Implications of Surface Seepage on the Effectiveness of Geologic Storage of Carbon Dioxide as a Climate Change Mitigation Strategy

Abstract

The probability that long-term geologic storage or sequestration of carbon dioxide (CO2) will become an important climate change mitigation strategy will depend on a number of factors—availability, capacity, and location of suitable sites; the cost of geologic storage compared to other climate change mitigation options; and public acceptance. Whether or not a site is suitable will be determined by establishing that it can meet a set of performance requirements for safe and effective geologic storage (PRGS). To date, no such PRGS have been developed. Establishing effective PRGS must start with an evaluation of how much CO2 might be stored and for how long the CO2 must remain underground to meet goals for controlling atmospheric CO2 concentrations. These requirements then provide a context for addressing the issue of what, if any, is an "acceptable surface seepage rate?" This chapter provides a preliminary evaluation of CO2 storage amounts, time-scales, and concordant performance requirements. Many subsurface processes such as solubility trapping, mineralization, diffusion, and residual gas trapping will attenuate the migration of CO2 as it moves toward the land surface. Therefore, performance requirements for surface seepage rates should not be construed as performance requirements for leakage from the primary storagereservoir.