Abstract

This paper presents a novel foam-assisted surfactant Chemical Enhanced Oil Recovery (CEOR) of the matrix oil in naturally fractured reservoirs. Foam reduces fluid mobility within fractures and diverts the injected surfactant solution into matrix for wettability alteration and IFT reduction. Single–well cyclic huff-n-puff and dual completion pilots are modeled to evaluate the effectiveness of this envisioned CEOR, assess process mechanisms and demonstrate recovery conformance. In order to perform these foam-surfactant injection studies, a dual porosity-dual permeability 3-D sector model of the gas cap in a fractured reservoir is constructed, and co-injections of foaming surfactant in the nitrogen gas stream are simulated. These pilot simulations implement a laboratory-based surfactant phase behavior and foam model along with a compositional technique that captures surfactant-oil-brine phase behavior and tracks IFT and rheology of microemulsion phases. Sensitivity studies to various CEOR process mechanisms, injectivity characteristics, reservoir parameters and conformance are explored to guide an optimized pilot design scheme within operational constraints to evaluate and monitor the extent of oil recovery efficiency. The results show that while only a fraction of the released matrix oil is captured in the pilot arrangements due to conformance, considerable volumes of oil drain from the gas cap matrix blocks down to the oil column, thus substantiating the applicability of this envisioned foam-surfactant CEOR for naturally fractured reservoirs. Cyclic huff-n-puff injection is shown to be a more appropriate configuration for single-well pilot testing.

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