A two-scale hydromechanical model for fault zones accounting for their heterogeneous structure

Abstract

Fault zones show generally hetergeneous structures constituted of a fault core surrounded by damaged zones containing different fracture families. Taking into account this hetergeneous architecture of fault zones on their hydromechanical response to a pore pressure increase in their vicinity is the main goal of the present paper. The hydromechanical behavior of a fault running across a reservoir during a CO2 injection scenario has been modeled by a two-scale model. At the fault zone scale, statistically distributed fractures are considered to evaluate the equivalent permeability of the fault zone. At the site scale, a specific fault model that takes into account the permeability of different parts of the fault zone is used. The change of the permeability of each damage zone due to the pressure build-up within the reservoir is taken into account. Finally, the proposed model is used to perform large-scale simulations of the injection operation through a multilayered geological site. The model permits to simulate brine flow through the fault zone. The failure reactivation risk can also be estimated through the failure criterion of the fault core’s materials, here considered following an elastic perfectly plastic Drucker–Prager criterion.