Method for evaluating adsorption characteristics of surfactant at oil-water interface

Abstract

The invention discloses a method for evaluating adsorption characteristics of a surfactant at an oil-water interface. The method comprises the following steps: step 1, constructing a multi-molecular system model containing the surfactant, water-phase molecules and oil-phase molecules; 2, performing dynamic molecular calculation on the polymolecular system model to enable the model system to reach an equilibrium state to obtain a polymolecular equilibrium system model; and step 3, evaluating multiple interface properties of the current surfactant by studying adsorption and aggregation of the multi-molecular equilibrium system model on the oil-water interface. The method is realized by adopting a simulation method, and has the advantages of short period, accurate result and the like.

Description

Technical Field

[0001] The invention relates to the research field of surfactant oil recovery, and in particular to an evaluation method for the adsorption characteristics of olefin sulfonate as a surfactant at an oil-water interface based on molecular dynamics simulation. Background Art

[0002] As an important oilfield chemical agent, surfactants can significantly reduce the interfacial tension between oil and water and change the wettability of reservoirs, thereby improving crude oil recovery. Surfactants are molecules that have both hydrophilic and hydrophobic groups. Their unique amphiphilic molecular structure causes the molecules to adsorb on the phase interface and form a monomolecular film structure. Surfactant molecules with different structures have different structural properties of the interfacial film formed at the oil-water interface, which ultimately leads to differences in oil recovery effects.

[0003] At present, there are many problems in the experimental process of evaluating and screening surfactants for oil recovery. The most important one is that the time and space scale of traditional experiments are large, and there are defects such as difficulty in separating impurities, long cycles, and difficulty in restoring high-temperature and high-pressure reservoir conditions. It is difficult to capture the diffusion and aggregation state of molecules in the system. Moreover, the existing technology lacks research on the microstructure of the oil recovery system, making it difficult to establish the connection between the surfactant molecular structure-interface performance-oil recovery effect.

[0004] The prior art provides a scheme entitled "The Effect of Surfactant Structure on the Wetting Modification of Lignite", which studies the characteristics of surfactants on the coal surface through potentiometric measurement, infrared spectroscopy semi-quantitative analysis and thermodynamic analysis calculation.

[0005] The prior art provides a scheme entitled "Study on Static Adsorption Characteristics of Binary Composite System Surfactants", which uses an interfacial tension tester to conduct research on the adsorption characteristics of crude oil with a binary composite system of non-ionic surfactants and polymers.

[0006] The prior art provides a scheme entitled "Study on the Adsorption and Retention Characteristics of Amphiphilic Polymers / Surfactants on Rock Minerals", in which the performance of the selected amphiphilic polymer / surfactant binary system was evaluated by viscosity method and rheology method.

[0007] In summary, the existing technology is mainly studied through experimental methods, but lacks corresponding simulation research methods, and has not formed a complete simulation evaluation system. Therefore, in view of the problem that there is a lack of relevant experimental procedures for evaluating surfactant flooding in the existing technology, it is necessary to propose a corresponding experimental scheme for simulating and evaluating the adsorption characteristics of surfactants at the oil-water interface. Summary of the invention

[0008] One of the technical problems to be solved by the present invention is the need to provide a technical solution that can comprehensively evaluate the adsorption characteristics of surfactants at the oil-water interface regarding multiple interfacial properties, thereby efficiently and conveniently restoring the high temperature and high pressure environmental state of the oil reservoir.

[0009] In order to solve the above technical problems, an embodiment of the present application proposes a method for evaluating the adsorption characteristics of surfactants at the oil-water interface, including: step one, constructing a multi-molecular system model including surfactants, water phase molecules and oil phase molecules; step two, performing kinetic molecular calculations on the multi-molecular system model to make the model system reach an equilibrium state, and obtaining a multi-molecular equilibrium system model; step three, evaluating multiple interfacial properties of the current surfactant by studying the adsorption and aggregation of the multi-molecular equilibrium system model at the oil-water interface.

