ASP design for the Minnelusa formation under low-salinity conditions: Impacts of anhydrite on ASP performance

► We designed ASP blends based only on fluid–fluid interactions and phase behavior. ► We compared recovery from model rock (less reactive) with rock containing anhydrite. ► Geochemical observations and modeling show why anhydrite affects water chemistry. ► Our results explain why NaOH should be used in contrast with Na2CO3 in Minnelusa rock. Alkali–surfactant–polymer (ASP), surfactant–polymer (SP) and alkali–polymer (AP) flooding have been recognized as potentially effective Chemical Enhanced Oil Recovery (EOR) techniques. The alkali in ASP or AP flooding blends interacts with formation minerals, markedly with anhydrite in the case of eolian deposits. As a result, water chemistry after the injection of an engineered chemical blend is unlikely to be governed only by fluid–fluid interactions at reservoir conditions. To investigate rock-fluid interactions, Berea and available rock samples from an oil-bearing Minnelusa reservoir in Wyoming, an eoalian formation, are used in coreflooding experiments. Further, a robust ASP blend at optimal salinity was designed for the DC Minnelusa crude oil. Secondary waterflooding, tertiary ASP injection, polymer drive and finally a brine flush are subsequently completed in coreflooding experiments. Oil recovery, pressure drop, surfactant concentration, pH, and viscosity are measured during or immediately after each experiment; water chemistry is analyzed in effluent samples. Findings show the potential of the chemical blends to improve oil recovery significantly under low-salinity conditions (