Application of chemistries for waterflooding has traditionally required a significant upfront investment in core flood testing. Investments of this sort equate to money and time spent on a reservoir screening tool which does not guarantee an accurate translation into pilots. The aim of this paper is to explore core flood results in conjunction with pilot results for conventional and unconventional reservoirs where microemulsions are deployed in order to enhance oil recovery.
Microemulsions act as a delivery platform for solvent (terpene) and surfactant mixtures throughout a given rock volume. Their ability to alleviate damage and change the energetics of surfaces is believed to enhance mobilization of oil. They’re optimized for a given reservoir in the laboratory based on fluid-fluid and fluid-rock interactions. This includes adsorption (persistency), asphaltene wash-off, demulsification, drop size, and interfacial tension testing. We in turn label changes in injectivity of water as well as increases in oil production as indicators of success in core floods and pilots.
The above strategy has led to microemulsion optimization in Taylorton Bakken (which is more conventional) and Lower Shaunavon (which is more unconventional) in SE and SW Saskatchewan, Canada. These are characterized by changes in permeability, temperature, mineralogy (quartz vs calcite), oil (paraffinic vs asphaltenic) and water (high vs low salinity). This study demonstrates a beneficial core flood and pilot response in conventional reservoirs using microemulsions. What’s however interesting and noteworthy is that the core flood response is negligible in unconventionals (<5% incremental oil recovery) due in part to asphaltenes plating out on the core’s exterior surface during restoration of wettability, whereas the pilot response is quite positive.
The major highlight of this work is the need to address the discrepancy in core flood testing and pilot results in unconventional reservoirs. This is required before core flood testing can be used as a reliable screening tool for unconventional reservoirs. We’ve furthermore demonstrated the beneficial impact of microemulsions in both conventional and unconventional reservoirs as well as the need for optimization based on fluid-fluid and fluid-rock interactions.