Salt precipitation and CO₂/brine flow distribution under different injection well completions

Carbon capture and sequestration is a viable technology to reduce the concentration of CO₂ emitted to the atmosphere. Salt precipitation due to dry-supercritical CO₂ causes a reduction of permeability, having adverse effects on well injectivity and pressure build-up. This study evaluated the salt precipitation, brine flux patterns, and pressure build-up for two well constructions, (1) partially perforated (4 injection intervals) and (2) fully perforated throughout the target formation. Both well designs showed non-localized salt precipitation in low-k formations (5×10^-15 and 50×10^-15m²) and localized precipitation in high-k (250×10^-15 and 500×10^-15m²). It was also found that two distinct brine flux patterns occurred; under low-k conditions the brine flux was outward and parallel to CO₂ migration and precipitation became limited. While under high-k conditions there developed back-flow of the brine which amplified salt precipitation. When this process occurred, the permeability reduction was orders of magnitude greater than when non-localized salt precipitation occurred. This reduction resulted in pressure build-up near the well in regions of the reservoir in which it occurred. Optimal injection conditions were found to be in reservoirs of mid-range permeability; which allowed for adequate pressure dissipation and minimized salt precipitation.