Displacement efficiency and storage characteristics of CO₂ in low permeability reservoirs: An experimental work

Over the past decades, CO2 flooding in low-permeability porous media has continued to grow. Furthermore, propelled by the current movement toward CO2 sequestration, the flooding of CO2 is expected to further increase. Thus, it is of scientific significance to study the mechanism of displacement of CO2 flooding as well as the CO2 storage characteristics. In this study, CO2 miscible/immiscible flooding experiments were conducted on two low permeability samples to study the difference between them. Specifically, the effect of oil displacement and CO2 storage coefficient for different displacement models were measured and compared. In addition, nuclear magnetic resonance (NMR) tests and frozen pelleting experiments were conducted. The NMR tests clarified the lower limit of pore throat where oil can be displaced by CO2 miscible/immiscible flooding. Furthermore, the frozen pelleting experiments analyzed the distribution characteristics of the remaining oil before and after CO2 miscible/immiscible flooding. The investigation showed that the development efficiency of CO2 miscible flooding is higher than CO2 immiscible flooding in low permeability reservoirs. The results also indicated that CO2 miscible flooding increases the recovery of hard-to-produce semi-bound oil phase and CO2 storage coefficient with CO2 miscible displacement is more significant than that with CO2 immiscible flooding. The data from this study is a critical input for reservoir simulation, which sheds light on the CO2 miscible/immiscible flooding in low permeability reservoirs.