| The objective of this research was to identify high performance surfactant formulations and design efficient core floods for a limestone reservoir with high salinity formation brine. Microemulsion phase behavior experiments were conducted to identify best chemicals formulation (including surfactants, alcohol, alkali, polymer and electrolyte) for core flood test. A successful formulation should be one clear stable phase at reservoir conditions, fluid microemulsion phase, fast equilibration and high solubilization ratio. Formulations with glycol ether alcohols were easier to achieve one clear stable phase than formulations with sec-butanol. Primary surfactant-to-cosurfactant ratio and alcohol concentration were fine tuned to obtain fluid microemulsion phase and sufficiently high solubilization ratio. Core floods with optimized formulation validated its high oil recovery efficiency (95-99%) in Berea sandstone cores with synthetic formation brine. The effect of surfactant slug size, surfactant slug/polymer drive viscosity and formation brine composition was discussed to design more efficient core flood. The properties of the aqueous phase from chemical flood, e.g. total dissolved solids, viscosity and pH were measured to help understand oil displacement process in the core during the chemical flood. Core floods in Indiana limestone cores yielded low oil recovery (27-41%) suffering from large dispersion of the core. Recommendations were made to improve oil recovery on future limestone core floods and field application. |
