Shale is characterized by extremely low permeability nanopores. In a subsurface environment, multiple components coexist in nanopores and complicate the prediction of shale gas extraction rate. Studying the interaction among different fluids under nano-confinement is critical to understanding the effects of nanoscale phenomena on the production decline. We employed Grand Canonical Monte Carlo and Molecular Dynamics simulations to investigate the properties of fluid/kerogen system under reservoir conditions including gas adsorption, swelling, wettability, and transport. Our results indicate that CO2 interacts more strongly with kerogen compared to CH4 and H2O. The preferential interaction of CO2 with kerogen leads to many important consequences. Firstly, the adsorption of a CO2:CH4 binary mixture onto kerogen indicates that more CO2 adsorbs onto kerogen structure compared to CH4. Secondly, our simulation results suggest that CO2 can diffuse through water and replace a large quantity of CH4 in the carbon nanopore. Thirdly, kerogen swells more significantly upon CO2 adsorption, compared to CH4 adsorption. Finally, our data indicate that in vacuum, water partially wets the kerogen surface. However, in the supercritical CO2 atmosphere, water forms a spherical droplet at the kerogen interface. Our results also indicate that a thin layer of CO2 forms between kerogen and water, and acts as a lubricant to enhance water flow rate in a kerogen nanochannel. Our work provides molecular-level insight into the production decline curve, chemo-mechanical properties of porous materials, and suggests a new mechanism and engineering approach to reduce energy consumption of a nanofluidic system.

Molecular simulation of the multicomponent interaction in kerogen nanopore

2019 Spring National Meeting

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