Molecular insights into the natural gas regulating tight oil movability

YN Zhang and SJ Li and XJ Dou and S Wang and YF He and QH Feng, ENERGY, 270, 126895 (2023).

DOI: 10.1016/j.energy.2023.126895

Unconventional reservoirs development by gas injection has gained extensive attentions in recent years. As an injector gas, natural gas is one of the most promising fluids that is used in EOR process. However, the effect of natural gas on tight oil movability in nano-pores is still ambiguous. In this study, molecular dynamics simulations have been employed to generate insights into the tight oil movability under different gas contents and gas types. Simulation results demonstrate that the higher the methane content, the lower the migration resistance of the system, despite the gradually decreased migration rate. By analyzing the dynamic pathway, threshold migration resistance, and interface characteristics, the optimum molar range of gas content range for mixing methane with tight oil is 0.4-0.6. On this basis, the effects of four kinds of heavy hydrocarbon gases were investigated. Compared with methane, the four heavy hydrocarbon gases have little effect on the migration resistance, but all four gases can significantly improve the oil-gas miscibility and migration rate. In addition, ethane and propane can further reduce the oil-gas-water IFT, and they are the best gases to promote tight oil migration. This study provides a more in-depth understanding of natural gas injection to develop tight oil.

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