Pore-scale shale oil in-situ modification multi-field coupling numerical simulation method

Abstract

The invention discloses a pore-scale shale oil in-situ modification multi-field coupling numerical simulation method, and relates to the technical field of shale oil exploitation. The system comprises a model hypothesis module, a mathematical model module, a model solving and parameter setting module and a result analysis module. Based on the system, the invention further provides a multi-field coupling numerical simulation method for in-situ upgrading of shale oil with medium and low maturity in pore scale, and the multi-field coupling phenomenon in the in-situ upgrading process of shale oil with medium and low maturity can be accurately simulated through reasonable model assumption and mathematical model construction in combination with an effective numerical solution strategy and parameter setting. According to the method, dynamic changes of various chemical components in the kerogen multistage pyrolysis process and interaction of a chemical field, a temperature field and a seepage field are considered, and the simulation result is more accurate and reliable; in addition, through grid independence verification, a proper grid subdivision scheme is selected, and the calculation efficiency is improved while the calculation precision is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of shale oil exploitation, and particularly to a multi-field coupling numerical simulation method for in-situ upgrading of shale oil at pore scale. Background Art

[0002] As an important part of unconventional oil and gas resources, shale oil is playing an increasingly important role in the global energy pattern. With the gradual depletion of traditional oil and gas resources, the efficient exploitation of unconventional energy sources such as shale oil has become a key way to relieve energy pressure and ensure energy security. The in-situ upgrading technology for medium and low maturity shale oil is regarded as one of the core technologies to improve the exploitation efficiency of shale oil because it can convert low-quality shale oil into light oil and gas that are easier to exploit and utilize in-situ underground. However, the development of this technology faces many challenges, and the accurate understanding and simulation of complex physical and chemical reactions and multi-field coupling phenomena during in-situ upgrading are key problems.

[0003] During the in-situ upgrading process of medium and low maturity shale oil, complex processes in multiple disciplinary fields such as chemistry, thermotics, and fluid mechanics are involved. From a chemical perspective, the thermal decomposition of kerogen is an extremely complex process, including multiple kinetic reactions, involving dynamic changes of multiple chemical components, and there is a competitive relationship in the yields of various products under different heating conditions. At present, although some experimental studies have explored the pyrolysis reaction of kerogen, due to the limitations of experimental conditions, it is difficult to comprehensively and deeply reveal the microscopic mechanism and macroscopic laws during the reaction process.

[0004] In terms of thermotics, the heat transfer during the pyrolysis of kerogen involves two ways: heat conduction and heat convection, and the heat transfer process interacts with the changes of chemical components. On the one hand, the pyrolysis reaction requires heat drive, and chemical reaction heat will be generated during the reaction process, which makes the distribution and change of the temperature field extremely complex; on the other hand, the change of temperature will in turn affect the chemical reaction rate and the physical properties of the fluid, further increasing the complexity of the heat transfer process. Existing heat transfer models have problems such as insufficient accuracy and incomplete consideration of factors when dealing with this complex multi-field coupling problem, and cannot accurately predict the change of the temperature field.

[0005] In the field of fluid mechanics, the flow behavior of products such as heavy oil, light oil, and gas generated by the pyrolysis of kerogen in porous media is also very complex. The flow of these mixed fluids in pores is not only affected by pore structure and fluid properties, but also closely related to pyrolysis reactions and temperature changes. Most traditional seepage models are based on simple assumptions and are difficult to accurately describe the real flow situation of shale oil in complex pore structures, resulting in large errors in the prediction of shale oil production and recovery rate.

[0006] In addition, due to the vast differences in the geological conditions of shale, there are significant differences in its pore structure, permeability, mineral composition and other properties, which further increases the difficulty of simulation. Existing numerical simulation methods and systems often cannot comprehensively consider these complex factors and are difficult to effectively simulate the in-situ upgrading process of shale oil under different geological conditions.

