Abstract:

As a kind of tertiary oil recovery technology, CO₂ flooding can substantially improve the oil recovery ratio which in China started late on its researching and applying, and now is more likely to be sporadic pilot tests. After more than ten years of exploration in Qintong sag, Subei basin, CO₂ flooding pilot tests has been conducted and applied in 5 low permeability oil fields. This paper studied the 5 low permeability oil fields with one-dimensional tubule simulation and reservoir numerical simulation, and on this basis, carried out researches of gas injection timing, the slug size, and the gas injection parts. This text stated that improving  the miscible pressure in the early injection can more effectively shorten the two phase transition zone, increase the CO₂dissolution rate, reduce the viscosity of oil phase and interfacial tension of oil and  gas, thus,can increase the degree of miscible. In terms of the  low permeability reservoir in Subei basin, early injection as well as large size slug can be considered as a mature and effective method to improve  oil recovery.

Key words: CO₂ flooding, early injection, slug size, gas injection part, low permeability reservoir