Coupling of gOcad, COMSOL and 3D-Stress codes to estimate stress induced permeability variations in a fault zone.

@inproceedings{LefevreGM2013,
 abstract = { Permeability variation with fault activation is a question of interest for seismologists and reservoir engineers in the predictions and the risk assessments of natural or induced earthquakes and fault leakage. Such studies are often performed at large scale considering simplistic representations of fault architecture and properties. In this paper, we propose a method to estimate the permeability tensor variations related to three-dimensional fault architecture and state of stress using a high-accuracy 3D numerical representation of fault zone heterogeneities at the meter scale. The studied fault zone, is located in the French Institute for Radiological Protection and Nuclear Safety (IRSN) underground laboratory located at Tournemire (SW France) in the Toarcian shale formation. The fault corresponds to a 2m thick and a few hundred meters long vertical strike-slip fault zone. One fully cored borehole crosses the intact rock, the fault damage and the gouge zones with a dip of 21° and a direction normal to the fault's direction. Fractures, joints and veins with different filling are identified as the main fault zone structures with optical logging of the borehole wall. A 3D reconstruction of existing heterogeneities is conducted with gOcad. Then, 3D gOcad model is meshed and exported (i) in a flow calculation model to estimate the permeability tensor using COMSOL software and (ii) in an effective stress calculation model to estimate the influence of different regional stress scenarios on the fault zone deformations using 3D-Stress software.
Permeability values of 10-16 m2 are computed, a factor of 105 to 106 higher than the intact rock values measured in the field. Such high values probably overestimated the real fault zone permeability as we only considered open fractures simple geometry without any filling material. Nevertheless, the fault damage zone clearly appears as the highest permeability zone where stress analysis shows that the actual stress state may favor tensile reopening of fractures with a moderate risk of fault slip activation. The gOcad-COMSOL-3D-Stress coupling thus appears as an interesting way to estimate meter scale fault zone properties and their potential hydromechanical activation. Such simple analysis can be used for borehole stability analyses, and to help defining hydrofracking strategies in horizontal holes intersecting fault zones. },
 author = { Lefèvre, Mélody AND Guglielmi, Yves AND Henry, Pierre AND Viseur, Sophie AND Gout, Claude AND Dick, P. },
 booktitle = { Proc. 33rd Gocad Meeting, Nancy },
 title = { Coupling of gOcad, COMSOL and 3D-Stress codes to estimate stress induced permeability variations in a fault zone. },
 year = { 2013 }
}