A rock surface wettability prediction method and system

Abstract

This application discloses a rock surface wettability prediction method and system that accurately predicts changes in rock surface wettability during CO2 geological storage. The method includes: constructing structural models of CO2 molecules, structural models of individual molecules contained in a brine simulating fluid, and a structural model of the rock surface; based on the constructed structural models, using molecular dynamics simulation to simulate the CO2-brine-rock system under target formation conditions; calculating the contact angle of a brine simulating fluid droplet on the rock surface after the simulated CO2-brine-rock system reaches equilibrium; and adjusting the target formation conditions to calculate the contact angle of the brine simulating fluid droplet on the rock surface under different target formation conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of CO2 geological storage, and more particularly to a method and system for predicting rock surface wettability. Background Art

[0002] The extensive use of fossil fuels such as coal, oil, and natural gas has led to an increase in atmospheric carbon dioxide (CO2) concentrations, exacerbating the greenhouse effect. Geological storage of CO2 is an effective way to reduce CO2 emissions. This involves compressing and injecting CO2 into strata for long-term, safe isolation and storage, thereby reducing direct emissions into the atmosphere.

[0003] The wettability of the CO2-brine-rock system (i.e., the wettability of the rock surface) is the main factor affecting CO2 geological storage. Accurately predicting the wettability of the rock surface is of great significance to CO2 geological storage.

[0004] At present, through experiments, we can basically determine the relationship between the wetting angle of brine droplets on the rock surface and its influencing factors. However, as the formation conditions change, the changes in the wettability of the rock surface during CO2 geological storage are generally difficult to observe in experiments. Summary of the Invention

[0005] In view of this, the present invention provides a rock surface wettability prediction method and system to accurately predict the changes in rock surface wettability during CO2 geological storage.

[0006] A rock surface wettability prediction method, comprising:

[0007] Construct structural models of CO2 molecules, structural models of individual molecules contained in the brine simulation fluid, and structural models of the rock surface;

[0008] Based on the constructed structural models, molecular dynamics simulation was used to simulate the CO2-brine-rock system under target formation conditions.

[0009] When the simulated CO2-brine-rock system reaches equilibrium, the contact angle of the brine simulated liquid droplet on the rock surface is calculated;

[0010] Adjust the target formation conditions and calculate the contact angle of the brine simulation fluid droplet on the rock surface under different target formation conditions.

[0011] Optionally, the saline simulation liquid is pure water or sodium chloride aqueous solution.

[0012] Optionally, construct a structural model of the rock surface, including:

[0013] Rocks include organic and inorganic components. A graphene model is used to simulate the organic components of rocks, and a mineral crystal model is used to simulate the inorganic components of rocks, thereby constructing a structural model of the rock surface.

[0014] Optionally, after constructing the structural model of CO2 molecules, the structural models of each molecule contained in the brine simulated fluid, and the structural model of the rock surface, the method further includes:

[0015] Structural optimization is performed on each constructed structural model.

[0016] Optionally, based on the constructed structural models, molecular dynamics simulation methods are used to simulate the CO2-brine-rock system under target formation conditions, including:

[0017] Build a cube simulation box;

[0018] Placing the structural model of the rock surface in the cubic simulation box, placing the structural model of the CO2 molecule and the structural models of each molecule contained in the brine simulation liquid in the cubic simulation box above the structural model of the rock surface, and setting target formation conditions such as temperature, pressure, and brine concentration to simulate the CO2-brine-rock system under the target formation conditions;

[0019] The pressure of the target formation is adjusted by the number of CO2 molecules placed in the box, the brine concentration of the target formation is adjusted by the number of molecules contained in the brine simulation fluid placed in the box, and the temperature of the target formation is directly input as a temperature parameter.

[0020] Optionally, the calculating the contact angle of the brine simulated liquid droplet on the rock surface includes:

[0021] Take the projection of the droplet in the axial direction, fit the projection curve with the circle equation, and calculate the contact angle of the droplet on the rock surface.

[0022] A rock surface wettability prediction system, comprising:

[0023] A structural model building unit, used to build a structural model of CO2 molecules, a structural model of each molecule contained in a brine simulation fluid, and a structural model of a rock surface;

[0024] The system simulation unit is used to simulate the CO2-brine-rock system under the target formation conditions using molecular dynamics simulation methods based on the constructed structural models;

[0025] The contact angle calculation unit is used to calculate the contact angle of the brine simulation liquid droplet on the rock surface after the simulated CO2-brine-rock system reaches equilibrium;

[0026] Parameter setting unit, used to adjust target formation conditions;

[0027] The rock surface wettability prediction system also uses the system simulation unit and the contact angle calculation unit to calculate the contact angle of the brine simulation liquid droplet on the rock surface under different target formation conditions according to the adjusted target formation conditions.

