A Prototype Near-Field GIS Model to Characterize Acute Risks of Sequestered CO 2Release Through Orphan Wells

Abstract

Characterization of terrain-specific risk posed by potential future CO 2release from orphan wells remains a major carbon storage technology gap. For such wells, risk analysis has focused on aggregate long-term future impacts of seepage at rates on the order of 1 g/m 2per day on storage goals but not of potential future large-scale venting through overlooked unsealed orphan wells, which may dominate CO 2-loss scenarios. Flux measures made on Crystal Geyser, in Utah, indicate that such loss could range from 10 to 100,000 kg/day per site, and so is acutely hazardous in unfavorable meteorological and terrain circumstances. To characterize potential risk from such abrupt discharges, a prototype heavy-gas near-field dispersion model was coupled to a Geographic Information Systems (GIS) algorithm to evaluate terrain-related impacts on lethal downwind CO 2concentration as a function of wind speed. By eliminating low-risk areas, application of the risk model to a potential sequestration site in west-central Indiana allowed a 30-fold gain in the cost effectiveness of surveying the site for unsealed orphan wells. After improvements to better model near-field CO 2dispersion in complex terrains, this type of approach could be used to rapidly screen large areas proposed for future CO 2sequestration for relative potential risk, and thereby prioritize them to design, or comply with, regulatory risk management goals.