CN115326647A - surfactant-CO 2 Method for researching behavior of crude oil miscible interface - Google Patents
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- 239000010779 crude oil Substances 0.000 title claims abstract description 87
- 238000000034 method Methods 0.000 title claims abstract description 42
- 239000004094 surface-active agent Substances 0.000 claims abstract description 55
- 238000000329 molecular dynamics simulation Methods 0.000 claims abstract description 37
- 229910052500 inorganic mineral Inorganic materials 0.000 claims abstract description 23
- 239000011707 mineral Substances 0.000 claims abstract description 23
- 238000004088 simulation Methods 0.000 claims abstract description 21
- 239000003921 oil Substances 0.000 claims abstract description 8
- 238000011160 research Methods 0.000 claims abstract description 8
- 125000000524 functional group Chemical group 0.000 claims abstract description 7
- 239000011324 bead Substances 0.000 claims description 23
- 238000005381 potential energy Methods 0.000 claims description 20
- 230000003993 interaction Effects 0.000 claims description 14
- 238000004422 calculation algorithm Methods 0.000 claims description 10
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 8
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 7
- 229910021389 graphene Inorganic materials 0.000 claims description 6
- 239000002245 particle Substances 0.000 claims description 6
- 230000000737 periodic effect Effects 0.000 claims description 6
- 239000010453 quartz Substances 0.000 claims description 6
- 230000009881 electrostatic interaction Effects 0.000 claims description 5
- 238000005411 Van der Waals force Methods 0.000 claims description 4
- 238000005452 bending Methods 0.000 claims description 4
- 238000009826 distribution Methods 0.000 claims description 4
- 238000005457 optimization Methods 0.000 claims description 4
- 239000003795 chemical substances by application Substances 0.000 claims description 3
- 238000010276 construction Methods 0.000 claims description 3
- 229920000642 polymer Polymers 0.000 claims description 3
- 230000033444 hydroxylation Effects 0.000 claims description 2
- 238000005805 hydroxylation reaction Methods 0.000 claims description 2
- 239000005416 organic matter Substances 0.000 claims description 2
- 230000005501 phase interface Effects 0.000 claims 1
- 239000003079 shale oil Substances 0.000 abstract description 6
- 230000009467 reduction Effects 0.000 abstract description 5
- 238000006073 displacement reaction Methods 0.000 abstract description 3
- 239000000463 material Substances 0.000 description 12
- 230000015572 biosynthetic process Effects 0.000 description 5
- 238000004364 calculation method Methods 0.000 description 4
- HXBYBCASAVUYKF-GVYWOMJSSA-N (4r,5s,6r,7r)-4,5,6,7,8-pentahydroxyoctane-2,3-dione Chemical compound CC(=O)C(=O)[C@H](O)[C@@H](O)[C@H](O)[C@H](O)CO HXBYBCASAVUYKF-GVYWOMJSSA-N 0.000 description 3
- 238000012512 characterization method Methods 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 238000001179 sorption measurement Methods 0.000 description 3
- 150000001335 aliphatic alkanes Chemical class 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 239000003945 anionic surfactant Substances 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 238000005187 foaming Methods 0.000 description 2
- 239000012634 fragment Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- SNRUBQQJIBEYMU-UHFFFAOYSA-N Dodecane Natural products CCCCCCCCCCCC SNRUBQQJIBEYMU-UHFFFAOYSA-N 0.000 description 1
- LPTITAGPBXDDGR-IWQYDBTJSA-N [(2r,3r,4s,5r)-3,4,5,6-tetraacetyloxyoxan-2-yl]methyl acetate Chemical compound CC(=O)OC[C@H]1OC(OC(C)=O)[C@H](OC(C)=O)[C@@H](OC(C)=O)[C@@H]1OC(C)=O LPTITAGPBXDDGR-IWQYDBTJSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000011362 coarse particle Substances 0.000 description 1
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- 239000002086 nanomaterial Substances 0.000 description 1
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- 239000007787 solid Substances 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
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Abstract
The invention discloses a surfactant-CO 2 A method for researching the behavior of a crude oil miscible interface, belonging to CO 2 The technical field of oil displacement. The surfactant-CO 2 The method for researching the behavior of the crude oil miscible interface comprises the following steps: providing surfactant-CO 2 -a crude oil miscible system model, and after developing and optimizing a coarse-grained molecular dynamics force field, performing coarse-grained molecular dynamics simulation based on the coarse-grained molecular dynamics force field, and acquiring data every 1ps to calculate interface parameters of a simulation system. The invention researches and analyzes the CO reduction of a surfactant by multi-component crude oil in an organic matter-mineral slit of a shale reservoir 2 Influence rule of minimum miscible pressure of miscible flooding and CO-philic with different functional groups 2 The influence behavior of the surfactant on the stability of the oil-gas interface is disclosed, so that the influence rule of the surfactant on the oil-gas interface is revealed on a molecular levelIs convenient to screen out CO suitable for shale oil reservoir 2 The best surfactant for flooding.
