Simulation method of carbon dioxide enhanced pressure-controlled migration and coupling utilization of cheese root pyrolysis products

Abstract

The application discloses a simulation method for carbon dioxide reinforced pressure-controlled migration and coupling operation of cheese root pyrolysis products, and comprises the following steps: S1, dividing the pyrolysis stage of cheese root and determining typical pyrolysis products of cheese root; S2, establishing a pressure-controlled migration pore system, restoring typical pyrolysis products of the pressure-controlled migration pore system and controlling the pressure of the pressure-controlled migration pore system, then performing migration simulation of the pyrolysis products, and obtaining a migration and enrichment completed cheese root pore system; S3, performing molecular simulation of the enriched products according to the migration and enrichment completed cheese root pore system. The application can realize the whole process of organic coupling of shale oil pyrolysis hydrocarbon generation, migration and production operation on a molecular scale, can realize the simulation of the hydrocarbon generation region pyrolysis product to the hydrocarbon migration channel region without pyrolysis product under the pressure control, and provides technical support for the production of shale oil.

Description

Technical Field

[0001] This invention relates to the field of in-situ shale oil upgrading technology, and in particular to a simulation method for the pressure-controlled transport and coupled motion of carbon dioxide-enhanced kerogen pyrolysis products. Background Technology

[0002] Shale oil, as an important supplement to China's stable crude oil production, accounts for only 6% of its reserves due to its high viscosity and poor fluidity. In-situ upgrading technology, an environmentally friendly and economical method for converting heavy components into lighter components under high-temperature conditions, has become a research hotspot in the shale oil extraction field. This technology not only effectively reduces viscosity through physical heating but also improves oil fluidity through chemical reactions.

[0003] In addition to various mobile hydrocarbon components, medium- to low-maturity shale oil in tight rock formations also contains a large amount of unpyrolyzed bitumen, gum, kerogen, and other solid organic matter. As the main source material and storage space for shale oil reservoirs, the coupled behavior of pyrolysis-hydrocarbon generation-hydrocarbon migration-fluid movement directly affects the effectiveness of in-situ upgrading technologies such as carbon dioxide injection-enhanced pyrolysis in shale oil.

[0004] For studying the coupled behavior of hydrocarbon generation, expulsion, and fluid mobilization during kerogen pyrolysis, the commonly used method is the high-temperature, high-pressure pyrolysis-expulsion co-measurement experimental method. This method involves placing the sample in a closed, high-pressure reactor for high-temperature pyrolysis and simulating hydrocarbon expulsion under three selectable conditions: open, closed, and semi-closed systems. Gas chromatography-mass spectrometry (GC-MS) is used to monitor the released hydrocarbon components in real time. This method can accurately simulate the pyrolysis-expulsion behavior of kerogen samples at the laboratory level, but no reported methods have been found to study the coupling of kerogen pyrolysis-expulsion with product mobilization. Furthermore, this method is mainly used to quantitatively analyze the composition of products after kerogen pyrolysis hydrocarbon generation and expulsion, but it cannot effectively analyze the microscopic mechanisms of the pyrolysis-expulsion process.

[0005] Compared to the aforementioned laboratory experimental methods, molecular simulation methods have the potential to elucidate the microscopic mechanisms of the coupled process of hydrocarbon generation, expulsion, and fluid mobilization in kerogen pyrolysis at the nanoscale and atomic level. However, current reported molecular simulation studies focus on the hydrocarbon generation behavior of kerogen pyrolysis, lacking a molecular simulation technique scheme that couples the entire process of hydrocarbon generation, expulsion, and fluid mobilization in kerogen pyrolysis. Summary of the Invention

[0006] To address the aforementioned problems, this invention aims to provide a simulation method for the pressure-controlled transport and coupled motion of carbon dioxide-enhanced kerogen pyrolysis products.

[0007] The technical solution of the present invention is as follows: A simulation method for pressure-controlled transport and coupled motion of carbon dioxide-enhanced kerogen pyrolysis products includes the following steps: S1: Divide the pyrolysis stages of kerogen and determine the typical pyrolysis products of kerogen; S2: Establish a pressure-controlled transport pore system, recover the typical pyrolysis products of the pressure-controlled transport pore system and control the pressure of the pressure-controlled transport pore system, and then perform pyrolysis product transport simulation to obtain a kerogen pore system with complete transport enrichment; S3: Based on the kerogen pore system after the migration and enrichment are completed, perform molecular simulation of the coupled kinetics of the enrichment products.

[0008] Preferably, in step S1, the pyrolysis stage of kerogen includes a primary pyrolysis stage, a secondary pyrolysis stage, and a carbon dioxide-enhanced pyrolysis stage. Typical pyrolysis products of kerogen include gas components, light shale oil components, and heavy shale oil components.

[0009] As a preferred embodiment, the pyrolysis stage of kerogen specifically includes the following sub-steps: S11: Select kerogen structural units that are similar in type and maturity to the target reservoir kerogen and construct a molecular model of the kerogen matrix structure. S12: Based on the molecular model of the kerogen matrix structure, the pyrolysis molecular simulation of the kerogen matrix structure during the heating process is carried out using the reaction force field molecular dynamics method. S13: Based on the evolution characteristics of pyrolysis products and pore structure simulated by pyrolysis molecules, the pyrolysis stages of kerogen are divided; When the kerogen is mainly composed of macromolecules that break down to generate heavy components and a large number of free radicals, forming larger pores, then this temperature range is classified as a primary pyrolysis stage. When the pyrolysis products are mainly short-chain hydrocarbons, free radicals recombine to generate light components, macropores split into micropores, and pore connectivity is improved, then this temperature range is divided into a secondary pyrolysis stage. S14: Based on the molecular model of the kerogen matrix structure, carbon dioxide is adsorbed in the matrix structure by the giant canonical Monte Carlo method, and the structural relaxation of the carbon dioxide-containing kerogen matrix is ​​carried out by molecular dynamics. S15: Based on the carbon dioxide-containing kerogen matrix model after structural relaxation, the pyrolysis molecular simulation of the carbon dioxide-containing kerogen matrix structure during the heating process was carried out using the reactive force field molecular dynamics method, and this process was divided into a carbon dioxide-enhanced pyrolysis stage.

