Progress toward a stochastic rock mechanics model of engineered geothermal systems

Willis-Richards, J.; Watanabe, Kimio; Takahashi, Hidenori

doi:10.1029/96jb00882

Cited by 177 publications

(117 citation statements)

References 16 publications

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“…Fractures in the crust are distributed away from the fault following a power law [e.g., Savage and Brodsky, 2011] but are only hydraulically conductive if they are critically stressed within the local stress state [e.g., Barton et al, 1995]. Continuous shear strain imposed by tectonic loading ( E 12 ∕ t) promotes aperture dilation [e.g., Willis-Richards et al, 1996], assuming strain rates are greater than chemical and mechanical healing rates; the spatial profile in strain can be strongly affected by shallow creep. Hydromechanical coupling between fracture aperture and flow rate (e.g., the "cubic" law) leads to spatial variations in effective permeability and mechanical compliance, with strong enhancements located near the fault [e.g., Chester and Logan, 1986].…”

Section: Spectral Responsementioning

confidence: 99%

Pore pressure sensitivities to dynamic strains: Observations in active tectonic regions

Barbour

2015

JGR Solid Earth

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Triggered seismicity arising from dynamic stresses is often explained by the Mohr‐Coulomb failure criterion, where elevated pore pressures reduce the effective strength of faults in fluid‐saturated rock. The seismic response of a fluid‐rock system naturally depends on its hydromechanical properties, but accurately assessing how pore fluid pressure responds to applied stress over large scales in situ remains a challenging task; hence, spatial variations in response are not well understood, especially around active faults. Here I analyze previously unutilized records of dynamic strain and pore pressure from regional and teleseismic earthquakes at Plate Boundary Observatory (PBO) stations from 2006 to 2012 to investigate variations in response along the Pacific/North American tectonic plate boundary. I find robust scaling response coefficients between excess pore pressure and dynamic strain at each station that are spatially correlated: around the San Andreas and San Jacinto fault systems, the response is lowest in regions of the crust undergoing the highest rates of secular shear strain. PBO stations in the Parkfield instrument cluster are at comparable distances to the San Andreas Fault (SAF), and spatial variations there follow patterns in dextral creep rates along the fault, with the highest response in the actively creeping section, which is consistent with a narrowing zone of strain accumulation seen in geodetic velocity profiles. At stations in the San Juan Bautista (SJB) and Anza instrument clusters, the response depends nonlinearly on the inverse fault‐perpendicular distance, with the response decreasing toward the fault; the SJB cluster is at the northern transition from creeping‐to‐locked behavior along the SAF, where creep rates are at moderate to low levels, and the Anza cluster is around the San Jacinto Fault, where to date there have been no statistically significant creep rates observed at the surface. These results suggest that the strength of the pore pressure response in fluid‐saturated rock near active faults is controlled by shear strain accumulation associated with tectonic loading, which implies a strong feedback between fault strength and permeability: dynamic triggering susceptibilities may vary in space and also in time.

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Section: Spectral Responsementioning

confidence: 99%

Pore pressure sensitivities to dynamic strains: Observations in active tectonic regions

Barbour

2015

JGR Solid Earth

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“…Willis-Richards 1996;Bruel, 2007). In such an approach, the fracture responses upon shear failure may be calculated based on a local elastic solution for an assumed circular shaped fracture of certain radius.…”

Section: Permeability Changesmentioning

confidence: 99%

Coupled THM Modeling of Hydroshearing Stimulation in Tight Fractured Volcanic Rock

et al. 2014

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In this study, we use the TOUGH-FLAC simulator for coupled thermo-hydro-mechanical (THM) modeling of well stimulation for an Enhanced Geothermal System (EGS) project. We analyze the potential for injection-induced fracturing and reactivation of natural fractures in a porous medium with associated permeability enhancement. Our analysis aims to understand how far the EGS reservoir may grow and how the hydroshearing effect depends upon system conditions. We analyze the enhanced reservoir, or hydrosheared zone, by studying the extent of the failure zone using an elasto-plastic model, and accounting for permeability changes as a function of the induced stresses. Results, for both fully saturated and unsaturated medium cases, demonstrate how the EGS reservoir growth depends on the initial fluid phase, and how the reservoir extent changes as a function of two critical parameters: the coefficient of friction and the permeabilityenhancing factor. Moreover, whereas the stimulation is driven by the pressure exceeding a hydroshearing threshold, the modeling also demonstrates how the injection-induced cooling boosts the stimulation a bit farther.

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“…Different models can be used to describe the increase of fracture aperture by shearing. Most commonly, the models described by Barton et al [89] and Willis-Richards et al [90] are used. For granite, they were compared experimentally by Chen et al [91].…”

Section: Fluid Flowmentioning

confidence: 99%

Induced seismicity in geothermal reservoirs: A review of forecasting approaches

Gaucher

Schoenball

Heidbach

et al. 2015

Renewable and Sustainable Energy Reviews

153

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In order to reach Europe's 2020 and 2050 targets in terms of greenhouse gas emissions, geothermal resources will have to contribute substantially to meeting carbon-free energy needs. However, public opinion may prevent future large-scale application of deep geothermal power plants, because induced seismicity is often perceived as an unsolicited and uncontrollable side effect of geothermal development. In the last decade, significant advances were made in the development of models to forecast induced seismicity, which are either based on catalogues of induced seismicity, on the underlying physical processes, or on a hybrid philosophy. In this paper, we provide a comprehensive overview of the existing approaches applied to geothermal contexts. This overview will outline the advantages and drawbacks of the different approaches, identify the gaps in our understanding, and describe the needs for geothermal observations. Most of the forecasting approaches focus on the stimulation phase of enhanced geothermal systems which are most prone to generate seismic events. Besides the statistical models suited for realtime applications during reservoir stimulation, the physics-based models have the advantage of considering subsurface characteristics and estimating the impact of fluid circulation on the reservoir. Hence, to mitigate induced seismicity during major hydraulic stimulations, application of hybrid methods in a decision support system seems the best available solution. So far, however, little attention has been paid to geochemical effects on the failure process and to production periods. Quantitative modelling of induced seismicity still is a challenging and complex matter. Appropriate resources remain to be invested for the scientific community to continue its research and development efforts to successfully forecast induced seismicity in geothermal fields. This is a prerequisite for making this renewable energy resource sustainable and accessible worldwide.

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Progress toward a stochastic rock mechanics model of engineered geothermal systems

Cited by 177 publications

References 16 publications

Pore pressure sensitivities to dynamic strains: Observations in active tectonic regions

Pore pressure sensitivities to dynamic strains: Observations in active tectonic regions

Coupled THM Modeling of Hydroshearing Stimulation in Tight Fractured Volcanic Rock

Induced seismicity in geothermal reservoirs: A review of forecasting approaches

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