[0010] Preferably, in the method, step one comprises: establishing a monolayer of surfactant, water phase molecules and oil phase molecules respectively; establishing a three-phase molecular system model according to the force field parameters and topology files of the surfactant and oil phase molecules, wherein the force field parameters include but are not limited to atomic charge, potential function, bond length, bond angle and dihedral angle.

[0011] Preferably, the method, in the process of constructing the three-phase molecular system model, includes: splicing left and right surfactant monolayer models on both sides of the water phase molecular model, and then splicing an oil phase molecular model on both sides of the left and right surfactant monolayer models.

[0012] Preferably, in the method, step 2 includes: using the steepest descent method to minimize the energy of the multi-molecular system model; using NVE and NVT ensembles to perform equilibrium simulation on the multi-molecular system model that has been subjected to energy minimization, thereby obtaining the multi-molecular equilibrium system model, wherein the NVE ensemble is first used to carry out a pre-equilibrium simulation based on a preset first holding time, and then the NVE and NVT ensembles are used to carry out a finished product simulation based on a preset second holding time for the pre-equilibrium system simulation, and the second holding time is greater than the first holding time.

[0013] Preferably, the method needs to set a plurality of simulation conditions suitable for different simulation stages in the pre-equilibrium simulation stage and the finished product simulation stage, wherein the plurality of simulation conditions include but are not limited to target temperature, target pressure, step size, temperature coupling mode, pressure coupling mode, temperature coupling relaxation time, pressure coupling relaxation time, ensemble mode, cutoff radius and calculation method of electrostatic interaction, and cutoff radius and calculation method of van der Waals interaction.

[0014] Preferably, in the method, the multiple interface properties include but are not limited to: mass density curve, interfacial tension, interface formation energy, interface thickness, interface coverage, distribution pattern of water molecules near the surfactant head group, number of hydrogen bonds, calculation of surfactant sequence parameters and effective length of alkyl group.

[0015] Preferably, in the method, in the analysis of the interface performance, the interfacial tension is expressed by the following expression:

[0016]

[0017] Wherein, σ represents the interfacial tension, L Z Indicates the size of the box in the Z direction, P xx , P yy and P zz They represent the components of pressure parallel to the XY interface and perpendicular to the XY interface respectively.

[0018] Preferably, the method and the interface formation energy can be expressed by the following expression:

[0019]

[0020] Wherein, IFE represents the interface formation energy, E total represents the total energy of the surfactant oil-water interface system, n represents the number of surfactant molecules, E single represents the energy of a single surfactant molecule in a vacuum system, E blank It represents the total energy of the blank control system containing only oil and water phase without surfactant.

[0021] Preferably, in the method, the calculation formula of the interface coverage is:

[0022]

[0023] Where: coverage represents the interface coverage, n blank It represents the number of water molecules whose distance to decane molecules is less than or equal to 0.5 nm in the blank control system containing only oil and water phase without surfactant, n surface It represents the number of water molecules whose distance to the decane molecules is less than or equal to 0.5 nm in the surfactant oil-water interface system.

[0024] Preferably, in the method, the surfactant is an olefin sulfonate type surfactant, and the olefin sulfonate type surfactant is an α-olefin sulfonate or an internal olefin sulfonate;

[0025] Compared with the prior art, one or more embodiments of the above scheme may have the following advantages or beneficial effects:

[0026] The present invention proposes a method for evaluating the adsorption characteristics of surfactants at the oil-water interface. The method provided by the present invention improves the evaluation of the adsorption characteristics of surfactants at the oil-water interface at the molecular level, effectively establishes an experimental process for evaluating the adsorption characteristics of surfactants, thereby solving many problems in the experimental process. It improves the defects of surfactants in traditional experiments, such as difficulty in separating impurities, long cycles, and difficulty in restoring high-temperature and high-pressure reservoir conditions. The adsorption of surfactant molecules at the oil-water interface is described from the atomic and molecular scales at a microscopic perspective, and the structural properties of surfactant monolayers under high-temperature and high-pressure conditions are analyzed. It helps to establish a direct connection between the molecular structure of surfactants, interface performance, and oil displacement effect, and provides theoretical guidance for applications in the field of improving crude oil recovery. In addition, the evaluation method provided by the present invention is simulated and implemented using computer software, and has the advantages of short cycles and accurate results.