[0010] Preferably, in step S2, the pressure-controlled transport pore system includes a kerogen pore channel region in the middle, a pyrolysis product region on the left side of the channel, and a hydrocarbon accumulation region on the right side of the channel.

[0011] Preferably, in step S2, restoring the typical pyrolysis products of the pressure-controlled transport pore system specifically includes the following sub-steps: based on the pressure-controlled transport pore system, combined with the pyrolysis stage of the kerogen and the typical pyrolysis products of the kerogen, a set number of typical pyrolysis product mixture components are loaded into the pyrolysis product region of the pressure-controlled transport pore system using the giant canonical Monte Carlo method, thereby restoring the typical pyrolysis products of the pressure-controlled transport pore system.

[0012] Preferably, step S2, controlling the pressure of the pressure-controlled transport pore system, specifically includes the following sub-steps: The internal pressure of the pressure-controlled transport pore system is regulated by using heavier inert gas atoms as a medium. The parameters ε and σ in the Lennard-Jones potential energy function of the medium are used as adjustment parameters. The influence of σ and ε on the interaction energy between the pressure-regulating gas medium and the pyrolysis products is determined by the controlled variable method, and ε and σ are determined based on the results. Based on the adjusted force field parameters, molecular dynamics simulation of the pressure-regulating gas medium molecules was performed using the NPT ensemble under the target temperature condition. The relationship curve between the density and pressure of the pressure-regulating gas medium was obtained by refitting the simulation. Based on the relationship curve, the pressure in different regions inside the pressure-controlled transport pore system can be adjusted by changing the amount of pressure-regulating gas medium filled in.

[0013] Preferably, adjusting the pressure in different regions inside the pressure-controlled transport pore system by adjusting the amount of pressure-regulating gas medium filled according to the relationship curve specifically includes the following sub-steps: First, based on the target control pressure and the aforementioned relationship curve, the corresponding pressure regulating gas medium density is determined. Then, the total mass of the pressure-regulating gas medium is determined by combining the pore volume of the pressure-controlled region, and the total quantity of gas medium in the pressure-controlled region is calculated: (1) In the formula: m The total mass of the pressure-regulating gas medium is expressed in grams. ρ The density of the pressure-regulating gas medium is expressed in g / cm³. 3 ; V The volume of the pressure-regulating gas medium is in cm³. 3 ; (2) Finally, the adsorption simulation of the pressure-regulated gas medium was carried out in regions using the giant canonical Monte Carlo algorithm based on the fixed atomic mass method.

[0014] Preferably, in step S2, when simulating the transport of pyrolysis products... First, the boundary layer near the pore channel outlet of the hydrocarbon accumulation zone is opened to connect the hydrocarbon accumulation zone and the pore channel zone. Molecular dynamics simulation is carried out to achieve diffusion equilibrium of the pressure regulating gas medium inside the hydrocarbon accumulation zone and the pore channel zone, thereby achieving pressure equilibrium of the pressure regulating gas medium inside the system. Subsequently, the boundary layer near the pore channel entrance of the pyrolysis product region was opened to connect the pyrolysis product region and the pore channel region. Molecular dynamics simulations were then conducted to allow the mixed fluid components and pressure-regulating gas medium in the pyrolysis product region to migrate to the hydrocarbon accumulation region through the pore channel region until the pressure and pyrolysis product distribution of the entire system reached equilibrium.

[0015] Preferably, in step S3, two depletion mining mobilization modes are used to perform molecular simulation of the coupled mobilization of enrichment products; wherein... Mode 1 is: after the products of carbon dioxide-enhanced kerogen pyrolysis are transported and enriched, they flow to the bottom of the well along new seepage channels under the bottom pressure differential. Mode 2 is as follows: After the products of carbon dioxide-enhanced kerogen pyrolysis migrate and accumulate, they flow to the bottom of the well under the pressure differential at the bottom of the well along the pore channels of the original migration and accumulation process.

[0016] As a preferred option, for Mode 1, in the kerogen pore system after migration and enrichment, the pyrolysis products of the reservoir enrichment zone are retained, while the pyrolysis products of the pore channel zone and the pyrolysis product zone, as well as the pressure-controlled gas medium, are deleted, and the pyrolysis product zone is redefined as the bottom-hole production zone. Subsequently, molecular dynamics simulations are carried out to make the pyrolysis products of the reservoir enrichment zone flow to the bottom-hole production zone through the pore channel zone. For Mode 2, in the kerogen pore system after migration and enrichment, the pyrolysis products in the reservoir enrichment zone and the pyrolysis products in the pore channels during the migration and enrichment process are retained. The pressure-controlled gas medium and the residual pyrolysis products in the pyrolysis product zone of the entire system are deleted, and the pyrolysis product zone is redefined as the bottom-hole production zone. Subsequently, molecular dynamics simulations are carried out to make the pyrolysis products in the reservoir enrichment zone flow back to the bottom-hole production zone through the migration and enrichment channel zone.

