Physicochemical aspects of enhanced oil recovery (EOR) from heavy high-viscosity deposits, developed in natural mode and combined with thermal methods, using systems based on surface-active substances (surfactants), coordinating solvents and complex compounds are considered, which chemically evolve in situ to acquire colloidal-chemical properties that are optimal for oil displacement. Thermobaric reservoir conditions, interactions with reservoir rock and fluids are the factors causing the chemical evolution of the systems. To enhance oil recovery and intensify the development of high-viscosity deposits, acid oil-displacing systems of prolonged action based on surfactants, inorganic acid adduct and polyatomic alcohol have been created. As a result of experimental studies of acid-base equilibrium in the systems with donor-acceptor interactions – polybasic inorganic acid and polyol, the influence of electrolytes, non-electrolytes and surfactants, the optimal compositions of the systems were selected, as well as concentration ranges of the components in the acid systems. When the initially acid system interacts with the carbonate reservoir to release CO2, the oil viscosity decreases 1.2-2.7 times, the pH of the system rises and this system evolves chemically turning into an alkaline oil-displacing system. As a result it provides effective oil displacement and prolonged reservoir stimulation. The system is compatible with saline reservoir waters, has a low freezing point (minus 20 ÷ minus 60 oC), low interfacial tension at the oil boundary and is applicable in a wide temperature range, from 10 to 200 oC. In 2014-2018 field tests of EOR technologies were successfully carried out to intensify oil production in the test areas of the Permian-Carboniferous deposit of high-viscosity oil in the Usinsk oil field, developed in natural mode and combined with thermal-steam stimulation, using the acid oil-displacing system based on surfactants, coordinating solvents and complex compounds. The pilot tests proved high efficiency of EOR technologies, as far as the oil production rate significantly increased, water cut decreased to intensify the development. The EOR technologies are environmentally safe and technologically effective. Commercial use of the EOR is promising for high-viscosity oil deposits.

INT R O DUCTIONPhysico-chemical control of filtration flows in the formation is considered to be a promising method to enhance oil recovery in oil fields developed by flooding . The methods increasing conformance by the injected Huid (water and gas) have been found to be the most effectave in West Siberia . At a later stage of flooding physico-chemical control of filtration flows in heterogeneous reservoirs is carried out by selective isolation, i .e . blocking of well drainaged and highly permeable zones, causing the drowing of producing we11s . It is convenient to employ gels with controled generation time [1, 2] .A novel method has been developed to enhance oil recovery Erom highly heterogeneous formations . The method is used to control filtration flows and to increase conformance onder flooding by thermoreversible polymer gels (TRPG) . TRPG are prepared Erom polymer solutions witti lower thermal critical solution point (LCSP). The formation heat energy causes gelation . Polymer solutions witti LCSP are capable to gelation in situ : at low temperaturen they are low viscous solutions, whereas at high temperatures they convent into gels . The process is reversible, i.e . at cooling gels dilute and become again low vistoon solutions, while reheating causes gelation . The process can be repeated many times . One can vary temperature and time of gelation by organic_ and inorganic additives, taking into account the specific formation conditions, i .e . temperature and water mineralization .By means of TRPG one can effectively reduce watercut, prevent gas breakthrough, eliminate gas tonen etc . In 1996-1997 pilot tests of thermoreversible gels have been carried out to enhance oil recovery in oil fields of West Siberia . The technologies are economically effectave and ecologically acceptable . The period of payback is about one year . PHYSIC O -C HEMI CAL AS P ECTS FOR GENE R ATI ON O F THERMOREVERSIBLE POLYMER GELSHydrodynamic and physico-chemical aspects of gelation in heterogeneous formations have been studied . Gel-forming systems have been developed . They have various gelation time -from some hoorn to soiree days in the temperature range from 40 to 1 00°C. Aqueous polymer solutions witti LCSP veere used as gel-forming systems . Added veere the components to control time and gelation temperature . These gel-forming systems veere named METKA systems .

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