Molecular insight into the tight oil movability in nano-pore throat systems

Understanding the movability mechanism of tight oil in nano-pore throat systems is vital for evaluating the oil accumulation and enhancing oil recovery. In this study, molecular dynamics simulations have been employed to generate insights into the tight oil movability in quartz, calcite, and two kaolinite nano-pore throats. Simulation results demonstrate that the migration behavior and migration resistance of tight oil are closely related with mineral types. Specifically, the migration resistance is in the order of Fkaolinite (0 0 1) > Fkaolinite (0 0 −1) > Fcalcite > Fquartz. Herein, the highest resistance of hydrophilic kaolinite is contributed by its extremely strong Jamin effect, while the higher resistance of calcite and moderate lipophilic kaolinite than quartz can be ascribed as stronger oil-pore interactions. Combining the reservoir characteristics and molecular simulation results, it can be concluded that sandstone tight oil is the easiest to accumulate, hydrophilic clay lacks accumulation potential, while carbonate and moderate lipophilic clay are expected to become key areas of tight oil exploration and development in the future. Furthermore, the threshold pore size of tight oil accumulation is proposed based on the migration resistance and basin overpressure characteristics, which can provide theoretical support for tight oil exploration. Overall, this study highlights the effect of complex geological heterogeneity on tight oil movability, which could facilitate future studies on the evaluation of tight oil accumulations.