Competing Controls of Effective Stress Variation and Chloritization on Friction and Stability of Faults in Granite: Implications for Seismicity Triggered by Fluid Injection

Zhang, Fengshou; Huang, Rui; An, Mengke; Min, Kyoung-Bok; Elsworth, Derek; Hofmann, Hannes; Wang, Xiaoguang

doi:10.1029/2022jb024310

Cited by 9 publications

(4 citation statements)

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“…(2015) and is believed to be a potential contributing factor to the aseismic transients measured in such cases. Velocity strengthening behavior has also been characterized in laboratory experiments on granite samples, in conditions similar to the ones expected at geothermal reservoir depth (Zhang et al., 2022). Velocity‐strengthening behavior could be explained by mineralization processes: minerals like chlorite favor velocity‐strengthening, while others like epidote lead to velocity‐weakening (An et al., 2021; Zhang et al., 2022).…”

Section: Discussionmentioning

confidence: 81%

“…Velocity strengthening behavior has also been characterized in laboratory experiments on granite samples, in conditions similar to the ones expected at geothermal reservoir depth (Zhang et al., 2022). Velocity‐strengthening behavior could be explained by mineralization processes: minerals like chlorite favor velocity‐strengthening, while others like epidote lead to velocity‐weakening (An et al., 2021; Zhang et al., 2022). For instance, in Basel, chlorite is expected to be present in the minerals along the fault, among others (Alt‐Epping et al., 2013).…”

Section: Discussionmentioning

confidence: 81%

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Control of Seismicity Migration in Earthquake Swarms by Injected Fluid Volume and Aseismic Crack Propagation

Danré,

Garagash,

De Barros

et al. 2024

JGR Solid Earth

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The evolution of fluid injection‐induced seismicity, generally characterized through the number of events or their seismic moment, depends on, among other factors, the injected fluid volume. Migration of seismicity is observed during those sequences and might be caused by a range of mechanisms: fluid pressure diffusion, fluid‐induced aseismic slip propagating along a stimulated fault, interactions between earthquakes. Recent theoretical and observational developments underline the important effect on seismicity migration of structural parameters, like fault criticality, or injection parameters, like flow rate or pressurization rate. Here, we analyze two well‐studied injection‐induced seismic sequences at the Soultz‐sous‐Fôret and Basel geothermal sites, and find that the evolution of the seismicity front distance primarily depends on the injected fluid volume. Based on a fracture mechanics model, we develop new equations relating seismicity migration to injected fluid volume and frictional and structural properties of the fault. We find that the propagation of a fluid‐induced aseismic slip front along the stimulated fault, triggering seismicity, explains well the observations made on the two sequences. This model allows us to constrain parameters describing the seismicity front evolution and explains the diversity of migration patterns observed in injection‐induced and natural earthquake swarms.

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Section: Discussionmentioning

confidence: 81%

Section: Discussionmentioning

confidence: 81%

Control of Seismicity Migration in Earthquake Swarms by Injected Fluid Volume and Aseismic Crack Propagation

Danré,

Garagash,

De Barros

et al. 2024

JGR Solid Earth

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“…Typical geological hosts for deep geothermal reservoirs are granitic and with abundant low‐grade metamorphic minerals (such as laumontite, chlorite and epidote) developed with in the reservoirs (An et al., 2021; Okamoto et al., 2019; Zhang, Hu, et al., 2024). In addition, typical EGS reservoirs often host pyrite, indicative as a geothermometer of hydrothermal intrusion >250°C (Zhang, Huang, et al., 2022; Zhang, Wen, et al., 2022)–with 250°C present within the stability field for chlorite. In addition, feldspar is hydrolyzed in a weakly alkaline environment at this temperature and with the potential to form chlorite (Yuguchi et al., 2021).…”

Section: Introductionmentioning

confidence: 99%

Frictional Properties of Feldspar‐Chlorite Gouges and Implications for Fault Reactivation in Hydrothermal Systems