[0027] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0029] Figure 1 Schematic diagram of the steps of a method for evaluating the adsorption characteristics of a surfactant at an oil-water interface according to an embodiment of the present application.

[0030] Figure 2 Schematic diagram of the initial configuration of two molecular examples of surfactants to be simulated in the method for evaluating the adsorption characteristics of surfactants at the oil-water interface according to an embodiment of the present application.

[0031] Figure 3 It is a schematic diagram of the initial configuration of constructing a multi-molecular system model based on two molecular examples of the surfactant to be simulated in the method for evaluating the adsorption characteristics of a surfactant at an oil-water interface in an embodiment of the present application.

[0032] Figure 4 This is a schematic diagram of the mass density distribution curve of a multi-molecular equilibrium system model formed based on two molecular examples of the surfactant to be simulated in the method for evaluating the adsorption characteristics of a surfactant at an oil-water interface in an embodiment of the present application.

[0033] Figure 5This is a schematic diagram of the distribution morphology of water molecules near the head group of a multi-molecular equilibrium system model formed based on two molecular examples of the surfactant to be simulated in the method for evaluating the adsorption characteristics of a surfactant at an oil-water interface in an embodiment of the present application.

[0034] Figure 6 This is a schematic diagram of the order parameters of the hydrocarbon chains of a multi-molecular equilibrium system model formed based on two molecular examples of the surfactant to be simulated in the method for evaluating the adsorption characteristics of a surfactant at an oil-water interface according to an embodiment of the present application. DETAILED DESCRIPTION

[0035] The following will describe the implementation methods of the present invention in detail with reference to the accompanying drawings and embodiments, so that the implementation process of how the present invention applies technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly. It should be noted that as long as there is no conflict, the various embodiments of the present invention and the various features in the embodiments can be combined with each other, and the technical solutions formed are all within the protection scope of the present invention.

[0036] In addition, the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions. Also, although a logical sequence is shown in the flowchart, in some cases, the steps shown or described can be performed in a sequence different from that here.

[0037] As an important oilfield chemical agent, surfactants can significantly reduce the interfacial tension between oil and water and change the wettability of reservoirs, thereby improving crude oil recovery. Surfactants are molecules that have both hydrophilic and hydrophobic groups. Their unique amphiphilic molecular structure causes the molecules to adsorb on the phase interface and form a monomolecular film structure. Surfactant molecules with different structures have different structural properties of the interfacial film formed at the oil-water interface, which ultimately leads to differences in oil recovery effects.

[0038] At present, there are many problems in the experimental process of evaluating and screening surfactants for oil recovery. The most important one is that the time and space scale of traditional experiments are large, and there are defects such as difficulty in separating impurities, long cycles, and difficulty in restoring high-temperature and high-pressure reservoir conditions. It is difficult to capture the diffusion and aggregation state of molecules in the system. Moreover, the existing technology lacks research on the microstructure of the oil recovery system, making it difficult to establish the connection between the surfactant molecular structure-interface performance-oil recovery effect.

[0039] The prior art provides a scheme entitled "The Effect of Surfactant Structure on the Wetting Modification of Lignite", which studies the characteristics of surfactants on the coal surface through potentiometric measurement, infrared spectroscopy semi-quantitative analysis and thermodynamic analysis calculation.

[0040] The prior art provides a scheme entitled "Study on Static Adsorption Characteristics of Binary Composite System Surfactants", which uses an interfacial tension tester to conduct research on the adsorption characteristics of crude oil with a binary composite system of non-ionic surfactants and polymers.

[0041] The prior art provides a scheme entitled "Study on the Adsorption and Retention Characteristics of Amphiphilic Polymers / Surfactants on Rock Minerals", in which the performance of the selected amphiphilic polymer / surfactant binary system was evaluated by viscosity method and rheology method.

