Transient evolution of permeability and friction in a slowly slipping fault activated by fluid pressurization

Abstract

The mechanisms of permeability and friction evolution in a natural fault are investigated in situ. During three fluid injection experiments at different places in a fault zone, we measured simultaneously the fluid pressure, fault displacements and seismic activity. Changes in fault permeability and friction are then estimated concurrently. Results show that fault permeability increases up to 1.58 order of magnitude as a result of reducing effective normal stress and cumulative dilatant slip, and 19-to-60.8% of the enhancement occurs without seismic emissions. When modeling the fault displacement, we found that a rate-and-state friction and a permeability dependent on both slip and slip velocity together reasonably fit the fault-parallel and fault-normal displacements. This leads to the conclusion that the transient evolution of fault permeability and friction caused by a pressure perturbation exerts a potentially dominant control on fault stability during fluid flow.

Fracture Permeability Enhancement During Fluid Injection Modulated by Pressurization Rate and Surface Asperities

“…Figure 4 illustrates that the transient permeability enhancement is evidently not controlled by the slip displacement change, in line with previous results on permeable in‐situ faults (Cappa, Guglielmi, & De Barros, 2022). In particular, the transient permeability enhancement in the first ∼0.24 mm slip displacement is larger at higher pressurization rates.…”

“…The root mean square error (RMSE) has a global minimum value at (Ψ = 0.08, D c = 0.4 μm), (Ψ = 0.93, D c = 0.16 μm) and (Ψ = 0.84, D c = 2.74 μm) in modeling the fluid injection experiments at a pressurization rate of 0.0004, 0.002 and 0.01 MPa/s, respectively (Figure S4 in Supporting Information ). The dilation factors (Ψ) in our best‐fit models are comparable to the values obtained in previous studies on laboratory fractures (Fang et al., 2017) and in‐situ faults (Cappa, Guglielmi, & De Barros, 2022). Our modeling results seem less sensitive to the critical slip distance ( D c ) within a range of less than one order of magnitude around the optimal value.…”

“…It is important to note that our experiments represent a case where the fracture has a high initial permeability and a slight velocity‐strengthening frictional behavior favoring aseismic slip during the fluid injection. The presented results support the hypothesis that the fluid pressurization rate and fracture surface asperities have a significant influence on the transient permeability evolution in a single deformable natural fracture and confirm that the slip velocity dependency of transient fracture permeability previously observed in the laboratory (Fang et al., 2017) and in situ (Cappa, Guglielmi, & De Barros, 2022) is a key process for fluid transport in fractures and faults. Nevertheless, it is important to highlight that our findings are particularly relevant to shallow aseismic slip and the accompanying changes in transient permeability, even though they might not comprehensively encompass the entire steady‐state range.…”

“…Rock fractures provide preferential fluid pathways that can transport thermal energy and shale oil and gas. A wealth of evidence from laboratory and field experiments suggests that hydro‐shearing, which involves injection‐induced slip along fractures and faults, is the primary contributor to enhancing reservoir permeability even when no proppants or acids are used (Barton et al., 2009; Cappa, Guglielmi, & De Barros, 2022; Cappa, Guglielmi, Nussbaum, et al., 2022; Guglielmi et al., 2015; Ishibashi et al., 2018; Jalali et al., 2018), but this process may also lead to unintentional and undesired large‐magnitude induced seismic events ( M w > 3) (Ji, Hofmann, Duan, & Zang, 2022; Keranen & Weingarten, 2018; Schultz et al., 2020; Zang et al., 2014). Thus, the ability to predict the transient permeability evolution of individual fractures is the key to accurately estimating fluid flow and reservoir response with controlled seismicity during injection.…”

Frictional properties of Opalinus Clay: influence of humidity, normal stress and grain size on frictional stability

“…Decametric scale in-situ fluid injection experiments performed directly within the 'Main Fault' structure were able to reactivate the 'Main Fault' with small displacement (i.e. from tens to about a hundred of microns) and associated seismic events (Guglielmi et al 2020;Jeanne et al 2018;Cappa et al 2022). During these in situ experiments, by measuring the pressure of the fluids and displacement signals directly from the fault, it was possible for the Authors to estimate the evolution of fault-parallel displacement (i.e.…”