Geochemical Controls on Organic and Inorganic Scale Deposition: Insights from CO2 Injection in Morrow Fluvial Sandstone

Abstract This study investigates the geochemical processes influencing the deposition of organic and inorganic scales during Carbon dioxide (CO2) injection in hydrocarbon reservoirs, with a focus on Morrow Fluvial Sandstone, Stewart Field, Kansas. CO2 injection, a widely used enhanced oil recovery (EOR) technique, can lead to paraffin wax and calcium sulfate (CaSO4) scale deposition, presenting complex flow assurance challenges. Understanding the mechanisms driving these processes is critical for optimizing production strategies and maintaining reservoir integrity. A combination of field data analysis and geochemical modeling was employed to evaluate conditions under which wax and CaSO4 scales form. Wax appearance temperature (WAT) analysis was used to assess changes in paraffin solubility across temperature ranges, while the effect of CO2 on light hydrocarbon extraction and WAT was also evaluated. Inorganic scale formation was modeled through geochemical simulations that considered temperature, pressure, and ion concentration variations post-CO2 injection. Results showed that CO2 initially lowers WAT and enhances paraffin solubility at low temperatures (e.g., 80°F), but over time, extraction of lighter hydrocarbons raises WAT and promotes solid-phase wax formation, reaching up to 5% near injection wells. In contrast, CaSO4 scaling occurs from the mixing of incompatible formation waters, leading to concentrations as high as 0.15 mol/L and the precipitation of anhydrite and gypsum near production wells, which significantly reduce permeability. These findings reveal that CO2-induced geochemical changes exacerbate both organic and inorganic deposition, underscoring the need for integrated management strategies. Unlike previous studies focusing on either wax or scale, this work highlights their interdependent behavior, and the dual challenge posed during CO2-EOR. The study contributes to the development of comprehensive flow assurance solutions and more robust production strategies in sandstone reservoirs.