Experimental study on influencing factors of CO2 huff and puff effect in the tight water-bearing reservoir

Abstract

The presence of a water phase in tight oil reservoirs is inevitable. To investigate the effect and influencing factors of the CO2 huff and puff technique on enhancing oil recovery in water-bearing tight oil reservoirs, CO2–water–crude oil phase experiments were conducted. The results reveal that the solubility of CO2 and the expansion coefficient of crude oil decrease with increasing water content in the system. Furthermore, CO2 huff and puff experiments were performed to analyze the effects of the number of huff and puff cycles, soaking time, soaking pressure, water saturation, and permeability on the performance of CO2 huff and puff under saturated/unsaturated water conditions. The experimental findings indicate that the oil recovery increases logarithmically with the number of huff and puff cycles. Increasing soaking time and soaking pressure gradually enhances recovery until reaching optimal soaking time and pressure. However, further increasing soaking time and pressure beyond the optimal values has minimal effect on recovery. Compared to the cases under unsaturated water conditions, the optimal number of huff and puff cycles, soaking time, and pressure are higher under saturated water conditions. Additionally, the CO2 huff and puff effect deteriorates with increasing water saturation in low permeability reservoirs.