[0042] In order to solve the above-mentioned technical problems, the present application embodiment proposes a method for simulating and evaluating the adsorption characteristics of surfactants at oil-water interface based on dynamic molecular science. First, the structural model of surfactant (taking olefin sulfonate as an example) and oil phase molecule is constructed respectively, and then the atomic charge, potential function, bond length, bond angle and dihedral angle of olefin sulfonate and oil phase molecule are obtained. Force field parameters and topological files, then a three-phase system model including olefin sulfonate, water phase molecule and oil phase molecule is established, then the molecular dynamics calculation of sufficient duration is carried out to the three-phase system based on the method of molecular dynamics simulation so that the system reaches equilibrium state, and finally the behavior of olefin sulfonate adsorption and aggregation at oil-water interface is quantitatively and qualitatively evaluated by comprehensively evaluating the interfacial properties of different aspects, and the experimental process of improving the adsorption characteristics of surfactants at oil-water interface is formed, so as to form a complete evaluation system. The method describes the microscopic morphology of surfactant from the perspective of atoms and molecules, and provides certain theoretical guidance for surfactants in the field of enhancing oil recovery.

[0043] Figure 1 Schematic diagram of the steps of the method for evaluating the adsorption characteristics of surfactants at the oil-water interface according to an embodiment of the present application. Figure 1 As shown, step S110 constructs a multi-molecular system model including surfactants, water phase molecules and oil phase molecules. Further, step S110 constructs a multi-molecular system model including surfactants, water phase molecules and oil phase molecules using software.

[0044] In one embodiment, the surfactant described in the embodiment of the present invention is preferably an olefin sulfonate surfactant, wherein the olefin sulfonate surfactant is α-olefin sulfonate (AOS) or internal olefin sulfonate (IOS).

[0045] In one embodiment, the oil phase molecule is a decane molecule. The water molecule uses the SPC / E model. The sodium ion uses the OPLS / AA model.

[0046] When constructing a multi-molecular system model, first construct the surfactant monolayer, water phase molecules and oil phase molecules respectively; then, based on the force field parameters and topology files of the constructed surfactant and oil phase molecules, establish a three-phase molecular system model including olefin sulfonate, water phase molecules and oil phase molecules. The force field parameters include but are not limited to: atomic charge, potential function, bond length, bond angle and dihedral angle.

[0047] Specifically, in the first step, the ChemSketch software is used to draw olefin sulfonates as the surfactant (to be simulated) in the experiment. In order to make the various interface performance data of olefin sulfonates as surfactants in the experiment more generally representative, the embodiment of the present invention draws α-olefin sulfonates and internal olefin sulfonates with the same carbon number (for example, both 18) for comparison.

[0048] Figure 2 Schematic diagram of the initial configuration of two examples of surfactant molecules to be simulated in the method for evaluating the adsorption characteristics of surfactants at the oil-water interface in an embodiment of the present application. Figure 2 As shown, the constructed AOS and IOS molecules both have 18 carbon atoms, the AOS molecule has only one long chain, and the IOS molecule has two tail chains, one long and one short.

[0049] When constructing the AOS surfactant monolayer box, we first use Gromacs software to construct a specified unit space (e.g., 5×5×3nm 3 ) empty box, and then insert a preset number (for example, 36) of AOS molecules into the box evenly with the head group pointing to the positive direction of the Z axis to form the AOS monolayer box on the left, and the preset number (for example, 36) of AOS molecules in the AOS monolayer box on the right are all oriented to the negative direction of the Z axis. Similarly, the monolayer box of the IOS surfactant is made in the same way as the AOS monolayer box.

[0050] Furthermore, when constructing the oil phase box, the Gromacs software was first used to construct a specified unit space (e.g., 5×5×10 nm 3 ) empty box, and then insert a preset number (e.g., 500) of decane molecules into the box. Then, the steepest descent method is used for energy minimization, followed by a NPNAT system simulation for a preset time (e.g., 5 ns), and finally the oil phase box is obtained.

