Abstract:

Through the study of many domestic and abroad field examples of CO₂ flooding after water flooding, it is discovered that after the injection of CO₂, the water cut of many production wells decreases sharply, and this phenomenon happens across the whole development phase, including the early stage of CO₂ injection which the CO₂ displacing front doesn’t reach production wells, the stage of little gas producing，and the stage of high gas-oil ratio. We take emphasis on discussing the development rules of low permeability reservoir before the breakthrough of CO₂，and on this stage oil-water two-phase fluid flow is the main flow type, and three-phase flow does not exist. The reason is that a majority of the injected CO₂ dissolved in local oil and water. According to the actual oilfield dynamic response and the results of in-house slim tube and long core flooding experiment，we explain the action between CO₂ and oil-water system，finally gain two conclusions. The first is that gas can drive crude oil reaching producers by traveling through local water. The second is that the displacement law is obviously different in different low permeability cores when CO₂ flooding starting from high water cut stage, for the special low permeability cores, the oil recovery before CO₂ breaking accounted for CO₂ total recovery of 73.27%, and after CO₂ breaking the recovery accounted for 26.73%.But for the average low permeability cores, the oil recovery before CO₂ breaking only accounted for CO₂ total recovery of 16.72%, and after CO₂ breaking the recovery accounted for 83.28%.

Key words: CO₂ flooding, low permeable, in-house experiments, water cut, development rules, petroleum