Fracture transmissivity as a function of normal and shear stress: First results in Opalinus Clay

Cuss, R.J.; Milodowski, Antoni E.; Harrington, J.F.

doi:10.1016/j.pce.2011.07.080

Cited by 42 publications

(56 citation statements)

References 13 publications

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“…15E and F), which is a texture proposed to indicate crack-seal processes during shearing (Koehn and Passchier, 2000), with growth of calcite into dilation sites. Dilatancy is consistent with a slight overconsolidation of OPA (Cuss et al, 2011;Ingram and Urai, 1999) during the evolution of the Main Fault (Nussbaum et al, 2011). Klinkenberg et al (2009) reported the occurrence of inter-particle cracks connecting larger grains in the surrounding of shear zones in synthetically deformed OPA.…”

Section: Veinssupporting

confidence: 61%

Microstructural evolution of an incipient fault zone in Opalinus Clay: Insights from an optical and electron microscopic study of ion-beam polished samples from the Main Fault in the Mt-Terri Underground Research Laboratory

Laurich

Urai

Desbois

et al. 2014

Journal of Structural Geology

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Section: Veinssupporting

confidence: 61%

Microstructural evolution of an incipient fault zone in Opalinus Clay: Insights from an optical and electron microscopic study of ion-beam polished samples from the Main Fault in the Mt-Terri Underground Research Laboratory

Laurich

Urai

Desbois

et al. 2014

Journal of Structural Geology

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“…However, a large population of the smallest pores beyond the resolution limit of this method (< 10 nm) is considerable. The micrometer-thin shears are found to be nonporous, even for pores < 10 nm using TEM, potentially enabling a trap of high fluid pressures inside gouge (see Zhang et al, 2001;Cuss et al, 2011). Such local high fluid pressures promote further strain localization, which likely occurred progressively due to the interplay of pore pressure generation, tectonic stress buildup and (slow) pore pressure dissipation.…”

Section: Physical Rock Properties Of Gougementioning

confidence: 99%

Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

Laurich

Urai

Vollmer³

et al. 2018

Solid Earth

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Abstract. We studied gouge from an upper-crustal, lowoffset reverse fault in slightly overconsolidated claystone in the Mont Terri rock laboratory (Switzerland). The laboratory is designed to evaluate the suitability of the Opalinus Clay formation (OPA) to host a repository for radioactive waste.The gouge occurs in thin bands and lenses in the fault zone; it is darker in color and less fissile than the surrounding rock. It shows a matrix-based, P-foliated microfabric bordered and truncated by micrometer-thin shear zones consisting of aligned clay grains, as shown with broad-ion-beam scanning electron microscopy (BIB-SEM) and optical microscopy. Selected area electron diffraction based on transmission electron microscopy (TEM) shows evidence for randomly oriented nanometer-sized clay particles in the gouge matrix, surrounding larger elongated phyllosilicates with a strict P foliation. For the first time for the OPA, we report the occurrence of amorphous SiO 2 grains within the gouge. Gouge has lower SEM-visible porosity and almost no calcite grains compared to the undeformed OPA.We present two hypotheses to explain the origin of gouge in the Main Fault: (i) "authigenic generation" consisting of fluid-mediated removal of calcite from the deforming OPA during shearing and (ii) "clay smear" consisting of mechanical smearing of calcite-poor (yet to be identified) source layers into the fault zone. Based on our data we prefer the first or a combination of both, but more work is needed to resolve this.Microstructures indicate a range of deformation mechanisms including solution-precipitation processes and a gouge that is weaker than the OPA because of the lower fraction of hard grains. For gouge, we infer a more ratedependent frictional rheology than suggested from laboratory experiments on the undeformed OPA.

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“…Relatively few experimental studies have been performed, usually at low stresses but to large shear offsets (e.g., Cuss et al, 2011;Gutierrez et al, 2000). However, Rutter and Mecklenburgh (2017) reported experimental data for flow through bedding-parallel cracks in shale at effective normal stresses (total normal stress minus pore fluid pressure, also known as Terzaghi effective pressure) up to 90 MPa and found that the initiation of shearing caused dramatic reduction in hydraulic transmissivity.…”

Section: Introductionmentioning

confidence: 99%

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

Rutter

Mecklenburgh

2018

JGR Solid Earth

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Transmissivity of fluids along fractures in rocks is reduced by increasing normal stress acting across them, demonstrated here through gas flow experiments on Bowland shale, and oil flow experiments on Pennant sandstone and Westerly granite. Additionally, the effect of imposing shear stress at constant normal stress was determined, until frictional sliding started. In all cases, increasing shear stress causes an accelerating reduction of transmissivity by 1 to 3 orders of magnitude as slip initiated, as a result of the formation of wear products that block fluid pathways. Only in the case of granite, and to a lesser extent in the sandstone, was there a minor amount of initial increase of transmissivity prior to the onset of slip. These results cast into doubt the commonly applied presumption that cracks with high resolved shear stresses are the most conductive. In the shale, crack transmissivity is commensurate with matrix permeability, such that shales are expected always to be good seals. For the sandstone and granite, unsheared crack transmissivity was respectively 2 and 2.5 orders of magnitude greater than matrix permeability. For these rocks crack transmissivity can dominate fluid flow in the upper crust, potentially enough to permit maintenance of a hydrostatic fluid pressure gradient in a normal (extensional) faulting regime.

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Fracture transmissivity as a function of normal and shear stress: First results in Opalinus Clay

Cited by 42 publications

References 13 publications

Microstructural evolution of an incipient fault zone in Opalinus Clay: Insights from an optical and electron microscopic study of ion-beam polished samples from the Main Fault in the Mt-Terri Underground Research Laboratory

Microstructural evolution of an incipient fault zone in Opalinus Clay: Insights from an optical and electron microscopic study of ion-beam polished samples from the Main Fault in the Mt-Terri Underground Research Laboratory

Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

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

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