Review on Pore Structure Characterization and Microscopic Flow Mechanism of CO2 Flooding in Porous Media

Understanding of pore structure and microscopic flow mechanism at pore-scale is significant for enhancing oil recovery by carbon dioxide (CO2) flooding. Herein, the pore structure characterization and the microscopic flow mechanism of CO2 flooding are analyzed and compared. The pore structure can be captured using experimental analysis, image analysis, and digital core technique. The digital core approach shows broad applications for pore structure characterization as it is reusable and visible. Pore-scale flow can be directly observed using visual models; however, the pressure and temperature that visual models can withstand need to be improved. Use of X-ray computed tomography (CT) and nuclear magnetic resonance (NMR) is preferred to monitor the fluid transport and distribution during CO2 displacement in actual cores. The flow in porous media can be also modeled by molecular dynamics (MD) and the lattice Boltzmann method (LBM). The LBM is efficient in simulating multiphase fluid flow in porous media because it achieves parallel computing and can deal with complex boundaries. Herein, detailed analysis for pore structure characterization and of the microscopic flow mechanism of CO2 flooding in porous media is presented, which can further help to design and optimize CO2 flooding schemes to improve oil recovery.