Molecular Simulation of Methane Sorption onto Kerogen Surface of Shale in Presence of Surfactant

Shale reservoirs, despite having abundance in hydrocarbon storage, offer significant challenges in terms of understanding the pore-scale and reservoir-scale phenomenon. Typically, hydraulic fracturing treatment is implemented to improve hydrocarbon productivity through the injection of fracturing fluid to induce the breakdown of the formation to create fractures, hence allowing a flow conduit for hydrocarbon to be produced at a higher flow rate of oil and/or gas. In this work, molecular dynamics (MD) simulation using GROMACS were utilized to create a 3D model comprised of methane (CH4), surfactant and graphite. Surfactant, as represented by the cationic cetyl trimethyl ammonium bromide (CTAB) was added along with water to represent water-based visco-elastic surfactant (VES) as an additive to reduce the surface tension of hydrocarbon to shale (represented by graphene). A realistic molecular model was created to examine the interaction of CTAB towards the adsorption pattern of methane onto graphene, in order to reveal the displacement efficiency of methane after wettability modification due to the effect of surfactant on the graphene on a nanoscale. The findings suggest that addition of CTAB as surfactant may enhance the production of methane though the reduction of IFT and adsorption capability of methane to the wall of shale. The result yielded consistent trends, where methane's tendency to stick to the adsorption site (at approximately 1.5 nm from the center of the system) was reduced and more methane molecules were accumulated at the center of the pore space. This study has uncovered the adsorption process and the effect of CTAB in altering the sorption behavior of methane towards shale. This would contribute to the enhancement of long-term shale gas production by providing more information on salinity and pressure sensitivity, enabling extraction to be done at a lower cost. © Copyright 2021, Society of Petroleum Engineers