Probabilistic Geomechanical Analysis of Compartmentalization at the Snøhvit CO 2 Sequestration Project
Pressure build-up caused by large-scale CO 2 injection is one of the key concerns during a carbon sequestration project. Large overpressures can potentially compromise seal integrity, reactivate faults, and induce concerning seismicity, among other hazards. Furthermore, pressure build-up is directly related with storage capacity. In this work we study the geomechanical response to CO 2 injection in the Tubåen Fm at Snøhvit, with the objective of understanding the potential for fault reactivation, leakage, and contamination of the producing interval in an adjacent block through the bounding faults. Furthermore, we evaluate the potential contribution of a structural component to reservoir compartmentalization. We combine simplified analytical models, based on critically stressed fracture theory and a Mohr-Coulomb failure criterion, with a quantitative risk assessment methodology to perform a rigorous uncertainty quantification. Large stress uncertainties are present and are reflected in the modeling results. It was found that under the “most likely” stress state (Strike-Slip and North-South maximum horizontal stress (S Hmax ) azimuth) the faults are fairly stable, and tensile hydrofracturing of the caprock would be expected before fault reactivation. In most of the analyzed cases, the critical pressure perturbation needed for reactivation is above 13 MPa, which was the limiting pressure increase before reaching the fracture pressure. Faults were found to be ~ 20% less stable when considering plausible variations in the orientation of S Hmax . In those cases, fault reactivation could be expected before caprock failure if injection continued, posing risks of induced seismicity, CO 2 leakage and/or contamination of the gas producing reservoir. Finally, a potential structural component in the compartmentalization and fluid migration is difficult to assess due to stress orientation uncertainty.