[0017] The beneficial effects of this invention are: This invention enables the organic coupling of the entire process of shale oil pyrolysis hydrocarbon generation, hydrocarbon migration, and extraction at the molecular scale. It can simulate the hydrocarbon migration process from pyrolysis products in the hydrocarbon generation area to the hydrocarbon migration channel area without pyrolysis products under controlled pressure, providing technical support for shale oil extraction. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic flowchart of the simulation method for the pressure-controlled transport and coupling of carbon dioxide-enhanced kerogen pyrolysis products according to the present invention. Figure 2 This is a schematic diagram of a pore model for simulating the transport of pyrolysis products in a specific embodiment; Figure 3 Here is a configuration diagram of helium atoms in a specific embodiment; wherein, (a) is a square configuration diagram of helium atoms, (b) is a boundary layer configuration diagram of helium atoms, and (c) is a pore configuration diagram of helium atoms; Figure 4 This is a schematic diagram illustrating the relationship between argon density and pressure in a specific embodiment. Figure 5 This is a schematic diagram of a pressure-controlled transport simulation process for pyrolysis products in a specific embodiment; Figure 6 This is a schematic diagram of two modes of coupled mining of pyrolysis products in a specific embodiment. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and technical features described in this application can be combined with each other. It should also be pointed out that, unless otherwise indicated, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terms "comprising" or "including" and similar words used in this invention refer to elements or objects preceding the word that encompass the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0021] like Figure 1 As shown, this invention provides a simulation method for the pressure-controlled transport and coupled motion of carbon dioxide-enhanced kerogen pyrolysis products, comprising the following steps: S1: Divide the pyrolysis stages of kerogen and determine the typical pyrolysis products of kerogen.

[0022] In one specific embodiment, the pyrolysis stage of kerogen includes a primary pyrolysis stage, a secondary pyrolysis stage, and a carbon dioxide-enhanced pyrolysis stage. Typical pyrolysis products of kerogen include gas components, light shale oil components, and heavy shale oil components.

[0023] In a specific embodiment, dividing the pyrolysis stage of kerogen specifically includes the following sub-steps: S11: Select kerogen structural units that are similar in type and maturity to the target reservoir kerogen and construct a molecular model of the kerogen matrix structure. S12: Based on the molecular model of the kerogen matrix structure, the pyrolysis molecular simulation of the kerogen matrix structure during the heating process is carried out using the reaction force field molecular dynamics method. S13: Based on the evolution characteristics of pyrolysis products and pore structure simulated by pyrolysis molecules, the pyrolysis stages of kerogen are divided; When the kerogen is mainly composed of macromolecules (organic matter fragments with more than 200 carbon atoms) that break down to generate heavy components and a large number of free radicals (free radical mass concentration greater than 2%), forming larger pores (pore diameter greater than 0.7 nm), then this temperature range is classified as a primary pyrolysis stage. When the pyrolysis products are mainly short-chain hydrocarbons, free radicals recombine to generate light components, and large pores split into small pores (pores with a diameter greater than 0.7 nm split into pores with a diameter less than 0.7 nm), the pore connectivity is improved, and this temperature range is divided into a secondary pyrolysis stage. S14: Based on the molecular model of the kerogen matrix structure, carbon dioxide is adsorbed into the matrix structure by the giant canonical Monte Carlo method (optionally, the concentration of carbon dioxide is 2%~5%), and the structural relaxation of the carbon dioxide-containing kerogen matrix is ​​carried out by molecular dynamics. S15: Based on the carbon dioxide-containing kerogen matrix model after structural relaxation, the pyrolysis molecular simulation of the carbon dioxide-containing kerogen matrix structure during the heating process was carried out using the reactive force field molecular dynamics method, and this process was divided into a carbon dioxide-enhanced pyrolysis stage.

[0024] In one specific embodiment, determining the typical pyrolysis products of kerogen specifically includes the following sub-steps: Based on the product type and quantity distribution characteristics of kerogen during heated pyrolysis and carbon dioxide-enhanced pyrolysis, one component from C1 to C4 is selected as the representative gaseous component in the hydrocarbon generation products, one component from C5 to C16 is selected as the representative light shale oil component, and one component from C17 to C25 is selected as the representative heavy shale oil component.

[0025] Based on the typical pyrolysis product ratios at different stages of kerogen pyrolysis, a mixed fluid consisting of gaseous, light shale oil, and heavy shale oil components was selected for the primary pyrolysis stage to exhibit a high oil-to-gas ratio. Similarly, for the secondary pyrolysis stage, a mixed fluid of all three types of components was selected to reflect the significant increase in the degree of light shale oil formation caused by the secondary cracking reaction. In the carbon dioxide-enhanced pyrolysis stage, a mixed fluid of all three types of components was selected to reflect the condensation reaction of some heavy components under high-temperature conditions.

[0026] S2: Establish a pressure-controlled transport pore system, recover the typical pyrolysis products of the pressure-controlled transport pore system and control the pressure of the pressure-controlled transport pore system, and then perform pyrolysis product transport simulation to obtain a kerogen pore system with complete transport enrichment.

[0027] In one specific embodiment, the pressure-controlled transport pore system includes a kerogen pore channel region in the middle, a pyrolysis product region on the left side of the channel, and a hydrocarbon accumulation region on the right side of the channel.

