Method for analyzing core occurrence state in oil reservoir flooding process

Abstract

This invention provides an analytical method for the core occurrence state during reservoir oil displacement. The method includes using Material Studio and LAMMPS software to analyze the core occurrence state at different stages of reservoir oil displacement. The core occurrence state includes at least two combinations of oil-phase, water-phase, or gas-phase occurrence states. The analytical method provided by this invention can clearly and intuitively display the oil / gas / water occurrence states at each stage of CO2 oil displacement; and can further explore the influence of changes in reservoir conditions such as temperature, pressure, and pore structure on the core occurrence state in micro- and nano-scale reservoirs, investigating the effects of environmental factors and differences in pore type on the core occurrence state at the micro- and nano-scale.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field shale oil development and production technology, and relates to an analysis method for the core occurrence state during reservoir oil displacement, specifically an analysis method for the oil / water / gas occurrence state during reservoir oil displacement. Background Technology

[0002] Petroleum, considered the "lifeblood of industry," is closely linked to economic development, social progress, and energy security. With socio-economic development, humanity's dependence on coal and oil continues to increase. However, existing oil reserves are declining, therefore, further research is needed to improve oil recovery rates in reservoirs.

[0003] Currently, the remaining reserves of conventional oil and gas resources are decreasing, and the exploitation of unconventional oil and gas resources such as tight oil and shale oil, with their huge reserves, has become a focus of attention for scholars and the oilfield production industry. The characteristics of shale, such as its well-developed micro- and nanopores, extremely low permeability, and porosity, make shale unsuitable for waterflooding. CO2, however, can reduce the viscosity and interfacial tension of crude oil, making it an effective method to improve the recovery rate of unconventional shale oil reservoirs. At the same time, as a greenhouse gas, CO2's impact on the environment is becoming increasingly significant. Injecting CO2 into oil and gas reservoirs can effectively improve crude oil recovery while achieving emission reduction, making it a project with both economic and social benefits.

[0004] As CO2 oil recovery development continues, the distribution patterns and phase characteristics of oil, gas, and water phases within the reservoir pore space change accordingly, leading to more complex occurrence states of these phases and impacting oil displacement efficiency to some extent. Therefore, studying the occurrence state is fundamental to clarifying the characteristics of micro- and nano-scale reservoirs and developing targeted gas injection enhancement strategies.

[0005] Recent nuclear magnetic resonance (NMR) experiments have revealed the fluid occurrence states within pore throats: macropores are primarily filled with free flow and capillary-bound flow; mesopores are dominated by bound flow with some free flow and electrochemically bound flow; and micropores are primarily filled with electrochemically bound flow. This provides support for a clear understanding of the crude oil occurrence states within micro- and nano-pores. However, shale oil exists in the nanoscale pores of tight reservoirs, making precise analysis at the nanoscale difficult using traditional experimental methods. Molecular dynamics (MD) simulations, as an effective means of studying fluid-solid interface behavior, can observe microscopic phenomena at the molecular scale, avoiding the multi-factor problems encountered in experiments.

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

[0007] To address the shortcomings of existing technologies, the present invention aims to provide an analytical method for the core occurrence state during reservoir oil displacement. This analytical method can clearly and intuitively display the oil / gas / water occurrence state at each stage of CO2 oil displacement; and can further explore the influence of changes in reservoir conditions such as temperature, pressure, and pore structure on the core occurrence state in micro- and nano-scale reservoirs, investigating the effects of environmental factors and differences in pore type on the core occurrence state.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] This invention provides a method for analyzing the core occurrence state during reservoir oil displacement, the method comprising:

[0010] Material Studio and LAMMPS software were used to analyze the occurrence state of cores during different stages of oil displacement in reservoirs;

[0011] The core occurrence state includes a combination of at least two of the following: oil phase occurrence state, water phase occurrence state, or gas phase occurrence state. Typical but not limited combinations include a combination of oil phase occurrence state and gas phase occurrence state, or a combination of oil phase occurrence state, water phase occurrence state, and gas phase occurrence state.

