Martin Lesueur, Thomas Poulet, Emmanouil Veveakis

Fluid injection or production in petroleum reservoirs affects the reservoir stresses such that it can even sometime reactivate dormant faults in the vicinity. In the particular case of deep car- bonate reservoirs, faults can also be chemically active; chemical dissolution of the fault core can transform an otherwise impermeable barrier to a flow channel. Due to the scale separation of the fault compared to the reservoir, implementation of highly non-linear multiphysics pro- cesses for the fault, needed for such phenomenon, is not compatible with simpler poromechan- ics controlling the reservoir behaviour. This contribution presents a three-scale finite element framework using the REDBACK simulator to account for those multiphysics couplings in faults during fluid production. This approach links the reservoir (km) scale - implementing porome- chanics both for the fault interface and its surrounding reservoir - with the fault at the meso-scale (m) - implementing a THMC reactivation model - and the micro-scale (μm) - implementing a hydro-chemical model on meshed μCT-scan images. This model can explain the permeability increase during fault reactivation and successfully replicate fault activation, evolution and deac- tivation features, predicted by common fault reactivation models, yet with continuous transitions between phases. The multiscale coupling allows to resolve the heterogenous propagation of the fault slip which proves to be independent of the initial highest slip tendency location. The in- fluence of the rock microstructure on fault and reservoir behaviour is quantified in a simulation where a hydraulically imperceptible difference in the microstructure’s geometry results in a dif- ferent duration of the reactivation event at the macro-scale. We demonstrate the advantage of dynamically upscaled laws compared to empirical laws as we capture permeability hysteresis during dissolution/precipitation of the fault.