Experimental Study on Oil–Gas Interaction Mechanism during Offshore Heavy Oil Gas Injection

Offshore heavy oil injection gas extraction is a highly scrutinized area in today's petroleum industry. However, the interaction mechanisms between oil and gas are not clear. To elucidate these mechanisms, an indoor experimental setup was established for research purposes. The effects of different types of gases on heavy oil expansion, mass transfer mechanisms between gas and heavy oil, the influence of gas injection on heavy oil phase behavior, and the testing of minimum miscibility pressures are investigated in this study. The results indicate that CO2 yields the best reduction in the heavy oil viscosity. Both forward and backward multiple contact mass transfer processes demonstrate nonmiscible multiple contact dynamic displacement mechanisms involving CO2 dissolution and condensation, as well as C1 extraction and coextraction. Nonmiscible multiple contact dynamic displacement of natural gas primarily involves limited dissolution and condensation of light hydrocarbon components and intermediate hydrocarbon components, with an extremely weak extraction effect. The minimum miscibility pressures are in the order of CO2 < natural gas < N2. This research provides important experimental evidence and theoretical guidance for further improving offshore heavy oil injection gas technology and practice.