Modeling method for arbitrary and random functional group modification on silica surface

Abstract

The present invention relates to a modeling method for arbitrarily controllable and randomly positioned modification of functional groups on the surface of silicon dioxide, comprising: introducing a primitive unit cell structure model of silicon dioxide; establishing a surface structure of silicon dioxide; performing 5×5 supercelling on the surface structure of the primitive unit cell in the XY two-dimensional direction to obtain a supercell structure with 100 oxygen atoms on the surface; defining a surface oxygen atom group, and obtaining information of each oxygen atom on the surface through programming; setting a variable N for determining that N methyl functional groups are generated on the surface; extracting oxygen atoms in a disordered array to obtain XYZ coordinate information of the extracted atoms; generating a C atom of a methyl functional group above the extracted atom, and the distance from the extracted atom in the Z direction is a bond length; the C atom of the methyl functional group forms a bond with the original surface oxygen atom, and hydrogenating the C atom to obtain a -CH 3 The present invention can accurately control the CH 3 Functional groups are used to modify the surface structure and construct microscopic models of different wettability of oil and gas reservoir minerals.

Description

Technical Field

[0001] The invention relates to the technical field of microscopic simulation of the petroleum and natural gas industry, and in particular to a method for establishing the modification of functional groups with different wettability on the surface of a mineral. Background Art

[0002] Wettability refers to the phenomenon that when two immiscible fluids come into contact with the solid surface of a rock, one of the phases spreads along the surface of the rock, resulting in a decrease in the surface free energy of the system. The phase that spreads along the surface of the rock is called the wetting phase [Yang Shenglai, Wei Junzhi. Reservoir Physics [M], Petroleum Industry Press]. Wettability is one of the important basic parameters of reservoir rocks in oil and gas reservoirs. Its characteristics directly affect the microscopic and macroscopic distribution characteristics of fluids in the rock pores, and also restrict the efficiency of oil and gas development. Therefore, in oil and gas development technology, surfactants are often added to change the wettability of mineral surfaces.

[0003] Surfactants are amphiphilic compounds with both hydrophobic and hydrophilic groups. By allowing surfactants to flow into and diffuse into the matrix, the wettability of reservoir rocks can be changed, while reducing interfacial tension and capillary pressure. The main mechanisms by which surfactants change wettability are: ion pair formation, surfactant adsorption, and micelle solubilization. Studies have shown that cationic surfactants, nonionic surfactants, zwitterionic surfactants, and anionic surfactants have better effects. Among them, nonionic surfactants mainly contain methyl or hydroxyl groups [Nguyen D, Wang D, Oladapo A, et al. Evaluation of Surfactants for Oil Recovery Potential in Shale Reservoirs[C] / / SPE Improved Oil Recovery Symposium. Society of Petroleum Engineers, 2014]. In addition, under certain temperature and pressure conditions, dimethyldichlorosilane can be used to modify the surface of nano-silica. As the amount of dimethyldichlorosilane increases, the number of hydroxyl groups on the surface of nano-silica decreases [Tang Hongbo, Li Meng, Ma Bingjie. Research on the process of modifying nano-silica with dichlorodimethylsilane [J]. Fine Petrochemicals, 2007 (06): 44-47]. Therefore, from a microscopic perspective, different wettability minerals can be characterized by different ratios of methyl and hydroxyl groups.

[0004] The molecular simulation method calculates thermodynamic parameters from the distribution of microscopic states, which can reflect the influence of micro-nanoscale interface effects. In recent years, molecular simulation has been widely used to study the interface effects of fluids in the oil and gas field and the interface characteristics in micro-nanopores. Researchers have used molecular simulation to establish mineral structures and conducted simulation studies on different surface wettabilities, investigating the effects of different crystal faces, hydrophilic and lipophilic functional groups on the adsorption of methane on quartz with different wettabilities [Wang Zhouhua, Zhao Jianfei, Bai Yin, Guo Ping, Liu Huang. Simulation study on the adsorption of methane on quartz modified with different wettabilities [J]. Journal of Southwest Petroleum University (Natural Science Edition), 2019, 41(06): 28-34], but its wettability model is a full coverage modification of the surface by specific functional groups. The researchers conducted a detailed study on different wettabilities [Jiao Hongyan, Dong Mingzhe, Liu Zhongwei, Jin Yanxin, Han Xu. Molecular dynamics simulation of the adsorption behavior of methane on quartz surfaces with different wettabilities in water environment [J]. Journal of China University of Petroleum (Natural Science Edition), 2014, 38(05): 178-183] and constructed several quartz surface models with different wettabilities in specific proportions. The degree of quartz surface modification n(-CH3): n(-OH) is 0:100, 25:75, 50:50, 75:25, 100:0. However, the surface modification ratio of the model studied is specific, and the distribution of functional groups is regular, which does not reflect the randomness of arbitrary proportions and the position of functional groups.

