Oil Displacement in Calcite-Coated Microfluidic Chips via Waterflooding at Elevated Temperatures and Long Times

In microfluidic studies of improved oil recovery, mostly pore networks with uniform depth and surface chemistry are used. To better mimic the multiple porosity length scales and surface heterogeneity of carbonate reservoirs, we coated a 2.5D glass microchannel with calcite particles. After aging with formation water and crude oil (CRO), high-salinity Water (HSW) was flooded at varying temperatures and durations. Time-resolved microscopy revealed the CRO displacements. Precise quantification of residual oil presented some challenges due to calcite-induced optical heterogeneity and brine-oil coexistence at (sub)micron length scales. Both issues were addressed using pixel-wise intensity calibration. During waterflooding, most of the ultimately produced oil gets liberated within the first pore volume (similar to glass micromodels). Increasing temperature from 22 degrees C to 60 degrees C and 90 degrees C produced some more oil. Waterflooding initiated directly at 90 degrees C produced significantly more oil than at 22 degrees C. Continuing HSW exposure at 90 degrees C for 8 days does not release additional oil; although, a spectacular growth of aqueous droplets is observed. The effect of calcite particles on CRO retention is weak on flat surfaces, where the coverage is similar to 20%. The calcite-rich pore edges retain significantly more oil suggesting that, in our micromodel wall roughness is a stronger determinant for oil retention than surface chemistry.

Automated summary

In this study, a 2.5D glass microchannel coated with calcite particles was used to mimic the multiple porosity length scales and surface heterogeneity of carbonate reservoirs. The results showed that flooding with high-salinity water at varying temperatures and durations can effectively enhance the liberation of crude oil in the reservoir. The experiment also revealed that wall roughness in the microscale model plays a more significant role in oil retention than surface chemistry.