[0051] Furthermore, when constructing the water phase box, the Gromacs software was first used to construct a specified unit space (5×5×15nm 3) empty cells, and then insert a preset number (e.g., 10100) of water molecules into the box. Then use the steepest descent method to minimize the energy, followed by a preset duration (e.g., 5ns) of NPNAT system simulation, and then use a specified number (e.g., 72) of sodium ions to replace some of the water molecules in the system. After the sodium ions replace the water molecules, the excess water molecules are deleted, and the total number of water molecules in the water box is controlled to be a specified number (e.g., 10000), and finally a water phase box is obtained.

[0052] In one embodiment, after completing the model drawing of olefin sulfonate, oil phase molecules and water phase molecules, CGenFF4.4 software is used to optimize the structure of olefin sulfonate surfactant and oil phase molecules, and obtain force field parameters such as atomic charge, potential function, bond length, bond angle and dihedral angle.

[0053] Next, a three-phase molecular system model was established based on the force field parameters and topology files of the surfactant and oil phase molecules. Specifically, in the process of assembling the constructed initial box models of olefin sulfonate, oil phase molecules and water phase molecules into a surfactant oil-water interface system box (i.e., a multi-molecular system model) according to a certain structure, first, Gromacs software was used to splice the left and right surfactant monolayer models on both sides of the water phase molecule model, and then an oil phase molecule model was spliced ​​on both sides of the left and right surfactant monolayer models, thereby forming a simulation system containing a dual surfactant interface.

[0054] Figure 3 Schematic diagram of the initial configuration of a multi-molecule system model constructed based on two molecular examples of surfactants to be simulated in the method for evaluating the adsorption characteristics of surfactants at the oil-water interface in an embodiment of the present application. Figure 3 As shown, Figure 3 The upper and lower figures are schematic diagrams of the initial configurations of AOS and IOS surfactants at the oil-water interface.

[0055] After the construction of the multi-molecule system model is completed, the process proceeds to step S120.

[0056] Step S120 performs dynamic molecular calculations on the multi-molecule system model constructed in step S110 to make the model system reach an equilibrium state, thereby obtaining a multi-molecule equilibrium system model.

[0057] In one embodiment, in order to make the multi-molecule system model reach an equilibrium state, the CHARMM force field is selected and the molecular dynamics simulation software Gromcas is used to perform molecular dynamics calculations on the constructed multi-molecule simulation system.

[0058] In step S120, first, the obtained multi-molecule system model is subjected to energy minimization processing using the steepest descent method. In one embodiment, the multi-molecule system model is subjected to energy minimization processing using the steepest descent method using Gromacs software.

[0059] Then, NVE and NVT ensembles are used to perform equilibrium simulation on the multi-molecule system model that has undergone energy minimization. First, the NVE ensemble is used to perform a pre-equilibrium simulation based on a preset first holding time, and then the NVE and NVT ensembles are used to perform a finished product simulation based on a preset second holding time for the pre-equilibrium system simulation. The second holding time is greater than the first holding time.

[0060] Pre-equilibrium simulation is a test of the multi-molecular system model in a pre-equilibrium state. The finished product processing is to further use more accurate and specific data information to set the multi-molecular system model in equilibrium state based on the pre-equilibrium state.

[0061] In the pre-equilibrium simulation stage and the finished product simulation stage, multiple simulation conditions applicable to different simulation stages need to be set respectively. Among them, the above multiple simulation conditions include but are not limited to target temperature, target pressure, step size, temperature coupling mode, pressure coupling mode, temperature coupling relaxation time, pressure coupling relaxation time, ensemble mode, electrostatic interaction cutoff radius and calculation method, and van der Waals interaction cutoff radius and calculation method.

[0062] In one embodiment, in the pre-equilibrium simulation stage, a pre-equilibrium simulation based on the first holding time is carried out (for example, the first holding time is 2ns). The pre-equilibrium simulation temperature is set to 353K, the pressure is 20MPa, the step size is 1fs, and the temperature coupling and pressure coupling both use Berendsen coupling, with relaxation times of 0.1ps and 0.5ps, respectively. The simulation is performed under the semi-isotropic conditions of the NPNAT ensemble. The electrostatic interaction is calculated using the particle mesh Ewald (PME) method, and the cutoff radius of the electrostatic interaction and the van der Waals interaction is 1.4nm.

