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.
Highlights
Low-permeability reservoirs possess poor reservoir physical properties
As an important technique to reduce the interlayer interferences, layer recombination is of important significance to reduce the differences of interlayer recovery percent and increase oil recovery (Shi et al 2006, Hu et al 2010; Cui and Zhao 2010)
During middle and late development period of lowpermeability reservoirs, permeability, effective thickness, crude oil viscosity and oil saturation of every single layer as well as threshold pressure gradient and artificial fractures all will influence the performance of layer recombination
Summary
Low-permeability reservoirs possess poor reservoir physical properties. To improve the productivity and economic profit, commingling production is generally used during early development stage. Keywords Layer recombination · Low-permeability reservoirs · High water cut stage · Apparent mobility contrast · Equivalent permeability
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