Parameter optimization for enhanced oil recovery: Mechanisms of WAG flooding in heterogeneous low permeability layers
HAO Hongda, ZHAO Fenglan, HOU Jirui, SONG Zhaojie, HOU Libin, WANG Zhixing, LI Wenfeng, FU Zhongfeng
1 Research Institute of Enhanced Oil Recovery, China University of Petroleum-Beijing, Beijing 102249, China 2 Basic Theory Laboratory of Improved Oil Recovery in Low Permeability Oil Fields, Tertiary Oil Recovery Key Laboratory, CNPC, Beijing 102249, China 3 Key Laboratory of Greenhouse Gas Sequestration and Oil Exploitation, Beijing 102249, China
Low gas displacement efficiency and gas channeling phenomena usually occur in heterogeneous slow permeability layers. Water alternating gas (WAG) and CO2 flooding can effectively improve the gas flooding efficiency. The adaptability of WAG flooding for low permeability layers with heterogeneity was confirmed through laboratory experiments. The mechanism of enhancing oil recovery was then revealed through analyzing the mobility control ability of WAG flooding. Better adaptability of WAG flooding was found in weakly heterogeneous reservoirs compared with homogeneous reservoirs. When applied in low permeability reservoirs with weak heterogeneity, WAG flooding can present excellent mobility control ability, which compels the injected fluid to displace the crude oil in the relatively low permeability layers, enlarges the swept volume of injected gas, and then improves the CO2 flooding efficiency. The parameter optimization results of WAG flooding showed in laboratory tests that: with a gas injection rate of 0.3 mL/min, a slug size of 0.1 PV and an injected gas/water ratio of 1:1, 21% of OOIP can be recovered by WAG flooding after water flooding in low permeability layers with heterogeneity.
