Experimental Study of Hydromechanical Behavior of Fracture of Vaca Muerta Gas Shale

Total E&P has developed an experimental set-up allowing creation shear fracture within a cylinder sample in a conventional triaxial cell thanks to two specific heels placed on the top and bottom of the sample. Permeability tests to gas and to water, as well as measurements of normal and shear displacements can be carried out using existing facilities of a triaxial cell. In the post-failure phase of shear fracturing, dilatancy angle of a fresh fracture measured on a Vaca Muerta shale is about 24° to 38° under 30 bars of confining pressure. Mechanical opening (normal displacement) induced by fracturing is about 400 µm. Hydraulic opening to water or to gas decreases significantly when confining pressure increased from 10 bars to 120 bars. Alteration of a fresh shale fracture surface by water is characterized by the change of the hydraulic opening to gas. After presentation of the experiment set-up, the main results obtained on the mechanical behavior of the fracture and the hydraulic behavior of fracture to water and to gas flow under various stress and injection conditions are presented and discussed.