Enhanced oil recovery at the mature oilfields can be achieved by chemical flooding with use of surfactants on surfactant-polymer (SP) or alkali-surfactant-polymer technology [1], [2]. A surfactant as part of a flooding composition allows you to change the wettability of the rock, reduce interfacial tension, increase the capillary number, and form an oil emulsion which provides a significant increase in the efficiency of oil displacement [3]. The polymer included in the oil-displacing composition increases its viscosity and allows the displacement front aligning by improving the ratio of the mobilities of the oil and water phases [4], [5]. The design of chemical flooding is carried out considering the geological and physical characteristics of the formation and the composition of formation fluids. When choosing an oil-displacing composition for a specific field, it is important to reliably assess the effectiveness of chemical flooding and predict a possible increase in oil recovery. This paper evaluates the effectiveness of SP flooding options by combining comprehensive laboratory studies and hydrodynamic modeling based on them.

A method is proposed for calculating low interfacial tension (IFT) based on molecular dynamics simulation of systems with superdense packing of surfactant molecules at the water–liquid hydrocarbon interface. The interfacial tension was calculated by the molecular dynamics method using the all-atom and coarse-grained models in water–alkane (decane, dodecane) two-phase systems in the presence of various individual surfactants. The following ionic and nonionic surfactants were considered: sodium dodecyl sulfate (SDS), cetyltrimethylammonium chloride (CTAC), sodium dodecylbenzenesulfonate (SDBS), sodium decet-6 sulfate C10E6SO4Na, hexaethylene glycol monodecyl ether (C10E6), triethylene glycol monononadecyl ether (C19E3), and octapropoxypentaethylene glycol monododecyl ether (C12P8E5). It was shown that the interfacial tension decreases to zero when surfactant adsorption increases to the limiting values.

In conditions of declining production and significant watercut in most of producing oil fields in Western Siberia, secondary recovery methods such as waterflooding are ineffective. Promising methods for increasing oil recovery are chemical enhanced oil recovery methods such as surfactant-polymer (SP) flooding. Designing the chemical composition for SP flooding one should take into account the geological, physical and geochemical features of the oil field: reservoir temperature, composition and properties of reservoir fluids and rocks. The aim of the article is to create the optimum formulation of surfactant-polymer system for certain oil field in Western Siberia. The integrated laboratory studies are conducted to prove successful of SP formulation. The aqueous solubility, phase behavior experiment, low interfacial tension, admissible values of dynamic adsorption and oil produced (40 %) during coreflood experiments shows that SP formulation T01 meet the requirements for effective SP flooding.

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.

A thermodynamic model has been formulated for the formation work of a molecular aggregate consisting of molecules of a nonionic surfactant and a solubilisate in a hydrocarbon–surfactant–water solution as a function of temperature, concentrations of the surfactant and hydrocarbon in the solution, and aggregation numbers of the surfactant and hydrocarbon in the aggregate. The model depends on the structural parameters and physical characteristics of surfactant and solubilisate molecules. Predictions of the model concerning the minimum and the saddle point of the aggregation work have been considered and the distributions of relative concentrations of aggregates over the aggregation numbers of the surfactant and solubilisate have been plotted at different concentrations of surfactant and hydrocarbon monomers in the solution. The fractions of the surfactant and solubilisate in the aggregates have been numerically estimated relative to the equilibrium concentrations of surfactant and solubilisate monomers, and the average aggregation numbers of the surfactant and solubilisate in the aggregates have been found. The possibility of the colossal accumulation of solubilisate molecules in the molecular aggregates has been shown. The aggregation and solubilization have been considered at equilibrium surfactant concentrations that are markedly lower than the critical micelle concentration in a pure surfactant solution. It has been found that the limiting concentrations of the nonionic surfactant and the solubilisate corresponding to the formation of stable nanoemulsions lie in rather narrow ranges, and it is unlikely to get into them as a result of the random search in laboratory experiments.

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.

The catalytic activity of the micellar form of cationic surfactants in the presence of copper salts under conditions of emulsion oxidation of cumene to cumene hydroperoxide (CHP) with oxygen (t = 75 degrees, p(O-2) = 0.1 MPa) was examined. The efficiency of micellar catalysis in the emulsion oxidation of cumene was found to depend on the nature of the ligand in the aniono complex of copper: Br- > Cl- > SO42- > CH3COO- and on the lipophilicity of the alkyltrimethylammonium cation: C-16 > C-14 > C-12. The selective CHP formation corresponds to the surfactant concentration ranging from CMC1 (critical micelle concentration) to CMC2 (micelle structure change).