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

Abstract

We present a series of controlled fluid injection experiments in the laboratory on a pre‐stressed natural rough fracture with a high initial permeability (∼10−13 m2) in granite using different fluid pressurization rates. Our results show that fluid injection on a fracture with a slight velocity‐strengthening frictional behavior exhibits dilatant slow slip in association with a permeability increase up to ∼41 times attained at the maximum slip velocity of 0.085 mm/s for the highest‐rate injection case. Under these conditions, the slip velocity‐dependent change in hydraulic aperture is a dominant process to explain the transient evolution of fracture permeability, which is modulated by fluid pressurization rate and fracture surface asperities. This leads to the conclusion that permeability evolution can be engineered for subsurface geoenergy applications by controlling the fluid pressurization rate on slowly slipping fractures.

Constraining temporal evolution of shear-induced dilatancy of rock fractures

“…The smaller dilation factor in gouge-filled fractures compared to our initially bare fractures may be due to the pre-compaction/consolidation of gouge before the tests, resulting in its lower sensitivity to velocity. The values of our best-fit 𝐷 c are generally consistent with the 𝐷 c reported on initially bare fractures ranging from several microns to millimeters (e.g., Marone & Cox, 1994;Fang et al, 2017;Ishibashi et al, 2018;Shen et al, 2022;Im et al, 2018;Ji et al, 2023). The range of dilation angle in our study is similar to that in previous studies, ranging from 0 to 30° (Chen et al, 2000;Melin, 2012;Yeo et al, 1998).…”

“…These parameters, however, may change with the slip of the fracture (e.g., Marone & Cox, 1994). Also note that the aperture here in this study is the mechanical aperture, which is not equivalent to the hydraulic aperture (Chen et al, 2000) that was used by Cappa et al (2018), Fang et al (2017) and Ji et al (2023). However, the congruence between alterations in hydraulic aperture and mechanical aperture may remain steadfast in permeable fractures within controlled laboratory settings (Fang et al, 2017;Ji et al, 2023) and natural field manuscript submitted to Geophysical Journal International conditions (Cappa et al, 2022).…”

“…The modelled fracture aperture considering both displacement-and velocity-dependent aperture changes can be expressed as (Ji et al, 2023),…”

“…In addition to the slip displacement, the slip velocity also influences the transient evolution of fracture aperture during fracture slip (Fang et al, 2017;Ji et al, 2023, Samuelson et al, 2009Segall & Rice, 1995). Particularly, when subject to a velocity change from vi-1 to vi, the transient evolution of incremental porosity (𝛥ε) of the gouge layer in a gouge-filled fracture can be expressed as (Rudnicki, 2022;Samuelson et al 2009;Segall & Rice, 1995;Sleep, 1995),…”

Fluid-driven aseismic fault slip with permeability enhancement and dilatancy

“…Dilatancy has been measured in many laboratory experiments [22][23][24][25][26][27][28]. Laboratory experiments also reveal changes in permeability from slip [29][30][31][32]. Dilatancy and permeability enhancement have also been observed in the shallow field experiments.…”