Abstract
The purpose of this paper is to research an oil tolerant foam agent as a displacing phase to improve oil recovery in the fractured-vuggy carbonate reservoir. The foamability and foam stability were tested to optimize the concentrations of the foam compositions, and its static performance was analyzed in the presence of crude oil. Meanwhile, a visualized fractured-vuggy physical model was designed and fabricated based on the geological condition of well S48 and well TK467 in Tahe oilfield, West China. The residual oil type and distribution after bottom water flooding in the visualized model were firstly summarized. Secondly, dynamic production performances of N2 flooding and oil-tolerant N2 foam flooding were comparatively studied. Finally, the two primary factors including positional relation between injection-production wells and injection methods were primarily studied.
Results indicate that the foamability and foam stability increase to a constant state when concentrations of surfactant and inorganic salt increase to 0.5 wt% and 0.35 wt%. And the polymer can significantly enhance the foam stability in the presence of oil. The displacing experiments in the model illustrate that the types of residual oil include oil trapped in the closed caves, "attic oil" on top of vugs, by-pass oil that can't be swept and oil film absorbed on the surface of fractures. The oil tolerant foam can stably accumulate in the vugs and expand swept volume due to gas mobility control. A better oil recovery can be achieved in foam injection by means of low positional flooding and high positional production. Besides, the oil recovery with slug foam injection is almost similar with continuous injection, but can significantly reduce the gas consumption.
