CO2 aquifer storage site evaluation and monitoring : understanding the challenges of CO2 storage : results of the CASSEM Project

Carbon capture and storage (CCS) brings new entrants to subsurface exploration and reservoir engineering who require very high levels of confidence in the technology, in the geological analysis and in understanding the risks before committing large sums of capital to high-cost drilling operations. Many of the subsurface techniques used for hydrocarbon exploration are capable of translation to CCS activities. Unfamiliarity may, however, lead new entrants to openly question their applicability in order to transform their current understanding to a level where large capital investment can be organisationally justified. For example, some may make the erroneous assumption that a good CO2 subsurface store should resemble the pressure vessel type of containment that is prevalent with surface installations. Basic concepts such as utilising the rock structure and mineralogy to control fluid flow and securing the CO2 by residual trapping (between the rock grains) or by dissolution, as a superior storage mechanism, are counter intuitive and challenging to communicate effectively. To achieve success and reliable operation in CO2 emission reduction for coal- and gas-burning electricity power generation, all elements of the CCS chain have to function. In 2008 the CO2 Aquifer Storage Site Evaluation and Monitoring project (CASSEM) was one of the first UK based projects to attempt integration and full-chain connectivity from, capture and transport to injection, storage and monitoring. Its research is aimed at development of workflows that describe a CCS entry path for a target audience of potential new entrants, i.e. power utilities, engineering sector and government. In contrast to other studies, the CASSEM project has applied the specification of the full CCS chain, using two exemplar sites (coal-fired power plants) with contrasting geological conditions in the subsurface, to tailor storage site selection and analysis. Centred on the Ferrybridge Power Station in Yorkshire (Figure 1.1), a ‘simple’ site underlain by a thick, uniform sandstone with diverse legacy information available was sought onshore in the English Midlands. The offshore extension of this (Bunter) sandstone has been highlighted as a large potential aquifer store for CO2 captured from power plants in eastern and South East England. A ‘complex’ site was sought offshore of eastern Scotland, centred on the Longannet Power Station on the Firth of Forth near Edinburgh (Figure 1.2). This site was intended to confront the difficulties of investigating subsea structures with sparse legacy and incomplete information from hydrocarbon investigations. The selected site is a faulted and folded geological structure and the issues of seismic reflection surveys, detection of faults and fractures, and quality of the target reservoir, are similar to those which challenge offshore hydrocarbon exploration beneath the North Sea. To complement the published research that arose from the CASSEM project (see bibliography of outputs) this book presents an overview of the results as multi-authored papers.