Wax Precipitation Modelling In Low-Temperature Reservoir Under Different Production Regimes

Most of oil fields in East Siberia are accumulated in low-temperature (12-20 °C) terrigenous reservoirs at depths about 1800 meters, disposed on crystalline basement. Such an oil has a high wax content (up to 5% by mass). Pressure and temperature conditions are close to wax appearance point. Thus, small temperature and pressure changes caused by production lead to wax precipitation around well. Damage pore space by wax particles results in formation of near-wellbore affected area that reduces well production.

In this paper, we develop mathematical model of multiphase well inflow complicated by wax precipitation caused by pressure and temperature changes. The model is based on results of special PVT analysis of wax precipitation (ultrasonic, high pressure microscope, particle size analysis, filtration tests) and analysis of oil thermal properties. The model includes simulation of non-isothermal multiphase multicomponent fluxes. Gas, oil and solid phases are considered. Calculation of wax phase transitions are based on known from the laboratory tests wax concentration in various pressure and temperature conditions. Clogging is simulated by permeability change according to porosity kinetic equation. Energy balance includes Joule-Thomson effect, adiabatic effect, heat production and absorption due to phase transitions. The model allows distribution of wax saturation, porosity and permeability to be evaluated in the area around well.

For a range of initial wax concentration, wellbore pressure, gas-oil ratio values calculations were performed and sensitivity of affected area size and skin-factor were estimated. In the case of high gas-oil ratio values, it was demonstrated that low wellbore temperature can lead to significant permeability decrease in the area. Influence of clogging on formation damage and well inflow parameters was also analyzed. Toolkit for estimation of optimal production regime in low-temperature reservoir for oil with high wax content was developed.