[0005] So far, in the context of oil and gas reservoir mineral research, in the process of simulation and calculation research on silica interfaces with different wettability and their wettability, researchers have established different silica surface structure models. However, due to the particularity of the oxygen atom structure on the silica surface, these models have shortcomings for different wettability modifications, mainly manifested in: full coverage of modified surfaces by specific functional groups, surface modification by CH3 / OH in a specific ratio, and no randomness in the functional group distribution rules. It is impossible to fully consider and effectively control the ratios of functional groups with different wettability in the model. Summary of the invention

[0006] The purpose of the present invention is to provide a modeling method with controllable modification ratio of functional groups on the surface of silica and random positions of functional groups, and to optimize key parameters in the modeling process. The method has reliable principle, high precision, simplicity and applicability, and can establish surface structure models of silica with different wettabilities by accurately controlling the surface structure modification of CH3 functional groups by 0% to 100%, thereby achieving the purpose of constructing microscopic models of different wettabilities of reservoir minerals in oil and gas reservoirs, thereby overcoming the defects and shortcomings in the prior art.

[0007] In order to achieve the above technical objectives, the present invention adopts the following technical solutions.

[0008] A modeling method for arbitrarily controllable and randomly positioned modification of functional groups on the surface of silica comprises the following steps in sequence:

[0009] (1) Import the original unit cell structure model of silica and check the unit cell parameters of silica.

[0010] Furthermore, the step (1) imports the original unit cell structure model of silicon dioxide, and the process is as follows: open Materials Studio software, import the silicon dioxide structure in metal-oxides under Structures, and the unit cell parameters are: a =0.4913nm, b =0.4913nm, c =0.54052nm, α =90°, β =90°, γ =120°.

[0011] (2) Establish the surface structure of silicon dioxide. The input parameters include the Miller index, thickness, surface atomic layer, and surface vector of the cut surface. The cut surface contains 4 oxygen atoms.

[0012] Furthermore, the step (2) establishes the surface structure of silicon dioxide, and the process is as follows: the surface operation is performed on the original unit cell structure model of silicon dioxide, the Miller index of the cut surface is [0,0,1], the thickness of 3 layers is 1.6216nm, 0.1157nm is selected as the surface atomic layer, the surface vector U is modified to [2,1,0], and V is modified to [0,1,0], and the original unit cell surface structure with 4 oxygen atoms cut out on the surface is obtained.

[0013] (3) A supercell structure of the silicon dioxide surface is established. A supercell structure with 100 oxygen atoms on the surface is obtained by performing 5×5 supercellization in the XY two-dimensional directions on the original unit cell surface structure. A vacuum layer is added along the Z direction to make it a supercell structure with a surface.

[0014] Furthermore, the step (3) establishes a supercell structure on the surface of silicon dioxide, and the process is as follows: a supercell structure with 100 oxygen atoms (100 = 4 oxygen atoms × 5 × 5) on the surface is obtained by supercelling the original cell surface structure in the XY two-dimensional direction; and a vacuum layer with a thickness of 2.0 nm is added to the supercell structure on the surface of silicon dioxide in the Z direction using a method for establishing a vacuum layer structure in Materials Studio software.

[0015] (4) Define the surface oxygen atom group, program to obtain the information of each surface oxygen atom, and shuffle the sequence of the surface oxygen atom array.

[0016] Furthermore, the step (4) refers to obtaining the XYZ position information of 100 oxygen atoms on the surface of the supercell structure established in step (3) using a perl script, and then using a shuffle function to shuffle the original serial numbers of the surface oxygen atom array.

[0017] (5) The variable N is set to determine the number of N methyl functional groups generated on the surface.

[0018] Furthermore, the step (5) refers to setting a variable N according to the number of functional groups, so as to determine that N methyl functional groups are generated on the surface, and 0≤N≤100.

[0019] (6) Extract the oxygen atoms in the random array and obtain the XYZ coordinate information of the extracted atoms.

[0020] Furthermore, the step (6) refers to extracting oxygen atoms from the disordered array using a shift function, thereby implementing a random process and saving the XYZ coordinate information of the extracted atoms for subsequent auxiliary determination of the atomic coordinates.

[0021] (7) A C atom with a methyl functional group is generated above the extracted atom. The C atom uses the XY coordinate information of the extracted atom, and the distance from the extracted atom in the Z direction is one bond length.

