Experimental Investigation of Non-Chemical CO2 Microbubbles EOR Performance in Low-Permeability Resevoirs

Abstract As a novel, economic, and environmentally friendly enhanced oil recovery (EOR) and carbon sequestration technology, non-chemical CO2 microbubble (MB) has potential applications in low permeability reservoirs. At present, there are only few studies available focusing on non-chemical MB EOR in low permeability reservoirs. Previous studies mainly focused on its storage efficiency in saline aquifers, and more research is needed to fully understand the EOR mechanism in low permeability. In this paper, the EOR performance and its mechanisms of non-chemical CO2 MB in low permeability reservoirs are experimentally investigated. For comparations, a series of CO2-based method were also included, such as CO2 injection, water altering gas and conventional foam. The results demonstrate that CO2 MB has competitive EOR performance to conventional foam injection. The increment oil recovery of microbubbles on 2.23×10−3 μm2 and 9.46×10−3 μm2 rock samples are 12.5% and 19.59% original oil in place (OOIP), respectively. In parallel coreflood experiment, the MB increased oil recovery by 10.73% and 17.92% of OOIP on core samples with the permeability of 9.43×10−3μm2 and 2.25×10−3μm2, respectively. The CT imaging shows that the core sample has lots of residual oil zones due to microheterogeneity. After MB flooding, the average residual oil saturation of the core sample is reduced from 42.15% to 33.5% and the horizontal and vertical residual oil zones are eliminated. The results of this study comprehensively evaluated the feasibility and EOR performance of non-chemical CO2 MB in low permeability reservoirs. Overall, the results suggest that non-chemical CO2 MB is an efficient EOR method which has better displacement efficiency and conformance control ability than other CO2-based non-chemical EOR method (CO2 injection and WAG).