Abstract
Carbon dioxide (CO2) flooding has a high microscopic displacement efficiency above the minimum miscibility pressure (MMP), but a low sweep efficiency due to gravity segregation and bypassing. In many fields, water-alternating-gas (WAG) is used to improve sweep efficiency, but early breakthrough and low sweep efficiency are common. The objective of this research is to evaluate the performance of polymer-alternating-gas (PAG) floods experimentally in the lab-scale. Continuous gas (CG), WAG and PAG flood experiments were performed in homogeneous and heterogeneous cores. Experiments conducted in homogeneous Berea cores showed that tertiary CG flooding and tertiary WAG flooding had similar incremental oil recovery and the tertiary PAG flooding had a lower incremental oil recovery. Heterogeneous core flood experiments showed that WAG flooding and PAG flooding had similar incremental oil recovery, which were slightly higher than that in the CG flooding. In linear cores, the gravity segregation effect is limited due to the small diameter of cores; so, the extent of bypassing is small. In heterogeneous cores, there is bypassing in CG floods due to permeability contrast and WAG / PAG floods help improve oil recovery. However, PAG oil recovery was no better than WAG oil recovery in these laboratory-scale core floods.
