The Genesis of the CO2 Storage Resources Management System (SRMS)

Abstract

Over the past decade, there have been many published methodologies to calculate carbon dioxide (CO2) storage that vary from volumetric assessments of pore volume to rigorous statistical representation of geologic heterogeneity with CO2-brine displacement efficiency. Many methods include a direct scientific or engineering calculation to estimate storage, rather than on the uncertainty in the estimate based on quantity and quality of data and the types of data available. The application of these methods to the same geologic formation may yield differences in the estimate by 2–5 orders of magnitude.As more data is collected for a potential or operating CO2 storage formation, the uncertainty range of the estimates normally reduces. A site with active CO2 injection will generally have storage estimates with the highest degree of certainty based on historical injection performance compared to a CO2 storage estimate of a site without a well or injection. Consequently, the maturity of the project is an important part of the certainty in a specific estimate.A qualitative method that classifies estimates based on data available and project maturity could give assurance to stakeholders. From a “full-chain” carbon capture and storage (CCS) project development perspective, industry, investors, regulators, and other stakeholders want to know that these estimates are attainable via real wells and real quantities of CO2 and are not a high-level pore volume assessment. Though there are several published classification systems, there is currently no broadly accepted method for classifying storage estimates in terms of the geologic uncertainty and project or development uncertainty.The petroleum industry has faced similar challenges. Over the decades, it has developed and widely adopted a Petroleum Resources Management System (PRMS) for classification of subsurface petroleum accumulations. This classification system clearly labels the certainty of the quantification of underground accumulation of petroleum that includes the relative certainty that the project is commercially viable and projected to proceed. For example, the PRMS differentiates between an oil accumulation that is assessed with very limited data as “exploratory or undiscovered” compared to more rigorous assessment of a “discovered” oil accumulation that is being actively developed and produced. This system also gives confidence levels within the highest level of classification estimates–proved, probable, and possible.However, there are differences between CO2 storage estimates and petroleum accumulation estimates. Petroleum accumulations are localized and have an initial estimate of the petroleum in place. However, CO2 storage may be more broadly available based on the presence of porous and permeable rocks throughout a sedimentary basin that may be within a geologic structure or on regional dip.The Society of Petroleum Engineers CCS Technical Section has formed a multi-society subcommittee to develop a unified classification system for CO2 storage estimates–the Storage Resources Management System (SRMS). This subcommittee has been tasked to develop a classification system that aims to provide the CCS community with a standardized storage resources classification, which provides all stakeholders with a system for comparing and contrasting CO2 storage estimates based on project and geologic certainty.Currently, the subcommittee plans to align the SRMS classification with that of the PRMS, so that analogs to the three PRMS classification of petroleum reserves, contingent resources, and prospective resources are identified. Though beyond the scope of this subcommittee, once a unified classification system is developed, a concerted effort to classify existing CO2 storage estimates into the SRMS methodology will be possible. Consequently, local and regional estimates of storage could then be combined to create a global estimate for a given classification. Ultimately, the SRMS will allow all stakeholders to have a pragmatic and informed assessment of the CO2 storage available within the bounds of subsurface variability and uncertainty, which will remove a challenge to commercialization of CO2 storage.