[0028] Optionally, the rock surface wettability prediction system further includes: a structure optimization unit for performing structural optimization on each constructed structure model.

[0029] Optionally, the system simulation unit is specifically used to construct a cubic simulation box; placing a structural model of the rock surface in the cubic simulation box, placing a structural model of the CO2 molecule and a structural model of each molecule contained in the brine simulation liquid in the cubic simulation box above the structural model of the rock surface, setting target formation conditions such as temperature, pressure, and brine concentration, thereby simulating the CO2-brine-rock system under the target formation conditions;

[0030] The pressure of the target formation is adjusted by the number of CO2 molecules placed in the box, the brine concentration of the target formation is adjusted by the number of molecules contained in the brine simulation fluid placed in the box, and the temperature of the target formation is directly input as a temperature parameter.

[0031] Optionally, the contact angle calculation unit is specifically used to obtain the projection of the droplet in the axial direction, fit the projection curve with a circle equation, and calculate the contact angle of the droplet on the rock surface.

[0032] As can be seen from the above technical solution, the present invention does not adopt experimental testing methods, but instead adopts molecular dynamics simulation methods to predict the changes in the wettability of the rock surface during the geological storage of CO2, thereby avoiding experimental errors and the huge workload caused by repeated experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 This is a flow chart of a rock surface wettability prediction method disclosed in an embodiment of the present invention;

[0035] Figure 2a A schematic diagram of a rock surface structural model disclosed in an embodiment of the present invention placed in a cubic simulation box;

[0036] Figure 2bThis is a schematic diagram of the initial state of a CO2-brine-rock system simulation disclosed in an embodiment of the present invention;

[0037] Figure 2c This is a schematic diagram of a CO2-brine-rock system simulation after reaching equilibrium according to an embodiment of the present invention;

[0038] Figure 2d A schematic diagram of contact angle calculation disclosed in an embodiment of the present invention;

[0039] Figure 3 This is a schematic diagram of the structure of a rock surface wettability prediction system disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] For the purpose of reference and clarity, the technical terms, abbreviations or acronyms used below are summarized as follows:

[0041] CO2: chemical formula for carbon dioxide;

[0042] Na + : Chemical formula of sodium ion;

[0043] Cl-: chemical formula of chloride ion;

[0044] NaCl: The chemical formula for sodium chloride.

[0045] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0046] See also Figure 1 The embodiment of the present invention discloses a method for predicting rock surface wettability, comprising:

[0047] Step S01: constructing a structural model of CO2 molecules, a structural model of each molecule contained in the brine simulation fluid, and a structural model of the rock surface.

[0048] Step S02: Based on the constructed structural models, a molecular dynamics simulation method is used to simulate the CO2-brine-rock system under target formation conditions.

[0049] Specifically, rock is a naturally porous material containing a large number of irregular, multi-scale pores. The pores within the rock formation provide ample storage space for CO2 geological storage. Some of these pores contain brine, and CO2 geological storage is significantly affected by the wettability of the CO2-brine-rock system (i.e., the wettability of the rock surface). Therefore, accurately predicting the wettability of the rock surface is crucial when studying CO2 geological storage.

[0050] Experimental testing of rock surface wettability is subject to certain experimental errors and requires a significant workload due to repeated testing. Therefore, the present invention does not employ experimental testing, but instead uses molecular dynamics simulation to predict changes in rock surface wettability during CO2 geological storage.

[0051] Molecular dynamics simulation is an important simulation method in the microscopic field of matter that simulates atoms and molecules in evaluating and predicting material structure and properties. For convenience, a cubic simulation box is generally used for simulation calculations. Based on this, the embodiment of the present invention respectively constructs a structural model of CO2 molecules, a structural model of each molecule and ion contained in the brine simulation liquid, a structural model of the rock surface, and a cubic simulation box. The dimensions of the box in the x, y, and z directions can be set according to actual needs (for example, the dimensions of the box in the x, y, and z directions are all set to 10 nm), and periodic boundary conditions are set for the box in the x, y, and z directions; the structural model of the rock surface is placed in the cubic simulation box, the structural model of the CO2 molecules and the structural models of each molecule / ion contained in the brine simulation liquid are placed in the cubic simulation box and above the structural model of the rock surface, and target formation conditions such as temperature, pressure, and brine concentration are set (the pressure of the target formation is adjusted by the number of CO2 molecules placed in the box, the brine concentration of the target formation is adjusted by the number of each molecule contained in the brine simulation liquid placed in the box, and the temperature of the target formation is directly input as a temperature parameter), thereby simulating the CO2-brine-rock system under the target formation conditions.

