TOWARD A UNIFORM STANDARD FOR EVALUATING SITES FOR GEOLOGICAL STORAGE OF CARBON DIOXIDE

To achieve the minimum goals of the 2015 Paris Agreement on climate change the volume of carbon capture and geological sequestration (CCS) needs to increase by over 2 orders of magnitude by 2050 (IEAGHG, “CCS in Energy and Climate Scenarios”, 2019/5, July 2019). While a very large number of potential CCS sites must be evaluated, ranked, and brought on line in that period most existing criteria for evaluating suitability of potential CCS sites are highly subjective and subject to biases, are incomplete, and are unsubstantiated. In order to facilitate the evaluation of large numbers of potential CCS sites, and to promote reliable and repeatable comparisons across a large portfolio of potential CCS sites, we are formulating and testing a comprehensive set of objective geologic CCS site selection criteria that have distinct metrics.

Geological and reservoir engineering criteria against which to evaluate and rank potential CCS sites in saline aquifers and depleted oil and gas reservoirs fall into two general categories, Reservoir and Retention. For example, with respect to Reservoir, CO2 injectivity (a reservoir engineering concern) relies on reservoir permeability, porosity, homogeneity, thickness and pre-injection pressure and temperature state. Storage capacity (a geological concern) depends on reservoir geometry and areal extent, permeability, porosity, homogeneity, thickness, and pre-injection pressure. With respect to Retention we might be concerned about the presence of faults. Geologically faults may represent potential CO2 migration pathways (a retention concern) for which structural geometry, displacement characteristics, cross-fault juxtaposition, fault zone materials, and stress state play a role. From the reservoir engineering perspective, faults may limit injectivity by compartmentalizing the reservoir (fault population density and fault transmissivity) and reducing injectivity. For each of these examples the distinct metrics for the governing parameters are arrayed from good to poor and the evaluation team chooses which applies to the site in question. Once all criteria are evaluated a final scoring is calculated and applied to the category in question (e.g., Reservoir). From the scoring prospective CCS sites may be ordered into a rank list and decisions made accordingly.