Description
Technical Field
The invention belongs to CO 2 The technical field of oil displacement, in particular to a surfactant-CO 2 A method for researching the behavior of a crude oil miscible interface.
Background
Because shale reservoirs have the characteristics of low porosity, ultra-low permeability and extensive development of nano pores, experimental research on shale oil usually has greater limitations, such as the limitations of high-temperature and high-pressure conditions. In recent years, molecular dynamics simulation technology has shown great application potential in quantitative characterization such as fluid-solid adsorption and interfacial tension in nanomaterials, and is gaining favor in the petroleum field gradually.
Currently, surfactants reduce CO 2 The research of the minimum miscible pressure of the crude oil is still in an exploration stage, the molecular dynamics simulation of the interface behavior by the existing surfactant mainly focuses on researching the oil-water interface behavior, the dynamic simulation is carried out on a single crude oil component by mostly adopting a dissipative particle dynamics method, and the influence of shale organic matters and minerals is not considered, so that the simulation result is not in accordance with the reality and the production practice is difficult to guide. In addition, the existing laboratory simulation method is long in time consumption and high in operation cost.
Disclosure of Invention
The invention aims to provide a surfactant-CO 2 Method for studying the behaviour of a miscible interface of crude oil by studying CO on the basis of a coarse-grained force field molecular dynamics (CG-MD) simulation 2 Interface behavior and influence rule of miscible-phase flooding surfactant, so that CO which is most suitable for improving shale oil reservoir is screened 2 The surfactant with oil displacement efficiency not only greatly reduces the experimental cost, but also solves the technical problem that the existing molecular dynamics simulation result does not accord with the actual productionAnd practical application can be guided on a theoretical level.
In order to achieve the above purpose, the embodiment of the invention adopts the following technical scheme:
in an embodiment of the present invention, there is provided a surfactant-CO 2 -a method for investigating the behaviour of a miscible interface of a crude oil, comprising the steps of:
s101: providing surfactant-CO 2 -a crude oil miscible system model;
s102: the method is used for developing and optimizing a coarse-grained molecular dynamics force field, and specifically comprises the following steps:
the surfactant-CO is added 2 Simulating a crude oil miscible system model into a full atomic system model, and performing full atomic molecular dynamics simulation to obtain a full atomic system initial model;
converting the full-atom system initial model into a coarse-grained molecular structure, and representing the coarse-grained molecular structure by using predefined beads to obtain a coarse-grained system model;
counting the bond length and bond angle of the coarse-grained bead structure in the coarse-grained system model, and respectively calculating potential energy parameters K of interaction between the same coarse-grained beads by using formulas (1) and (2) b 、R 0 、K 0 And theta 0 ；
Wherein, in the formula (1), U b Is a key telescopic potential energy K b Is a factor, R is a bond length, R 0 Is a bond length balance value; in formula (2), U θ Is key angle bending potential energy, K 0 Is a factor, theta is a bond angle, theta 0 Is an angle balance value;
and fitting a free energy curve of interaction between different coarse-grained beads by using a formula (3) to obtain a Lennar-Jones potential energy parameterD 0 And R 0 ；
Wherein, in the formula (3), U LJ9-6 Is van der Waals force, R is bond length, R 0 Is a balance value of bond length, D 0 Is the depth of the potential well;
potential energy parameter D to Lennar-Jones 0 And R 0 Fitting optimization is carried out, so that macroscopic performance parameters of the coarse-grained system model are matched with experimental data, and a coarse-grained molecular dynamics force field is obtained;
s103: developing molecular dynamics simulation, specifically comprising:
based on the coarse-grained molecular dynamics force field, the surfactant-CO is added 2 The crude oil miscible system model is pre-simulated for 10-20ps under a regular ensemble to enable the simulation system to be in relaxation balance, then the simulation is conducted for 2.0ns under the regular ensemble, data are collected every 1ps, and interface parameters of the simulation system are calculated.