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

[0013] As a preferred embodiment of the present invention, the analysis method includes the following steps:

[0014] (1) Construct a reservoir shale pore structure model using Materials Studio software;

[0015] (2) Perform 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 steady-state distribution of oil / gas / water three phases;

[0016] (3) Based on step (2), perform non-equilibrium molecular dynamics (NEMD) simulation to obtain the CO2 oil displacement process;

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

[0018] This invention utilizes Material Studio software to construct the pore structure of shale, and then simulates the specific process of CO2 flooding using equilibrium molecular dynamics (EMD) and non-equilibrium molecular dynamics (NEMD) simulations. Those skilled in the art can analyze the occurrence states of oil, gas, and water phases at various stages and even at different times based on the flooding process presented by the software. The gas phase occurrence state described in this invention refers to the occurrence state of CO2, and the oil phase occurrence state refers to the occurrence state of alkane organic compounds, specifically divided into adsorbed and free states.

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

[0020] The molecular structures of silica, water, CO2, and oil phases were constructed and optimized using Material Studio software, with the α-cristobalite crystal planes along... Crystallographic cutting and hydrophilic manipulation of the silica molecular structure yielded a hydrophilic reservoir shale pore model.

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

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

[0023] Preferably, the alkane organic compound includes any one or a combination of at least two of hexane, octane, decane or pentadecane. Typical but non-limiting combinations include combinations of octane and decane, combinations of octane and hexane, combinations of octane, decane and hexane, or combinations 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 embodiment of the present invention, the hydrophilic operation includes: attaching a hydrogen atom to each oxygen atom on the silicon dioxide molecular structure to achieve surface hydroxylation.

[0026] This invention achieves hydrophilicity in reservoir shale pore models by hydroxylating silica surfaces, making the constructed walls more consistent with the actual characteristics of shale.

[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 equilibrium molecular dynamics (EMD) simulation in step (2) uses the NVT ensemble.

[0029] Preferably, the NVT ensemble is configured with The temperature of the thermostat is 320~350K, for example, it can be 320K, 325K, 330K, 335K, 340K, 345K or 350K, but is not limited to the listed values. Other values ​​within the range that are not listed are also applicable.

[0030] Preferably, the NVT ensemble is configured with The pressure of the thermostat is 15~25MPa, for example, it can be 15MPa, 17MPa, 19MPa, 21MPa, 23MPa or 25MPa, but is not limited to the listed values. Other values ​​not listed within the range are also applicable.

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

[0032] This invention uses equilibrium molecular dynamics (EMD) simulation to optimize the initial state of the oil and water phases in shale pores, and minimizes the energy of the oil, water and gas phases respectively to obtain 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 displacement process in step (3) is 10~35MPa, for example, it can be 10MPa, 13MPa, 16MPa, 19MPa, 22MPa, 25MPa, 28MPa, 31MPa or 34MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the CO2 displacement temperature during the CO2 oil displacement 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. Other unlisted values ​​within the 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. Other unlisted values ​​within the range are also applicable.

[0037] It is worth noting that this invention simulates shale reservoirs in unconventional oil fields. The unique properties of shale rock, with its low porosity and permeability, make it difficult for water to flow within the reservoir. Therefore, the water cut in shale oil reservoirs is relatively low. Typically, the water cut in unconventional shale oil reservoirs can be as low as 5% or even lower. Furthermore, there is a waterless production period in the reservoir, during which the water cut is less than 2%, which can be considered as 0% water-free. When the water cut is low, the influence of water can be ignored in the simulation, and only the occurrence state of the crude oil is investigated. The high water cut scenario in this invention simulates the presence of a 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: using parameters of each displacement period during the CO2 flooding process to analyze the occurrence state of the core.

[0039] As a preferred embodiment of the present invention, the parameters include any one or at least a combination of two of density, interaction energy, or residence time. 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 oil phase molecules in the adsorption layer.

[0041] It is worth noting that for conventional crack pores, the existence form of each phase in the pore is mainly determined by 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 interconnected pores, molecular density images cannot intuitively show the oil and water films 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 embodiment of the present invention, the method for analyzing the core occurrence state during reservoir oil displacement includes the following steps:

[0043] (1) Construct a reservoir shale pore structure model using Material Studio software;

[0044] Using Material Studio software, the molecular structures of silica, water, CO2, and octane were constructed and optimized, with the α-cristobalite crystal planes along... Crystallographic directional cutting was used to achieve surface hydroxylation by attaching hydrogen atoms to each oxygen atom on the surface, thus establishing a hydrophilic micro / nano reservoir shale pore model.

[0045] (2) Perform equilibrium molecular dynamics (EMD) simulation on the micro-nano reservoir shale pore structure model obtained in step (1), optimize the initial state of the oil and water phases in the pores, minimize the energy of oil, water and CO2 respectively, and obtain the micro-nano reservoir shale pore structure with steady-state distribution of oil / gas / water three phases.

