Experimental Study on Key Factors of CO2 Huff and Puff in Tight Oil Reservoir

China has abundant tight oil resources, but due to the unsolved energy supplement problems, the low production and low efficiency of multi-staged fracturing horizontal wells in tight oil reservoirs are very serious, how to solve these problems has become the key to the efficient development of tight oil resources in China. In this article a set of “energy storage tank” device was innovatively designed to simulate infinite formation and CO2 huff and puff experimental research of tight oil reservoir was carried out. An indoor experimental scheme was developed based on the field production parameters and the effects of three key factors: CO2 huff and puff cycle, injection volume, and soak time on the recovery of CO2 huff and puff were analyzed. The experimental results show: a non-uniform distribution of the remaining oil around the fractures in the core was observed after the huff and puff experiment. Remaining oil at the core end connected to the “energy storage tank” was relatively less; during the process of CO2 huff and puff, with the increase of CO2 injection, the range of interaction between CO2 and oil extends to the depth of the reservoir. The oil replacement efficiency by CO2 is lower than that without using “energy storage tank” during the process of the flowback. Huff and puff recovery is mainly concentrated in the first three cycles; under the same huff and puff conditions, the longer the soak time is, the higher the huff and puff recovery is, but with the increase of soak time, the increase of recovery decreases. The “energy storage tank” device designed in this paper can realistically simulate the actual CO2 huff and puff process in infinite formation, which overcomes the disadvantages of the existing indoor CO2 huff and puff experiments and improves the experimental accuracy.