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.

Improving the availability of crude oil is the primary problem in tight oil development. In this paper, displacement experiment and online nuclear magnetic resonance detection technology are combined to analyze the production characteristics and effects of crude oil injected into tight oil reservoirs by CO₂, CH₄, active water and formation water, and by comparing the gas-oil ratio, water cut and injection-production pressure difference of each displacement medium. In the process of tight oil reservoir development, the potential of different displacement media to improve the degree of production is determined, and the optimal displacement media is selected. The effect of CO₂ injection in tight core samples in Fuyu area is the best, and the recovery degree reaches 60%. for reservoirs with a large proportion of pores less than 0.1 μm, CO₂ flooding can achieve effective mobility; in reservoirs with a large proportion of pores above 1 μm, the displacement efficiency by formation water is higher than that of other media. It is expected that this study can provide support for the optimization of tight oil development plans.