[0052] The process of constructing the structural model of each molecule contained in the saline simulated liquid is as follows:

[0053] Formation water has been in contact with rocks and crude oil in the formation for a long time, and usually contains a considerable amount of metal salts, such as potassium salts, sodium salts, calcium salts, magnesium salts, etc., especially potassium salts and sodium salts, so it is called brine. The high salt content in formation water is its biggest feature that distinguishes it from surface water. When constructing the structural model of each molecule contained in the brine simulation fluid, in order to simplify the calculation, the salinity of the formation water can be ignored, and pure water can be used to simulate the formation water. At this time, constructing the structural model of each molecule contained in the brine simulation fluid is to construct the structural model of the water molecule. Of course, in order to further improve the accuracy of formation water simulation, the salinity of formation water can be considered. Since the highest content of cations and anions in formation water are Na and N respectively, the salinity of formation water can be taken into consideration. + and Cl-, so the formation water can be simulated by NaCl aqueous solution. At this time, the microstructure model of formation water is constructed by constructing water molecules, Na + and Cl - The structural model of + and Cl - The number of batteries must be equal to ensure charge neutrality.

[0054] Optionally, after constructing the structural models of the CO2 molecule and each molecule contained in the brine simulant, they should also be structurally optimized to improve the accuracy of the model construction. In specific implementations, the structural models of each molecule contained in the brine simulant and the CO2 molecule can be drawn using the 3D modeling sketching software Skech tool in the materials performance simulation software Materials Studio. These can then be structurally optimized using the materials performance simulation software Materials Studio to obtain the minimum energy conformation.

[0055] The process of constructing the structural model of the rock surface is as follows:

[0056] Rocks consist of both organic and inorganic components. The process of constructing a structural model of the rock surface is the process of constructing both the organic and inorganic component models of the rock based on the pore distribution of the target rock formation.

[0057] This embodiment of the present invention recommends using a graphene model to simulate the organic components of rocks, but this is not a limitation. In specific implementations, a three-layer graphene model can be constructed using the open-source VMD software to simulate the rock's organic components. Inorganic components of rocks, such as silica, can be simulated using a mineral crystal model. The material properties simulation software Material Studio provides ready-made crystal structures for use. Inorganic component models can also be constructed directly using Materials Studio's 3D modeling sketching software, which includes crystal structures for various inorganic rocks.

[0058] Optionally, after constructing the structural model of the rock surface, it should also be structurally optimized to improve the accuracy of the model construction.

[0059] The following takes pure water to simulate formation water as an example. Figure 2a to Figure 2c Here is an illustration of the process of simulating the CO2-brine-rock system under target formation conditions using molecular dynamics simulation: Figure 2a to Figure 2c The dashed line in represents the boundary of the cube box simulation. Figure 2a to Figure 2c The shaded area in the figure represents the structural model of the rock surface placed in the cubic simulation box. Figure 2b to Figure 2c The circle marked with 1 represents a CO2 molecule, and the circle marked with 2 represents a water molecule; Figure 2a This is a schematic diagram of the rock surface structure model placed in a cubic simulation box. Figure 2b is the initial state of the CO2-brine-rock system simulation, Figure 2c It is the state after the CO2-brine-rock system reaches equilibrium.

[0060] Step S03: When the simulated CO2-brine-rock system reaches equilibrium, the contact angle of the brine simulated liquid droplet on the rock surface is calculated.

[0061] Specifically, the wettability of a rock surface (i.e., the wetting properties of a liquid on the rock surface) can be determined by directly measuring the contact angle of a brine droplet on the rock surface. In this embodiment of the present invention, measuring the rock surface wettability can be simplified to measuring the contact angle of a brine simulant droplet on a graphene surface under target formation conditions. In practice, the NVT ensemble within the molecular dynamics method is used to simulate the contact angle of a brine simulant droplet on a graphene surface under specified target formation conditions.

