Experimental Study on the Optimization of CO2 Displacement and Huff-n-Puff Parameters in the Conglomerate Reservoirs of the Xinjiang Oilfield

Addressing the issue of poor water injection development effectiveness caused by strong water sensitivity damage in the conglomerate reservoirs of the Xinjiang Oilfield, this paper carries out experimental research on CO2 displacement and CO2 huff-n-puff to improve oil recovery in reservoirs under the conditions of reservoirs (86 °C, 44 MPa) by using a high-temperature and high-pressure large physical modeling repulsion device based on the artificial large-scale physical modeling of conglomerate oil reservoirs in the Xinjiang oilfield. The results showed that at any displacement rate, CO2 displacement exhibits the trend where oil production initially increases and then decreases. The higher the gas injection rate, the higher the initial oil well production, and the shorter the time it takes for CO2 to break through to the bottom of the well. After a breakthrough, production declines more rapidly. The oil recovery rate varies with different gas injection rates, initially increasing and then decreasing as the injection rate changes. The highest oil recovery rate was observed at an injection rate of 1.5 mL/min (equivalent to 38 t/d in the field). The efficiency of CO2 displacement with multiple injection-production cycles is low; on the same scale of gas injection, single-cycle injection and production were more effective than multiple-cycle injection and production. CO2 huff-n-puff can improve oil recovery, with a higher CO2 injection pressure and a longer shut-in time leading to greater oil recovery. As the shut-in time increases, the efficiency of CO2 oil exchange also improves. The strong supply capacity of the large physical model results in a tendency for the oil production curves of multiple huff-n-puff cycles to converge.