Abstract:

In order to effectively solve the problems of difficult gas injection in S358 high pour-point reservoir and low oil displacement efficiency caused by gas channeling due to high mobility ratio of gas flooding after fracturing, laboratory experiments of gas injection phase and long core displacement mechanism have been carried out. Through the PVT phase state experiment of the high pour-point oil injected by CO₂, dry gas, flue gas, and oxygen-reduced air（N₂ 90 %+O₂ 10 %）under the formation conditions, the characteristic mechanisms of the above four injection gas such as the solubilization expansion, viscosity reduction and tension reduction have been analyzed. CO₂ is preferred as the injection gas. Through five groups of high temperature and high pressure long core flooding experiments with different combination methods, the effect of CO₂ combination flooding on channeling prevention and extraction is evaluated. The experimental results show that the displacement effects of both CO₂+weak gel and CO₂+foam are the best two, and the final displacement efficiency is 70.101 % and 68.212 % respectively. The research results show that the injection of CO₂ combined flooding slug increases the displacement resistance and reduces the fracture conductivity, which plays a key role in improving the microscopic sweep volume. Among them, both the CO₂+weak gel and CO₂+foam displacement methods have the best extraction effects. The research results can provide an experimental basis for the efficient development of high pour point oil in this block.

Key words: low permeability and high pour-point reservoirs, gas injection combined flooding, solubilization swelling, extraction, long core displacement, oil displacement efficiency