[0062] In molecular dynamics simulation, when the droplet shape is roughly stable and the CO2 density distribution does not change with the simulation time, it can be determined that the system has reached equilibrium. After the system reaches equilibrium, take the axial projection of the droplet, such as Figure 2d Using the circular equation to fit the projected curve, the contact angle θ of the droplet on the rock surface is calculated, thereby determining the wettability of the rock surface. The changing trend of the contact angle reflects the changing trend of the rock surface wettability: the smaller the contact angle, the more hydrophilic it is; the larger the contact angle, the less hydrophilic it is.

[0063] Step S04: adjusting the target formation conditions and calculating the contact angle of the brine simulation liquid droplet on the rock surface under different target formation conditions.

[0064] Specifically, the target formation conditions (such as rock composition, temperature, pressure, gas composition, and droplet composition) are adjusted. Based on the constructed structural models, molecular dynamics simulations are used to simulate the CO2-brine-rock system under these adjusted target formation conditions. Once the simulated CO2-brine-rock system reaches equilibrium, the contact angle of the brine droplet on the rock surface is calculated. Repeating this operation repeatedly can reveal how the rock surface wettability changes during the geological storage of CO2.

[0065] Corresponding to the above method embodiment, the present invention also discloses a rock surface wettability prediction system, such as Figure 3 Shown, including:

[0066] The structural model building unit 100 is used to build a structural model of the CO2 molecule, a structural model of each molecule contained in the brine simulation fluid, and a structural model of the rock surface;

[0067] The system simulation unit 200 is used to simulate the CO2-brine-rock system under target formation conditions using a molecular dynamics simulation method based on the constructed structural models;

[0068] The contact angle calculation unit 300 is used to calculate the contact angle of the brine simulated liquid droplet on the rock surface after the simulated CO2-brine-rock system reaches equilibrium;

[0069] Parameter setting unit 400, used to adjust target formation conditions;

[0070] The rock surface wettability prediction system also uses the system simulation unit 300 and the contact angle calculation unit 400 to calculate the contact angle of the brine simulation liquid droplet on the rock surface under different target formation conditions according to the adjusted target formation conditions.

[0071] Optionally, the saline simulation liquid is pure water or sodium chloride aqueous solution.

[0072] Optionally, in any of the rock surface wettability prediction systems disclosed above, the structural model construction unit 100 is specifically used to simulate the organic components of the rock using a graphene model and simulate the inorganic components of the rock using a mineral crystal model, thereby constructing a structural model of the rock surface.

[0073] Optionally, in any of the rock surface wettability prediction systems disclosed above, the rock surface wettability prediction system further includes: a structure optimization unit, which is used to perform structural optimization on each constructed structure model.

[0074] Optionally, in any of the rock surface wettability prediction systems disclosed above, the system simulation unit is specifically used to construct a cubic simulation box; a structural model of the rock surface is placed in the cubic simulation box, a structural model of the CO2 molecule and a structural model of each molecule contained in the brine simulation liquid are placed in the cubic simulation box above the structural model of the rock surface, and target formation conditions such as temperature, pressure, and brine concentration are set, thereby simulating the CO2-brine-rock system under the target formation conditions;

[0075] The pressure of the target formation is adjusted by the number of CO2 molecules placed in the box, the brine concentration of the target formation is adjusted by the number of molecules contained in the brine simulation fluid placed in the box, and the temperature of the target formation is directly input as a temperature parameter.

[0076] Optionally, in any of the rock surface wettability prediction systems disclosed above, the contact angle calculation unit 300 is specifically used to obtain the axial projection of the droplet, fit the projection curve with a circle equation, and calculate the contact angle of the droplet on the rock surface.

[0077] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0078] The terms "first," "second," and the like in the specification and claims of the present invention and the accompanying drawings are used to distinguish between similar objects and are not necessarily used to describe a specific order or precedence. Furthermore, the terms "comprises," "comprising," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, product, or apparatus comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, product, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a" does not preclude the presence of additional identical elements in the process, method, product, or apparatus comprising the element.

[0079] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the above description has generally described the components and steps of each example according to their functions. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

[0080] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein may be implemented directly using hardware, a software module executed by a processor, or a combination of the two. The software module may be placed in a random access memory (RAM), internal memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

[0081] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, i.e., they may be located in one place or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of the present embodiment. Persons of ordinary skill in the art will be able to understand and implement the present invention without inventive effort.

