Sacrificial Agent for Reducing Adsorption of Anionic Surfactants

Abstract

Abstract An important economical factor affecting Enhanced Oil Recovery (EOR) is the adsorption of surfactants on the rocks. Sacrificial agents may be used to reduce the adsorption of surfactants. An alkali (traditionally, sodium carbonate or sodium hydroxide) is often used as sacrificial adsorption agent; however, sodium carbonate is not an effective sacrificial agent in the presence of anhydrite in the rocks due to the reaction between sodium carbonate and sparingly-soluble anhydrite. Therefore, it is essential to develop a sacrificial adsorption agent that can act effectively in the presence of anhydrite. In this work, sodium polyacrylate is evaluated as a sacrificial agent, and is compared to many other conventional or recently- recommended sacrificial agents, and has shown advantage over all of them for the case of presence of anhydrite. Some experiments have been conducted to demonstrate the ineffectiveness of sodium carbonate as sacrificial agent in the presence of anhydrite. Effect of molecular weight of sodium polyacrylate is tested, and it is found that increase in molecular weight results in decrease in adsorption of surfactant until a certain molecular weight of polyacrylate is reached after which molecular weight has no further effect on reducing adsorption of surfactant. Addition of polyacrylate was shown to reduce adsorption of a selected anionic surfactant on different outcrop minerals, including Carlpool dolomite, industrial calcite, kaolinite, Berea sandstone, and Indiana limestone. To prove the point further, application of polyacrylate was tested with two different anionic surfactants. Adsorption of polyacrylate itself is measured in the presence and absence of surfactant and showed to be independent of the presence of surfactant. The effect of concentration of divalent ions and salinity in the brine on effectiveness of sodium polyacrylate as sacrificial agent has been evaluated on different minerals/rocks. Finally, dynamic adsorption data has been presented in different concentrations of sodium polyacrylate. All these experiments demonstrate the advantage of using sodium polyacrylate as sacrificial adsorption agent for anionic surfactants even in the presence of anhydrite in the rock.