[0022] (8) The C atom of the methyl functional group forms a bond with the surface oxygen atom, which is hydrogenated to become a -CH3 functional group. The remaining oxygen atoms are hydrogenated to become -OH functional groups. Steps (6) to (8) are repeated until a surface structure with a specified number of functional groups N is obtained.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The CH3 / OH ratio of the functional groups that characterize wettability in the model of the present invention can be effectively controlled, and the modification degree of the CH3 functional group can be arbitrarily set between 0% and 100%. In addition, the functional groups are randomly distributed, which reduces the differences caused by artificially setting distribution rules and is more consistent with the grafting results of the wettability-modified functional groups.

[0025] (2) The model of the present invention is simple in design, the functional group components are replaceable, and a mixed wettability mineral surface system can be constructed.

[0026] (3) The present invention adopts a supercell structure, which can effectively control the size of the constructed model, thereby facilitating better control of the proportion of functional groups in the constructed model. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0028] Figure 1 It is the primitive unit cell structure of silicon dioxide.

[0029] Figure 2 is the supercell structure that defines the surface oxygen atom groups.

[0030] Figure 3 This is a top view of the surface structure with a CH3 functional group modification degree of 7%.

[0031] Figure 4 This is a top view of the surface structure with a CH3 functional group modification degree of 71%. DETAILED DESCRIPTION

[0032] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims, they are all protected. Example

[0033] This embodiment provides a modeling method in which the modification ratio of functional groups on the surface of silica is controllable and the positions of functional groups are random. This method can accurately control the surface modification degree of CH3 functional groups to be 0% to 100%, and comprises the following specific steps:

[0034] Step 1) Importing the unit cell structure of silicon dioxide, such as Figure 1 Open the Materials Studio software and import the silicon dioxide structure in metal-oxides under Structures. The unit cell parameters of the silicon dioxide crystal are as follows: a =0.4913nm, b =0.4913nm, c =0.54052nm, α =90°, β =90° and γ =120°;

[0035] Step 2) Establishing the surface structure of the original unit cell, using the silicon dioxide original unit cell imported in step 1), performing a surface cut operation on it, the parameters that need to be input are: Miller index of the cut surface [0,0,1], thickness of 3 layers totaling 1.6216nm, the cut surface is the oxygen atomic layer at 0.1157nm, modifying the surface vectors to U[2,1,0], V[0,1,0], and obtaining the original unit cell surface structure with 4 oxygen atoms cut out of the surface;

[0036] Step 3) Establish a supercell structure on the surface of silicon dioxide. By supercelling the original cell surface structure in the XY two-dimensional direction by 5×5, a supercell structure with 100 oxygen atoms on the surface is obtained. Use the method of establishing a vacuum layer structure in the Materials Studio software to add a vacuum layer with a thickness of 2.0 nm to the Z direction of the silicon dioxide surface supercell structure, such as Figure 2 As shown;

[0037] Step 4) Define groups for surface oxygen atoms, such as Figure 2 The gray atoms in the middle surface layer represent 100 oxygen atoms. The XYZ position information of all oxygen atoms on the surface is obtained using a perl script, and then the shuffle function is used to shuffle the original sequence numbers of the surface oxygen atom array.

[0038] Step 5) According to the number of functional groups, the variable N needs to be set to determine the generation of N methyl functional groups on the surface, in particular, 0≤N≤100. If N=7 is set, 7 methyl functional groups will be generated after running; if N=71 is set, 71 methyl functional groups will be generated; if N=100 is set, a surface model with full coverage of methyl functional groups will be generated;

[0039] Step 6) Using the shift function to extract oxygen atoms from the random array, a random process is implemented in this way; the XYZ coordinate information of the extracted atoms is saved for subsequent auxiliary determination of atomic coordinates;

[0040] Step 7) generating a C atom of a methyl functional group above the extracted atom, the atom uses the XY coordinate information of the extracted atom, and the distance from the extracted atom in the Z direction is a bond length;

[0041] Step 8) The C atom of the generated methyl functional group forms a bond with the original surface oxygen atom and hydrogenates it to form a -CH3 functional group; the remaining surface oxygen atoms are hydrogenated to form hydroxyl -OH functional groups. Repeat steps (6) to (8) until the specified number of times N is completed, and a surface structure corresponding to the number of functional groups N is generated. Figure 3 The top view of the surface structure with a CH3 functional group modification degree of 7% is shown. In the figure, the Y-shaped triangle is the CH3 functional group, and the remaining ball-and-stick models are OH functional groups, that is, n(-CH3): n(-OH)=7:93; Figure 4 Shown is a top view of the surface structure with a CH3 functional group modification degree of 71%, that is, n(-CH3): n(-OH)=71:29.

