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The paper discusses the problem of structural transition of heavy oil found in Carboniferous reservoirs–the strategic reserve of the Republic of Tatarstan. Heavy oil is characterized by increased concentration of high-molecular compounds (asphaltenes, resins, paraffin) and by high viscosity (30-200 mPa·s). Because of various physical and chemical processes and change of thermodynamic in-situ conditions, rheological properties of oil change at all stages of the oil extraction process. Considering that temperature is the critical parameter that controls oil viscosity, yield strength, pour point, wax crystallization and precipitation, knowledge of the relationship between the temperature and the rheological properties of oil is very important for planning of reservoir management operations. Selection of the efficient field development strategy and production enhancement methods seems impossible without knowledge about phase transition temperature in reservoirs with in-situ temperature approximating to the transition temperature. For the purpose of this study, the transition temperature was calculated by the indirect method from viscosity vs. temperature relationships and the following approximation of the exponent for solid-like and liquid-like states. The exponents’ crossing is the point (temperature) of phase transition. For laboratory research, we used the rotary rheometer RHEOTEST RN 4.1. Oil rheological properties were determined for the temperature range from 1°C to 40°C, effective viscosity for each temperature value was determined for the range from 1 to 60 s-1. |
References
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