Systematic Phase Behaviour Study and Foam Stability Analysis for Optimal Alkaline/Surfactant/Foam Enhanced Oil Recovery

Abstract

Alkaline-Surfactant-Foam (ASF) flooding is a recently introduced enhanced oil recovery (EOR) method. This paper presents laboratory study of this ASF to better understand its mechanisms. The focus is on the interaction of ASF chemical agents with oil and in the presence and absence of naphthenic component and in-situ soap generation. The impact of alkali, IFT reduction, in-situ soap generation and oil acid number were systematically studied by measurement of phase behaviour, interfacial tension and foam stability. Phase behaviour results indicate the synergistic effect between the generated soap and synthetic surfactant, which gives wider range of optimal salinity in terms of IFT reduction. The novel alkali-surfactant formulation lowered IFT between oil and aqueous phase from nearly 30 mN/m to 10-1 - 10-3 mN/m. This means that chemical formulation can create low tension foam flooding with higher capillary number than conventional foam for displacing oil from porous media. In the foam stability analysis of ASF agent in the presence and absence of oil, several characteristics such as foam volume evolution, foam half decay time, liquid fraction of foam were measured over a wide range of surfactant, alkali, electrolyte and naphthenic acid concentration. Bulk foam stability tests demonstrated that stability of foam diminishes in presence of oil with high in-situ soap generation. The obtained results for foam stability in the presence of oil were successfully interpreted in terms of phenomenological theory of entering/spreading/bridging coefficient, lamella number and pseudo-emulsion film. The discussed method in this paper can be successfully applied to formulate high performance chemical agents for achievement of improved foam flooding according to reservoir fluid condition, i.e. properties of crude oil and formation water.