Risk Assessment of Selected CCS Wells through Feature, Event, and Process Method and Comparison of the Barrier Effect.

To reduce the CO release in the atmosphere, the carbon capture and sequestration (CCS) technique presents a solution in which the CO is captured from the emitting source and injected into a suitable geological formation in the subsurface. For the CCS project to be successful, CO must be trapped underground for hundreds of years. In that respect, good integrity plays an important role as it ensures that the injected CO remains sequestrated in the subsurface. Hence, this study presents a risk assessment technique with the help of which critical elements that can compromise the integrity of the CCS well can be identified. The approach taken for the risk assessment is based on the feature, event, and process (FEP). However, this method gives a qualitative analysis, and to convert it to a semiquantitative one, FEP is integrated with an interaction matrix, incident potential matrix (IPM), and cause-effect plot diagram. In this paper, risk assessment was conducted on two fictitious wells with different well configurations. It was found that cement and casing were the most vulnerable components, while formation water and subsidence were the most problematic elements in the given well system. It was also concluded that the number of plugs and their location in the well could increase or decrease the intensity of the risk levels in the CCS wells.