ASP Experiments in Indiana Limestone using NaOH to Reduce Surfactant Retention

摘要

Alkaline-surfactant-polymer (ASP) coreflood experiments using Indiana limestone were conducted to test the effectiveness of sodium hydroxide in reducing surfactant retention on limestones. Low concentrations of sodium hydroxide of only about 0.3 wt% increase the pH to about 12.6. The high pH reduces the adsorption of anionic surfactants by changing the surface charge of the limestone from positive to negative as well as having other favorable geochemical effects. Sodium carbonate could not be used in these experiments to increase the pH because the Indiana Limestone rock contained gypsum, which causes calcium carbonate to precipitate when it dissolves. Another advantage of sodium hydroxide is that much lower concentrations are needed compared to sodium carbonate because of its lower molecular weight. No adverse reactions between the sodium hydroxide and limestone were observed and the propagation of the pH in the corefloods was observed to be extremely favorable. The tertiary oil recovery was high and the surfactant retention using sodium hydroxide was low compared to experiments without alkali and compared to typical retention values reported in the literature for carbonates.