[0028] In the above embodiments, the kerogen pore channel region is constructed based on the target reservoir kerogen matrix structure model. The shape and size of the pore channels can be adjusted according to the characterization results of the target kerogen pore structure. The pore channel wall thickness needs to be greater than the cutoff radius used in the molecular simulation. The pore channel region has an inlet that can communicate with the pyrolysis product region and an outlet that can communicate with the hydrocarbon accumulation region.

[0029] The pyrolysis product region and the hydrocarbon accumulation region are symmetrically distributed on both sides of the pore channel region, each consisting of two boundary layers perpendicular to the pore channel cross-section. The boundary layer near the pore channel inlet and outlet temporarily separates the pore channel region, pyrolysis product region, and hydrocarbon accumulation region, enabling independent pressure control within each region. The boundary layer farther from the pore channel shields the model from periodicity in the migration direction, preventing direct cross-flow of pyrolysis products between the pyrolysis product region and the hydrocarbon accumulation region. The atoms constituting the boundary layer are relatively light inert gases with stable physical properties and weak adsorption of pyrolysis products and pressure-controlling atoms. The spacing between the inert gas atoms in the boundary layer is set to 1 Å. Under this spacing condition, the energy state of the boundary layer atomic system is relatively stable, avoiding calculation errors caused by excessively high energy, and effectively preventing pressure-controlling atoms from escaping from the boundary layer.

[0030] In one specific embodiment, the recovery of typical pyrolysis products of the pressure-controlled transport pore system includes the following sub-steps: based on the pressure-controlled transport pore system, combined with the pyrolysis stage of the kerogen and the typical pyrolysis products of the kerogen, a set number of typical pyrolysis product mixture components are loaded into the pyrolysis product region of the pressure-controlled transport pore system using the giant canonical Monte Carlo method, thereby recovering the typical pyrolysis products of the pressure-controlled transport pore system.

[0031] In one specific embodiment, controlling the pressure of the pressure-controlled transport pore system specifically includes the following sub-steps: Heavier inert gas atoms (relative atomic mass greater than 35) are used as the medium to regulate the internal pressure of the pressure-controlled transport pore system. To avoid interference from the pressure-regulating gas medium itself on the distribution and transport of pyrolysis products, the potential energy parameters of the pressure-regulating gas medium need to be optimized. This invention uses the ε and σ parameters of the pressure-regulating gas medium in the Lennard-Jones potential energy function as adjustment parameters, and uses the controlled variable method to investigate the influence of σ and ε on the interaction energy between the pressure-regulating gas medium and the pyrolysis products. Based on the original parameters σ and ε of the pressure-regulating gas medium molecules under the original force field, firstly, the value of parameter ε is kept constant, and the value of parameter σ is adjusted to obtain the interaction energy between the pressure-regulating gas medium and the pyrolysis products under different conditions. Combining the magnitude of this interaction energy and the effective collision diameter of the pressure-regulating gas medium, the optimized parameter σ value is determined. This value can effectively increase the effective collision diameter of the pressure-regulating gas medium, reduce its permeability in the kerogen matrix, thereby preventing it from entering the matrix in large quantities, and maintain a low interaction energy between the pressure-regulating gas medium and the pyrolysis products. Next, based on the unchanged value of parameter σ under the original force field, the value of parameter ε was adjusted to obtain the interaction energy between the pressure-regulating gas medium and the pyrolysis products under different conditions. Selecting a reasonable value for parameter ε resulted in a weaker interaction energy between the pressure-regulating gas medium and the pyrolysis products, thereby reducing the adsorption effect.

[0032] Based on the adjusted force field parameters, molecular dynamics simulations of the pressure-regulated gas medium were performed using the NPT ensemble under target temperature conditions. The relationship curve between the density and pressure of the pressure-regulated gas medium was obtained by refitting the simulation.

[0033] Based on the established relationship curve between the density and pressure of the pressure-regulating gas medium, the pressure in different regions within the system is controlled by adjusting the amount of pressure-regulating gas medium filled. First, based on the target control pressure and the density-pressure relationship curve, the corresponding density of the pressure-regulating gas medium is determined. Next, the total mass of the pressure-regulating gas medium is determined based on the pore volume of the region to be pressure-controlled (Formula 1), and the total quantity of gas medium in that pressure-controlled region is calculated (Formula 2).

[0034] (1) In the formula: m The total mass of the pressure-regulating gas medium is expressed in grams. ρ The density of the pressure-regulating gas medium is expressed in g / cm³. 3 ; V The volume of the pressure-regulating gas medium is in cm³. 3 ; (2) Then, the adsorption simulation of the pressure-regulated gas medium is performed in regions using the giant canonical Monte Carlo algorithm based on a fixed atomic weight method. In this invention, for subsequent simulation of pyrolysis product transport, the pressure in the pyrolysis product region needs to be greater than the pressure in the pore channel region and the hydrocarbon accumulation region, while the pressures in the pore channel region and the hydrocarbon accumulation region are the same.

[0035] In one specific embodiment, when simulating the transport of pyrolysis products... First, the boundary layer near the pore channel outlet of the hydrocarbon accumulation zone is opened to connect the hydrocarbon accumulation zone and the pore channel zone. Molecular dynamics simulation is carried out to achieve diffusion equilibrium of the pressure regulating gas medium inside the hydrocarbon accumulation zone and the pore channel zone, thereby achieving pressure equilibrium of the pressure regulating gas medium inside the system. Subsequently, the boundary layer near the pore channel entrance of the pyrolysis product region was opened to connect the pyrolysis product region and the pore channel region. Molecular dynamics simulations were then conducted to allow the mixed fluid components and pressure-regulating gas medium in the pyrolysis product region to migrate to the hydrocarbon accumulation region through the pore channel region until the pressure and pyrolysis product distribution of the entire system reached equilibrium.

