CO2-regulated octane flow in calcite nanopores from molecular perspectives

Enhanced hydrocarbon recovery from shale/tight reservoirs by CO2 injection has gained extensive attentions in recent years. However, the effect of CO2 on oil flow in shale/tight nanoporous media is still ambiguous. In this work, we used molecular dynamics simulations to study the structural and dynamic properties of CO2 and nC(8) mixtures in calcite nanopores. We found that CO2 is preferably adsorbed on the calcite surface, forming a thin CO2 film. When CO2 content is low, CO2 displaces nC(8) molecules on the pore surface, while CO2-nC(8) mixing does not occur in other regions. As the nC(8) molecules on the pore surface are immobile, the effect of CO2 on nC(8) total flow rate is negligible. As CO2 content further increases, only after the CO2 adsorption layer on the pore surface is fully saturated, CO2 can mix with nC8 in other regions to dramatically reduce the effective viscosity of CO2-nC(8) mixtures. As a result, nC(8) total flow rate drastically increases. This work provided important insights into the effect of CO2 on oil flow in calcite nanopores in relation to the CO2-EOR in shale/tight reservoirs.

Automated summary

The study shows that CO2 forms a thin film in calcite nanopores, and only after the CO2 adsorption layer is fully saturated, can it mix with nC8 to reduce viscosity and increase total flow rate.