Mixing in a three‐phase system: Enhanced production of oil‐wet reservoirs by CO2 injection

We recreate three‐phase reservoir conditions (high‐pressure/temperature) using a microfluidics system and show that the use of scCO2 for restimulation operations, such as hydraulic fracturing, can enhance mixing and production. The results inform hydrocarbon extraction from deep shale formations, which has recently generated an energy boom that has lowered hydrocarbon costs. However, production decreases rapidly and methods to increase efficiency or allow restimulation of wells are needed. In our experiments, the presence of residual brine from initial production creates spatiotemporal variability in the system that causes the injected scCO2 to more effectively interact‐mix with trapped hydrocarbon, thereby increasing recovery. We apply volume‐averaging techniques to upscale brine saturation, which allows us to analyze the complex three‐phase system in the framework of well characterized two‐phase systems. The upscaled three‐phase system behaves like a two‐phase system: greater mixing with larger non‐wetting content and higher heterogeneity. The results are contrary to previous observations in water‐wet systems. Key Points Mixing in three‐phase systems Residual brine enhances mixing between scCO2 and hydrocarbons in oil‐wet rocks Restimulation operations in hydraulic fracturing: Alternatives to water