Repurposing a Depleted Natural CO2 Dome for Permanent CO2 Sequestration

Summary This study explores the potential of repurposing the Sheep Mountain dome, a natural CO2 dome in Colorado, for geological carbon sequestration. Traditionally, geological CO2 sequestration efforts have focused on saline aquifers and oil and gas reservoirs, with little attention given to natural CO2 domes despite their proven capability for long-term CO2 containment over millions of years. The Sheep Mountain dome has been actively producing CO2 for over 40 years, with the produced CO2 transported to the Midland Basin, Texas, for enhanced oil recovery (EOR) since 1983. Given the dome is nearing depletion but retains existing infrastructure, which reduces initial capital expenditures, it presents an attractive candidate for converting a CO2 production site into a carbon storage site. In this assessment, well logs from 37 wells facilitated the construction of a static geological model. Monthly CO2 production data were then used to history-match the upscaled fluid flow model and a simulation model was created to analyze reinjection of approximately 30 million metric tons of CO2 [0.58 trillion cubic feet (Tcf)] over 30 years through five wells. This volume represents about 41% of the total CO2 produced from the field so far (1.4 Tcf). Next, we studied the leakage potential of the field through the existing legacy wells. Field observations revealed that interfaces between casing-cement and cement-formation are not likely leakage pathways. Employing 1 md as the leakage permeability of the legacy well barrier system, the study projects a leakage amount of 0.04 metric tons out of the 30 million metric tons injected, underscoring the feasibility of utilizing this nearly depleted dome for permanent anthropogenic CO2 sequestration. Moreover, the dome’s proximity to major CO2 emission facilities may ensure a readily available CO2 source with minimal transportation costs, reinforcing its suitability as a long-term carbon sequestration site. To the best of our knowledge, this is the first comprehensive study on assessing the feasibility of repurposing depleted natural CO2 domes for anthropogenic CO2 sequestration.