[0036] S3: Based on the kerogen pore system after the migration and enrichment are completed, perform molecular simulation of the coupled kinetics of the enrichment products.

[0037] In one specific embodiment, two depletion exploitation mobilization modes are used for molecular simulation of enrichment product coupling mobilization; wherein... Mode 1 is: after the products of carbon dioxide-enhanced kerogen pyrolysis are transported and enriched, they flow to the bottom of the well along new seepage channels under the bottom pressure differential. Mode 2 is as follows: After the products of carbon dioxide-enhanced kerogen pyrolysis migrate and accumulate, they flow to the bottom of the well under the pressure differential at the bottom of the well along the pore channels of the original migration and accumulation process.

[0038] In a specific embodiment, for Mode 1, in the kerogen pore system after migration and enrichment, the pyrolysis products of the reservoir enrichment zone are retained, while the pyrolysis products of the pore channel zone and the pyrolysis product zone, as well as the pressure-controlled gas medium, are deleted, and the pyrolysis product zone is redefined as the bottom-hole production zone; subsequently, molecular dynamics simulations are performed to make the pyrolysis products of the reservoir enrichment zone flow to the bottom-hole production zone through the pore channel zone. For Mode 2, in the kerogen pore system after migration and enrichment, the pyrolysis products in the reservoir enrichment zone and the pyrolysis products in the pore channels during the migration and enrichment process are retained. The pressure-controlled gas medium and the residual pyrolysis products in the pyrolysis product zone of the entire system are deleted, and the pyrolysis product zone is redefined as the bottom-hole production zone. Subsequently, molecular dynamics simulations are carried out to make the pyrolysis products in the reservoir enrichment zone flow back to the bottom-hole production zone through the migration and enrichment channel zone.

[0039] In a specific embodiment, taking a low-maturity shale oil reservoir as an example, the simulation method for pressure-controlled transport and coupled motion of carbon dioxide-enhanced kerogen pyrolysis products described in this invention is used to simulate it, specifically including the following steps: (1) Dividing the pyrolysis stages of kerogen Type IA kerogen structural units, similar in type and maturity to those of the target reservoir, were selected. By integrating eight kerogen units and incorporating kerogen structural relaxation, a molecular model of the kerogen matrix structure was constructed. Using a ReaxFF 6.0 force field under the NVT ensemble, the simulation temperature of the kerogen matrix structure was gradually increased, and pyrolysis simulations of the kerogen matrix were conducted at temperatures of 800 K, 1000 K, 1200 K, 1400 K, 1600 K, 1800 K, and 2000 K.

[0040] For type IA kerogen, when it is observed that the initial fracture mainly produces larger molecular structures of C40+, a small amount of small molecule light components, and a small amount of free radicals, and the kerogen matrix is ​​broken down into a structure containing several large pores, it can be identified as the first pyrolysis stage. When it is observed that the residual macromolecular structure further decomposes, the main products are C1-C4 light gas components and C5-C16 light oil components, the number of free radicals reaches a peak and begins to decrease, the pores gradually become smaller, and the number of pores increases, it can be identified as the second pyrolysis stage.

[0041] Next, the carbon dioxide molecule was geometrically optimized to obtain a stable configuration, and then the carbon dioxide adsorption process was simulated at 300 K using the grand canonical Monte Carlo method. Finally, the structural relaxation and pyrolysis simulations were performed again on the kerogen model after adsorbing carbon dioxide molecules. This process was divided into a carbon dioxide-enhanced pyrolysis stage.

[0042] (2) Determine the typical pyrolysis products of kerogen. Based on the product type and quantity distribution characteristics of type IA kerogen during pyrolysis, CH4 was selected as the representative gaseous component in the hydrocarbon generation products, and C was selected as the representative gaseous component in the hydrocarbon generation products. 10 H 22 Representing the light shale oil component, C was selected. 20 H 42 This represents the heavy shale oil component.

[0043] Based on the typical pyrolysis product ratios of type IA kerogen at different pyrolysis stages, in the first pyrolysis stage, the system was configured with 400 CH4 molecules and 100 C molecules. 10 H 22 Molecules and 20 C 20 H 42 The molecules exhibit a high oil-to-gas ratio. The product quantity distribution changes significantly during the secondary pyrolysis stage, with 1450 CH4 molecules and 25 C molecules. 10 H22 Molecules and 5 C 20 H 42 The molecules indicate that the secondary pyrolysis reaction significantly increases the degree of lightness; the number of products in the gas pyrolysis stage is adjusted to 1100 CH4 molecules and 50 C molecules. 10 H 22 Molecules and 10 C 20 H 42 The molecules show that some of the recombinant components undergo condensation reactions under high temperature conditions.

[0044] (3) Establish a pressure-controlled transport pore system Figure 2 The kerogen pore system used for pressure-controlled transport simulation consists of the kerogen pore channel region—the central channel, the pyrolysis product region—the left-side pores, and the hydrocarbon accumulation region—the right-side pores.

[0045] The central pores were constructed based on the IA-type kerogen matrix structure model described in step (1). First, a superlattice treatment was performed, expanding the matrix by a factor of 3 in the x-direction and by a factor of 2 in both the y and z-directions, constructing a cuboid matrix block with dimensions of 100.35 Å (length) × 66.91 Å (width) × 66.91 Å (height). Then, the ranges of the X, Y, and Z coordinates were sequentially set to obtain a cuboid matrix block with dimensions of 60 Å (length) × 80 Å (width) × 60 Å (height). Subsequently, based on the characterization results of the IA-type kerogen pore structure, vacuum layer thicknesses of 1 nm, 2 nm, and 4 nm were set to construct slit-like kerogen matrix pore channel models with pore widths of 1 nm, 2 nm, and 4 nm, respectively. The pore channel wall thickness was set to 1.5 nm, which is greater than the cutoff radius (1.2 nm) used in molecular simulations.

