Study on the mechanism of CO2 composite system assisted steam stimulation of oil recovery efficiency in heavy oil reservoirs

Injecting CO2 and foaming agents can effectively improve the recovery rate of high cycle steam huff and puff. In this paper, firstly, the influence of oil saturation and injection plug on recovery rate is analyzed using a sand filled pipe physical simulation device. Then, combined with reservoir parameters, the influence of reservoir thickness, interlayer thickness, and oil saturation on the economic limits of development is elucidated. Thirdly, reservoir engineering methods are used to analyze the appropriate timing for injecting foaming agents into the study area. Results show that (a) CO2 dissolves in crude oil, increasing its internal elastic energy and forming a solution gas drive. (b) When the oil saturation is 40 %, the cyclic oil increase is 109 tons, and the oil to gas ratio is 1.09; when the oil saturation is 35 %, the cyclic oil increase rapidly decreases to 38 tons. (c) For the research area, foaming agents should be intervened as early as possible. Foaming agent concentration is 0.4%.