Impact-Driven Pressure Management for Leaky CO2 Storage Systems

Large-scale pressure buildup in response to carbon dioxide injection in the subsurface may limit the dynamic storage capacity of suitable formations, because over-pressurization can impact caprock integrity, induce micro-seismicity in critically stressed faults, drive CO2 and/or brine up conductive features into shallow groundwater resources, and affect existing subsurface activities such as oil and gas production. It has recently been suggested that pressure management schemes involving the extraction of native fluids from storage formations may be used to control subsurface pressure increases caused by CO2 injection, thereby limiting the possibility of unwanted effects such as brine leakage to shallow freshwater aquifers and also reducing the potentially large Areas of Review, which in the U.S. EPA's regulation for CO2 sequestration projects are the subsurface domains that need to be characterized for local conductive features in order to obtain a permit. Our study presents application of a newly developed analytical solution to evaluate the effectiveness of fluid extraction in managing pressure buildup caused by CO2 injection and storage. We use a hypothetical yet complex example case with multiple leaky wells and a critically stressed fault. Different pressure management schemes involving (passive) pressure relief wells, active extraction wells, combinations of both, disposal of brine, and/or re-injection of brine were tested with respect to predefined performance criteria, such as the maximum allowable pressure near the conductive fault. Options for optimal well placement were also evaluated, comparing near-field arrays of extraction wells (i.e., near the injection wells) with far-field arrays (e.g., near the fault). Far-field well placement allows for a significant reduction in the brine extraction rates needed to keep pressure increase below the target performance criterion. Based on these findings, we developed the concept of "impact-driven pressure management (IDPM)", with which we mean fluid extraction schemes that are optimized to meet local performance criteria (i.e., schemes that limit pressure increases primarily where environmental impact is a concern). Compared to simple pressure management schemes that often assume near-field and volume-equivalent extractions, IDPM can lead to significant cost reduction, in particular if brines need to be disposed at the surface and no beneficial use is possible.