Scientific considerations related to regulation development for CO2 sequestration in brine formations

Abstract

Carbon management through the underground injection of CO2 into subsurface brine formations is being actively studied. If there are no technological constraints for implementation, there could be a large number of wells constructed for injecting a large volume of CO2. It is therefore important, in parallel with current scientific studies, to consider the appropriate, science-based regulatory framework for CO2 injection. The Environmental Protection Agency (EPA) Underground Injection Control (UIC) program, authorized under the Safe Drinking Water Act (SDWA), has extensive experience in regulating the injection of mainly liquid wastes into geologic formations in the United States. The federal requirements and permit process implemented by EPA and the Primacy States since 1980 have played a critical role in the safety of subsurface disposal of liquid wastes in the US. Physically and chemically, there are significant differences between CO2 and common liquid wastes. Its viscosity and density are much lower and, under injection pressure in the deep formation, it may be under supercritical conditions. Because of the lower density and viscosity, CO2 leakage through the confining strata may be greater when compared to currently injected liquid wastes. Also, the chemical interactions of CO2 with the geologic formation have their own characteristics. All these scientific factors need to be evaluated to identify new guidelines for appropriate regulatory and monitoring controls. The paper reviews current UIC regulations, injection-well classification scheme and monitoring requirements, and identifies the unique factors related to the physical and chemical processes in the subsurface associated with CO2 injection. Implications of these scientific considerations for regulation development are discussed.