[0007] To sum up, there is currently a lack of effective methods and systems that can comprehensively and accurately simulate the complex physical and chemical reactions and multi-field coupling phenomena during the in-situ upgrading process of medium- to low-maturity shale oil. This not only limits the in-depth understanding of the in-situ upgrading process of medium- to low-maturity shale oil, but also restricts the research and development and optimization of related extraction technologies, resulting in low extraction efficiency and high costs for medium- to low-maturity shale oil. Therefore, developing a method that can accurately simulate the multi-field coupling process of in-situ upgrading of medium- to low-maturity shale oil at the pore scale has important practical significance for promoting the efficient development and utilization of shale oil resources. Summary of the Invention

[0008] The purpose of the present invention is to propose a multi-field coupling numerical simulation method for in-situ upgrading of shale oil at the pore scale to solve the problems raised in the above background technology. The present invention realizes the two-way coupling of the chemical field, temperature field and seepage field and can effectively simulate the in-situ upgrading process of medium- to low-maturity shale oil.

[0009] To achieve the above purpose, the present invention adopts the following technical solutions:

[0010] A multi-field coupling numerical simulation method for in-situ upgrading of shale oil at the pore scale, including a model assumption module, a mathematical model module, a model solution and parameter setting module, and a result analysis module; wherein:

[0011] The model assumption module is used to set the assumption conditions in the simulation process, including ignoring the influence of water, not considering fluid phase change, regarding the pyrolysis products as a mixed fluid phase, using Darcy's law to describe the flow of the mixed fluid, and considering the matrix porous characteristics to be homogeneous and isotropic.

[0012] The mathematical model module includes a chemical field (pyrolysis reaction kinetics) model, a temperature field (heat transfer in porous media) model and a seepage field (fluid flow in porous media) model, and is used to describe the physical and chemical reactions and fluid flow during the in-situ upgrading process of medium- to low-maturity shale oil.

[0013] The model solution and parameter setting module includes a numerical solution strategy, network division, independence verification, and simulation condition and parameter setting, and is used to realize the solution of the model and parameter optimization.

[0014] A result analysis module is used to analyze the yield changes of various products, the mass ratio changes of each fluid component at different temperatures, and the changes of relevant physical parameters during the in-situ upgrading process of medium- and low-maturity shale oil obtained by simulation, so as to evaluate the correctness and effectiveness of the simulation results.

[0015] Preferably, the chemical field (pyrolysis reaction kinetics) model uses multiple thermal decomposition reactions to characterize the decomposition process of kerogen, and calculates the chemical reaction rate constant through the Arrhenius equation, and its formula is expressed as:

[0016]

[0017] Among them, K l represents the chemical reaction rate constant; A l represents the frequency factor; E l represents the reaction activation energy; R g represents the ideal gas constant; T represents the temperature;

[0018] The mass conservation equation is used to describe the mass change of fluid components, and its formula is expressed as:

[0019]

[0020] Among them, represents the porosity; ρ f represents the density of the fluid mixture; w represents the mass fraction; represents the gradient operator; u f represents the velocity vector; j represents the effective diffusion flux; R represents the mass source generated by the chemical reaction; the subscript i represents different fluid components;

[0021] At the same time, the porosity change and effective diffusion flux calculation during the kerogen pyrolysis process are considered, and their formulas are expressed as:

[0022]

[0023] Among them, represents the initial porosity; ρ ker,0 represents the initial mass concentration of kerogen; D represents the diffusion coefficient.

[0024] Preferably, the temperature field (heat transfer in porous media) model couples heat conduction and heat convection, describes the temperature field change through the control equation, uses the mass fraction and density weighting method to characterize the thermal properties of the mixed fluid, and takes into account the chemical reaction heat source. The specific content is as follows:

[0025] The control equation of the temperature field is expressed as:

[0026]

[0027] Among them, C f represents the specific heat capacity at constant pressure; Q represents the heat source; λ t represents the effective thermal conductivity of the porous medium, and its definition is:

[0028]

[0029] Among them, λ s represents the thermal conductivity of shale; λ f represents the thermal conductivity of the mixed fluid; a weighted method that comprehensively considers the mass fraction and density is used to characterize the fluid mixture to describe the dynamic evolution of fluid components during the multi-stage pyrolysis process of kerogen, and its definition is as follows:

[0030]

[0031] In the above formula, (ρC) eff is defined as:

[0032] [[ID=2�]]

[0033] Among them, ρ s represents the shale density; C s represents the specific heat capacity at constant pressure of shale; the specific heat capacity at constant pressure C f of the fluid mixture is calculated by the formula:

[0034]

[0035] The heat source Q includes the external heat source Q in and the chemical reaction heat Q r :

[0036] Q = Q in + Q r

[0037] Among them, the chemical reaction heat Q r is expressed as:

[0038] Q r = ∑ n -K n ΔH n M n

[0039] Among them, K n , ΔH n and M n respectively represent the chemical reaction rate, reaction enthalpy value, and mass concentration of the reactants of the nth pyrolysis reaction.

