The influence of fault reactivation on injection-induced dynamic triggering of permeability evolution

Abstract

Summary Mechanisms controlling fracture permeability enhancement during injection-induced and natural dynamic stressing remain unresolved. We explore pressure-driven permeability (k) evolution by step-increasing fluid pressure (p) on near-critically-stressed laboratory fractures in shale and schist as representative of faults in sedimentary reservoirs/seals and basement rocks. Fluid is pulsed through the fracture with successively incremented pressure to first examine sub-reactivation permeability response that then progresses through fracture reactivation. Transient pore pressure pulses result in a permeability increase that persists even after the return of spiked pore pressure to the null background level. We show that fracture sealing is systematically reversible with the perturbing pressure pulses and pressure-driven permeability enhancement is eminently reproducible even absent shear slip and in the very short term (order of minutes). These characteristics of the observed fracture sealing following a pressure perturbation appear similar to those of the response by rate-and-state frictional healing upon stress/velocity perturbations. Dynamic permeability increase scales with the pore pressure magnitude and fracture sealing controls the following per-pulse permeability increase, both in the absence and presence of reactivation. However, initiation of the injection-induced reactivation results in a significant increase in the rate of permeability enhancement (dk/dp). These results demonstrate the role of frictional healing and sealing of fractures at interplay with other probable processes in pore pressure-driven permeability stimulation, such as particle mobilization.

A micromechanical analysis of marble pulverization under quasi-static progressive cyclic loading

“…The generation and mobilization of rock proppants and rock fragments are the key to understanding the underlying physics of permeability evolution due to the important role they play in the permeability enhancement process in Earth's crust (Candela et al, 2014;Elkhoury et al, 2011) and geo-energy reservoirs (Yildirim et al, 2020;Ji et al, 2022). The effect of cyclic loading on sample crack development can be divided into two parts: Cyclic loading with lower peak stress simply compacts the gaps between rock grains and heals micro-cracks and cleavage planes within rocks (Ghasemi et al, 2021).…”

Interaction of natural and hydraulic fractures: the impact on reservoir pressure buildup and risk of shear fault reactivation in the Upper Devonian Duvernay Formation, Fox Creek, Alberta

“…Indeed, the finite-discrete element numerical simulations and laboratory triaxial experiments have shown that fracturing at meso-scale can result in enhancing localized permeability in tight shales with 0 to 5 orders of magnitude (Hyman et al 2016 ). More complex, dynamic permeability evolution was observed in laboratory experiments of fracture permeability with periods of permeability enhancement induced by hydro-shearing interchanging with periods of slow continuous permeability loss caused by chemo-mechanical compaction during periods of pre- and post-stimulation hold phases (Yildirim et al 2020 ).…”