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IEA Greenhouse Gas R&D Programme

James-Craig cropFaults are known to act as low permeability sealing zones but can also act as conduits allowing the flow of fluids across and up the structure. This project was commissioned to review fault properties and how they mjosirt be influenced by fluids including CO2 in solution. The report explains the significance of fault structures, the nature of deformation and how this influences permeability. It also reviews classic and some experimental methods to assess fault properties.

Reactivation of faults can be assessed using both analytical and numerical approaches, but assessment is usually based on the Mohr-Coulomb failure criterion. This method can be used to determine the critical injection pressure. Numerical modelling can provide predictions of fault stability at different scales and incorporate different parameters such as the geometry of different faults. Numerical methods can be effective for identifying leakage potential and seal failure especially where dilatancy and stress dependent permeability changes occur.
Experimental tests on minerals and rock samples exposed to CO2 tentatively indicate that the coefficient of friction is not radically changed, however, this conclusion is based on limited exposure to CO2.

There is limited observational data on stress regimes and direct pore pressure measurements from core samples from cap rocks and fault zones. Acquisition of key data can enhance stress regime modelling and fault behavior. The next stage of research is to review real fault permeability through reservoir formations and cap rocks. A new study will be commissioned during 2015.