Study on the Influence of Reservoir Wettability on Shale oil Flow Characteristics by Molecular Dynamics Simulation

Based on molecular dynamics simulation, the shale nanopore model in combination with XRD results are used to simulate the non-homogeneous wettability characteristics of shale pores. The equilibrium and non-equilibrium molecular dynamics simulations are conducted to investigate the shale oil flow in nanopores with single mineral and heterogeneous mineral wettability. The results indicate that the lipophilicity rank is calcite pore > kaolinite pore > quartz pore with the interaction energy of 968.37 kcal/mol, 784.28 kcal/mol, and 569.72 kcal/mol, respectively. The friction coefficient of shale oil flow in calcite pores is 5 times and 8 times that of quartz pores and kaolinite pores. The high lipophilicity means the mineral pore surface provides high resistance for shale oil. And there has decreased overall flow rate and increased effective viscosity with the increase in flow resistance. The flow rate of all shale oil components decreases with the increase in molecular polarity. And there has different flow rate along the horizontal direction of pore, which is divided into start-up zone, acceleration zone, and smooth zone. The wettability of pores is not affected by pore size. But the overall flow rate of shale oil increases and the effective viscosity decreases with increasing pore size. The overall lipophilicity of shale pore surface decreases with the increase in temperature. The driving force has a significant effect on the peak density, overall flow rate, and effective viscosity of adsorbed shale oil. Proper driving force results in a portion of adsorbed shale oil transforms from immobile fluid to movable fluid.