This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 133804, ’CO2 Storage Capacity - Combining Geology, En gineering, and Economics,’ by W.G. Allinson, SPE, Y. Cinar, SPE, P.R. Neal, SPE, J. Kaldi, SPE, and L. Paterson, SPE, Cooperative Research Centre for Greenhouse Gas Technologies, prepared for the 2010 SPE Asia Pacific Oil & Gas Conference and Exhibition, Brisbane, Australia, 18-20 October. The paper has not been peer reviewed.
The authors contend that any capacity-estimation method requires a combination of geological, engineering, and economic analysis to provide rigorous capacity estimates. Also, the classification of capacity estimates should follow concepts in the existing SPE Petroleum Resources Management System (PRMS) as closely as possible. Definitions of petroleum resources can be applied to storage capacity, and a storage-capacity classification system is recommended.
As technology for carbon capture and storage (CCS) moves from research to deployment, there is a need to estimate the amount of carbon dioxide (CO2) that can be stored safely and securely in the subsurface. Much of the literature on estimating the capacity of geological sites for storing CO2 focuses on determining the total pore volume of a formation and then applying a “storage-efficiency factor” to quantify the portion of this resource that could be accessed for storage. Theoretical and practical pitfalls of such storage-capacity-estimation methods are identified. A more-appropriate means of estimating CO2-storage capacity uses a combination of geological, reservoir-engineering, and economic analyses. Such an approach leads directly to definitions of capacity that have direct correlation with SPE definitions of reserves and resources. Unless otherwise stated, the term “storage capacity” is used loosely here to mean that part of the Earth’s crust in which CO2 can be stored either practically or economically.
Estimating Storage Capacity
A difficulty in determining storage capacity by traditional methods and by use of reservoir simulation and economics is defining the area and thickness of the potential storage formation. Possibly straightforward for a structural trap having a single high-permeability sandstone layer bounded by sealing shale layers, these definitions become more difficult for interbedded sands and shales of varying quality, which leads to definitions that involve permeability- or porosity-cutoff values (usually defined without reference to commercial factors). In some cases, the thickness can be determined from techniques such as reflection seismology and geophysical well logging with some satisfactory accuracy. However, estimating the area can be particularly challenging.