Thermo-hydro-mechanical processes in fractured rock formations during a glacial advance

Selvadurai, A. P. S.; Suvorov, A. P.; Selvadurai, Paul Antony

doi:10.5194/gmd-8-2167-2015

Cited by 40 publications

(16 citation statements)

References 87 publications

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“…For both EL and HS models, the calibrated maximum aperture is well within the range found in laboratory experiments for granite (Lee and Cho, 2002;Luo et al, 2017), while the residual aperture agrees with analysis of in-situ pressure tests (Rutqvist et al, 1998). Also the final calibrated permeability is similar to measured value for fractures in granite (Selvadurai, 2015). The calibrated solution is non-unique given the large number of parameters.…”

Section: Elastic Opening Vs Hydroshearingsupporting

confidence: 57%

Joint opening or hydroshearing? Analyzing a fracture zone stimulation at Fenton Hill

Rinaldi

Rutqvist

2019

Geothermics

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In this study, we analyze a deep hydraulic stimulation of a fracture zone that was conducted as part of the classical Fenton Hill Hot Dry Rock Program in the 1970s. At the time, it was suggested that a pre-existing fracture or multiple fractures within the fracture zone were jacked open by injectioninduced increase in pressure. In this study, we analyze the same stimulation experiment, but investigate the possibility of an alternative mechanism of shear reactivation of pre-existing fractures. We conduct modeling that accounts for both jacking (or elastic-fracture opening) and shear-slip dilation and demonstrate that injection-induced shear reactivation (or hydroshearing) could have occurred simultaneously with seismic events of magnitudes lower than what can be felt by humans. In fact, simulations considering shear reactivation seem to better match observed fluid recovery after multiple injection cycles. Shear reactivation and shear dilation results in locked-open fractures, especially near the injection well that provides permeability of higher flow recovery. We then investigate the sensitivity of the proposed model by varying some of the critical parameters such as maximum aperture, dilation angle, as well as fracture density. Interestingly, none of the simulated cases resulted in a large event that could have been felt by humans, but did result in a cumulative seismic magnitude of less than 1 for each given stimulation step. These results suggest that a permanent irreversible permeability increase of several orders of magnitude can be obtained by hydroshearing in a "seismically" safe manner.

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Section: Elastic Opening Vs Hydroshearingsupporting

confidence: 57%

Joint opening or hydroshearing? Analyzing a fracture zone stimulation at Fenton Hill

Rinaldi

Rutqvist

2019

Geothermics

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“…Ustaszewksi et al [2008] studied fault slip induced by postglacial rebound in a Swiss alpine valley and connected the formation of uphill-facing scarps with postglacial unloading. In the context of hazard assessment for a deep repository, the role of coupled thermo-and hydromechanical bedrock responses to a glacial cycle (ice sheet) has been previously studied [Boulton et al, 2004;Chan et al, 2005;Vidstrand et al, 2008;Selvadurai et al, 2015]. However, such studies lack holistic treatment coupling an alpine valley glacier with adjacent rock slopes.…”

Section: Introductionmentioning

confidence: 99%

Beyond debuttressing: Mechanics of paraglacial rock slope damage during repeat glacial cycles

et al. 2017

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Cycles of glaciation impose mechanical stresses on underlying bedrock as glaciers advance, erode, and retreat. Fracture initiation and propagation constitute rock mass damage and act as preparatory factors for slope failures; however, the mechanics of paraglacial rock slope damage remain poorly characterized. Using conceptual numerical models closely based on the Aletsch Glacier region of Switzerland, we explore how in situ stress changes associated with fluctuating ice thickness can drive progressive rock mass failure preparing future slope instabilities. Our simulations reveal that glacial cycles as purely mechanical loading and unloading phenomena produce relatively limited new damage. However, ice fluctuations can increase the criticality of fractures in adjacent slopes, which may in turn increase the efficacy of fatigue processes. Bedrock erosion during glaciation promotes significant new damage during first deglaciation. An already weakened rock slope is more susceptible to damage from glacier loading and unloading and may fail completely. We find that damage kinematics are controlled by discontinuity geometry and the relative position of the glacier; ice advance and retreat both generate damage. We correlate model results with mapped landslides around the Great Aletsch Glacier. Our result that most damage occurs during first deglaciation agrees with the relative age of the majority of identified landslides. The kinematics and dimensions of a slope failure produced in our models are also in good agreement with characteristics of instabilities observed in the field. Our results extend simplified assumptions of glacial debuttressing, demonstrating in detail how cycles of ice loading, erosion, and unloading drive paraglacial rock slope damage.

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“…Also, the void fraction ( 1 %) is neglected in the calculations. The values for the bulk moduli and shear moduli for the various minerals were obtained from published literature (Alexandrov et al, 1964;Anderson and Nafe, 1965;Carmichael, 1990;Sisodia and Verma, 1990;Moos et al, 1997;Redfern and Angel, 1999;Schilling et al, 2003;Zhu et al, 2007;Mavko et al, 2009;Lin, 2013). In the multi-phasic approach, the objective is to determine the overall bulk modulus for the solid mineralogical phase by considering the bulk moduli for the separate mineral constituents and their volume fractions.…”

Section: Mineralmentioning

confidence: 99%

A multi-phasic approach for estimating the Biot coefficient for Grimsel granite

Selvadurai

Nejati

2019

Solid Earth

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Abstract. This paper presents an alternative approach for estimating the Biot coefficient for the Grimsel granite, which appeals to the multi-phasic mineralogical composition of the rock. The modelling considers the transversely isotropic nature of the rock that is evident from both the visual appearance of the rock and determined from mechanical testing. Conventionally, estimation of the compressibility of the solid material is performed by fluid saturation of the pore space and pressurization. The drawback of this approach in terms of complicated experimentation and influences of the unsaturated pore space is alleviated by adopting the methods for estimating the solid material compressibility using developments in theories of multi-phase materials. The results of the proposed approach are compared with estimates available in the literature.

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Thermo-hydro-mechanical processes in fractured rock formations during a glacial advance

Cited by 40 publications

References 87 publications

Joint opening or hydroshearing? Analyzing a fracture zone stimulation at Fenton Hill

Joint opening or hydroshearing? Analyzing a fracture zone stimulation at Fenton Hill

Beyond debuttressing: Mechanics of paraglacial rock slope damage during repeat glacial cycles

A multi-phasic approach for estimating the Biot coefficient for Grimsel granite

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