Investigation on oil recovery and countercurrent imbibition distance coupling carbonated water with surfactant in shale oil reservoirs

Carbonated water (CW) is defined as water in which CO 2 has been dissolved. Utilizing CW as the imbibition fluid enables the simultaneous exploitation of capillary forces and CO 2 diffusion, resulting in enhanced oil recovery (EOR) and facilitating CO 2 sequestration. Nevertheless, the literature reveals a notable scarcity of research on the imbibition of CW in shale oil reservoirs. In this study, the imbibition experiments involving formation water, surfactant, CW, and active carbonated water (ACW) were conducted on shale cores, considering reservoirspecific temperatures and pressures. Furthermore, the countercurrent imbibition distance (CID) for these fluids was quantitatively characterized using online computed tomography scanning. The EOR performance, alongside the CID and countercurrent imbibition recovery (CIR), is further compared to highlight differences in effectiveness among the fluids. The experimental results demonstrate the imbibition recovery for formation water is 10.66 %. CW and ACW can significantly enhance the imbibition recovery, achieving 28.82 % and 34.65 %, respectively, both of which are higher than surfactant. The CID and CIR for formation water are 1.125 cm and 2.35 %, respectively. While surfactant can increase the imbibition spread area and the efficiency of imbibitiondriven oil recovery to some extent, CW and ACW exhibit even great efficacy, evidenced by their higher CIDs of 1.875 cm and 2.375 cm, and CIRs of 7.09 % and 9.30 %, respectively. This paper, for the first time, investigates the imbibition recovery, CID and CIR of CW and ACW in shale matrices, which uncovers the potential for CW/ ACW imbibition in enhancing shale oil recovery.