[0040] Preferably, the seepage field (porous medium flow) model follows Darcy's law to describe the flow of the mixed fluid in the porous medium, uses the Kozeny-Carman relationship to characterize the relationship between porosity and permeability, and satisfies the law of conservation of mass. The specific content is as follows:

[0041] Define the flow of the mixed fluid in the porous medium as:

[0042]

[0043] where k represents the shale permeability; p represents the pressure; μ f represents the viscosity of the fluid mixture, and its calculation formula is:

[0044]

[0045] As the kerogen continues to crack, the porosity of the porous medium gradually increases, which in turn leads to an increase in permeability. The simplified Kozeny-Carman relationship is used to describe the relationship between porosity and permeability:

[0046]

[0047] The fluid flow in the porous medium is governed by the principle of conservation of mass, expressed as:

[0048]

[0049] Preferably, the numerical solution strategy adopts a segregated solution method, automatically adjusts the time step according to the convergence, and sets a finer time step in the initial stage;

[0050] The network division uses a Delaunay triangular network and sets a boundary layer on the surface of the kerogen to achieve grid refinement;

[0051] The independence verification is tested by designing network generation scenarios with different numbers of grids, and the grid division scheme that makes the simulation results stable is selected;

[0052] The simulation conditions and parameter settings include setting the initial porosity, permeability, initial mass concentration of kerogen, heating rate of the simulation area, and other physicochemical parameters of related substances.

[0053] The present invention further protects a numerical simulation method for in-situ upgrading of medium and low maturity shale oil with multi-field coupling, including the following steps:

[0054] S1. Establish a model: Based on the model assumption module, construct a mathematical model module in the simulation software, including numerical models of the chemical field (pyrolysis reaction kinetics) model, temperature field (porous medium heat transfer) model, and seepage field (porous medium flow) model, and define the geometric shape and material properties;

[0055] S2, Solution settings: Based on the model solution and parameter setting module, select the segregated solution method, set the initial time step, perform mesh generation, and select an appropriate mesh scheme according to the independence verification, and set the initial conditions and parameters of the simulation;

[0056] S3, Simulation run: Based on the model assumption module, mathematical model module, and model solution and parameter setting module, construct a numerical simulation model; run the numerical simulation model to obtain simulation results;

[0057] S4, Result analysis: Analyze the yield changes of various products, the mass ratio changes of each fluid component, and the changes in relevant physical parameters in the simulation results, and evaluate the correctness and effectiveness of the simulation results.

[0058] Compared with the prior art, the following beneficial effects are achieved:

[0059] The present invention proposes a numerical simulation method for multi-field coupling of in-situ upgrading of shale oil at pore scale. Through reasonable model assumptions and mathematical model construction, combined with effective numerical solution strategies and parameter settings, it can accurately simulate the multi-field coupling phenomenon during the in-situ upgrading process of medium and low maturity shale oil. The specific advantages are as follows:

[0060] (1) The present invention takes into account the dynamic changes of multiple chemical components during the multi-stage pyrolysis of kerogen, as well as the interaction between the chemical field, temperature field, and seepage field, and the simulation results are more accurate and reliable;

[0061] (2) Through grid independence verification, the present invention selects an appropriate mesh generation scheme, which improves the calculation efficiency while ensuring the calculation accuracy; the simulation results obtained in the embodiments are consistent with the existing research, verifying the correctness of the model, providing a powerful tool for the research and development of in-situ upgrading technology of shale oil, helping to improve the shale oil extraction efficiency and reduce the extraction cost. Brief Description of the Drawings

[0062] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings involved in the embodiments are briefly introduced below. Obviously, the drawings in the following description are only schematic illustrations of some embodiments of the present invention, and those skilled in the art can also construct other forms of drawings based on these drawings without creative efforts.

