A New Classification System for Evaluating CO2 Storage Resource/Capacity Estimates

Abstract

Abstract Carbon dioxide (CO2) storage estimates are a critical component of the decision-making process when considering the implementation of large-scale CO2 storage in the subsurface. In order to compare storage resource/capacity estimates, both the scale of the estimate and the type of estimate must be considered. To date, the classification of resources and commodities has been used almost exclusively for valuable materials that can be economically extracted from the subsurface, e.g., hydrocarbons, metal ore, coal, etc. These industries have benefited from the establishment of classification systems with consistent terms and definitions that have gained international acceptance and allow for systematic accounting and comparison of resources across geological, geographical, and jurisdictional boundaries. As the carbon capture and storage (CCS) industry grows, there is increasing need for an accepted classification system that describes the available CO2 storage resource. While the classification systems used in the mining and hydrocarbon industries have elements that are instructive and sometimes indirectly applicable with respect to CO2, the direct application of those systems is largely insufficient. This is because, in the context of geological CO2 storage, the desired resource is not something to be removed from a subsurface reservoir but rather the accessible pore volume of the reservoir itself. Although much work has been accomplished, particularly by the Carbon Sequestration Leadership Forum (CSLF), and the U.S. Department of Energy (DOE) in the Carbon Sequestration Atlas of the United States and Canada, inconsistencies in definitions related to CCS exist between groups, and a widely accepted set of definitions for discussing CO2 storage resource and capacity has not yet been established. In order to move the CCS industry toward a useful set of definitions and provide a consistent set of terms, an improved classification system has been developed to not only address the level of the assessment but also the scale at which the assessment was made. Introduction Carbon capture and storage (CCS) represents an emerging set of technologies aimed at reducing the amount of anthropogenic carbon dioxide (CO2) that reaches the atmosphere by injecting and storing it in geological formations. Several targets have been identified as amenable to the injection and storage of CO2, most notably oil and gas reservoirs, saline formations, and unminable coal seams. Other potential targets have been proposed for future use, including basalts and organic shales; however, they are not considered for this paper. Within these target formations, a variety of trapping mechanisms must be considered, e.g., physical, solubility, and mineral. Each of the trapping mechanisms varies in its permanence and relevance over different timescales, with physical trapping beneath a low-permeability cap rock the most notable in the short term.