Quantitative Decision Analysis for Co2 Storage Conformance Management: A Synthetic Case Study at Smeaheia, North Sea

In this work, we propose a workflow for quantifying the value of a candidate monitoring strategy for conformance management decisions. A value of information (VOI) analysis framework is constructed by combining a quantitative conformance verification workflow and an economic model via decision tree analysis. The presented workflow is applied to a synthetic case study based on the Smeaheia storage aquifer, where the uncertainty on the transmissibility of an important fault poses a risk to the conformance of the reservoir pressure behaviour. By incorporating information from candidate monitoring configurations to better constrain the forecasts of the ensemble of model realizations used to characterize the inherent geological uncertainties, an assessment of the time-dependent ability of detecting deviations from conforming behaviour is achieved and followed by an economic evaluation of the considered alternatives for pressure control actions. Using data-driven approximations, the analysis can be repeated for several monitoring configurations (type of measurement, location, measurement error and timing of measurement) accounting for plausible outcomes of the analysed measurements. This allows us to determine the expected value of the storage operation for each monitoring configuration, and for possible actions available to the operator for remediating unwanted storage site development. The results obtained show that the value achieved from monitoring depends on both the timing and information content of the measurements. Direct and indirect (imperfect) observations of the quantity of interest for conformance might not always be sufficient to guarantee perfectly accurate conformance statements and conformance management decisions. This highlights the practical value of addressing decision problems in quantitative terms to support the design of CO2 storage systems by gaining insight into the effectiveness of monitoring and corrective actions.