[0046] Figure 2 The kerogen porous system includes multiple boundary layers. In this embodiment, the atoms constituting the boundary layers are helium atoms, which have stable physical properties and weak adsorption of pyrolysis products and pressure-controlled atoms. First, a square configuration composed of four helium atoms is constructed ( Figure 3 (a) where the spacing between helium atoms is set to 1 Å. Under this spacing condition, the energy state of the helium atom system is relatively stable, which can avoid calculation errors caused by excessive energy, and can also effectively prevent argon atoms from escaping from the helium atom layer. Based on this, a corresponding helium atom boundary layer model is constructed using the superlattice method, setting the u direction to 80 Å and the v direction to 60 Å, to obtain a helium atom boundary layer model with dimensions of 80 Å (length) × 60 Å (width). Figure 3 (b)). Subsequently, a layer-building simulation was performed on the constructed helium atom boundary layer, setting the vacuum layer thickness to 60 Å, thereby obtaining the corresponding pore structure model ( Figure 3(c)). The pores on both sides of the central channel have the same size, which are cuboid structures with a length of 6 nm, a width of 6 nm, and a height of 8 nm.

[0047] (4) Restore typical pyrolysis products Based on the kerogen controlled transport simulation system built in step (3), and combined with the kerogen pyrolysis stage and corresponding typical pyrolysis products determined in steps (1) and (2), the giant canonical Monte Carlo method is used to load a set number of typical pyrolysis product mixture components into the left pore of the simulation system.

[0048] (5) Controlling pressure during transport In this example, argon molecules are chosen as the medium to regulate the internal pressure of the system. To avoid interference from the argon molecules themselves with the distribution and migration of pyrolysis products, the potential energy parameters of the argon molecules need to be optimized. Using the ε and σ parameters in the Lennard-Jones potential function of argon molecules as adjustment parameters, the influence of σ and ε on the interaction energy between argon molecules and pyrolysis products is investigated using the controlled variable method.

[0049] Under a CVFF force field, the initial parameters of argon molecules are σ = 3.822 Å and ε = 0.2381 kcal / mol. First, keeping ε = 0.2381 kcal / mol constant, the values ​​of σ are adjusted to 1.822 Å, 2.822 Å, 3.822 Å, 4.822 Å, and 5.822 Å to obtain the interaction energy between argon molecules and pyrolysis products under different conditions. Combining the magnitude of this interaction energy with the effective collision diameter of argon molecules, the optimized parameter σ value is determined. Subsequently, keeping σ = 3.822 Å constant, the values ​​of ε are adjusted to 0.0381 kcal / mol, 0.1381 kcal / mol, 0.2381 kcal / mol, 0.3381 kcal / mol, and 0.4381 kcal / mol to obtain the interaction energy between argon molecules and pyrolysis products under different conditions. The optimized parameter ε value results in a weaker interaction energy between argon molecules and pyrolysis products.

[0050] Based on the adjusted force field parameters, molecular dynamics simulations of argon molecules were performed using the NPT ensemble at 423 K. The relationship between the density and pressure of argon molecules was obtained through refitting the simulation, as shown in the figure below. Figure 4 As shown.

[0051] Based on the established relationship curve between argon molecule density and pressure, the pressure in different regions of the system was controlled by adjusting the number of argon molecules used. First, for the right-side hydrocarbon accumulation zone, a target pressure of 20 MPa was set. Using the density-pressure relationship curve, the corresponding argon molecule density was determined to be 0.2114 g / cm³. Next, the total mass of the pressure-regulating gas medium was determined based on the pore volume of the hydrocarbon accumulation zone (Formula 1), and the total quantity of the gas medium in the hydrocarbon accumulation zone was calculated (Formula 2). Using the same method, the number of argon atoms in the left-side pyrolysis product zone under pressures of 40 MPa, 60 MPa, and 80 MPa, and in the central kerogen pore channel zone under pressure of 20 MPa, with widths of 1 nm, 2 nm, and 4 nm, were further calculated. The specific results are shown in Table 1. Table 1. Number of argon atoms in each region under different pressures and channel widths.

[0052] Then, using the grand canonical Monte Carlo algorithm, based on a fixed atomic weight method, argon adsorption simulation was performed in different regions, thereby obtaining a complete simulation. Figure 2 The pyrolysis product transport model is shown.

[0053] (6) Simulated pyrolysis product transport Based on the above simulation system for the transport of kerogen pyrolysis products and pressure ( Figure 5 (a) This simulation reproduces the dynamic migration process of pyrolysis products in an actual reservoir. The migration simulation process consists of two key stages. First, the boundary layer near the outlet of the central channel in the left pore is opened to connect the left pore and the central channel. Molecular dynamics simulations are then performed to achieve diffusion equilibrium of the pressure-regulating gas medium inside the left pore and the central channel, thus achieving argon molecule pressure equilibrium within the system. Figure 5 (b) The simulation used the optimized CVFF force field and was performed under an isothermal condition of 423 K using the NVT ensemble. The simulation duration was 100 ps.