In a preferred implementation of an embodiment of the invention, the surfactant-CO 2 -the method of constructing a crude oil miscible system model comprises:
providing a crude oil molecular model, a surfactant molecular model and an organic matter-mineral slit model;
introducing CO 2 The crude oil molecular model and the surfactant molecular model are simultaneously filled in the organic matter-mineral slit model to obtain surfactant-CO 2 -crude oil miscible system model.
In a preferred implementation of an embodiment of the invention, the surfactant-CO 2 -the method of constructing a crude oil miscible system model further comprises:
the surfactant-CO is added 2 The model of the mixed phase system of crude oil is subjected to an energy minimization process to make the energy of the model converge to 1 x 10 -4 kcal/mol。
In a preferred implementation of the embodiments of the invention, the crude oil molecular model, the CO 2 And the filling number of the surfactant molecule model in the organic matter-mineral slit model is respectively 800, 2000 and 10.
In a preferred implementation manner of the embodiment of the present invention, the method for constructing the crude oil molecular model includes:
after the components and the mass percentages shown in the following table 1 are combined into the mixed oil, a crude oil molecular model is constructed by using molecular simulation software;
TABLE 1 crude oil molecular model Components and percentages by weight
In a preferred implementation manner of the embodiment of the present invention, the method for constructing the surfactant molecular model includes:
using a plurality of CO-philic polymers having different functional groups 2 The surfactant-like agent is used as a research object, and a molecular model of the surfactant is constructed by utilizing molecular simulation software.
In a preferred implementation manner of the embodiment of the present invention, the method for constructing the organic matter-mineral slit model includes:
selecting five layers of graphene as an organic wall surface of a slit in the shale reservoir, and selecting a quartz surface subjected to hydroxylation as a mineral wall surface of the slit in the shale reservoir;
and in molecular simulation software, performing simulation combination on the selected five layers of graphene and the quartz surface to obtain an organic matter-mineral slit model.
In a preferred implementation manner of the embodiment of the invention, in the molecular dynamics simulation, the Nos-Hoover algorithm is used for controlling the temperature and the pressure of the calculation system, and the temperature of the relaxation equilibrium is 344.3K.
In a preferred implementation of an embodiment of the invention, the long range force electrostatic interaction is calculated using a particle-particle-particle summation method with a truncation radius of 2nm using periodic boundary conditions in the molecular dynamics simulation.
In a preferred implementation of an embodiment of the present invention, in the molecular dynamics simulation, the Velocity of the system is initially assigned by a maxwell-boltzmann distribution and is controlled by a Velocity-Verlet algorithm.
Compared with the prior art, the advantages or beneficial effects of the embodiment of the invention at least comprise:
the surfactant-CO provided by the embodiment of the invention 2 A method for researching the behavior of a crude oil miscible interface, and provides a surfactant-CO 2 After the crude oil miscible model, the coarse particle size molecular dynamics force field is developed and optimized for molecular dynamics simulation, and the reduction of CO of the surfactant by multi-component crude oil can be researched 2 Influence rule of minimum miscible pressure of miscible flooding and CO-philic with different functional groups 2 The influence behavior of the surfactant on the stability of the oil-gas interface is disclosed, so that the influence rule of the surfactant on the oil-gas interface is disclosed on a molecular level, and the optimal surfactant suitable for shale oil reservoirs is screened conveniently. More importantly, the molecular dynamics simulation method not only greatly reduces the cost, but also solves the problem that the existing molecular dynamics simulation result does not accord with the actual production, thereby being capable of guiding the practical application on the theoretical level.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. It is obvious that the drawings in the following description are only some embodiments described in the present invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.