[0046] The EMD simulation was performed using LAMMPS software, utilizing the NVT ensemble, and was set to... The temperature of the thermostat is 320~350K, and the pressure is 15~25MPa;

[0047] (3) Based on step (2), perform non-equilibrium molecular dynamics (NEMD) simulation and use LAMMPS software to simulate the CO2 oil displacement process;

[0048] During the CO2 flooding process, the CO2 displacement pressure is 10~35MPa, the temperature is 320~350K, and the water cut in the reservoir is 0%-80%.

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

[0050] The occurrence state analysis refers to the analysis of parameters during each displacement stage in the CO2 oil displacement process; the parameters include any one or a combination of at least two of density, interaction energy, or residence time.

[0051] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all 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 core occurrence state during reservoir oil displacement provided by the present invention can be used to analyze 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 core occurrence state during reservoir oil displacement provided by the present invention can determine the influence of a single factor on the oil / gas / water occurrence characteristics during the oil displacement process;

[0055] (3) The present invention can clarify the dynamic change process of the occurrence state of each phase in the pores of each stage of the CO2 displacement process by the change of the occurrence state of each phase in different stages.

[0056] (4) The method for analyzing the core occurrence state during reservoir flooding provided by this invention is the basis for clarifying the characteristics of micro-nano-sized reservoirs and for developing gas injection enhancement strategies. Attached Figure Description

[0057] Figure 1 This is the density distribution diagram provided in Embodiment 1 of the present invention;

[0058] Figure 2 This is an oil / gas density image provided in Embodiment 1 of the present invention;

[0059] Figure 3 This is a schematic diagram of the interaction between oil, gas, and wall surface provided in Embodiment 1 of the present invention;

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

[0061] Figure 5 This is a two-dimensional density map provided in Embodiment 3 of the present invention;

[0062] Figure 6 This is a residence time analysis diagram provided in Embodiment 3 of the present invention. Detailed Implementation

[0063] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0064] Example 1

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

[0066] (1) Construct a reservoir shale pore structure model using Material Studio software;

[0067] Using Material Studio software, the molecular structures of silica, CO2, and octane were constructed and optimized, and the α-cristobalite crystal planes were aligned along... Crystallographic directional cutting was used to achieve surface hydroxylation by attaching hydrogen atoms to each oxygen atom on the surface, thus establishing a hydrophilic micro / nano reservoir shale pore model.

[0068] The reservoir shale pore structure model is a single-pore shale fracture with a pore length of 17 nm and a width of 6 nm.

[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. Energy minimization is performed on oil and CO2 respectively to obtain the micro / nano reservoir shale pore structure with steady-state distribution of oil / gas two phases. The density distribution of oil in the optimized system is analyzed to obtain the following results: Figure 1 The density distribution diagram shown;

[0070] The EMD simulation was performed using LAMMPS software, utilizing the NVT ensemble, and was set to... The thermostat has a temperature of 333 K and a pressure of 20 MPa.

[0071] (3) Based on step (2), perform non-equilibrium molecular dynamics (NEMD) simulation and use LAMMPS software to simulate the CO2 oil displacement process;

[0072] During the CO2 flooding process, the CO2 displacement pressure was 25 MPa, the temperature was 333 K, and the reservoir water cut was 0%.

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

[0074] The assignment state analysis includes: drawing as shown in the figure. Figure 2 The oil / gas density image shown is as follows: Figure 3 The diagram shows the interaction between oil / gas / wall. Table 1 provides the CO2 / oil boundary layer thickness at different displacement times.

[0075] This embodiment simulates a micro / nano reservoir shale pore structure model that does not consider water content, but only the presence of an oil phase. This embodiment uses... Figure 1 It can clearly show the distribution of various components in the early stage of displacement and the state of oil phase in the pores. It can be analyzed that an ordered and dense three-layer oil film adsorption layer is formed near the wall, with each adsorption layer on each side being about 5 Å thick and the middle being in a free state.

