Methodology for designing and evaluating chemical systems for improved oil recovery

The purpose of this research was to demonstrate the methodology for development of high performance chemical systems for improved oil recovery (IOR). Previous studies have shown that high performing surfactant formulations can be quickly identified and optimized by assessing the microemulsion phase behavior and aqueous phase homogeneity. Similarly, in this research, extensive phase behavior assessments were performed for many combinations of chemical slug components that included various surfactants, co-surfactants, co-solvents, alkali and polymers. Methodical planning, preparation, execution, observations and recording of phase behavior experiments and results enabled selection of the best performing chemical components and their concentrations were optimized. A total of five formulations showed good microemulsion phase behavior but only three passed the aqueous stability requirement. These three formulations were then evaluated in core floods. Out of the three formulations, one consistently gave high residual oil recovery ranging between 86%--91% at reservoir temperature with both soft brine (NaCl only) and synthetic formation brine. Synthetic formation brine for Trembley contained a high concentration of divalent cations in addition to monovalent yet it had a minimal effect on oil recovery, proving that the formulation was robust at even high salinity contrast with formation brine. The formulation was therefore recommended for further studies on limestone cores. Pressures across the sandstone cores and its subsections, and effluent's microemulsion and aqueous phase properties were utilized to explain the performance of formulations and oil displacement process in the sandstone cores. Corefloods showed that slug size, surfactant concentration, salinity and viscosity of chemical systems were important chemical flood design parameters that also impacted the oil recovery.