FIG. 1 is a surfactant molecular structure used in the construction of a surfactant molecular model according to an embodiment of the present invention;
fig. 2 is an organic-mineral slit model constructed by an embodiment of the present invention;
FIG. 3 is a surfactant-CO constructed in accordance with an embodiment of the present invention 2 -a crude oil miscible system model;
FIG. 4 shows a CO provided by an embodiment of the present invention 2 -shale oil interfacial tension versus pressure curve;
FIG. 5 is a surfactant CO reduction scheme for various crude oil compositions provided by an embodiment of the present invention 2 And (4) influence rule of minimum miscible pressure.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the embodiments described below are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention provides a method for researching the behavior of a surfactant-CO 2-crude oil miscible interface, which comprises the following steps:
s101: in the Material Studio molecular simulation software, the surfactant-CO is constructed 2 -a crude oil miscible system model, as shown in figure 3;
in the present example, a surfactant-CO was constructed 2 -the crude oil miscible system model preferably comprises:
respectively constructing a crude oil molecule model, a surfactant molecule model and an organic matter-mineral slit model in Material Studio molecular simulation software, and then filling the crude oil molecule model, CO in the organic matter-mineral slit model 2 And a surfactant molecular model to obtain surfactant-CO 2 Model of crude oil miscible system, in which the model of crude oil molecules, CO, in the organic-mineral slit model 2 And the filling number of the surfactant molecule model in the organic matter-mineral slit model is 2000, 800 and 10 respectively;
surfactant-CO using conjugate gradient algorithm 2 The model of the mixed phase system of crude oil is subjected to an energy minimization process to make the energy of the model converge to 1 x 10 -4 kcal/mol。
In embodiments of the present invention, constructing the crude oil molecular model preferably comprises:
the components and the mass percentage shown in the following table 1 are combined into mixed oil, and then a crude oil molecular model is constructed through Material Studio molecular simulation software;
TABLE 1 crude oil molecular model Components and percentages by weight
In an embodiment of the present invention, constructing the surfactant molecule model preferably includes:
using four CO-philic compounds with different functional groups 2 The surfactant-like agent is used as a research object, and a surfactant molecular model is constructed by utilizing Material Studio molecular simulation software. Among them, the four surfactants preferred in this embodiment are AOT-type surfactant, triple-chain anionic surfactant TC1 4 Low foaming surfactant LS 45 And peracetylglucose dodecaalkane.
S102: developing and optimizing a coarse-grained molecular dynamics force field preferably includes:
in the Material Studio molecular simulation software, surfactant-CO was used 2 Simulating a crude oil miscible system model into a full atomic system model, and performing full atomic molecular dynamics simulation to obtain a full atomic system initial model;
converting the full-atom system initial model into a coarse-grained molecular structure, and representing the coarse-grained molecular structure by using predefined beads to obtain a coarse-grained system model, wherein the predefined bead types are shown in the following table 2;
TABLE 2 predefined bead types
| Bead name | Represents a whole atom fragment | Relative mass |
| A1 | CH 3 -CH 2 -CH 2 - | 43 |
| A2 | CH 3 -CH 2 | 29 |
| A3 | -CH 2 -CH 2 -CH 2 - | 42 |
| A4 | CO 2 | 44 |
| A5 | -COO- | 44 |
| A6 | C-OAc | 71 |
| A7 | -C(CH 3 ) 3 | 57 |
| A8 | -C＝O-O-C- | 56 |
| A9 | -C-SO 3 | 92 |
Counting the bond length and bond angle of the coarse-grained bead structure by adopting an average and standard deviation method in a coarse-grained system model, and respectively calculating the potential energy parameter K of the interaction between the same coarse-grained beads by utilizing formulas (1) and (2) b 、R 0 、K 0 And theta 0， ；
Wherein, in the formula (1), U b Is a key telescopic potential energy K b Is a factor, R is a bond length, R 0 Is a bond length balance value; in formula (2), U θ Is key angle bending potential energy, K 0 Is a factor, theta is a bond angle, theta 0 Is an angle balance value;
and fitting a free energy curve of interaction between different coarse-grained beads by using a formula (3) to obtain a Lennar-Jones potential energy parameter D 0 And R 0 ；
Wherein, in the formula (3), U LJ9-6 Is van der Waals force, R is bond length, R 0 Is a balance value of bond length, D 0 Is the depth of the potential well;
potential energy parameter D to Lennar-Jones 0 And R 0 Fitting optimization is carried out, so that macroscopic performance parameters (density, interfacial tension and the like) of the coarse-grained system model are matched with experimental data, and a coarse-grained molecular dynamics force field is obtained.
