CO2-Brine Displacement in Geological CO2 Sequestration: Microfluidic Flow Model Study

Abstract:

Geological CO₂ sequestration is a promising method to reduce atmospheric CO₂ and deep saline aquifers is one of the most important options due to their capacity for CO₂ storage. Thus, a better understanding of two immiscible brine-CO₂ mobility and its saturation, including invading patterns in deep saline aquifers as CO₂ storage sites is required. Lenormand (1990) explored the invading patterns of two immiscible fluids in porous media with a transition region and three dominant regions: capillary fingering, viscous fingering, and stable displacement. These are determined by two main aspect ratios N_m and N_c through experimental studies using micromodel. Micromodel provides the opportunity to discover unrecognized processes, and test existing theories and assumptions in fluid flow through porous media. In this study, the micromodel was used to explore the effects of the scCO₂ injecting velocity and ionic strength on invading patterns in geological CO₂ sequestration. When scCO₂ was injected into the micromodel that has already saturated with brine, the brine in the micromodel was displaced by injected scCO₂. Continuous scCO₂ injection into the micromodel leaded the scCO₂ to pass through the micromodel. And the scCO₂-brine displacement distribution in the micromodel remained constant during additional 100 PV scCO₂ injection after injecting scCO₂ passed through micromodel. When scCO₂ passed through the porous media, the scCO₂-brine displacement distribution represented the maximum displacement ratio. Results showed that scCO₂-brine displacement ratios increased with: elevated pressures in the range of 3MPa~8MPa, decreased ionic strength from 5M to 1M NaCl, and increased scCO₂ injecting velocity up to 40 μL/min. Also, N_m and N_c obtained in this study are located in transition region of the invading patterns suggested by Lenormand (1990).