[0082] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the embodiments of the present invention. Therefore, the embodiments of the present invention are not limited to the embodiments shown herein, but are intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A rock surface wettability prediction method, characterized in that: include: Construct structural models of CO2 molecules, structural models of individual molecules contained in the brine simulation fluid, and structural models of the rock surface; Based on the constructed structural models, molecular dynamics simulation was used to simulate the CO2-brine-rock system under target formation conditions. When the simulated CO2-brine-rock system reaches equilibrium, the contact angle of the brine simulated liquid droplet on the rock surface is calculated; Adjust the target formation conditions and calculate the contact angle of the brine simulant droplet on the rock surface under different target formation conditions; The rock surface structural model is constructed by: rock comprises organic and inorganic components, a graphene model is used to simulate the organic components of the rock, and a mineral crystal model is used to simulate the inorganic components of the rock, thereby constructing the rock surface structural model; The method uses a molecular dynamics simulation method based on the constructed structural models to simulate the CO2-brine-rock system under the target formation conditions, including: constructing a cubic simulation box; placing the structural model of the rock surface in the cubic simulation box, placing the structural model of the CO2 molecule and the structural models of the molecules contained in the brine simulation liquid in the cubic simulation box above the structural model of the rock surface, and setting the three target formation conditions of temperature, pressure and brine concentration to simulate the CO2-brine-rock system under the target formation conditions; wherein the pressure of the target formation is adjusted by the number of CO2 molecules placed in the box, the brine concentration of the target formation is adjusted by the number of molecules contained in the brine simulation liquid placed in the box, and the temperature of the target formation is directly input as a temperature parameter.

2. The rock surface wettability prediction method according to claim 1, characterized in that: The saline simulation liquid is pure water or sodium chloride aqueous solution.

3. The rock surface wettability prediction method according to claim 1, characterized in that: After constructing the structural model of CO2 molecules, the structural models of each molecule contained in the brine simulated fluid, and the structural model of the rock surface, the method further includes: Structural optimization is performed on each constructed structural model.

4. The rock surface wettability prediction method according to claim 1, characterized in that: The method of calculating the contact angle of a brine simulated liquid droplet on a rock surface includes: Take the projection of the droplet in the axial direction, fit the projection curve with the circle equation, and calculate the contact angle of the droplet on the rock surface.

5. A rock surface wettability prediction system, characterized in that: include: A structural model building unit, used to build a structural model of CO2 molecules, a structural model of each molecule contained in a brine simulation fluid, and a structural model of a rock surface; The system simulation unit is used to simulate the CO2-brine-rock system under the target formation conditions using molecular dynamics simulation methods based on the constructed structural models; The contact angle calculation unit is used to calculate the contact angle of the brine simulation liquid droplet on the rock surface after the simulated CO2-brine-rock system reaches equilibrium; Parameter setting unit, used to adjust target formation conditions; The rock surface wettability prediction system further utilizes the system simulation unit and the contact angle calculation unit to calculate the contact angle of the brine simulation liquid droplet on the rock surface under different target formation conditions according to the adjusted target formation conditions; The rock surface structural model is constructed by: rock comprises organic and inorganic components, a graphene model is used to simulate the organic components of the rock, and a mineral crystal model is used to simulate the inorganic components of the rock, thereby constructing the rock surface structural model; The system simulation unit is specifically used to construct a cubic simulation box; the structural model of the rock surface is placed in the cubic simulation box, the structural model of the CO2 molecule and the structural model of each molecule contained in the brine simulation liquid are placed in the cubic simulation box and above the structural model of the rock surface, and the three target formation conditions of temperature, pressure and brine concentration are set to simulate the CO2-brine-rock system under the target formation conditions; wherein the pressure of the target formation is adjusted by the number of CO2 molecules placed in the box, the brine concentration of the target formation is adjusted by the number of each molecule contained in the brine simulation liquid placed in the box, and the temperature of the target formation is directly input as a temperature parameter.

6. The rock surface wettability prediction system according to claim 5, characterized in that: The rock surface wettability prediction system further includes: a structure optimization unit, which is used to perform structure optimization on each constructed structure model.

7. The rock surface wettability prediction system according to claim 5, characterized in that: The contact angle calculation unit is specifically used to obtain the projection of the liquid droplet in the axial direction, fit the projection curve with a circle equation, and calculate the contact angle of the liquid droplet on the rock surface.

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