A method for quantitatively characterizing fluid adsorption by rock pore surfaces

Abstract

The application relates to a method for quantitatively characterizing fluid adsorption on a rock pore surface, comprising the following steps: establishing a molecular simulation initial model based on the molecular structure and physical parameters of the rock and the fluid; giving the molecular simulation initial model an initial velocity and a force field, and starting the movement of the molecules; after the model is in a thermal equilibrium state, recording the coordinate information of each fluid molecule at each time step; taking the rock pore surface Z0 as a starting point, dividing the whole model into n series of cuboid intervals with equal intervals of Delta r along the Z axis; solving the model ensemble average, and then calculating the atomic number density in each cuboid; drawing a fluid atomic number density diagram along the Z axis, and then determining the adsorption layer and the homogeneous phase zone; and calculating the atomic number density ratio in the adsorption layer and the homogeneous phase zone, which is the adsorption capacity of the rock surface to the component. The method can accurately calculate the adsorption capacity of the solid surface, and provides theoretical support for subsequent research on fluid flow mechanism and analysis of flow characteristics.

Description

Technical Field

[0001] This invention relates to a method for quantitatively characterizing fluid adsorption on the pore surface of rocks, belonging to the field of petroleum development technology. Background Technology

[0002] When a fluid comes into contact with the porous surface of a rock, one or more components of the fluid accumulate on the solid surface; this phenomenon is called adsorption. The magnitude of adsorption capacity depends on the strength of the interaction between the rock surface and the fluid molecules; it is a natural property of rocks. Adsorption is of great significance in the field of petroleum development. At the microscopic scale, it is the result of the interaction between the fluid and the solid surface, and between fluids themselves, influencing fluid distribution and flow characteristics. At the macroscopic scale, it affects the fluid flow equation, controls the flow rate of oil, gas, and other fluids in rock pores, and directly relates to oil and gas recovery rates. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for quantitatively characterizing fluid adsorption on porous surfaces, which can accurately calculate the adsorption capacity of solid surfaces and provide theoretical support for subsequent research on fluid flow mechanisms and analysis of flow characteristics.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for quantitatively characterizing fluid adsorption on rock pore surfaces includes:

[0006] An initial molecular simulation model was established based on the molecular structure and physical property parameters of rocks and fluids.

[0007] An initial velocity and force field are given to the molecular simulation model, and the molecules begin to move. After the model reaches thermal equilibrium, the coordinate information of each fluid molecule at each time step is recorded.

[0008] Starting from the rock pore surface Z0, the entire model is divided into n series of cuboid intervals with equal spacing Δr distributed along the Z-axis;

[0009] Solve for the ensemble mean of the model, and then calculate the atomic number density in each cuboid;

[0010] Plot the fluid atomic number density along the Z-axis to determine the adsorption layer and homogeneous region;

[0011] The ratio of the atomic number density in the adsorption layer to that in the homogeneous region is calculated, which represents the adsorption capacity of the rock surface for this component.

[0012] The method for quantitatively characterizing fluid adsorption on rock pore surfaces preferably divides the entire model into n series of cuboid intervals with equal spacing Δr distributed along the Z-axis, starting from the rock pore surface Z0, as follows:

[0013] Using the rock pore surface Z0 as the base, divide the rock along the Z-axis into several cuboid intervals i = 1, 2, 3...n, with the width Δr of each cuboid being... The length of the cuboid in the X / Y direction is consistent with the length of the entire system in the X / Y direction.

[0014] The method for quantitatively characterizing fluid adsorption on rock pore surfaces preferably involves solving the ensemble average of the model and then calculating the atomic number density in each cuboid, as detailed below:

[0015] The number of fluid molecules falling into the cuboid interval at each time step t after thermal equilibrium is calculated. The average number of atoms in each interval after ensemble averaging is obtained by formula (1), and then the atomic number density is obtained by formula (2).

[0016]

[0017]

[0018] In the formula, N represents the average number of atoms. i N represents the number of atoms falling into the i-th cuboid interval at the current time step. t To calculate the total number of time steps when taking the ensemble average, V i ρ is the volume of the i-th cuboid interval. N For the desired atomic number density, t equil This is the time it takes for the system to reach thermal equilibrium.

