This review discusses the theoretical basis and examples of implementation of various molecular modeling approaches to the investigation of the properties of surfactants. These surfactant properties include the ability to reduce the interfacial tension and alter the wettability and viscosity of solutions for the purposes of chemical flooding of crude oil reservoirs. A comparative analysis of the advantages and disadvantages of the existing molecular dynamics simulation methods is further provided. It is shown that molecular modeling methods can significantly facilitate the choice of surfactants for specific oil field conditions and can serve as a potential alternative to experimental measurements.

Methods of enhanced oil recovery in general and surfactant-polymer flooding in particular are considered as tertiary methods for the development of mature oil fields in Western Siberia, with the potential to increase oil recovery to 60-70% of the initial geological reserves. To select an effective mixture of surfactants and polymer for surfactantpolymer flooding, laboratory tests were carried out in which the thermal stability, phase behaviour, interfacial tension and rheology of the formulations were tested. Filtration experiments were also carried out to optimize the volumes of injected fringes and the concentrations of reagents in them. At the final stage, single well chemical tracer tests (SWCTT) were carried out to assess the effectiveness of surfactant-polymer flooding on two wells of the Kholmogorskoye field. In order to investigate different technical and economic models of surfactant-polymer exposure, SWCTT tests were conducted with the same surfactant, but with a different design. The results of the SWCTT tests showed that the residual oil saturation in the affected area after injection of the surfactant-polymer solution decreased by about 11% compared to water flooding, which is about a third of the residual oil after flooding. The tested surfactant showed acceptable efficiency under suboptimal temperature conditions, which is favorable for the use of the selected surfactant-polymer composition for neighboring deposits and formations with different reservoir temperatures, but similar water composition. In general, the results of the conducted field tests correlate with the results of the main laboratory experiments for the selected surfactant.

All-atom molecular dynamics has been employed to study the processes of self-aggregation and solubilization in aqueous solutions that contain decane, ionic and nonionic surfactants, and additives of salts. In particular, micellization of an anionic surfactant (sodium dodecyl sulfate) in an aqueous solution has been simulated in the presence of a hydrocarbon (decane) at preset temperature and pressure and different initial surfactant and hydrocarbon concentrations in the solution. Moreover, self-aggregation has been simulated in systems containing water, decane, and a mixture of anionic (sodium dodecyl sulfate) and nonionic (hexaethylene glycol monodecyl ether, C 10 E 6 ) both in a salt-free solution and in the presence of sodium chloride, calcium chloride, or a mixture thereof. Diffusion coefficients have been calculated for aggregates consisting of hydrocarbon and surfactant aggregates, and the viscosities of corresponding aqueous solutions have been estimated. The viscosities have been calculated in simulation cells containing either one or several aggregates.

Enhanced oil recovery in mature fields can be implemented using chemical flooding with the addition of surfactants using surfactant-polymer (SP) or alkaline-surfactant-polymer (ASP) flooding. Chemical flooding design is implemented taking into account reservoir conditions and composition of reservoir fluids. The surfactant in the oil-displacing formulation allows changing the rock wettability, reducing the interfacial tension, increasing the capillary number, and forming an oil emulsion, which provides a significant increase in the efficiency of oil displacement. The article is devoted with a comprehensive study of the formed emulsion phase as a stage of laboratory selection of surfactant for SP or ASP composition. In this work, the influence of aqueous phase salinity level and the surfactant concentration in the displacing solution on the characteristics of the resulting emulsion was studied. It was shown that, according to the characteristics of the emulsion, it is possible to determine the area of optimal salinity and the range of surfactant concentrations that provide increased oil displacement. The data received show the possibility of predicting the area of effectiveness of ASP and SP formulations based on the characteristics of the resulting emulsion.

Enhanced oil recovery in mature fields can be implemented using chemical flooding with the addition of surfactants using surfactant-polymer (SP) or alkaline-surfactant-polymer (ASP) flooding. Chemical flooding design is implemented taking into account reservoir conditions and composition of reservoir fluids. The surfactant in the oil-displacing formulation allows changing the rock wettability, reducing the interfacial tension, increasing the capillary number, and forming an oil emulsion, which provides a significant increase in the efficiency of oil displacement. The article is devoted with a comprehensive study of the formed emulsion phase as a stage of laboratory selection of surfactant for SP or ASP composition. In this work, the influence of aqueous phase salinity level and the surfactant concentration in the displacing solution on the characteristics of the resulting emulsion was studied. It was shown that, according to the characteristics of the emulsion, it is possible to determine the area of optimal salinity and the range of surfactant concentrations that provide increased oil displacement. The data received show the possibility of predicting the area of effectiveness of ASP and SP formulations based on the characteristics of the resulting emulsion.