In shale gas and shale oil resources, hydrocarbons are generally stored in pores that are nanometers to tens of nanometers in size. In these pores, capillary pressure affects the phase behavior of hydrocarbon mixtures and the mobility of gas and oil phases. In this talk, I will present modeling of vapor-liquid equilibrium and simulation of multiphase flows under strong capillary pressures. Vapor-liquid equilibrium calculations are important for predicting the fractions and properties of gas and oil phases during primary production of oil. In a porous medium with pore size distributions, our calculations show that the capillary force increases with increasing gas saturation, and it is likely that the smallest pores are always filled with oil during production. These calculations are useful for determining the properties of fluids and their distributions within a porous medium. In our group, we use both experiments and simulations to study multiphase flows. Using a color-gradient based lattice Boltzmann method, we simulated the displacement of a wetting fluid by a non-wetting fluid, driven by a constant pressure differential. As the pressures of phases can be directly obtained from the simulations, we were able to track the evolution of the pressure distributions inside the porous media. When the capillary number is low, significant differences between the pressures and the pressure gradients of the two phases are observed. This work shows that, when the capillary pressure is strong, the common assumption adopted in the experiments that the two phases have equal pressure gradients should be revisited. The limitations of the lattice Boltzmann simulations observed will also be discussed.

Xiaolong Yin received BS in Mechanics from Peking University, MS in Mechanical Engineering from Lehigh University, and PhD in Chemical Engineering from Cornell University. He conducted postdoctoral research in Chemical Engineering at Princeton University before joining the faculty of Petroleum Engineering Department at Colorado School of Mines. He is now an associate professor, a faculty member of the Energy Modeling Group and the Marathon Center of Excellence of Reservoir Studies, and the co-director of the Unconventional Reservoir Engineering Project consortium. He is an associate editor of the SPE Journal and the Journal of Natural Gas Science and Engineering.