Reservoir geomechanics for assessing containment in CO2 storage: A case study at Ketzin, Germany

This reservoir geomechanical study assesses the impact on top and fault seals integrity of fluid pressure changes associated with carbon dioxide (CO2) storage in a saline formation. The case studied is the CO2SINK experiment at in Ketzin, Germany, where up to 60 ktons of CO2 are being injected. Injection commenced in June 2008. A 3-dimensional (3D) geomechanical model of the site is built through integrated analyses of geologic, seismic, logging, drilling, and laboratory test data. First, the grid is expanded from a reservoir model up to surface, down to basement and laterally by about 3 times the pressure perturbation dimensions, while honouring all available structural, stratigraphic and lithological data. The grid cells are populated with density, poroelastic and strength properties upscaled from a 1-dimensional (1D) mechanical model built and validated along the Ktzi 201/2007 CO2 injector well. Cells cut by faults are considered an equivalent medium representative of a jointed rock mass. The 3D geomechanical model is then dynamically linked to the reservoir model. Static equilibrium prior to injection is achieved by applying initial fluid pressure and gravity loads, as well as stress boundary conditions chosen so as to match in situ stress measurements. Stress path and rock deformation associated with CO2 injection are then simulated. Pressure change data is passed from the flow simulator to the geomechanical simulator at selected time steps. Calculated stress path and strains are then used to investigate the possible occurrence and location of caprock failure and fault reactivation. Other results, such as ground surface elevation changes and sources of uncertainties are also highlighted. No failure is observed in the caprock and faults remain stable during CO2 injection operations. Limited vertical displacement (maximum 5 mm) is predicted at surface.