Pressurized fluid flow within the mechanical stability domain of fault zones in shale

¹ Université Grenoble Alpes, Université. Savoie Mont Blanc, CNRS, IRD, IFSTTAR, ISTerre, 38000 Grenoble, France
² Lawrence Berkeley National Laboratory, Earth and Environmental Science Area, 1 Cyclotron road, M/S 74R316C, Berkeley, CA 94720
³ CEREGE, Aix-Marseille University–CNRS–IRD, Marseille, France
⁴ Total S.A., Pau, France

^* Corresponding author: frederic.donze@univ-grenoble-alpes.fr

Abstract

Fracture interaction mechanisms and reactivation of natural discontinuities under fluid pressurization conditions inside fault zone can represent critical issues in risk assessment of caprock integrity. A field injection test, carried out in a damage fault zone at the decameter scale i.e. mesoscale, has been studied using a Distinct Element Model. Considering the complex structural nature of a fault zone, the contribution of fracture sets on the bulk permeability has been investigated during a hydraulic injection. It has been shown that their orientation for a given in-situ stress field plays a major role. However, if homogeneous properties are assigned to the fracture planes in the model, the limited irreversible displacements cannot be reproduced. Despite these limited displacements (40 µm maximum), the transmissivity increased by a factor of 10-100. These results provide insights in fracture controlled permeability of fault zones depending on the geometrical properties of the fractures and their resulting hydro-mechanical behavior for a given in–situ stress field.