The evolving perception of risk during reservoir evaluation projects for geological storage of CO2

Abstract

If carbon dioxide is to be stored in geological strata other than depleted hydrocarbon reservoirs (e.g. in saline aquifers), relatively little information will typically be available about the potential reservoirs. Significant risk associated with such projects therefore derives from uncertainty in reservoir evaluation. This paper describes a risk elicitation exercise carried out during geological reservoir evaluation for two exemplar carbon capture and storage (CCS) projects. A project-specific Features, Events and Processes (FEPs) register was developed through a structured elicitation process and discussions with experts. The register was used to elicit experts’ perception of risk early in each project and thereafter at regular intervals, finding that the risk was moderate or low for the majority of FEPs. Where FEPs were perceived as high risk, lack of information and uncertainty tended to be the most influential factor. The results of the risk assessments were instrumental in identifying key project activities aimed at reducing uncertainty and addressing the highest areas of risk. Using the relatively inexpensive techniques of reprocessing legacy seismic data and conducting a hydrogeological study of the region around the storage site, uncertainty was reduced and the experts’ perception of risk was lowered by the new information. However the risk assessment results also showed changes occurring in the absence of new information and where experts declared no change to their perception of risk. It is therefore vital to understand the uncertainty in the risk assessment results which can clearly be affected by factors other than information related to the storage formations.