Alkaline surfactant polymer formulation for carbonate reservoirs

This paper presents a systematic study to investigate the applicability of alkaline-surfactant-polymer (ASP) process as an enhanced oil recovery method to Saudi Arabian carbonate reservoirs. Several alkalis were first screened to test their compatibility with the injected sea water that has large quantities of divalent ions. Then surfactant-polymer, alkali-surfactant, and alkali-surfactant- polymer interactions at the reservoir temperature (90°C) were investigated. Static adsorption of surfactant on reservoir carbonate rocks were also investigated at the same temperature. Interfacial tension (IFT) measurements were made between the slugs formulated and crude oil from the same reservoir. Two surfactants were tested, Triton X-102 and Ethoxylated sulfonate (Dodiflood B1083), and the polymer tested was FLOCON 4800C. The results of the compatibility tests showed that the ASP slug has to be prepared using softened seawater and be protected by a pre- and afterflush softening seawater slugs. B1083 surfactant was found to be a promising candidate surfactant for the adverse conditions of the Saudi Arabian carbonate reservoir. A combination of NaHCO₃ and Na₂CO₃ was found to significantly reduce the adsorption level of B1083 surfactant on carbonate rock at low surfactant concentrations (<1% by wt.). This is very desirable for formulation of a cost-effective ASP slug.