2. GEOLOGICAL CHARACTERISATION OF THE SITE

The first step in site selection is the screening of potentially suitable formations and structures against specific criteria. The most developed criteria are for CO2 storage in saline aquifers (Chadwick et al., 2006), and pertain to safety and feasibility issues. In the case of hydrocarbon fields and coal beds, the available criteria are not as comprehensive.

In the case of saline aquifers, there is a sequence of capacity estimate types that form a conceptual storage capacity pyramid (e.g. Bachu, 2003; Kaldi and Gibson-Poole, 2008) ranging from initial assessments of theoretical storage capacity based on regional geology to matched capacity estimates based on field scale feasibility studies and field testing. Hydrocarbon fields and, to a lesser extent, coal beds have a narrower range of capacity categories and uncertainties because of the pre-existing knowledge available from long-term production activities.

The insufficient knowledge about saline aquifer formations and structures, as well as public concerns in the case of onshore CO2 storage, requires that site selection in this case should include comprehensive assessment of the quality and integrity of caprock followed by assessment of the safety and feasibility of CO2 storage in the reservoir.

Based on the results of CO2 storage site safety and feasibility studies, storage site ranking is carried out by weighing the site scores for all criteria.