Chemical methods for enhanced oil recovery in general and surfactant-polymer (SP) flooding in particular are considered as a promising technology for developing mature oil fields in Western Siberia, with the potential to increase oil recovery to 60-70% of the initial geological reserves. The selection of an effective mixture of surfactants and polymer for SP flooding is a complex and multi-stage process. Usually, the choice of chemical composition and modeling on the hydrodynamic model is carried out under isothermal condition. However, recently some authors have been paying attention to the temperature aspects of SP flooding. According to these studies, the change in reservoir temperature because of long-term injection of unheated water can play a decisive role in the choice of chemical composition and hydrodynamic simulation of SP flooding. Firstly, temperature significantly affects oil-water interfacial tension (IFT), on which the oil displacement coefficient of the SP composition depends. Secondly, the viscosity of the polymer solution and, consequently, the sweeping efficiency during SP flooding depends on the temperature.
In this article, the temperature profile was evaluated in the SP flooding pilot site, where flooding with unheated water was carried out for 12 years. Initially, the downhole temperature in the injection well was calculated based on analytical functions, which was then confirmed by field studies. As it turned out, the downhole temperature in the injection well is 42°C, which is 45°C less than the initial reservoir temperature. At the second stage, with the help of analytical functions and hydrodynamic simulation, the temperature profile in the SP flooding pilot site was estimated. Calculations have shown that the injection of unheated water over a 12-year period significantly cooled the reservoir in the pilot area. The temperature around the well designed for injection of the SP composition is 70°C, which is 17°C less than the initial reservoir temperature and with further injection of the unheated SP composition, the temperature around this well will fall. This circumstance must be considered when choosing surfactants and polymers that must have effective oil-displacing properties over a wide temperature range.
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