[0063] The Gromacs software was used to use the pre-equilibrium simulation structure as the initial structure to carry out the finished product simulation based on the second holding time (for example, the second holding time was 10ns). The finished product simulation temperature was set to 353K, the pressure was 20MPa, the step size was 1fs, the temperature coupling was Nose-Hoover coupling, and the relaxation time was 0.1ps. The pressure coupling was Parrinello-Rahman coupling, and the relaxation time was 0.5ps. The simulation was performed under the semi-isotropic conditions of the NPNAT ensemble. The electrostatic interaction was calculated using the particle mesh Ewald (PME) method, and the cutoff radius of the electrostatic interaction and the van der Waals interaction was 1.4nm.

[0064] In this way, after the pre-equilibrium simulation and the finished product simulation, the equilibrium configuration and simulation trajectory of the dual surfactant interface system are finally obtained, thereby entering step S130.

[0065] Step S130 evaluates multiple interfacial properties of the current surfactant by studying the adsorption and aggregation of the multi-molecular equilibrium system model obtained in step S120 at the oil-water interface. The multiple interfacial properties include but are not limited to: mass density curve, interfacial tension, interfacial formation energy, interfacial thickness, interfacial coverage, distribution of water molecules near the surfactant head group, number of hydrogen bonds, calculation of surfactant sequence parameters, and effective length of alkyl groups.

[0066] In one embodiment, during the analysis of the mass density curve, the mass density curve is directly obtained by using the built-in gmx density command in the Gromacs software. Figure 4 This is a schematic diagram of the mass density distribution curve of a multi-molecular equilibrium system model formed based on two molecular examples of the surfactant to be simulated in the method for evaluating the adsorption characteristics of the surfactant at the oil-water interface in an embodiment of the present application. Figure 4 As shown, the mass density distribution curves of the AOS multi-molecular equilibrium system model and the IOS multi-molecular equilibrium system model at the oil-water interface are respectively shown.

[0067] In one embodiment, in the analysis of interfacial tension, the interfacial tension is expressed using the following expression:

[0068]

[0069] Where σ represents the interfacial tension, L Z Indicates the size of the box in the Z direction, P xx , P yy and P zz They represent the components of pressure parallel to the XY interface and perpendicular to the XY interface respectively.

[0070] In one embodiment, in the analysis of interface formation energy, the interface formation energy is expressed using the following expression:

[0071]

[0072] Where IFE represents the interface formation energy, E total represents the total energy of the surfactant oil-water interface system, n represents the number of surfactant molecules, E single represents the energy of a single surfactant molecule in a vacuum system, E blank It represents the total energy of the blank control system containing only oil and water phase without surfactant.

[0073] In one embodiment, in the analysis of the surfactant interfacial film thickness, the surfactant interfacial film thickness is the distance from the point where the oil phase density is 90% of its bulk density to the point where the water phase density is 90% of its bulk density in the Z-axis mass density distribution curve, and the average is taken for the left and right interfaces in the same system.

[0074] In one embodiment, in the analysis of interface coverage, the calculation formula of interface coverage is:

[0075]

[0076] Among them, coverage represents the interface coverage, n blank It represents the number of water molecules whose distance to decane molecules is less than or equal to 0.5 nm in the blank control system containing only oil and water phase without surfactant, n surface It indicates the number of water molecules whose distance to decane molecules is less than or equal to 0.5 nm in the surfactant oil-water interface system.

[0077] In one embodiment, in the analysis of the distribution morphology of water molecules near the head group, the distribution morphology of water molecules near the surfactant head group is obtained by calculating the radial distribution function using the gmxrdf command built into the Gromacs software. Specifically, the central atom sulfur (S) of the hydrophilic head group of the surfactant is selected as the reference atom, and the oxygen atom (OW) and hydrogen atom (HW) on the water molecule are selected to calculate the radial distribution function.

