Experimental study on CO2 huff and puff in the Daqing Fuyu tight oil reservoir with online NMR

Tight oil is a typical unconventional resource, and enhancing its recovery rate remains a challenge in current development efforts. In this study targeting the Daqing Fuyu tight oil reservoir, we combine a high-temperature and high-pressure long core physical simulation apparatus and a high-temperature and high-pressure online Nuclear Magnetic Resonance (NMR) testing system to conduct indoor simulation experiments on CO₂ huff and puff in long cores. The results indicate that in the process, it is primarily the oil from micro-pores that is initially mobilized, but further along mobilization of fluids from a portion of sub-micro-pores and nanopores is enhanced, with an efficiency ranging from 25 to 33 %. It was also found that there exist optimal conditions for huff and puff pressure, soaking time, and huff and puff cycles. Additionally, excessive extraction of light components by CO₂ can prove disadvantageous for further improvement in huff and puff efficiency. This study can provide insight into the mechanisms of and data support for the development of CO₂ huff and puff strategies in tight oil reservoirs, thereby contributing to the formulation of effective development plans.