Influence of shear and deviatoric stress on the evolution of permeability in fractured rock

Abstract

[1] The evolution of permeability in fractured rock as a function of effective normal stress, shear displacement, and damage remains a complex issue. In this contribution, we report on experiments in which rock surfaces were subject to direct shear under controlled pore pressure and true triaxial stress conditions while permeability was monitored continuously via flow parallel to the shear direction. Shear tests were performed in a pressure vessel under drained conditions on samples of novaculite (Arkansas) and diorite (Coso geothermal field, California). The sample pairs were sheared to 18 mm of total displacement at 5 mm/s at room temperature and at effective normal stresses on the shear plane ranging from 5 to 20 MPa. Permeability evolution was measured throughout shearing via flow of distilled water from an upstream reservoir discharging downstream of the sample at atmospheric pressure. For diorite and novaculite, initial (preshear) fracture permeability is 0.5-1 Â 10 À14 m 2 and largely independent of the applied effective normal stresses. These permeabilities correspond to equivalent hydraulic apertures of 15-20 mm. Because of the progressive formation of gouge during shear, the postshear permeability of the diorite fracture drops to a final steady value of 0.5 Â 10 À17 m 2 . The behavior is similar in novaculite but the final permeability of 0.5 Â 10 À16 m 2 is obtained only at an effective normal stress of 20 MPa.

Effects of fractal surface roughness and lithology on single and multiphase flow in a single fracture: An experimental investigation

“…Experimental materials representing the single fractures were handled as either natural and synthetically created fractures or replica models of both types (Yeo et al, 1998;Chen et al, 2000;Auradou et al, 2001;Zimmerman et al, 2004;Watanabe et al, 2005;Nowamooz et al, 2009;Radilla et al, 2013). Parallel rock plates roughened artificially (Faoro et al, 2009;Schmittbuhl et al, 2008) or idealized fracture models with simulated roughness (Chen et al, 2009) were also used in the experiments. The importance of working with realistic fractures representing complicated roughness geometry rather than the idealized ones was emphasized by Qian et al (2005).…”

Influence of Normal and Shear Stress on the Hydraulic Transmissivity of Thin Cracks in a Tight Quartz Sandstone, a Granite, and a Shale

“…Other studies on "hard" rocks that reported a marked decrease in crack transmissivity with shearing, and attributed it to the formation of frictional wear products, include Faoro et al (2009) for diorite and novaculite and Tanikawa et al (2010) for porous sandstone. Reductions in transmissivity through the formation of cataclastic shear bands in porous sandstones are well known (e.g., Ballas et al, 2015).…”

The role of permeability evolution in fault zones on the structural and hydro-mechanical characteristics of shortening basins

“…Conceptually, elevated permeabilities within fault zones are expected as the porosity increases by fracturing and dilation and new hydraulic connections are established. Permeability increases as large as 3 orders of magnitude have been reported (Faoro et al, 2009;Zhu and Wong, 1999) due to shearing. Mechanical compaction and also diagenesis over geological timescales further complicates the problem as permeability reduction up to 3 orders of magnitude can occur as a result of mineral precipitation Schechte and Gidley, 1969).…”