Layer recombination technique for waterflooded low-permeability reservoirs at high water cut stage

Abstract

Layer recombination is an important technique to improve the oil recovery of waterflooded low-permeability reservoirs, especially at high water cut stage. This technique significantly increases the oil recovery percent of relatively lower-permeability layers when all the formation layers are perforated and produced simultaneously. Parameters such as formation permeability, crude oil viscosity, remaining oil saturation, the presence of hydraulic fractures or others have an impact on the production performance after layer recombination. It is quite difficult to take all these influencing factors into consideration when making layer recombination decisions. Therefore, this paper proposes the ‘apparent mobility’ as the decision index of layer recombination for low-permeability reservoirs at high water cut stage, and the optimal apparent mobility contrast values for layer recombination under different producing pressure drop are obtained. The equivalent permeability of fractured layers is introduced into the apparent mobility. This technique has been applied to the layer recombination treatment of Block Five of Bonan oilfield in Shengli oilfield of SINOPEC, and the oil recovery increased approximately 3.1% compared with the previous commingling production scenario, which confirmed the validity of this proposed method.