Surfactant-less alkali-cosolvent-polymer floods for an acidic crude oil

Alkali-surfactant-polymer floods can increase the oil recovery in many reservoirs by lowering interfacial tension (IFT). Surfactants are the most expensive chemicals in these processes. However, surfactant requirement is low in case of crude oils which contain naphthenic acids. These acids with the addition of an alkali generate in-situ soap which results in lowering the oil-water IFT. The goal of this work is to investigate if surfactants can be eliminated from the formulation in case of sufficiently acidic crude oils to reduce the cost. Low IFT formulations were obtained by varying the alkali concentration in the absence of synthetic surfactants. A cosolvent was added to lower the viscosity of microemulsions and to obtain the low IFT region in the desired salinity range. Various cosolvents were systematically tested to obtain the desired phase behavior. For comparison, alkali-surfactant-polymer (ASP) and alkali-cosolvent-polymer (ACP) formulations were developed for the same crude oil using synthetic surfactants. One-dimensional ASP and ACP corefloods were performed in sandstone cores to test these formulations. The ASP coreflood showed 84.5% oil recovery and 0.1 mg/g-rock surfactant retention in a Berea core. ACP corefloods showed 80-90% oil recovery in Berea cores and minimal cosolvent retention, and 97% recovery in a Boise core. The study shows that comparable oil recoveries could be obtained from ASP and ACP corefloods for a sufficiently acidic crude oil, provided the cosolvent selection is performed carefully.