[0078] Figure 5 This is a schematic diagram of the distribution of water molecules near the head group of a multi-molecular equilibrium system model formed based on two molecular examples of the surfactant to be simulated in the method for evaluating the adsorption characteristics of the surfactant at the oil-water interface in an embodiment of the present application. Figure 5As shown, the (AOS) S-OW curve represents the distribution morphology of oxygen atoms in the AOS multi-molecular equilibrium system model; the (IOS) S-OW curve represents the distribution morphology of oxygen atoms in the IOS multi-molecular equilibrium system model; the (AOS) S-HW curve represents the distribution morphology of hydrogen atoms in the AOS multi-molecular equilibrium system model; the (IOS) S-HW curve represents the distribution morphology of hydrogen atoms in the IOS multi-molecular equilibrium system model.

[0079] In one embodiment, in the analysis of the order parameter of the surfactant hydrocarbon chain, the order parameter of the surfactant hydrocarbon chain is calculated using the gmx order command built into the Gromacs software. The calculation formula of the order parameter of the hydrocarbon chain is:

[0080]

[0081] Among them, S Z represents the order parameter of the i-th carbon atom, and ω represents the angle between the vector pointing from the i-1th carbon atom to the i+1th carbon atom and the Z axis.

[0082] Figure 6 This is a schematic diagram of the order parameters of the hydrocarbon chains of a multi-molecular equilibrium system model formed based on two molecular examples of the surfactant to be simulated in the method for evaluating the adsorption characteristics of a surfactant at an oil-water interface according to an embodiment of the present application. Figure 6 It can qualitatively show the changing state of the carbon-hydrogen chain sequence parameters of different molecular structures of AOS and IOS in the AOS and IOS multi-molecular equilibrium system models.

[0083] In one embodiment, in the analysis of the effective length of the alkyl group, the effective length of the alkyl group of the surfactants AOS and IOS is calculated as follows:

[0084] (θ≥90°)r e =r 1

[0085] (θ<90°)r e =r 1 -r s ·cos f(x) θ

[0086] Among them, r e represents the effective length of the alkyl group; r l Indicates the length of the long chain; r srepresents the length of the short chain; since the AOS molecule has one long chain and the IOS molecule has two tail chains, one long and one short, θ represents the angle between the long chain and the short chain of the IOS molecule; f(x) represents the relationship function between the long and short chains in the molecular configuration to be evaluated (such as the IOS molecule) and the angle θ; x represents the coordinate position of the carbon atoms and hydrogen atoms in the long and short chains in the molecular configuration to be evaluated (such as the IOS molecule) relative to the center of the molecule, which is obtained from the molecular simulation results.

[0087] The embodiments of the present invention qualitatively or quantitatively describe the interfacial properties of AOS and IOS surfactants at the oil-water interface from different aspects, thereby forming an experimental evaluation system for evaluating the adsorption characteristics of surfactants at the oil-water interface.

[0088] The present invention relates to a method for evaluating the adsorption characteristics of surfactants at an oil-water interface based on dynamic molecular simulation. The method uses computer software to complete the interfacial performance evaluation of surfactants at the oil-water interface in various aspects, forming a complete experimental process for evaluating the adsorption characteristics of surfactants. The analysis of interfacial performance in the present invention also provides certain theoretical guidance in the field of improving crude oil recovery.

[0089] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any person familiar with the technology within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

[0090] It should be understood that the embodiments disclosed in the present invention are not limited to the specific structures, processing steps or materials disclosed herein, but should be extended to equivalent substitutions of these features understood by ordinary technicians in the relevant field. It should also be understood that the terms used herein are only used for the purpose of describing specific embodiments and are not meant to be limiting.

[0091] The "one embodiment" or "embodiment" mentioned in the specification means that the specific features, structures or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment" or "embodiment" appearing in various places throughout the specification do not necessarily refer to the same embodiment.

