Micro-Displacement and Storage Mechanism of CO2 in Tight Sandstone Reservoirs Based on CT Scanning

Tight sandstone reservoirs are ideal locations for CO2 storage. To evaluate the oil displacement efficiency and storage potential of CO2 in the tight sandstone reservoir in the Huang 3 area of the Changqing Oilfield, four kinds of displacement experiments were conducted on core samples from the Chang 8 Formation in the Huang 3 area. These experiments were performed using microdisplacement equipment, digital core technology, and an online CT scanning system; the different oil displacement processes were recorded as three-dimensional images. The results show that the CO2 flooding alternated with water scheme can improve crude oil recovery the most. Comparing the cores before and after the displacement shows that the amount of crude oil in pores with larger sizes decreases more. The remaining oil is mainly in thin films or is dispersed and star-shaped, indicating that the crude oil in the medium and large pores is swept and recovered. The CO2 displacement efficiency is 41.67-55.08%, and the CO2 storage rate is 38.16-46.89%. The proportion of remaining oil in the throat of the small and medium-sized pores is still high, which is the key to oil recovery in the later stages.