Experimental study of the benefits of sodium carbonate on surfactants for enhanced oil recovery
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The objective of this work was to evaluate chemical interactions in phase behavior experiments that make surfactant-polymer formulations with alkali complex to design. This experimental study of sodium carbonate shows improvement of microemulsion phase behavior with many crude oils in addition to its classical use to produce soap in-situ and raise pH to reduce potential for surfactant adsorption. Soap is generally not sufficient by itself for chemical flooding because it has low tolerance to calcium ions and low optimal salinity. The blending of synthetic surfactant with sodium carbonate is needed to increase the optimum salinity, increase the tolerance to calcium, and reduce the sensitivity to changes in salinity by broadening the active salinity window. Sodium carbonate can also be added to the surfactant formulation to adjust electrolyte concentration for optimal salinity. Evidence suggests that additional consideration should be given to sodium carbonate in enhanced oil recovery applications because of benefits that extend beyond the traditional application. The research presented in this work discusses experiments that were conducted for the purpose of studying the benefits of sodium carbonate on surfactant phase behavior. After phase behavior screening, the formulations were tested to demonstrate their performance in porous media. Core floods were conducted to test the potential use of chemical flooding for a field application with several low acid crude oils. Two of the core flood experiments with Berea sandstone reduced the residual oil below 1% with chemical injection. An acceptable pressure gradient was maintained and good sweep was obtained using an AMPS polymer at high temperature. Polymer was needed to make the slug and drive sufficiently viscous to recover the mobilized oil and reduce surfactant retention through good sweep efficiency. The experiments reported in this research have contributed to an ongoing effort to design a suitable alkali-surfactant-polymer chemical formulation for the application in a high permeability, high temperature (85 ºC) sandstone reservoir located in Indonesia.