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.
Enhanced oil recovery from high-viscosity oil deposits by acid systems based on surfactants, coordining solvents and complex compounds