[0063] Figure 1 It is a schematic diagram of multi-field coupling during in-situ thermal upgrading mentioned in Embodiment 1 of the present invention;

[0064] Figure 2 It is a schematic diagram of grid generation mentioned in Embodiment 1 of the present invention, where (a) is an enlarged view of boundary layer grid refinement, and (b) is the grid generation of the numerical model;

[0065] Figure 3 It is a comparison chart of heavy oil production of different mesh generation schemes for the mesh independence test mentioned in Embodiment 1 of the present invention;

[0066] Figure 4 It is the change of solid component mass concentration, average porosity and average permeability during in-situ thermal upgrading in Embodiment 1 of the present invention. Among them, the upper part is the average temperature, the mass concentration of kerogen and various chars, and the lower part is the average porosity and average permeability;

[0067] Figure 5 It is the change of fluid component content during in-situ thermal upgrading of medium-low maturity shale oil mentioned in Embodiment 1 of the present invention, including methane (C1), other gases (C2-C5), light oil (C6-C 20 ) and heavy oil (C 21 -C 45 ). Detailed implementation manners

[0068] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0069] Next, a multi-field coupling numerical simulation method for in-situ upgrading of pore-scale shale oil proposed by the present invention will be described in conjunction with relevant accompanying drawings and specific examples. The specific content is as follows.

[0070] Embodiment 1:

[0071] The present invention proposes a multi-field coupling numerical simulation method for in-situ upgrading of pore-scale shale oil, and further designs a multi-field coupling numerical simulation system for pore-scale medium-low maturity shale oil that matches it based on the proposed system. The specific content is as follows:

[0072] 1. Model assumption module

[0073] The microscopic model for in-situ upgrading includes the rock skeleton of inorganic matter and the organic matter component kerogen. Under the supply of a stable heat source, the temperature of the microscopic model gradually rises, and the kerogen is gradually decomposed into heavy oil, light oil, gas, methane and different types of coke as the temperature rises. The chemical components decomposed from the kerogen can be transferred in the porous medium through diffusion and convection. In order to simulate the complex in-situ upgrading process of medium-low maturity shale oil, the following assumptions are made in this example:

[0074] (1) The simulated temperature is much higher than the boiling point of water, and the influence of water can be ignored;

[0075] (2) The influence of fluid phase change is not considered during the simulation process;

[0076] (3) The heavy oil, light oil, gas, and methane generated during the pyrolysis reaction are in a mixed fluid phase:

[0077] (4) The flow of the mixed fluid can be described by Darcy's law;

[0078] (5) The porous properties of the matrix are uniform and isotropic.

[0079] 2. Mathematical Model

[0080] 2.1 Chemical Field (Pyrolysis Reaction Kinetics) Model

[0081] The thermal decomposition of kerogen is a very complex process, which involves multiple kinetic reactions and is accompanied by dynamic changes in multiple chemical components. The decomposition process of kerogen is characterized by 7 thermal decomposition reactions, as shown in Table 1.

[0082] Table 1 Kinetic Data of the Reaction Model

[0083]

[0084]

[0085] During the pyrolysis of kerogen, due to different heating conditions, there is competition among the yields of methane, hydrocarbon gases, heavy oil, light oil, and various cokes. When the temperature of the simulation system reaches 300 degrees Celsius, kerogen gradually begins to crack. Among them, kerogen and the four cokes are solid components, and their mass changes depend on the pyrolysis reaction. The change in mass concentration can be expressed as:

[0086]

[0087] Among them, M represents the mass concentration; K represents the reaction rate constant; t represents the heating time; the subscripts 1 to 7 represent different cracking reaction stages; ker represents kerogen; HO, LO, and Hg represent heavy oil, light oil, and other gases respectively; ck1 to ck4 represent different types of cokes generated in different reaction stages; the reaction rate constant during the pyrolysis process is calculated using the Arrhenius equation, specifically expressed as:

[0088]

[0089] Among them, A represents the frequency factor; E l represents the reaction activation energy; Rg represents the ideal gas constant; T represents the temperature; the subscript l represents the cracking reaction stage.

