Brine migration through fault zones: 3D numerical simulations for a prospective CO2 storage site in Northeast Germany

Upward brine migration as a result of CO2 injection into a saline aquifer could endanger freshwater resources, especially in faulted reservoirs. The present study determines the impact of pressure increase and fault permeability on brine displacement processes to assess potential freshwater salinization. For that purpose, different fault leakage scenarios were carried out by numerical modelling of a prospective storage site in Northeast Germany using a newly developed workflow that includes the grid transfer from the geological model generated with the applied pre-processing software Petrel to the reservoir simulator TOUGH2 and the implementation of virtual elements for the discrete description of fault zones. The results show that compartmentalization due to closed boundaries and faults cause the highest pressurization within the storage formation. Closed boundaries generally lead to higher brine migration rates especially if a number of permeable faults is present, whereas the permeability of fault zones only has a minor impact and does not influence salinization of shallower aquifers significantly. Although the salinity in shallower aquifers increases more sharply in the vicinity of the faults, with an average salinity increase by a maximum of 0.24%, the risk of freshwater salinization is estimated as low under the given circumstances for the potential site at Beeskow-Birkholz.