[0042] By comparison, it can be seen that this method effectively controls the CH3 / OH ratio of the functional groups that characterize wettability, and the modification degree of the CH3 functional group can be set arbitrarily between 0% and 100%. Furthermore, when the model is larger, such as when the number of surface atoms reaches 10,000, the controllability is higher, and the modification degree can reach two decimal places. In addition, by comparing the positions of the functional groups, it can be seen that their random distribution reduces the functional group distribution rules caused by artificial settings. Furthermore, the CH3 functional group can be replaced by other functional groups to construct a mixed wettability mineral surface model.

[0043] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A modeling method for randomly modifying functional groups on the surface of silica, comprising the following steps: (1) Import the original unit cell structure model of silica and check the unit cell parameters of silica; (2) Establish the silicon dioxide surface structure. The input parameters include the Miller index, thickness, surface atomic layer, and surface vector of the cut surface. The cut surface contains 4 oxygen atoms. (3) Establishing a supercell structure on the surface of silicon dioxide, by performing 5×5 supercelling in the XY two-dimensional direction of the original unit cell surface structure to obtain a supercell structure with 100 oxygen atoms on the surface; adding a vacuum layer along the Z direction to make it a supercell structure with a surface; (4) Define the surface oxygen atom group, program to obtain the information of each surface oxygen atom, and shuffle the sequence of the surface oxygen atom array; (5) Setting the variable N is used to determine the number of N methyl functional groups generated on the surface; (6) Extracting oxygen atoms from the random array and obtaining the XYZ coordinate information of the extracted atoms; (7) Generate a C atom with a methyl functional group above the extracted atom. The C atom uses the XY coordinate information of the extracted atom, and the distance from the extracted atom in the Z direction is one bond length; (8) The C atom of the methyl functional group forms a bond with the surface oxygen atom, which is hydrogenated to become a -CH3 functional group. The remaining oxygen atoms are hydrogenated to become -OH functional groups. Steps (6) to (8) are repeated until a surface structure with a specified number of functional groups N is obtained.

2. The modeling method for randomly modifying functional groups on the surface of silicon dioxide according to claim 1, characterized in that: The process of step (1) is as follows: Open Materials Studio software, import the silicon dioxide structure in metal-oxides under Structures, and the unit cell parameters are: a =0.4913nm, b =0.4913nm, c =0.54052nm, α =90°, β =90°, γ =120°.

3. The modeling method for arbitrarily controllable and randomly positioned functional group modification of silicon dioxide surface according to claim 1, characterized in that: The process of step (2) is as follows: a surface cut operation is performed on the original unit cell structure model of silicon dioxide, the Miller index of the cut surface is [0,0,1], the thickness is 3 layers with a total thickness of 1.6216nm, 0.1157nm is selected as the surface atomic layer, the surface vector U is modified to [2,1,0], and V is modified to [0,1,0], and the original unit cell surface structure with 4 oxygen atoms cut out is obtained.

4. The modeling method for arbitrarily controllable and randomly positioned functional group modification on the surface of silicon dioxide according to claim 1, characterized in that: The process of step (3) is as follows: a supercell structure with 100 oxygen atoms on the surface is obtained by 5×5 supercelling the original cell surface structure in the XY two-dimensional direction; a vacuum layer with a thickness of 2.0 nm is added to the silicon dioxide surface supercell structure in the Z direction using a method of establishing a vacuum layer structure in Materials Studio software.

5. The modeling method for arbitrarily controllable and randomly positioned functional group modification of silicon dioxide surface according to claim 1, characterized in that: The step (4) refers to obtaining the XYZ position information of 100 oxygen atoms on the surface of the supercell structure established in step (3) using a perl script, and then using the shuffle function to shuffle the original serial numbers of the surface oxygen atom array.

6. The modeling method for arbitrarily controllable and randomly positioned functional group modification of silicon dioxide surface according to claim 1, characterized in that: The step (5) refers to setting a variable N according to the number of functional groups, which is used to determine that N methyl functional groups are generated on the surface, and 0≤N≤100.

7. The modeling method for randomly modifying functional groups on the surface of silicon dioxide according to claim 1, characterized in that: The step (6) refers to using the shift function to extract oxygen atoms from the random array, thereby realizing a random process and saving the XYZ coordinate information of the extracted atoms for subsequent auxiliary determination of the atomic coordinates.

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