[0019] The method for quantitatively characterizing fluid adsorption on rock pore surfaces, preferably,

[0020] The ratio of the atomic number density in the adsorption layer to that in the homogeneous region is calculated, which represents the adsorption capacity of the solid rock surface for this component, as detailed below:

[0021]

[0022] In the formula, ρ a ρ is the number density value of the adsorption layer. u This represents the number density value in the homogeneous region.

[0023] A second aspect of the present invention provides an apparatus for quantitatively characterizing fluid adsorption on the surface of rock pores, comprising:

[0024] The first processing unit is used to establish an initial molecular simulation model based on the molecular structure and physical property parameters of rocks and fluids.

[0025] The second processing unit is used to give the molecular simulation initial model an initial velocity and force field. The molecules start to move. After the model is in thermal equilibrium, the coordinate information of each fluid molecule at each time step is recorded.

[0026] The third processing unit is used to divide the entire model into n series of cuboid intervals with equal spacing Δr distributed along the Z-axis, starting from the rock pore surface Z0.

[0027] The fourth processing unit is used to solve the ensemble average of the model, and then calculate the atomic number density in each cuboid;

[0028] The fifth processing unit is used to draw a fluid atomic number density map distributed along the Z-axis, thereby determining the adsorption layer and the homogeneous region;

[0029] The sixth processing unit is used to calculate the ratio of the atomic number density in the adsorption layer to that in the homogeneous region, which is the adsorption capacity of the rock surface for this component.

[0030] A third aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the method for quantitatively characterizing fluid adsorption on the pore surface of rocks as described in any of the preceding claims.

[0031] A fourth aspect of the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, when the processor executes the computer program, it implements the steps of the method for quantitatively characterizing fluid adsorption on the pore surface of rocks as described in any one of the preceding claims.

[0032] The present invention has the following advantages due to the adoption of the above technical solutions:

[0033] 1. This invention calculates the atomic number density in each spatially divided cuboid interval by solving the ensemble average of the model, thereby determining the ratio of the atomic number density in the adsorption layer to that in the homogeneous layer, and finally obtaining a characterization index of the solid surface's adsorption capacity for fluids. This method is simple to operate, inexpensive to test, and can accurately and quickly calculate the adsorption capacity of rock pore surfaces.

[0034] 2. The method for quantitatively calculating the adsorption of fluids on pore surfaces at the nanoscale provided by this invention can realize rapid adsorption capacity calculation, which is not only simple and feasible to operate, but also significantly reduces costs.

[0035] 3. The characterization method of the present invention does not require any experimental testing, which reduces research costs and shortens the operation cycle, thereby achieving the goal of cost reduction and efficiency improvement. This method can be widely used in the study of adsorption determination of solid surfaces at the nanoscale. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a method for calculating adsorption on the surface of rock pores at the nanoscale according to an embodiment of the present invention.

[0037] Figure 2 This is a schematic diagram of the cuboid interval division in the initial molecular simulation model provided in this embodiment of the invention;

[0038] Figure 3 This is a schematic diagram illustrating how the adsorption layer and homogeneous region are determined from the atomic number density distribution diagram, and the adsorption capacity of the solid surface is calculated, according to this embodiment of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," "third," "fourth," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect.

[0041] Due to scale and environmental limitations, conventional experimental methods are insufficient for conducting adsorption studies at the nanoscale, let alone quantitatively characterizing them. Therefore, molecular dynamics simulations are frequently applied to fundamental research at the microscale. In molecular simulations, fluid molecules stack at the fluid / solid surface after interacting with it, forming an "adsorption layer." Under thermal equilibrium, the number of molecules within the adsorption layer and the number of molecules in the homogeneous region far from the solid surface are in dynamic equilibrium, meaning the number of molecules remains constant. The ratio of the ensemble average of the molecular number densities in both regions is then calculated, providing a characterization index for fluid adsorption.

[0042] This invention calculates the atomic number density in each spatially divided cuboid interval by solving the system ensemble average, thereby determining the ratio of the atomic number density in the adsorption layer to that in the homogeneous layer, and finally obtaining a characterization index of the solid surface's adsorption capacity for fluids. This method is simple to operate, inexpensive to test, and can accurately and quickly calculate the adsorption capacity of rock pore surfaces.

[0043] The technical solution of the present invention will be described below with reference to specific embodiments.

