Mechanisms of Crude Oil Mobilization in Multiscale Pore Throats of Tight Oil Reservoirs with Different Huff-n-Puff Agents

In this study, typical tight oil cores were selected to carry out perform huff-n-puff experiments under different media and shut-in times. Nuclear magnetic resonance (NMR) was used to characterize the utilization of crude oil in three-scale pores during huff-n-puff, and the differences of matrix fractured cores were compared. The results show that the three huff and puff media all show that submicron pores are the main absolute contributors, but there are essential differences in pore size selectivity mechanism and timeliness: the huff and puff of water shows the law of short-soak macropore priority response and long-soak multi-scale synergy; under the present experimental conditions, CO2 huff-n-puff exhibits the high time efficiency and favorable multi-scale synergy due to its strong diffusion and dissolution ability. N2 huff and puff is highly dependent on the fracture channel to establish an effective pressure response, and it is almost difficult to effectively use the nanopores. This study reveals the internal mechanisms whereby the properties of huff-n-puff media and the pore structure synergistically control multi-scale crude oil production, and provides a theoretical basis for the optimization of huff-n-puff media and the shut-in system in tight oil reservoirs.