Microscopic Mechanisms of Asphaltene Behavior during CO 2 Flooding in Shale Reservoirs: A Molecular Dynamics Study for Mitigation of Pore Throat Blockage

CO 2 flooding is widely recognized as one of the most effective techniques for enhancing the oil recovery in shale reservoirs. However, the pore throat blockage caused by asphaltene precipitation significantly impedes the efficient expulsion of crude oil, thus severely reducing production output. To address this, a comprehensive understanding of the underlying microscopic mechanisms is crucial for preventing pore throat blockage and optimizing recovery efficiency. In this study, molecular dynamics simulations were utilized to elucidate the intricate processes of asphaltene precipitation, aggregation, adsorption, detachment, and entrainment within shale quartz nanopores under CO 2 flooding conditions. Additionally, the influence of differential displacement pressure on these processes is rigorously examined. The findings delineate a two-stage mechanism: (1) Initially, asphaltene precipitates, accumulates, and adsorbs onto the nanopore walls as the light components are extracted by CO 2 from the crude oil and (2) subsequently, as the crude oil is rapidly displaced, asphaltene precipitates are exfoliated, entrained, and expelled from the nanopores by CO 2 . A higher differential displacement pressure accelerates the displacement rate, leading to earlier initiation of crude oil expulsion by CO 2 . Conversely, insufficient differential displacement pressure may lead to the formation of stable asphaltene precipitates at the pore exit, ultimately causing complete pore throat blockage. These insights offer critical guidance for enhancing the efficiency of CO 2 flooding in shale reservoirs.