S103: carrying out molecular dynamics simulation, which specifically comprises the following steps:
based on the coarse-grained molecular dynamics force field, periodic boundary conditions are adopted, andsurfactant-CO 2 Pre-simulating 10-20ps by a crude oil miscible system model under a regular ensemble, raising the temperature of a simulation system to a certain threshold, continuously pre-simulating for 2.5ns, balancing the relaxation of the simulation system, then carrying out simulation for 2.0ns, collecting data every 1ps, and calculating the interface parameters of the simulation system. Wherein, periodic boundary conditions are adopted in the three directions of x, y and z.
In the embodiment of the invention, the Nos é -Hoover algorithm is preferably used for controlling the temperature and the pressure of the calculation system, and the temperature of relaxation equilibrium is 344.3K.
In the present example, long range force electrostatic interactions were calculated using periodic boundary conditions, preferably using the particle-particle-particle summation method, with a cutoff radius of 2nm. Wherein the calculation accuracy is 1.0 × 10 -4 。
In an embodiment of the present invention, the Velocity of the system is initially assigned by a Maxwell-Boltzmann distribution and is controlled by the Velocity-Verlet algorithm.
The technical solution of the present invention will be further described in detail with reference to the following specific examples.
Example 1
This example 1 provides a surfactant-CO 2 -a method for investigating the behaviour of a miscible interface of crude oil, comprising the steps of:
constructing a crude oil molecular model: the components and the mass percentages shown in the following table 1 were combined into the mixed oil, and then a crude oil molecular model was constructed in the Material Studio molecular simulation software.
TABLE 1 crude oil molecular model Components and mass percents
Constructing a surfactant molecular model: with AOT surfactant and triple-chain anionic surfactant TC1 4 Low foaming surfactant LS 45 And four surfactants of total acetyl glucose dodecane are used as research objects, and the surface activity is constructed by utilizing Material Studio molecular simulation softwareAgent molecule model, as shown in figure 1.
Constructing an organic matter-mineral slit model: five layers of graphene are respectively selected as an organic matter wall surface of a slit in the shale reservoir and a hydroxylated quartz surface is selected as a mineral wall surface of the slit. In the Material Studio molecular simulation software, five layers of graphene and hydroxylated quartz are combined to obtain an organic matter-mineral slit model, as shown in fig. 2.
Construction of surfactant-CO 2 Crude oil miscible system model: in Material studio molecular simulation software, 800 crude oil molecular models and 2000 COs are used 2 And filling 10 surfactant molecule models in the organic matter-mineral slit model to obtain surfactant-CO 2 -a crude oil miscible model;
using conjugate gradient algorithm to treat surfactant-CO 2 The miscible model of the crude oil is subjected to an energy minimization process to converge the energy to 1X 10 -4 kcal/mol to obtain surfactant-CO 2 Crude oil miscible system model, as shown in fig. 3.