[0090] Define the heavy oil, light oil, mixed hydrocarbon gas, and methane gas generated after kerogen pyrolysis as fluid components. The mass conservation equations for various fluid components in a porous medium include a diffusion term, a convection term, and a pyrolysis reaction term. The mass balance is expressed using the respective mass fraction w:

[0091]

[0092] Among them, represents the porosity of the porous medium; ρ f represents the density of the fluid mixture; w represents the mass fraction; u f represents the velocity vector; j represents the effective diffusion flux; R represents the mass source in a chemical reaction; the subscript i represents different fluid components. The density of the fluid mixture is closely related to the fluid component content, and the density of the mixed fluid is calculated by the mass fraction weighting method:

[0093] ρ f = ∑ i ρ i w i (8)

[0094] The change in porosity during kerogen pyrolysis is expressed as:

[0095]

[0096] Among them, represents the initial porosity; ρ ker，0 represents the initial mass concentration of kerogen; the effective diffusion flux is described by Fick's law and calculated by the Millington Quirk model:

[0097]

[0098] Among them, D represents the diffusion coefficient;

[0099] The mass source from chemical reactions of various fluid components is:

[0100] R HO = 0.279K1M ker - K2M HO (11)

[0101] R LO = 0.143K1M ker + 0.373K2M HO - K3M LO (12)

[0102] R Hg = 0.018K1M ker + 0.156K2M HO + 0.595K3MLO +0.031K5M ck1 +0.003K6M ck2 -K4M Hg (13)

[0103]

[0104] 2.2 Temperature field (heat transfer in porous media) model

[0105] During the kerogen pyrolysis process, the heat transfer mode is the combined action of heat conduction and heat convection. The control equation of the temperature field is expressed as:

[0106]

[0107] where, T represents temperature; C represents specific heat capacity at constant pressure; Q represents heat source term; λ t represents the effective thermal conductivity of the porous medium, and the specific definition is:

[0108]

[0109] where, λ s represents the thermal conductivity of shale; λ f represents the thermal conductivity of the mixed fluid; In order to describe the dynamic evolution of fluid components during the multi-stage pyrolysis of kerogen, a weighted method considering both mass fraction and density is adopted to characterize the fluid mixing, specifically as:

[0110]

[0111] (ρC) in Equation (15) eff is defined as:

[0112]

[0113] where, ρ s represents the density of shale; C s represents the specific heat capacity of shale at constant pressure; The specific heat capacity of the mixed fluid at constant pressure can be calculated by the following formula:

[0114]

[0115] The heat source term Q mainly includes the external heat source Q in and the chemical reaction heat Q r :

[0116]

[0117] The chemical reaction heat Q r is expressed as:

[0118] Q r = ∑n -K n ΔH n M n (21)

[0119] Among them, K n , ΔH n and M n respectively represent the chemical reaction rate, reaction enthalpy value, and mass concentration of reactants in the nth pyrolysis reaction.

[0120] 2.3 Seepage field (porous media flow) model

[0121] The petroleum and natural gas products after kerogen pyrolysis are a mixed fluid, and their flow in porous media follows Darcy's law, which is defined as:

[0122]

[0123] Among them, k represents the permeability of shale; p represents the pressure of the fluid; μ f represents the viscosity of the mixed fluid, which is specifically expressed as:

[0124]

[0125] Due to the continuous cracking of kerogen, the porosity in the porous media region gradually increases, resulting in an increase in permeability k. In this example, the simple Kozeny-Carman relation is used to characterize the relationship between porosity and permeability:

[0126]

[0127] During the seepage process, the fluid flow satisfies mass conservation:

[0128]

[0129] 3. Model solution and parameter setting

[0130] 3.1 Numerical solution strategy

[0131] The physical and chemical reactions and fluid flow during the in-situ upgrading of medium- and low-maturity shale oil involve chemical fields, temperature fields, and seepage fields. In this example, two-way coupling of chemical fields, temperature fields, and seepage fields is carried out in the simulation model; the chemical field is calculated by customizing partial differential equations; the temperature field and seepage field are calculated through the porous media heat transfer module and the Darcy's law module of groundwater flow, and their coupling relationship is as Figure 1 shown.

[0132] 3.2 Mesh division

[0133] During the simulation, the physical model was meshed using a Delaunay triangular network. In addition, in order to accurately capture the changes in fluid components during the kerogen pyrolysis process, a boundary layer was set on the surface of the kerogen during the mesh division process to achieve mesh refinement at the coupling interface. The numerical mesh division model is as Figure 2 shown.

[0134] 3.3 Independence verification

[0135] In order to pursue higher computational efficiency and save computing costs, a grid independence test was carried out in this example to prove the rationality of the network generation scenario selected by the present invention. Therefore, four different network generation scenarios with different grid numbers were designed in this example as shown in Table 2.

