For the water-flooded reservoir at ultra-high water cut stage, the ratio of oil and water relative permeability and the water saturation deviate from the linear relationship and show the downwarping trend in the semi-log coordinate, and the conventional water drive curves show the upwarping trend. Aiming at predicting the dynamic, recoverable reserve and recovery of oilfields at ultra-high water cut stage, a new formula characterizing the relation between the ratio of oil and water relative permeability and the water saturation was proposed, derivation of a new water drive curve was done by reservoir engineering methods, and the formula of recoverable reserve and recovery was derived. Comparison of the new water drive curve and the conventional one through numerical simulation and field application showed higher accuracy and better adaptability resulted from the new water drive curve, which solved the problems of upwarping and big prediction error in curves of ultra-high water cut stage.
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