S102: developing and optimizing a coarse-grained molecular dynamics force field, which sequentially comprises the following steps:
(1) Quantitative characterization of bond interaction parameters
In Material studio molecular simulation software, the surfactant-CO is mixed 2 Simulating a crude oil miscible system model into a full atomic system model, and performing full atomic molecular dynamics simulation to obtain a full atomic system initial model;
converting the full-atom system initial model into a coarse-grained molecular structure, and representing the coarse-grained molecular structure by using predefined beads to obtain a coarse-grained system model, wherein the predefined bead types are shown in the following table 2;
TABLE 2 predefined bead types
| Bead name | Represents a whole atom fragment | Relative mass |
| A1 | CH 3 -CH 2 -CH 2 - | 43 |
| A2 | CH 3 -CH 2 | 29 |
| A3 | -CH 2 -CH 2 -CH 2 - | 42 |
| A4 | CO 2 | 44 |
| A5 | -COO- | 44 |
| A6 | C-OAc | 71 |
| A7 | -C(CH 3 ) 3 | 57 |
| A8 | -C＝O-O-C- | 56 |
| A9 | -C-SO 3 | 92 |
Counting the bond length and bond angle of the coarse-grained bead structure in the coarse-grained system model, and respectively calculating potential energy parameters K of interaction between the same coarse-grained beads by using formulas (1) and (2) b 、R 0 、K 0 And theta 0 ；
Wherein, in the formula (1), U b Is key telescopic potential energy K b Is a factor, R is a bond length, R 0 Is a bond length balance value; in formula (2), U θ Is key angle bending potential energy, K 0 Is a factor, theta is a bond angle, theta 0 Is an angle balance value;
(2) Quantitative characterization of non-bond interaction parameters
Non-bonding interactions include van der waals interactions and coulombic electrostatic interactions. The Lennar-Jones potential function is used to describe the van der waals interaction between different beads. Fitting the free energy curve of the interaction between different coarse-grained beads by using a formula (3) to obtain a Lennar-Jones potential energy parameter D 0 And R 0 (ii) a Then to Lennar-Jones potential energy parameter D 0 And R 0 Fitting optimization is carried out, so that macroscopic property parameters such as density, interfacial tension and the like of a simulation system are matched with experimental data;
wherein, in the formula (3), U LJ9-6 Is van der Waals force, R is bond length, R 0 Is a balance value of bond length, D 0 Is the depth of the potential well;
s103: carrying out molecular dynamics simulation, which specifically comprises the following steps:
in Material studio molecular simulation software, based on the coarse-grained molecular dynamics force field, adopting a normal ensemble (NVT), and using a Nose-Hoover algorithm to control the temperature and pressure of a calculation system, wherein the temperature of relaxation equilibrium is 323.15-348.15K; calculating the long-range force electrostatic interaction by using a particle-particle-particle addition method under the periodic boundary condition, wherein the truncation radius is 2nm; the speed of the system is initially assigned by a maxwell-boltzmann distribution and is controlled by the Velocity-Verlet algorithm. For the surfactant-CO 2 The crude oil miscible system model carries out simulation for 2.0ns, the simulation step length is 1fs, data are collected every 1ps, and interface parameters of a simulation system are analyzed.
1)CO 2 Analysis of the interfacial tension of crude oil
Before and after adding the surfactant, CO at the temperature of 344.3K 2 The interfacial tension of shale oil as a function of pressure, as shown in figure 4. As can be seen from fig. 4: at different pressures, CO 2 And the interface tension and the pressure between the oil and the crude oil have good linear relation, and the pressure when the interface tension is zero is obtained by linearly extrapolating the curve, wherein the pressure is the minimum miscible pressure. At the temperature of 344.3K, the minimum miscible pressure before adding the surfactant is 10.4MPa, and the minimum miscible pressure after adding the surfactant is reduced to different degrees, wherein the minimum miscible pressure after adding the total acetyl glucose dodecaalkane is 7.4MPa. Therefore, the total acetyl glucose dodecaalkane can remarkably reduce CO 2 The minimum miscible pressure of crude oil is the optimal surfactant.