[0136] Table 2 Grid information for grid independence verification

[0137]

[0138] The comparison of the heavy oil (C 21 -C 45 ) production of different grid generation scenarios is as Figure 3 shown. As can be seen from Figure 3 , during the simulation, the production curve of Grid 4 has a large difference, and there are obvious differences from the calculation results of other network scenarios. Then, as the number of grids increases, the calculation results of heavy oil production become more stable. The results between Grid 54833 and Grid 84961 are almost the same, indicating that any further grid optimization will not produce different calculation results. Therefore, the network generation scenario of Grid 2 (grid number 54866) was selected for the mesh division of the numerical model in this example.

[0139] 3.4 Simulation conditions and parameters

[0140] Considering that the seepage capacity of medium and low maturity shale oil is poor in its original state, its initial porosity and permeability were set to 0.013 and 6×10 -4 mD, respectively. It is assumed that there is a stable heat source in the simulation area, and its heating rate is 10 K / min. The initial mass concentration of kerogen is set to 1250 kg / m 3 , and other parameters are shown in Table 3.

[0141] Table 3. Parameters used in the numerical simulation process

[0142]

[0143] 4. Results and discussion

[0144] 4.1 Kerogen pyrolysis characteristics

[0145] The changes in the mass concentration of solid components, average porosity, and average permeability during in-situ thermal upgrading are as follows Figure 4 shown, where Figure 4 The upper part shows the changes in average temperature, kerogen mass, and various cokes during the in-situ thermal upgrading of medium- and low-maturity shale oil. The entire kerogen pyrolysis process can be divided into three stages: the preheating stage, the pyrolysis conversion stage, and the pyrolysis completion stage.

[0146] Figure 4 The lower part shows the changes in average porosity and average permeability with temperature during the kerogen pyrolysis process. The above changes are divided into four different stages, and the kerogen cracking stage is considered to be the stage where the average porosity and average permeability increase rapidly, followed by a slow increase stage.

[0147] 4.2 Production characteristics

[0148] The changes in the fluid component content of medium- and low-maturity shale oil during in-situ thermal upgrading are as follows Figure 5 shown Figure 5 showing the production changes of petroleum and natural gas products during the in-situ thermal upgrading of medium- and low-maturity shale oil. As the pyrolysis process progresses, at the initial stage of heating, the decomposition of kerogen leads to a rapid increase in the production of heavy oil and light oil, and subsequently, due to the consumption of kerogen, the production gradually decreases.

[0149] In summary Figure 5 The results are consistent with the product change characteristics of medium- and low-maturity shale oil during in-situ thermal upgrading, verifying the correctness of the model.

[0150] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. A numerical simulation method for in-situ upgrading of medium- and low-maturity shale oil with multi-field coupling, characterized in that, The method is realized based on the multi-field coupling numerical simulation of in-situ upgrading of medium and low maturity shale oil. The system includes a model assumption module, a mathematical model module, a model solution and parameter setting module, and a result analysis module. Among them: The model assumption module is used to set the assumption conditions in the simulation process, including ignoring the influence of water, not considering fluid phase change, regarding the pyrolysis products as a mixed fluid phase, using Darcy's law to describe the flow of the mixed fluid, and assuming that the matrix porous characteristics are homogeneous and isotropic. The mathematical model module includes a chemical field model, a temperature field model, and a seepage field model, and is used to describe the physical and chemical reactions and fluid flow in the process of in-situ upgrading of shale oil. The model solution and parameter setting module includes a numerical solution strategy, network division, independence verification, and simulation condition and parameter setting, and is used to realize the solution of the model and parameter optimization. The result analysis module is used to analyze the yield changes of various products, the mass ratio changes of each fluid component at different temperatures, and the changes of relevant physical parameters in the process of in-situ upgrading of shale oil, so as to evaluate the correctness and effectiveness of the simulation results. The method includes the following steps: S1. Establish a model: Based on the model assumption module, construct a mathematical model module in the simulation software, including numerical models of a chemical field model, a temperature field model, and a seepage field model, and define the geometric shape and material properties. S2. Solution settings: Based on the model solution and parameter setting module, select a segregated solution method, set the initial time step, perform grid division, and select a suitable grid scheme according to the independence verification, and set the initial conditions and parameters of the simulation. S3. Simulation run: Based on the model assumption module, the mathematical model module, and the model solution and parameter setting module, construct a numerical simulation model; run the numerical simulation model to obtain the simulation results. S4. Result analysis: Analyze the yield changes of various products, the mass ratio changes of each fluid component, and the changes of relevant physical parameters in the simulation results, and evaluate the correctness and effectiveness of the simulation results.

