Geological storage of CO₂ : a statistical approach to assessing performance and risk

Probabilistic Risk Assessment (PRA) is a methodology for evaluating complex, long timeframe, process-driven problems such as the geological storage of carbon dioxide (CO₂). Probabilistic and deterministic risk assessments were conducted in order to evaluate the geological storage of CO₂ from a risk assessment perspective within the context of a large enhanced oil recovery (EOR) project being carried out in the Weyburn Field. This area is part of the Williston Basin that extends across the borders of Saskatchewan and North Dakota. A unique, computationally-efficient model CQUESTRA-1 (CQ-1) was developed to assess the thousands of cases required for a PRA, that statistically quantify the uncertainty associated with the many features, events and processes including their interactions over the long-term geological storage of CO₂. This paper examined the application of the PRA methodology to the Weyburn Field as part of the IEA Weyburn CO₂ Monitoring and Storage Project and discussed its use with data from an operating EOR pattern. In order to identify those parameters that most influence releases to the biosphere and storage of CO₂ in the geological formations surrounding the reservoir, sensitivity analysis was also used. Deterministic calculations can also be carried out using CQ-1. The use of CQ-1 in a deterministic mode is demonstrated with a base case study that uses the current best estimate of parameter values based on field or laboratory data and expert opinion. It was concluded that the PRA method excels at defining overall uncertainty due to individual parameter uncertainty. 7 refs., 7 figs