2) CO after addition of surfactant 2 Analysis of the interfacial stability of crude oils
The examples of the invention are based on the use of surfactants in crude oil/CO 2 The equilibrium configuration of the interfacial adsorption is calculated by using the formula (4) 2 The interfacial energy of formation of the system is shown in Table 3 below。
Wherein IFE is the interfacial energy of formation of the surfactant; e total The total energy of the system after the surfactant is adsorbed on the interface to reach the equilibrium; e Sur Is the energy of 1 surfactant molecule; e ref Is the total energy before the corresponding system surfactant is adsorbed; n is the number of surfactants.
TABLE 3 interfacial energy formation (kJ. Mol) of surfactant at oil-gas interface -1 )
From table 3, it can be seen that: this example adds four CO-philic compounds with different functional groups 2 After the surfactant, CO 2 The Interfacial Formation Energy (IFE) of the crude oil is negative, which shows that the adsorption of the four surfactants on the oil-gas interface enhances the thermodynamics of the interface and is favorable for forming CO 2 Miscible, smaller values are more favorable for the formation of thermodynamically stable interfaces.
3) CO reduction of different crude oil component pairs 2 Influence of minimum miscible pressure
With other conditions unchanged, the mass percentage of the crude oil molecules was varied and 3 different cases were constructed, as shown in table 4 below.
TABLE 4 different crude oil compositions
| Case 1 | |
|
|
| CH 4 | 100 | 64 | 55 |
| C 2 H 6 | 88 | 60 | 50 |
| C 6 H 14 | 60 | 60 | 50 |
| C 9 H 20 | 60 | 88 | 76 |
| C 16 H 34 | 64 | 100 | 80 |
| C 9 H 7 N | 10 | 10 | 31 |
| C 6 H 12 O 2 | 8 | 8 | 27 |
| CH 4 S | 10 | 10 | 31 |
The simulation result is shown in fig. 5, and it can be seen from fig. 5 that: when the alkane ratio decreases, CO 2 Can be miscible with crude oil at relatively low pressure, but CO increases with the carbon number of alkane 2 The minimum miscible pressure with crude oil shows a very marked tendency to increase, especially when the polymer fraction is high.
As can be seen from the above description, this example utilizes molecular dynamics simulation to study a sample containing different CO-affinities 2 CO-philic of functional groups 2 Surfactant CO reduction 2 Influence rule of miscible phase pressure, and introduces shale wall and CO 2 The interaction of the surfactant and the crude oil system reveals the molecular particle flowing rule in the shale nano-pore canal under the actions of molecules, wall surfaces and the like on a molecular level, thereby greatly reducing the manpower, material resources and financial resources of a simulation experiment and providing guidance suggestions for practical application on a theoretical level.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (10)
1. surfactant-CO 2 Behavior of miscible interfaces of crude oilsThe research method is characterized by comprising the following steps:
s101: providing surfactant-CO 2 -a crude oil miscible system model;
s102: the method is used for developing and optimizing a coarse-grained molecular dynamics force field, and specifically comprises the following steps:
the surfactant-CO is added 2 Simulating a crude oil miscible system model into a full atomic system model, and performing full atomic molecular dynamics simulation to obtain a full atomic system initial model;
converting the full-atom system initial model into a coarse-grained molecular structure, and representing the coarse-grained molecular structure by using predefined beads to obtain a coarse-grained system model;
counting the bond length and bond angle of the coarse-grained bead structure in the coarse-grained system model, and respectively calculating the potential energy parameter K of the interaction between the same coarse-grained beads by using formulas (1) and (2) b 、R 0 、K 0 And theta 0 ；
Wherein, in the formula (1), U b Is key telescopic potential energy K b Is a factor, R is a bond length, R 0 Is a bond length balance value; in the formula (2), U θ Is the bending potential energy of a key angle, K 0 Is a factor, theta is a bond angle, theta 0 Is an angle balance value;
and fitting a free energy curve of interaction between different coarse-grained beads by using a formula (3) to obtain a Lennar-Jones potential energy parameter D 0 And R 0 ；
Wherein, in the formula (3), U LJ9-6 Is van der Waals force, R is bond length, R 0 Is a balance value of bond length, D 0 Is the depth of the potential well;
to Lennar-Jones potential energy parameter D 0 And R 0 Fitting optimization is carried out, so that macroscopic performance parameters of the coarse-grained system model are matched with experimental data, and a coarse-grained molecular dynamics force field is obtained;
s103: developing molecular dynamics simulation, specifically comprising:
based on the coarse-particle-size molecular dynamics force field, the surfactant-CO is added 2 The crude oil miscible system model is pre-simulated for 10-20ps under a regular ensemble to enable the simulation system to be in relaxation balance, then the simulation is conducted for 2.0ns under the regular ensemble, data are collected every 1ps, and interface parameters of the simulation system are calculated.
