Experimental study of microemulsion characterization and optimization in enhanced oil recovery : a design approach for reservoirs with high salinity and hardness

The objective of this research was to develop a systematic laboratory approach, and design a high performance chemical flood for a problematic reservoir with formation brine having high salinity and hardness. Aqueous and microemulsion phase behavior tests have previously been shown to be a rapid, inexpensive and highly effective means to select the best chemicals and minimize the need for relatively expensive core flood tests. Phase behavior tests were therefore done with various combinations of surfactants, co-solvents and alkali for several crude oils and reservoir conditions, including the problematic reservoir of interest for design. Extensive phase behavior testing identified performance trends of chemicals at different concentrations, which could be interpolated for optimization. The trends were ultimately used to develop an approach to design potential chemical flood formulations for the problematic reservoir of interest. Using this approach, several formulations were designed showing good performance in phase behavior testing. One of the formulations was then validated in a core flood experiment to give nearly 100% oil recovery with very low surfactant adsorption. The chemical flood design used a salinity gradient that was robust enough with withstand the sharp salinity contrast of the formation brine and surfactant slug at the displacement front. Salinity analysis of core flood effluent showed how Type III microemulsion conditions were targeted to most effectively mobilize residual oil.