[0044] like Figure 1 As shown, the method for quantitatively characterizing adsorption on the surface of rock pores at the nanoscale provided by this invention includes the following steps:

[0045] Step 1: Based on the molecular structure that makes up rocks and fluids, establish an initial molecular simulation model. The model contains all molecular position information and bonding information, and defines coordinate axes.

[0046] Step 2: Assign force field parameters, set temperature, and give the initial model a random initial velocity. After the molecules are subjected to intermolecular forces, they begin to move. Once the model is in thermal equilibrium, record the coordinate information of each fluid molecule at each time step. There is no need to establish additional coordinates here, because the initial model already includes the position information of atoms. Therefore, it is only necessary to export the position information of the fluid molecules after equilibrium from the digital model.

[0047] Step 3: Starting from the rock pore surface Z0, divide the entire model into n series of cuboid intervals with equal spacing Δr distributed along the Z-axis, such as... Figure 2 ;

[0048] Step 4: Solve for the ensemble mean of the model, and then calculate the atomic number density in each cuboid. Here, the ensemble mean is the average of the system over time.

[0049] Step 5: Draw a fluid atomic number density map along the Z-axis to determine the adsorption layer and homogeneous region.

[0050] Step 6: Calculate the ratio of the atomic number density in the adsorption layer to that in the homogeneous region, which is the adsorption capacity of the rock surface for this component.

[0051] In the above embodiments, preferably, the specific process of dividing the cuboid interval in step three is as follows:

[0052] After the model reaches thermal equilibrium, it is divided into cuboid intervals in space. Specifically, taking the rock pore surface Z0 as the base, several cuboid intervals (i = 1, 2, 3... n) are divided along the Z-axis, with the width Δr of each cuboid being... like Figure 2As shown. The length of the cuboid in the X / Y direction is consistent with the length of the entire system in the X / Y direction.

[0053] In the above embodiments, preferably, in step four, the ensemble average of the model is solved, and then the atomic number density in each cuboid interval is calculated. The specific process is as follows:

[0054] The number of fluid molecules falling within the cuboid interval at each time step t after thermal equilibrium is calculated. The average number of atoms in each interval after ensemble averaging is obtained by formula (1), and then the atomic number density is obtained by formula (2).

[0055]

[0056]

[0057] In the formula N represents the average number of atoms. i N represents the number of atoms falling into the i-th cuboid interval at the current time step. t To calculate the total number of time steps when taking the ensemble average, V i ρ is the volume of the i-th cuboid interval. N For the desired atomic number density, t equil This is the time it takes for the system to reach thermal equilibrium.

[0058] In the above embodiments, preferably, in steps five and six, an atomic number density distribution map is plotted to determine the adsorption layer and the homogeneous region, and the adsorption capacity is calculated.

[0059] Based on the known atomic number density of each cuboid region, a fluid atomic number density distribution diagram is plotted to determine the adsorption layer and the homogeneous region. For example... Figure 3 As shown in the figure, the atomic number density distribution information of the three fluid components is included. The gray "protrusions" at both ends are the adsorption layers of each component, and the "horizontal line" in the middle is the homogeneous region. The ratio of the number density value of the adsorption layer of each component to the number density value of the homogeneous region is calculated, as shown in formula (3), which is the adsorption capacity of the solid rock surface for the component, ψ.

[0060]

[0061] In the formula, ρ a ρ is the number density value of the adsorption layer. u This represents the number density value in the homogeneous region.

[0062] A second aspect of the present invention provides an apparatus for quantitatively characterizing fluid adsorption on the surface of rock pores, comprising:

[0063] The first processing unit is used to establish an initial molecular simulation model based on the molecular structure and physical property parameters of rocks and fluids.

[0064] The second processing unit is used to give the molecular simulation initial model an initial velocity and force field. The molecules start to move. After the model is in thermal equilibrium, the coordinate information of each fluid molecule at each time step is recorded.

[0065] The third processing unit is used to divide the entire model into n series of cuboid intervals with equal spacing Δr distributed along the Z-axis, starting from the rock pore surface Z0.

[0066] The fourth processing unit is used to solve the ensemble average of the model, and then calculate the atomic number density in each cuboid;

[0067] The fifth processing unit is used to draw a fluid atomic number density map distributed along the Z-axis, thereby determining the adsorption layer and the homogeneous region;

[0068] The sixth processing unit is used to calculate the ratio of the atomic number density in the adsorption layer to that in the homogeneous region, which is the adsorption capacity of the rock surface for this component.

