Geomechanical analyses of submarine CO2 injection in the geological formations in the German North Sea

CO₂ storage potential in sandstone formations in the German North Sea is investigated by GEOSTOR consortium. This contribution discusses some of the results from the investigation of the geotechnical impact of the storage process. We examine the injection pressure window with respect to the hydro-fractural risk of the reservoir layer or caprock in the vicinity of the injection well by performing coupled hydro-mechanical fracture analyses. Different modelling scales, formulations, failure parameters, and in-situ present day stresses are considered. The results show that 2D- or thin 3D-models may underestimate the material integrity and lead to early fracture initiation. Meanwhile, a medium-scale model of the geoformation may be advantageous in reducing computational burden while maintaining high accuracy. The results also show a good correlation with field-derived fracture gradients and formation strength tests data from the Dutch-German border.

To assess the geotechnical risk of induced seismicity on the offshore infrastructure, we enhanced our boundary element-finite element method dynamic simulator with the formulation to compute arbitrary layered half-space and double-couple dynamic sources. Verification of the numerical method shows an excellent agreement with the analytical solution. The hybrid method is able to take into account the spatially complex geometry of the geological structure. The results show that the impact of the storage process on the formations’ mechanical integrity or offshore infrastructure remains relatively low or manageable for the considered period.