A comparison of geomechanical effects at three 'megatonne' CO2 storage sites - Sleipner, Weyburn and in Salah

One of the major leakage risks during CO2 sequestration operations is that injection-induced geomechanical deformation may compromise the integrity of the sealing caprock through the creation or reactivation of fracture networks. In this paper we examine three major commercial-scale storage sites where CO2 is injected at rates approaching or greater than 1 megatonne of CO2 per year: Sleipner, Weyburn and In Salah. We find that deformation is controlled by the pore pressure increase during injection, meaning that large aquifers with good flow properties, such as Sleipner, represent the best targets for CO2 storage. Mature hydrocarbon reservoir targets, such as Weyburn, may already have a complex stress history with decades of production and fluid injection. In such cases numerical modelling is needed to fully understand a geomechanical response to CO2 injection that may not be expected or immediately intuitive. Where pore pressures do become elevated, such as at In Salah, deformation is likely to be more pronounced. In such situations, a comprehensive geomechanical monitoring and modelling program is recommended. In addition to our site-by-site analysis, we assess the efficacy of seismic, microseismic and geodetic methods for monitoring geomechanical deformation during operations.