[0054] Subsequently, a boundary layer opening was made in the left pore near the entrance of the central channel, connecting the left pore to the central channel. Molecular dynamics simulations were then performed to allow the mixed fluid components and argon molecules in the left pore to migrate through the central channel to the right pore until the overall system pressure and pyrolysis product distribution reached equilibrium. Figure 5 (c)). The simulation used the optimized CVFF force field and performed NVT ensemble simulation under isothermal conditions of 423 K, with the simulation duration extended to 1500 ps.

[0055] (7) Enrichment product coupling kinetics using molecular simulation This embodiment couples the transport and enrichment of pyrolysis products with mining operations at the nanoscale. Based on the kerogen pore system enriched by the above-mentioned transport, two depletion mining operation modes are designed.

[0056] In the first mode, after the products of carbon dioxide-enhanced kerogen pyrolysis migrate and accumulate, they flow towards the bottom of the well under a new seepage channel under bottom-hole pressure differential. For this mode, in the kerogen porosity system after migration and enrichment, the pyrolysis products in the right-side pores are retained, while the pyrolysis products and argon gas in the middle channel and left-side pores are deleted, and the left-side pores are redefined as the bottom-hole production zone. Subsequently, molecular dynamics simulations are performed to make the pyrolysis products in the right-side pores flow to the left-side pores through the middle channel (…). Figure 6 (a)). The simulation continued to use the optimized CVFF force field and was performed under an isothermal condition of 330 K using the NVT ensemble, with a simulation duration of 500 ps.

[0057] In the second mode, after the products of carbon dioxide-enhanced kerogen pyrolysis migrate and accumulate, they flow towards the bottom of the well under the bottom-hole pressure differential, following the pore channels from the original migration and accumulation process. This mode corresponds to the pyrolysis product mobilization process under pore channel blockage. For this mode, in the kerogen pore system after migration and enrichment, the pyrolysis products in the right-side pores and the middle channel are retained, while the argon gas in the entire system and the residual pyrolysis products in the left-side pores are deleted, redefining the left-side pores as the bottom-hole production zone. Subsequently, molecular dynamics simulations are performed, causing the pyrolysis products in the right-side pores to flow back through the middle channel to the left-side pores (…). Figure 6 (b) The simulation continued to use the optimized CVFF force field and was performed under an isothermal condition of 330 K using the NVT ensemble, with a simulation duration of 500 ps.

[0058] In summary, this invention enables molecular simulation at the molecular scale of the organic coupling of the entire process of shale oil pyrolysis hydrocarbon generation, hydrocarbon migration, and extraction, and can realize the migration of pyrolysis products from the hydrocarbon generation area to the hydrocarbon migration channel area without pyrolysis products under controlled pressure. Compared with the prior art, this invention represents a significant advancement.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A simulation method for pressure-controlled transport and coupled motion of carbon dioxide-enhanced kerogen pyrolysis products, characterized in that, Includes the following steps: S1: Divide the pyrolysis stages of kerogen and determine the typical pyrolysis products of kerogen; S2: Establish a pressure-controlled transport pore system, recover the typical pyrolysis products of the pressure-controlled transport pore system and control the pressure of the pressure-controlled transport pore system, and then perform pyrolysis product transport simulation to obtain a kerogen pore system with complete transport enrichment; S3: Based on the kerogen pore system after the migration and enrichment are completed, perform molecular simulation of the coupled kinetics of the enrichment products.

2. The simulation method for pressure-controlled transport and coupled motion of carbon dioxide-enhanced kerogen pyrolysis products according to claim 1, characterized in that, In step S1, the pyrolysis stage of kerogen includes a primary pyrolysis stage, a secondary pyrolysis stage, and a carbon dioxide-enhanced pyrolysis stage. Typical pyrolysis products of kerogen include gas components, light shale oil components, and heavy shale oil components.

3. The simulation method for pressure-controlled transport and coupled motion of carbon dioxide-enhanced kerogen pyrolysis products according to claim 2, characterized in that, The pyrolysis stage of kerogen specifically includes the following sub-steps: S11: Select kerogen structural units that are similar in type and maturity to the target reservoir kerogen and construct a molecular model of the kerogen matrix structure. S12: Based on the molecular model of the kerogen matrix structure, the pyrolysis molecular simulation of the kerogen matrix structure during the heating process is carried out using the reaction force field molecular dynamics method. S13: Based on the evolution characteristics of pyrolysis products and pore structure simulated by pyrolysis molecules, the pyrolysis stages of kerogen are divided; When the kerogen is mainly composed of macromolecules that break down to generate heavy components and a large number of free radicals, forming larger pores, then this temperature range is classified as a primary pyrolysis stage. When the pyrolysis products are mainly short-chain hydrocarbons, free radicals recombine to generate light components, macropores split into micropores, and pore connectivity is improved, then this temperature range is divided into a secondary pyrolysis stage. S14: Based on the molecular model of the kerogen matrix structure, carbon dioxide is adsorbed in the matrix structure by the giant canonical Monte Carlo method, and the structural relaxation of the carbon dioxide-containing kerogen matrix is ​​carried out by molecular dynamics. S15: Based on the carbon dioxide-containing kerogen matrix model after structural relaxation, the pyrolysis molecular simulation of the carbon dioxide-containing kerogen matrix structure during the heating process was carried out using the reactive force field molecular dynamics method, and this process was divided into a carbon dioxide-enhanced pyrolysis stage.

4. The simulation method for pressure-controlled transport and coupled motion of carbon dioxide-enhanced kerogen pyrolysis products according to claim 1, characterized in that, In step S2, the pressure-controlled transport pore system includes a kerogen pore channel region in the middle, a pyrolysis product region on the left side of the channel, and a hydrocarbon accumulation region on the right side of the channel.

