Evaluation of nanopore confinement during CO2 huff and puff process in liquid-rich shale formations

Abstract

CO2 huff and puff (CO2 huff-n-puff) with multistage hydraulic fracture has been proven to be a feasible approach to enhance oil recovery in shale/tight formations. The present study investigates the effect of pore confinement on the incremental recovery of the CO2 huff-n-puff process in shale formation. The results demonstrate that neglecting nanopore confinement has a large impact on production forecasts from unconventional assets especially when the pore size is considerably less than 10 nm. Failure to correct the changes in fluid properties due to pore confinement might lead to errors in simulation results. Fine gridding plays an important role during simulation setup. Moreover, CO2 molecular diffusion is the most important mechanism by which the gas tends to move from fractures into the matrix. Although a short injection time cannot increase oil recovery significantly, a long injection time (more than 5 months) might not be economically or technically feasible.