Abstract: Based on the Type II generalized water flooding characteristic curve, the concept of underground gas-water cut was introduced, and the Type II generalized gas-water miscible flooding characteristic curve was established on the basis of analogy. The mathematical model of gas-water cut corresponding to the Type II generalized gas-water miscible flooding characteristic curve can be transformed to describe the S-shaped gas-water cut variation and also the convex, S-convex, S-concave, concave, and other shapes of gas-water cut variations, when the characteristic values n and m take different values. This provides additional methods for evaluating development effects of gas-water miscible flooding. The paper put forward a general formula for the Type II gas-water miscible flooding characteristic curve and corresponding methods for solving the mathematical model of gas-water cut, and evaluated the development effects of the water-alternating-gas miscible flooding in the reservoir of Sanjianfang formation in Pubei oilfield and the gas cap + edge water miscible flooding in S31 reservoir in Jinzhou oilfield, respectively, showing a high fitting accuracy. This work provides a valuable reference for developing other oil reservoirs.

Key words: Pubei oilfield, Jinzhou oilfield, gas-water miscible flooding reservoir, Type II generalized gas-water miscible flooding characteristic curve, underground gas-water cut, variation, mathematical model