Hu,

Zhang,

Zhang

et al. 2024

Earth and Space Science

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As a particularly common mineral in granites, the presence of feldspar and feldspar‐chlorite gouges at hydrothermal conditions has important implications in fault strength and reactivation. We present laboratory observations of frictional strength and stability of feldspar (K‐feldspar and albite) and feldspar‐chlorite gouges under conditions representative of deep geothermal reservoirs to evaluate the impact on fault stability. Velocity‐stepping experiments are performed at a confining stress of 95 MPa, pore pressures of 35–90 MPa, and temperatures of 120–400°C representative of in situ conditions for such reservoirs. Our experiment results indicate that the feldspar gouge exhibits strong friction (μ ∼ 0.71) at all experimental temperatures (∼120–400°C) but when T > 120°C, the frictional response transitions from velocity‐strengthening to slightly velocity‐weakening. At constant confining pressure and temperature, increasing the pore pressure increases the friction coefficient (∼0.70–0.85) and the gouge remains slightly velocity weakening. The presence of alteration‐sourced chlorite leads to a transition from velocity weakening to velocity strengthening in the mixed gouge at experimental temperatures and pore pressures. As a ubiquitous mineral in reservoir rocks, feldspar is shown to potentially contribute to unstable sliding over ranges in temperature and pressure typical in deep hydrothermal reservoirs. These findings emphasize that feldspar minerals may increase the potential for injection‐induced seismicity on pre‐existing faults if devoid of chloritization.

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“…Typical geological hosts for deep geothermal reservoirs are granitic and with abundant low-grade metamorphic minerals (such as chlorite and epidote) developed with in the reservoirs (Okamoto et al, 2019;An et al, 2021). In addition, typical enhanced geothermal systems (EGS) reservoirs often host pyrite, indicative as a geothermometer of hydrothermal intrusion > 250°C (Zhang et al, 2022) -with 250 °C present within the stability field for chlorite. In addition, K-feldspar is hydrolyzed in a weakly alkaline environment at this temperature and with the potential to form chlorite.…”

Section: Introductionmentioning

confidence: 99%

Frictional Properties of Feldspar-chlorite Altered Gouges and Implications for Fault Reactivation in Hydrothermal Systems

Hu,

Zhang,

Zhang

et al. 2023

Preprint

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As a particularly common minerals in granites, the presence of feldspar and altered feldspar-chlorite gouges at hydrothermal conditions have important implications in fault strength and reactivation. We present laboratory observations of frictional strength and stability of feldspar (K-feldspar and albite) and altered feldspar-chlorite gouges under conditions representative of deep geothermal reservoirs to evaluate the impact on fault stability. Velocity‐ stepping experiments are performed at a confining stress of 95 MPa, pore pressures of 35-90 MPa and temperatures of 120-400°C representative of in situ conditions for such reservoirs. Our experiment results show that the feldspar gouge is frictionally strong (μ~0.71) at all experimental temperatures (~120-400℃) but transits from velocity-strengthening to velocity-weakening at T>120°C. Increasing the pore pressure increases the friction coefficient (~0.70-0.87) and the gouge remains velocity weakening, but this weakening decreases as pore pressures increase. The presence of alteration-sourced chlorite leads to a transition from velocity weakening to velocity strengthening in the mixed gouge at experimental temperatures and pore pressures. As a ubiquitous mineral in reservoir rocks, feldspar is shown to potentially contribute to unstable sliding over ranges in temperature and pressure typical in deep hydrothermal reservoirs. These findings emphasize that feldspar minerals may increase the potential for injection-induced seismicity on pre-existing faults if devoid of chlorite alteration.

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Competing Controls of Effective Stress Variation and Chloritization on Friction and Stability of Faults in Granite: Implications for Seismicity Triggered by Fluid Injection

Cited by 9 publications

References 90 publications

Control of Seismicity Migration in Earthquake Swarms by Injected Fluid Volume and Aseismic Crack Propagation

Control of Seismicity Migration in Earthquake Swarms by Injected Fluid Volume and Aseismic Crack Propagation

Frictional Properties of Feldspar‐Chlorite Gouges and Implications for Fault Reactivation in Hydrothermal Systems

Frictional Properties of Feldspar-chlorite Altered Gouges and Implications for Fault Reactivation in Hydrothermal Systems

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