2. The surfactant-CO according to claim 1 2 Method for investigating the behaviour of a miscible interface of crude oil, characterized in that the surfactant-CO is 2 The construction method of the crude oil miscible system model comprises the following steps:
providing a crude oil molecule model, a surfactant molecule model and an organic matter-mineral slit model;
introducing CO 2 The crude oil molecular model and the surfactant molecular model are simultaneously filled in the organic matter-mineral slit model to obtain surfactant-CO 2 -a crude oil miscible system model.
3. The surfactant-CO according to claim 2 2 Method for investigating the behaviour of a miscible interface of crude oil, characterized in that the surfactant-CO 2 -the method of constructing a crude oil miscible system model further comprises:
the surfactant-CO is added 2 The model of the crude oil miscible system is subjected to energy minimization treatment to make the energy thereof converge to 1 x 10 -4 kcal/mol。
4. The surfactant according to claim 3CO 2 -method for studying the behaviour of a miscible interface of a crude oil, characterized in that said molecular model of the crude oil, said CO 2 And the filling number of the surfactant molecule model in the organic matter-mineral slit model is respectively 800, 2000 and 10.
5. The surfactant-CO according to claim 2 2 The method for researching the behavior of the miscible interface of the crude oil is characterized in that the method for constructing the crude oil molecular model comprises the following steps:
after the components and the mass percentages shown in the following table 1 are combined into the mixed oil, a crude oil molecular model is constructed by using molecular simulation software;
TABLE 1 crude oil molecular model Components and percentages by weight
6. The surfactant-CO of claim 2 2 The method for researching the behavior of the crude oil miscible interface is characterized in that the method for constructing the surfactant molecular model comprises the following steps:
using a plurality of CO-philic polymers having different functional groups 2 The surfactant-like agent is used as a research object, and a molecular model of the surfactant is constructed by utilizing molecular simulation software.
7. The surfactant-CO according to claim 2 2 The method for researching the behavior of the crude oil miscible interface is characterized in that the method for constructing the organic matter-mineral slit model comprises the following steps:
selecting five layers of graphene as an organic matter wall surface of a slit in a shale reservoir, and selecting a quartz surface subjected to hydroxylation as a mineral wall surface of the slit in the shale reservoir;
and in molecular simulation software, performing simulated combination on the selected five layers of graphene and the quartz surface to obtain an organic matter-mineral slit model.
8. The surfactant-CO according to claim 1 2 A method for studying the behavior of a miscible interface of a crude oil, characterized in that, in the molecular dynamics simulation, the temperature and the pressure of the computational system are controlled using the no é -Hoover algorithm, the temperature of the relaxation equilibrium being 344.3K.
9. The surfactant-CO of claim 8 2 A method for investigating the behavior of a mixed phase interface of crude oil, characterized in that in the molecular dynamics simulation, long-range force electrostatic interaction is calculated using a particle-particle-particle summation method with a truncation radius of 2nm, using periodic boundary conditions.
10. The surfactant-CO of claim 8 2 -a method for studying the behaviour of a miscible interface of crude oil, characterized in that, in said molecular dynamics simulation, the Velocity of the system is initially assigned by maxwell-boltzmann distribution and controlled by the Velocity-Verlet algorithm.
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