2. A numerical simulation method for in-situ upgrading of shale oil at pore scale with multi-field coupling according to claim 1, characterized in that The chemical field model uses multiple thermal decomposition reactions to characterize the decomposition process of kerogen, and calculates the chemical reaction rate constant through the Arrhenius equation. Its formula is expressed as: Among them, K l represents the chemical reaction rate constant; A l represents the frequency factor; E l represents the activation energy of the reaction; R g represents the ideal gas constant; T represents the temperature; Use the mass conservation equation to describe the mass change of fluid components. Its formula is expressed as: wherein, represents porosity; ρ f represents the density of the fluid mixture; w represents the mass fraction; represents the gradient operator; u f represents the velocity vector; j represents the effective diffusion flux; R represents the mass source generated by the chemical reaction; the subscript i represents different fluid components; At the same time, consider the porosity change and effective diffusion flux calculation in the process of kerogen pyrolysis. Their formulas are expressed respectively as: Among them, represents the initial porosity; ρ ker,0 represents the initial mass concentration of kerogen; D represents the diffusion coefficient.

3. A pore-scale in-situ upgrading multi-field coupling numerical simulation method for shale oil according to claim 2, characterized in that, The temperature field model couples heat conduction and heat convection, describes the temperature field change through the control equation, uses the mass fraction and density weighting method to characterize the thermal characteristics of the mixed fluid, and takes into account the chemical reaction heat source. The specific content is as follows: The control equation of the temperature field is expressed as: Among them, C f represents the specific heat capacity at constant pressure; Q represents the heat source; λ t represents the effective thermal conductivity of the porous medium, which is defined as: Among them, λ s represents the thermal conductivity of shale; λ f represents the thermal conductivity of the mixed fluid; A weighted method that comprehensively considers the mass fraction and density is used to characterize the fluid mixture to describe the dynamic evolution of the fluid components during the multi-stage pyrolysis process of kerogen, and its definition is as follows: In the above formula, (ρC) eff is defined as: Among them, ρ s represents the shale density; C s represents the specific heat capacity at constant pressure of the shale; the calculation formula for the specific heat capacity at constant pressure C f of the fluid mixture is as follows: The heat source Q includes an external heat source Q in and the heat of chemical reaction Q r : Q = Q in +Q r Among them, the heat of chemical reaction Q r is expressed as: Q r = ∑ n -K n ΔH n M n Among them, K n , ΔH n and M n respectively represent the chemical reaction rate, reaction enthalpy value of the n-th pyrolysis reaction, and mass concentration of the reactant.

4. A numerical simulation method for in-situ upgrading of shale oil at pore scale with multi-field coupling according to claim 3, characterized in that The seepage field model follows Darcy's law to describe the flow of the mixed fluid in the porous medium, uses the Kozeny-Carman relationship to characterize the relationship between porosity and permeability, and satisfies the mass conservation law. The specific content is as follows: Define the flow of the mixed fluid in the porous medium as: where k represents permeability; p represents pressure; μ f represents the viscosity of the fluid mixture, and its calculation formula is: As the continuous cracking of kerogen progresses, the porosity of the porous medium gradually increases, which in turn leads to an increase in permeability; a simplified Kozeny-Carman relationship is used to describe the relationship between porosity and permeability: The fluid flow within the porous medium is governed by the principle of mass conservation, expressed as:

5. A numerical simulation method for in-situ upgrading of shale oil at pore scale with multi-field coupling according to claim 4, characterized in that The numerical solution strategy adopts a segregated solution method, automatically adjusts the time step according to convergence, and sets a finer time step in the initial stage; The network division adopts a Delaunay triangular network and sets a boundary layer on the kerogen surface to achieve grid refinement; The independence verification is tested by designing network generation scenarios with different numbers of grids, and the grid division scheme that stabilizes the simulation results is selected; The simulation conditions and parameter settings include setting the initial porosity, permeability, initial kerogen content of the oil shale, the heating rate of the simulation area, and the physical and chemical parameters of other related substances.

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