| The technology of CO2foam flooding takes full advantage of CO2foam effectiveblockage and displacement mechanism to improve oil recovery. In this paper, CO2foam as aneffective profile controlling technique is applied to overcome the early breakthrough of CO2flooding in heterogeneous reservoirs of Zhongyuan Oilfield.For the high temperature and high salinity of target reservoir conditions, foamingbehaviors of several surfactants affected by surfactant concentration, temperature, salinity andpressure are surveyed, aiming at evaluating and selecting the best surfactant which hasoutstanding salt and temperature resistance. The sealing performance of the foaming agentunder high temperature and high salinity is investigated by displacement experiments, and theenhanced oil recovery is also investigated by oil displacement experiments. The experimentresults show that the combination foaming agent of amphoteric and nonionic surfactants has agood foam stability. Foam resistance factor can be high and the oil recovery is enhancedlargely in the displacement experiments, proving that the foaming agent can also achieve agood sealing capacity during flowing in reservoir conditions. Moreover, the experimentresults also show that the resistance factor has a sensitive and positive correlation to half foamlife period which is the main factor to judge foam stability and sealing performance.CO2foam mechanistic model and relative permeability model are established based onthe theoretical analysis and displacement experiments. Combined with real reservoirconditions of target area in Zhongyuan oilfield, a three dimensional conceptual model of CO2foam flooding, which contains three phases and nine components, is developed. In this way,CO2foam flooding mechanism is investigated. The numerical simulation results show theEOR mechanism includes shutting off capacity and gas channeling control by decreasingmobility, gas up-flowing effect to improve the oil recovery, and improvement of the reservoirenergy. |
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