[0092] Although the embodiments disclosed in the present invention are as above, the above contents are only embodiments adopted for facilitating the understanding of the present invention and are not intended to limit the present invention. Any technician in the technical field to which the present invention belongs can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A method for evaluating the adsorption characteristics of surfactants at an oil-water interface, characterized in that: include: Step 1: construct a multi-molecular system model including surfactants, water phase molecules and oil phase molecules; Step 2, performing dynamic molecular calculations on the multi-molecular system model to make the model system reach an equilibrium state, thereby obtaining a multi-molecular equilibrium system model; Step 3: Evaluate multiple interfacial properties of current surfactants by studying the adsorption and aggregation of the multi-molecular equilibrium system model at the oil-water interface.

2. The method according to claim 1, characterized in that The step one comprises: Establish the surfactant monolayer, water phase molecules and oil phase molecules respectively; A three-phase molecular system model is established according to the force field parameters and topology files of the surfactant and oil phase molecules, wherein the force field parameters include but are not limited to atomic charge, potential function, bond length, bond angle and dihedral angle.

3. The method according to claim 2, characterized in that The process of constructing the three-phase molecular system model includes: The left and right surfactant monolayer models are spliced ​​on both sides of the water phase molecular model, and then an oil phase molecular model is spliced ​​on both sides of the left and right surfactant monolayer models.

4. The method according to any one of claims 1 to 3, characterized in that: The second step comprises: Using the steepest descent method, the multi-molecule system model is subjected to energy minimization processing; The multi-molecular system model that has undergone energy minimization is subjected to equilibrium simulation using the NVE and NVT ensembles, respectively, so as to obtain the multi-molecular equilibrium system model, wherein the NVE ensemble is firstly used to carry out a pre-equilibrium simulation based on a preset first holding time, and then the pre-equilibrium system simulation is subjected to a finished product simulation based on a preset second holding time using the NVE and NVT ensembles, respectively, and the second holding time is greater than the first holding time.

5. The method according to claim 4, characterized in that In the pre-equilibrium simulation stage and the finished product simulation stage, it is necessary to set up multiple simulation conditions suitable for different simulation stages, wherein the multiple simulation conditions include but are not limited to target temperature, target pressure, step size, temperature coupling mode, pressure coupling mode, temperature coupling relaxation time, pressure coupling relaxation time, ensemble mode, electrostatic interaction cutoff radius and calculation method, and van der Waals interaction cutoff radius and calculation method.

6. The method according to any one of claims 1 to 5, characterized in that: The multiple interfacial properties include, but are not limited to: mass density curve, interfacial tension, interfacial formation energy, interfacial thickness, interfacial coverage, distribution of water molecules near the surfactant head group, number of hydrogen bonds, calculation of surfactant sequence parameters and effective length of alkyl group.

7. The method according to claim 6, characterized in that In the analysis of interfacial properties, the interfacial tension is expressed using the following expression: Wherein, σ represents the interfacial tension, L Z Indicates the size of the box in the Z direction, P xx , P yy and P zz They represent the components of pressure parallel to the XY interface and perpendicular to the XY interface respectively.

8. The method according to claim 6, characterized in that The interface formation energy can be expressed using the following expression: Wherein, IFE represents the interface formation energy, E total represents the total energy of the surfactant oil-water interface system, n represents the number of surfactant molecules, E single represents the energy of a single surfactant molecule in a vacuum system, E blank It represents the total energy of the blank control system containing only oil and water phase without surfactant.

9. The method according to claim 6, characterized in that The calculation formula of the interface coverage is: Where: coverage represents the interface coverage, n blank It represents the number of water molecules whose distance to decane molecules is less than or equal to 0.5 nm in the blank control system containing only oil and water phase without surfactant, n surface It represents the number of water molecules whose distance to the decane molecules is less than or equal to 0.5 nm in the surfactant oil-water interface system.

10. The method according to any one of claims 1 to 9, characterized in that: The surfactant is an olefin sulfonate surfactant, and the olefin sulfonate surfactant is an α-olefin sulfonate or an internal olefin sulfonate; The oil phase molecules are decane molecules.

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