Phase Behaviour of Local Alkaline and Surfactants During Flooding

Abstract

The addition of natural and synthetic surfactants during chemical flooding recovers oil originally trapped by capillary forces through the reduction of the interfacial (adhesive) tension between the aqueous and oleic phases. As the interfacial tension reduces, the trapped oil droplets are mobilized forming a continuous oil bank thereby reducing the amount of residual oil saturation. The objective of phase behaviour is to determine the optimum salinity and to select the best compatible chemical composition for a specific application that can effectively enhance oil recovery. This study seeks to assess chemical compatibilities between alkaline –surfactant systems in the presence of calcium and magnesium ions; analyse synergy between alkali-surfactant slugs and crude oil to enable us to design an optimal low-cost, environmental friendly alkaline and surfactant floods for enhanced oil recovery. This is based on an understanding of fluid-fluid interactions. We conducted phase behaviour tests on selected local surfactants (AlkaSurf X, Moringa), bio-ethanol, local alkali (potash) and simulated formation brine. Aqueous stability and salinity scan experiments were conducted to determine the compatibility of the Alkaline–Surfactant systems with brine. Solutions free of precipitation were used for the interfacial-tension and phase behaviour analysis. Salinity scan results were used to calculate the solubilisation ratio and optimal salinity. Results indicate that the local Alkaline-Surfactant systems are highly tolerant of divalent ions. Also, results from pipette test showed that AlkaSurf X and Moringa alone attained a Type II (-) microemulsion, however, the addition of potash and co-surfactant at a controlled pH and concentration exhibited optimal salinity and a Type III microemulsion. This study shows that certain local alkali and surfactant can enhance oil recovery, even under harsh conditions, thus eliminating the use of harmful chemicals and need for brine softening processes which adds to the overall cost.