Effect of water film on oil flow in quartz nanopores from molecular perspectives

The knowledge about the underlying mechanisms of oil transport behavior with the presence of thin water film in hydrophilic quartz nanopores is crucial to oil migration and production in shale/tight oil reservoirs. In this work, we use molecular dynamic (MD) simulations to study the flow of nC(8) in quartz nanopores with the presence of thin water film under a reservoir condition (323 K and 20 MPa). We observed the formation of layering structure of water near the surfaces, while in nC(8)-water interface region, weakly ordered nC(8) structures form. In addition, a rapid change of fluid velocity, which is the typical feature of liquid-liquid slip, was observed in the nC(8)-water interface region. We also found that such liquid-liquid slip can be non-negligible in small nanopores. The apparent viscosity of total liquids in the nC(8)-water interface region can be only half of those of bulk water and nC(8), while the flux contributions of water and nC(8) in the nC(8)-water interface region are independent of pore sizes. Our work should shed lights into oil migration mechanisms with the presence of thin water film and provide important insights into the theoretical and numerical models for shale/tight oil production predictions.