[0069] A third aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the method for quantitatively characterizing fluid adsorption on the pore surface of rocks as described in any of the preceding claims.

[0070] A fourth aspect of the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, when the processor executes the computer program, it implements the steps of the method for quantitatively characterizing fluid adsorption on the pore surface of rocks as described in any one of the preceding claims.

[0071] This invention is described based on flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to specific embodiments. It should be understood that each block of the flowcharts and / or block diagrams, and combinations of blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing device to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing device, generate instructions for implementing the flowcharts and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0072] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0073] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for quantitatively characterizing fluid adsorption on the pore surface of rocks, characterized in that, include: An initial molecular simulation model was established based on the molecular structure and physical property parameters of rocks and fluids. An initial velocity and force field are given to the molecular simulation model, and the molecules begin to move. After the model reaches thermal equilibrium, the coordinate information of each fluid molecule at each time step is recorded. Starting from the rock pore surface Z0, the entire model is divided into n series of cuboid intervals with equal spacing Δr distributed along the Z-axis; Solve for the ensemble mean of the model, and then calculate the atomic number density in each cuboid; Plot the fluid atomic number density along the Z-axis to determine the adsorption layer and homogeneous region; The ratio of the atomic number density in the adsorption layer to that in the homogeneous region is calculated, which represents the adsorption capacity of the rock surface for this component.

2. The method for quantitatively characterizing fluid adsorption on rock pore surfaces according to claim 1, characterized in that, Starting from the rock pore surface Z0, the entire model is divided into n series of cuboid intervals with equal spacing Δr distributed along the Z-axis, as follows: Using the rock pore surface Z0 as the base, divide the rock along the Z-axis into several cuboid intervals i = 1, 2, 3...n, with the width Δr of each cuboid being... The length of the cuboid in the X / Y direction is consistent with the length of the entire system in the X / Y direction.

3. The method for quantitatively characterizing fluid adsorption on rock pore surfaces according to claim 1, characterized in that, The ensemble mean of the model is calculated, and then the atomic number density in each cuboid is calculated, as follows: The number of fluid molecules falling into the cuboid interval at each time step t after thermal equilibrium is calculated. The average number of atoms in each interval after ensemble averaging is obtained by formula (1), and then the atomic number density is obtained by formula (2). In the formula, N represents the average number of atoms. i N represents the number of atoms falling into the i-th cuboid interval at the current time step. t To calculate the total number of time steps when taking the ensemble average, V i ρ is the volume of the i-th cuboid interval. N For the desired atomic number density, t equil This is the time it takes for the system to reach thermal equilibrium.

4. The method for quantitatively characterizing fluid adsorption on rock pore surfaces according to claim 1, characterized in that, The ratio of the atomic number density in the adsorption layer to that in the homogeneous region is calculated, which represents the adsorption capacity of the solid rock surface for this component, as detailed below: In the formula, ρ a ρ is the number density value of the adsorption layer. u This represents the number density value in the homogeneous region.

5. An apparatus for quantitatively characterizing fluid adsorption on the pore surface of rocks, characterized in that, include: The first processing unit is used to establish an initial molecular simulation model based on the molecular structure and physical property parameters of rocks and fluids. The second processing unit is used to give the molecular simulation initial model an initial velocity and force field. The molecules start to move. After the model is in thermal equilibrium, the coordinate information of each fluid molecule at each time step is recorded. The third processing unit is used to divide the entire model into n series of cuboid intervals with equal spacing Δr distributed along the Z-axis, starting from the rock pore surface Z0. The fourth processing unit is used to solve the ensemble average of the model, and then calculate the atomic number density in each cuboid; The fifth processing unit is used to draw a fluid atomic number density map distributed along the Z-axis, thereby determining the adsorption layer and the homogeneous region; The sixth processing unit is used to calculate the ratio of the atomic number density in the adsorption layer to that in the homogeneous region, which is the adsorption capacity of the rock surface for this component.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the method for quantitatively characterizing fluid adsorption on the pore surface of rocks according to any one of claims 1-4.

7. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method for quantitatively characterizing fluid adsorption on the pore surface of rocks according to any one of claims 1-4.

Images