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

[0077] This embodiment is illustrated by... Figure 3 Table 1 shows the changes in the adsorption layer during CO2 displacement. As the displacement process proceeds, E oil-CO2The gradual increase in Eoil-CO2 provides 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 gradually become miscible. oil-wall Gradually decrease, E CO2-wall The gradual increase indicates that CO2 is adsorbed on the reservoir surface while oil molecules detach from the wall and enter the CO2 to be dissolved, and the adsorbed 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 core occurrence state during reservoir oil displacement, the method comprising the following steps:

[0082] (1) Construct a reservoir shale pore structure model using Material Studio software;

[0083] Using Material Studio software, the molecular structures of silica, water, CO2, and octane were constructed and optimized, with the α-cristobalite crystal planes along... Crystallographic directional cutting was used to achieve surface hydroxylation by attaching hydrogen atoms to each oxygen atom on the surface, thus establishing a hydrophilic micro / nano reservoir shale pore model.

[0084] Specifically, the reservoir shale pore structure model is a high water-cut oil reservoir, taking into account the effects of pore water cut, salinity, and ion type, and using Na... + and Ca 2+ Determine the degree of mineralization;

[0085] (2) Perform equilibrium molecular dynamics (EMD) simulation on the micro-nano reservoir shale pore structure model obtained in step (1), optimize the initial state of the oil and water phases in the pores, minimize the energy of oil, water and CO2 respectively, and obtain the micro-nano reservoir shale pore structure with steady-state distribution of oil / gas / water three phases.

[0086] The EMD simulation was performed using LAMMPS software, utilizing the NVT ensemble, and was set to... The thermostat has a temperature of 333K, a pressure of 20MPa, and a water content of 60%.

[0087] (3) Based on step (2), perform non-equilibrium molecular dynamics (NEMD) simulation and use LAMMPS software to simulate the CO2 oil displacement process;

[0088] During the CO2 oil displacement process, the CO2 displacement pressure was 25 MPa and the temperature was 333 K.

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

[0090] The assignment state analysis includes: providing, for example... Figure 4 The diagram showing the wetting angle analysis in water-containing / ion-containing pores illustrates that the presence of ions slows down changes in the occurrence state of water clusters, while the presence of Ca... 2+ At that time, due to the higher valence state, the cohesive force of water clusters is stronger, and the dispersion of water clusters is better than that containing Na. + Time is slow.

[0091] This embodiment is illustrated by... Figure 4 The effects of water and salt on the properties of multiphase interfaces can be analyzed.

[0092] Compared to Example 1, this example adds water molecules to the shale pores, with a water content of 60%. The analysis method in Example 1 can also be used to determine the oil / water / gas occurrence state in this example.

[0093] Example 3

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

[0095] (1) Construct a reservoir shale pore structure model using Material Studio software;

[0096] Using Material Studio software, the molecular structures of silica, water, CO2, and octane were constructed and optimized, with the α-cristobalite crystal planes along... Crystallographic directional cutting was used to achieve surface hydroxylation by attaching hydrogen atoms to each oxygen atom on the surface, thus establishing a hydrophilic micro / nano reservoir shale pore model.

[0097] The pore structure in the reservoir shale pore structure model is a wedge-shaped pore;

[0098] (2) Perform equilibrium molecular dynamics (EMD) simulation on the micro-nano reservoir shale pore structure model obtained in step (1), optimize the initial state of the oil and water phases in the pores, minimize the energy of oil, water and CO2 respectively, and obtain the micro-nano reservoir shale pore structure with steady-state distribution of oil / gas / water three phases.

[0099] The EMD simulation was performed using LAMMPS software, utilizing the NVT ensemble, and was set to... The thermostat has a temperature of 333 K and a pressure of 20 MPa.

[0100] (3) Based on step (2), perform non-equilibrium molecular dynamics (NEMD) simulation and use LAMMPS software to simulate the CO2 oil displacement process;

[0101] During the CO2 oil displacement process, the CO2 displacement pressure was 25 MPa and the temperature was 333 K.

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

[0103] The assignment state analysis is as follows: drawing as shown Figure 5 The two-dimensional density map shown, and as Figure 6 The diagram shows the residence time analysis.

[0104] This embodiment is illustrated by... Figure 5 The adsorption and stripping processes of oil / gas / water during the displacement can be clearly observed; this embodiment uses... Figure 6 The ease of oil phase stripping and the strength of adsorption performance can be obtained, further revealing the oil occurrence state during the displacement process.

[0105] Example 4

[0106] This embodiment provides an analytical method for the core occurrence state during reservoir oil displacement. The only difference between this analytical method and that of Embodiment 1 is:

[0107] This embodiment will describe step (2) as follows. The temperature of the thermostat was changed to 300K and the pressure to 10MPa.

