Effect of injection wells with partially perforated completion on CO2/brine flow distribution and injectivity

Abstract:

Carbon Capture and Sequestration is a viable technology to reduce the concentration of anthropogenic carbon dioxide emitted into the atmosphere. The success of an injection project requires large amounts of dry supercritical CO₂ to be injected into brine saturated aquifers within the subsurface. However, solid salt precipitation causes a reduction of permeability, having adverse effects on well injectivity as well as pressure build-up. This study evaluated the accumulation of precipitated salt, brine flux patterns, and pressure build-up for two well constructions, 1) partially completed with 4 injection intervals and 2) fully completed throughout the thickness of the target formation. This study found that when a partially completed well is implemented, precipitation of solid salt experiences a greater radial extent then a fully completed well. Both well designs showed non-localized salt precipitation in low permeability formations (5 and 50 mD) and localized salt precipitation at high permeability (250 and 500 mD). It was also found that two different brine flux patterns occurred; under low-k conditions the brine flux was primarily outward and parallel to the direction of the CO₂ migration and salt precipitation became limited. While under high-k conditions there developed back-flow of the brine to the tail of the plume as the plume experienced greater vertical movement, and the counter-flowing brine sustained the precipitation process amplifying salt precipitation. When this process occurred the permeability reduction factor became orders of magnitude less then when non-localized salt precipitation occurred, and formed an impermeable barrier around the injection well. The formation of this barrier was found to have the effect of increasing the pressure build-up near the well in regions of the reservoir in which it occurred. A sensitivity analysis on the anisotropic/isotropic nature of the reservoir and the value of the critical porosity was also conducted. The analysis revealed that an isotropic assumption of reservoir permeability may overestimate the degree of salt precipitation. Also that critical porosity has a high influence on the degree of salt precipitation in high-k reservoirs, the permeability reduction in both high and low-k reservoirs, and the pressure build-up in the near well region.