A preliminary attempt to combine in situ CT measurements with permeability tests of fractured granite cores

We introduced a core-flooding test equipment with the triaxial cell having been made available to in situ computed tomography (CT) scanning. Water flow-through tests were conducted on 38 mm-diameter fractured granite cores containing either saw-cut or rough fractures, subjected to a confining pressure varying from 5 to 20 MPa in a single loading-unloading cycle. We put a particular focus on fracture deformation and hydraulic performance of multiple fractures that were artificially assembled to form different fracture interconnection. Results show that in all the cases the permeability of the fractured granite cores nonlinearly decreases with increasing confining pressure, and was reduced by 80-90% when the confining pressure was increased to 20 MPa. Permeability recovery is very limited (10-30%) when the specimen was unloaded to the initial confining pressure of 5 MPa. Poorly-connected fractures show approximately half permeability of the well-connected fractures. Nonuniform deformation including changes in aperture and contact area in natural fractures were observed through CT image analysis. In the end, advantages and limitations of in situ imaging for quantitatively evaluating hydro-mechanical behavior of granite fractures at core-scale were discussed.