Abstract
Miscible gas flooding is an important approach for enhancing the recovery of unconventional oil reservoirs. The injected gas and crude oil components has a significant impact on the minimum miscible pressure. In order to clarify the miscibility characteristics and factors influencing the minimum miscibility pressure, combining PVT and slim tube experiments, the minimum miscibility pressure between Tuha low viscosity oil and different injected gas was measured. Additionally, chromatography experiments were conducted to study the composition changes of produced oil. The results indicate that when the injection pressure is higher than the minimum miscible pressure, the extraction effect of injected gas on heavy fraction (C16+) in crude oil is enhanced and the extraction effect on light alkanes (C1-C6) is reduced. The increase in the content of light alkanes (C1-C6) and middle distillates (C7-C15) in crude oil reduces the minimum miscibility pressure between crude oil and injected gas. Pipeline gas can effectively extract heavy fraction from crude oil, but its breakthrough time is early. Under the same pressure, earlier breakthrough time of injected gas makes it more difficult for the crude oil and injected gas to miscible. Through the analysis of experimental results, the following main conclusions are drawn: Immiscible flooding causes heavy fraction (C16+) in crude oil to remain, which might affect the physical properties of the reservoir, increasing the difficulty of subsequent development. Gas fingering phenomenon significantly influences the miscibility of injected gas and crude oil, and the viscosity ratio of injected gas and crude oil under high-pressure conditions can be used as an important criterion for screening injected gas.