Adsorption of Anionic Surfactants in Sandstones: Impact of Sacrificial Agents

Abstract

\n High surfactant adsorption remains a bottleneck for a field-wide implementation of surfactant floods. Although alkali addition lowers surfactant adsorption, alkali also introduces many complexities. In our systematic study, we investigated a simple and cost effective method to lower surfactant adsorption in sandstones without adding unnecessary complexities. Static and dynamic surfactant adsorption studies were conducted to understand the role of sacrificial agent sodium polyacrylate (NaPA) on adsorption of anionic surfactants n outcrop and resevoir sandstone corefloods. The dynamic retention studies were conducted with and without the presence of crude oil. Surfactant phase behavior studies were first conducted to identify surfactant blends that showed ultralow interfacial tension (IFT) with two crude oils at reservoir temperature (40°C). Base case dynamic retention data, in the absence of crude oil, was obtained for these surfactant formulations at their respective optimum salinities. NaPA was then added to these surfactant formulations and similar adsorption tests were conducted. Finally, oil recovery SP corefloods were conducted for each surfactant formulations, with and without adding NaPA, and oil recovery data including the surfactant retention was compared.\n Static adsorption of these surfactant formulations at their respective optimum salinities on crushed sandstone varied from 0.42-0.74 mg/g-rock. Their respective adsorptions lowered to 0.37-0.49 mg/g-rock on adding a small amount of NaPA. Surfactant retention in single-phase dynamic SP corefloods in the absence of crude oil in outcrop Berea cores was between 0.17 to 0.23 mg/g-rock. On adding a small amount of NaPA, the surfactant adsorption values lowered to 0.1 mg/g-rock. Oil recovery SP corefloods showed high oil recovery (~91% ROIP) and low surfactant retention (~0.1 mg/g-rock) on adding NaPA to the surfactant formulations.