5. The simulation method for pressure-controlled transport and coupled motion of carbon dioxide-enhanced kerogen pyrolysis products according to claim 1, characterized in that, In step S2, restoring the typical pyrolysis products of the pressure-controlled transport pore system specifically includes the following sub-steps: Based on the pressure-controlled transport pore system, combined with the pyrolysis stage of the kerogen and the typical pyrolysis products of the kerogen, a set number of typical pyrolysis product mixture components are loaded into the pyrolysis product region of the pressure-controlled transport pore system using the giant canonical Monte Carlo method, thereby restoring the typical pyrolysis products of the pressure-controlled transport pore system.

6. The simulation method for pressure-controlled transport and coupled motion of carbon dioxide-enhanced kerogen pyrolysis products according to claim 1, characterized in that, In step S2, controlling the pressure of the pressure-controlled transport pore system specifically includes the following sub-steps: The internal pressure of the pressure-controlled transport pore system is regulated by using heavier inert gas atoms as a medium. The parameters ε and σ in the Lennard-Jones potential energy function of the medium are used as adjustment parameters. The influence of σ and ε on the interaction energy between the pressure-regulating gas medium and the pyrolysis products is determined by the controlled variable method, and ε and σ are determined based on the results. Based on the adjusted force field parameters, molecular dynamics simulation of the pressure-regulating gas medium molecules was performed using the NPT ensemble under the target temperature condition. The relationship curve between the density and pressure of the pressure-regulating gas medium was obtained by refitting the simulation. Based on the relationship curve, the pressure in different regions inside the pressure-controlled transport pore system can be adjusted by changing the amount of pressure-regulating gas medium filled in.

7. The simulation method for pressure-controlled transport and coupled motion of carbon dioxide-enhanced kerogen pyrolysis products according to claim 6, characterized in that, According to the aforementioned relationship curve, adjusting the pressure in different regions within the pressure-controlled transport pore system by adjusting the amount of pressure-regulating gas medium filled specifically includes the following sub-steps: First, based on the target control pressure and the aforementioned relationship curve, the corresponding pressure regulating gas medium density is determined. Then, the total mass of the pressure-regulating gas medium is determined by combining the pore volume of the pressure-controlled region, and the total quantity of gas medium in the pressure-controlled region is calculated: （1） In the formula: m The total mass of the pressure-regulating gas medium is expressed in grams. ρ The density of the pressure-regulating gas medium is expressed in g / cm³. 3 ; V The volume of the pressure-regulating gas medium is in cm³. 3 ; （2） Finally, the adsorption simulation of the pressure-regulated gas medium was carried out in regions using the giant canonical Monte Carlo algorithm based on the fixed atomic mass method.

8. The simulation method for pressure-controlled transport and coupled motion of carbon dioxide-enhanced kerogen pyrolysis products according to claim 4, characterized in that, In step S2, when pyrolysis product transport simulation is performed, First, the boundary layer near the pore channel outlet of the hydrocarbon accumulation zone is opened to connect the hydrocarbon accumulation zone and the pore channel zone. Molecular dynamics simulation is carried out to achieve diffusion equilibrium of the pressure regulating gas medium inside the hydrocarbon accumulation zone and the pore channel zone, thereby achieving pressure equilibrium of the pressure regulating gas medium inside the system. Subsequently, the boundary layer near the pore channel entrance of the pyrolysis product region was opened to connect the pyrolysis product region and the pore channel region. Molecular dynamics simulations were then conducted to allow the mixed fluid components and pressure-regulating gas medium in the pyrolysis product region to migrate to the hydrocarbon accumulation region through the pore channel region until the pressure and pyrolysis product distribution of the entire system reached equilibrium.

9. The simulation method for pressure-controlled transport and coupled motion of carbon dioxide-enhanced kerogen pyrolysis products according to any one of claims 1-8, characterized in that, In step S3, two depletion mining dynamism modes are used to perform molecular simulations of the coupled dynamism of enrichment products; among them, Mode 1 is: after the products of carbon dioxide-enhanced kerogen pyrolysis are transported and enriched, they flow to the bottom of the well along new seepage channels under the bottom pressure differential. Mode 2 is as follows: After the products of carbon dioxide-enhanced kerogen pyrolysis migrate and accumulate, they flow to the bottom of the well under the pressure differential at the bottom of the well along the pore channels of the original migration and accumulation process.

10. The simulation method for pressure-controlled transport and coupled motion of carbon dioxide-enhanced kerogen pyrolysis products according to claim 9, characterized in that, For Mode 1, in the kerogen pore system after migration and enrichment, the pyrolysis products of the reservoir enrichment zone are retained, while the pyrolysis products of the pore channel zone and the pyrolysis product zone, as well as the pressure-controlled gas medium, are deleted. The pyrolysis product zone is redefined as the bottom-hole production zone. Subsequently, molecular dynamics simulations are carried out to make the pyrolysis products of the reservoir enrichment zone flow to the bottom-hole production zone through the pore channel zone. For Mode 2, in the kerogen pore system after migration and enrichment, the pyrolysis products in the reservoir enrichment zone and the pyrolysis products in the pore channels during the migration and enrichment process are retained. The pressure-controlled gas medium and the residual pyrolysis products in the pyrolysis product zone of the entire system are deleted, and the pyrolysis product zone is redefined as the bottom-hole production zone. Subsequently, molecular dynamics simulations are carried out to make the pyrolysis products in the reservoir enrichment zone flow back to the bottom-hole production zone through the migration and enrichment channel zone.

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