Risk‐based area of review estimation in overpressured reservoirs to support injection well storage facility permit requirements for CO2 storage projects

This paper presents a workflow for delineating a risk‐based area of review (AOR) to support a US Environmental Protection Agency (EPA) Class VI permit for a carbon dioxide (CO2) storage project. The approach combines semianalytical solutions for estimating formation fluid leakage through a hypothetical leaky wellbore with the results of physics‐based numerical reservoir simulations. The workflow is demonstrated using a case study for a hypothetical 180,000‐metric‐ton‐per‐year storage project located in the Plains CO2 Reduction (PCOR) Partnership region, which includes all or part of 10 states in the United States and four Canadian provinces. Under the scenario where the leaky wellbore is open to a saline aquifer (thief zone) between the overlying seal (cap rock) and the underground sources of drinking water (USDW), the risk‐based AOR is no larger than the areal extent of the CO2 plume in the storage reservoir because the pressure buildup in the storage reservoir beyond the CO2 plume is insufficient to drive formation fluids up a hypothetical leaky wellbore into the USDW. However, even under the conservative assumption that the leaky wellbore is not open to a thief zone, the incremental leakage beyond the areal extent of the CO2 plume is less than 400 m3 over 20 years. The approach outlined in this paper is designed to be protective of USDWs and comply with the Safe Drinking Water Act requirements and provisions for the EPA Class VI Underground Injection Control (UIC) Program (Class VI Rule) and North Dakota Administrative Code Chapter 43‐05‐01. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.