[0108] Example 5

[0109] This embodiment provides an analytical method for the core occurrence state during reservoir oil displacement. The only difference between this analytical method and that of Embodiment 1 is:

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

[0111] Example 6

[0112] This embodiment provides an analytical method for the core occurrence state during reservoir oil displacement. The only difference between this analytical method and that of Embodiment 1 is:

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

[0114] Example 1 of this invention provides an analysis process for the oil / gas occurrence state during CO2 displacement in a single pore of shale fractures; Example 2 provides an analysis process for the core occurrence state during CO2 displacement in a water-bearing single pore of shale fractures; Example 3 provides an analysis process for the core occurrence state during CO2 displacement in different reservoir environments; Examples 4-5 provide the influence 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 are more easily displaced, while under low temperature or high pressure environments, they can be more tightly adsorbed onto the reservoir wall.

[0115] In summary, the analytical method provided by this invention can clearly and intuitively display the occurrence state of oil / gas / water at each stage of CO2 flooding; and can further explore the influence of changes in reservoir conditions such as temperature, pressure, and pore structure on the occurrence state of cores in micro-nano scale reservoirs.

[0116] The applicant declares that the detailed structural features of the present invention are illustrated through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components selected in the present invention, additions 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 detailed process flow of this invention is illustrated by the above embodiments, but this invention is not limited to the above detailed process flow, that is, it does not mean that this invention must rely on the above detailed process flow to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the product of this invention, addition of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of this invention.

Claims

1. A method for analyzing the core occurrence state during reservoir oil displacement, characterized in that, The analytical method includes: The occurrence state of core samples during different stages of oil displacement in reservoirs was analyzed using Material Studio and LAMMPS software. The specific steps included: (1) Construct a reservoir shale pore structure model using Material Studio software; The construction includes: using Material Studio software to construct and optimize the molecular structures of silica, water, CO2, and oil phases, and along the α-cristobalite crystal planes. Crystallographic cutting and hydrophilic manipulation of the silica molecular structure yielded a hydrophilic reservoir shale pore model. The hydrophilic operation includes: attaching a hydrogen atom to each oxygen atom in the silicon dioxide molecular structure to achieve surface hydroxylation; (2) Perform equilibrium molecular dynamics simulation on the micro-nano reservoir shale pore structure model obtained in step (1), optimize the initial state of oil and water phases in the pores, minimize the energy of oil, water and CO2 respectively, and obtain the micro-nano reservoir shale pore structure with steady-state distribution of oil / gas / water three phases; The equilibrium molecular dynamics simulations were performed using LAMMPS software; the NVT ensemble was used in the equilibrium molecular dynamics simulations. (3) Based on step (2), perform non-equilibrium molecular dynamics simulation to obtain the CO2 oil displacement process; (4) Analyze the occurrence state of the core obtained in step (3) during the CO2 flooding process; The occurrence state of the core includes at least two of the following: oil phase occurrence state, water phase occurrence state, or gas phase occurrence state.

2. The analytical method according to claim 1, characterized in that, The oil phase molecules include alkane organic compounds.

3. The analytical method according to claim 2, characterized in that, The alkane organic compound includes any one or a combination of at least two of hexane, octane, decane, or pentadecane.

4. The analytical method according to claim 1, characterized in that, The reservoir shale pore structure model in step (1) includes a micro-nano reservoir shale pore structure model.

5. The analytical method according to claim 1, characterized in that, The NVT ensemble is set The temperature of the thermostat is 320~350K.

6. The analytical method according to claim 1, characterized in that, The NVT ensemble is set The pressure of the thermostat is 15~25MPa.

7. The analytical method according to claim 1, characterized in that, The non-equilibrium molecular dynamics simulation described in step (3) was performed using LAMMPS software.

8. The analytical method according to claim 1, characterized in that, In step (3), the CO2 displacement pressure during the CO2 oil displacement process is 10~35MPa.

9. The analytical method according to claim 1, characterized in that, In step (3), the CO2 displacement temperature during the CO2 oil displacement process is 320~350K.

10. The analytical method according to claim 1, characterized in that, In step (3), the water content in the reservoir during the CO2 flooding process is 0-80%.

11. The analytical method according to claim 1, characterized in that, The occurrence state analysis in step (4) includes: using parameters from each displacement stage during the CO2 flooding process to analyze the occurrence state of the core.

12. The analytical method according to claim 11, characterized in that, The parameters include any one or a combination of at least two of density, interaction energy, or residence time.

13. The analytical method according to claim 12, characterized in that, The residence time is the residence time of oil phase molecules in the adsorption layer.

Images