Analysis of in situ stress and fault reactivation potential for a major candidate storage aquifer

Within the Moray Firth, the Lower Cretaceous Captain Sandstone has been proposed as a prospective storage reservoir, with storage potential in depleting hydrocarbon fields, and more significantly, within the greater saline aquifer. Previous simulation studies of CO2 injection into the Captain Sandstone aquifer suggest storage capacities in the range 358 to 2495 Mt over a range of sensitivity scenarios. Storage at this scale will introduce the risk of fault reactivation as a consequence of elevated reservoir pressures. The transmissibility of previously stable faults may be enhanced due to reactivation, increasing the risk of CO2 migration from the storage reservoir. By studying both the geometry of faults and the contemporary stress field affecting the basin, it is possible to resolve the shear and normal stresses acting on faults which cut the reservoir formation and extend into the overburden towards the seabed, and to determine which faults (or parts of faults) are most susceptible to becoming reactivated under elevated pressure conditions. In order to do so, detailed knowledge of the pore pressure conditions at depth and the magnitude and orientations of the principal stresses are required, as are the properties of the faults themselves. Such an analysis is presented here at the basin-scale, focusing on the Captain Sandstone of the Inner Moray Firth Basin.