Hydraulic fracturing in CO₂ geological storage

Among the outstanding technical issues in CO₂ geological storage is the risk of hydraulic fracturing and migration of CO₂ in upper formations and to the atmosphere, the wellbore CO₂ injectivity and the storage capacity of the formation. We present a contribution on these issues based on conclusions of the modelling work of hydraulic fracturing in weak formations. The work was initially carried out with finite element analysis of a fully coupled elastoplastic hydraulic fracturing model and later was extended to analytical work based on a Mohr-Coulomb dislocation model where the complete slip process that is distributed around the crack tip was replaced by superdislocations that are placed in the effective centers of plastic deformation. Scaling of the FEM and analytical results enables the identification of a dominant parameter which defines the regimes of brittle to ductile propagation and the limit at which a mode-1 fracture cannot advance. We found that a hydraulically induced vertical fracture from CO₂ injection is more likely to propagate horizontally than vertically, remaining contained in the storage zone. The horizontal fracture propagation will have a positive effect on the injectivity and storage capacity of the formation.