Pore-scale mechanisms of the competition effects between temperature and solubility on the crude oil recovery during the CO2 huff-n-puff process

CO2 huff-n-puff technology has been acknowledged to enhanced oil recovery in tight oil reservoirs by improving oil mobility via CO2 dissolution. Temperature fluctuations induced on the reservoir depth have an impact on oil recovery by altering CO2 dissolution and oil mobility. A microscopic visualization simulation experiment was carried out under 2 MPa condition to observe the interactions between CO2 and crude oil at various temperatures (30, 45, 60, 75, and 90 °C). The contribution of viscosity reduction competition of temperature and CO2 dissolution to the improvement of crude oil mobility was thoroughly evaluated. The findings showed that CO2 dissolution dramatically lowers viscosity at 30–50 °C, facilitating oil mobility. Oil mobility and recovery are reduced by 8.2% as a result of CO2 dissolution decreasing with increasing temperature, while the volume of CO2 gas increases by 1.3 times. At 50–60 °C, the mobility of crude oil improves and the recovery increases significantly with the temperature, when the increment amplitude is about two times of the reduction in amplitude. Temperature-induced viscosity reduction predominates between 60 and 90 °C. Furthermore, the oil recovery is dominated by the matrix region at low temperatures (30–60 °C) and by the fracture region at high temperatures (75–90 °C), with both regions weighing more than 40% of the ultimate recovery. Therefore, CO2 huff-n-puff is more suitable at temperatures in the range of 50–60 °C in the extraction of tight oil reservoirs.