Abstract:
Among the outstanding technical issues in CO2 geological storage are the risks 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.
Introduction
According to the International Energy Association reports the CO2 capture and storage (CCS) must be part of the strategy for mitigating climate changes and keep the increase in the global temperature below the 2°C threshold (IEA, 2015). Though related technologies for CCS projects have been extensively developed in the Oil and Gas industry it still remains expensive to be materialized mainly due to the cost of capture and transportation. For the time being CCS projects are economically viable when they are combined with other benefits such as enhanced oil recovery. Deployment of CCS project at large scales in the near future is primarily a matter of policy decision of the international community on the climate change issue (European Commission 2009, Metz et al. 2005). The risk of CO2 leakage from geological formations with potential contamination of shallow water and soil resources or escape back to the atmosphere is still an outstanding issue highly debatable which, must be addressed by the research community.
