Parameter optimization and effect evaluation of CO_2 flooding after water flooding

Taking recovery factor enhancing degree and oil drainage rate as evaluation indexes,the injection-production parameters of water-CO2 gas alternation flooding in some block of Dagang Oilfield are optimized and flooding results are evaluated using the orthogonal experimental design and numerical simulation method.It is shown that the CO2 flooding after water flooding can effectively enhance recovery factor,optimal flooding parameters are the CO2 gas slug size of 0.05 PV,the gas-to-water ratio of 1∶2,CO2 injection rate of 40 000 m3/d,and the injection-production ratio of 1∶0.9.Appropriately increasing injection-production ratio is beneficial to keep the current formation pressure,increase the miscible degree of oil and CO2 and improve sweep efficiency of CO2 so as to improve the effect of CO2 flooding.Besides,in the water-gas(WAG) alternating flooding,about 50% of CO2 injected could be stored in the formation,which has the good geological sequestration effect of CO2.