT ensemble is set to 320-350K; Preferably, the pressure of the Nosé-Hoover thermostat in the NVT ensemble is set to 15-25 MPa.

6. The analysis method according to claim 2, characterized in that The endpoint of the equilibrium molecular dynamics (EMD) simulation is to minimize the energy of the oil phase, water phase and gas phase respectively.

7. The analysis method according to claim 2, characterized in that The non-equilibrium molecular dynamics (NEMD) simulation in step (3) is performed using LAMMPS software.

8. The analysis method according to claim 2, characterized in that In the CO2 flooding process of step (3), the CO2 displacement pressure is 10-35 MPa; Preferably, the CO2 displacement temperature during the CO2 flooding process in step (3) is 320-350K; Preferably, during the CO2 flooding process in step (3), the water content in the reservoir is 0-80%.

9. The analysis method according to claim 2, characterized in that The occurrence state analysis in step (4) includes: analyzing the occurrence state of the core using parameters at each displacement period during the CO2 flooding process.

10. The analysis method according to claim 9, characterized in that The parameters include any one of density, interaction energy or residence time, or a combination of at least two of them; Preferably, the residence time is the residence time of the oil phase molecules in the adsorption layer.

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