Microseismic signatures of non-linear pore-fluid pressure diffusion

Hummel, N.; Müller, Tobias M.

doi:10.1111/j.1365-246x.2009.04373.x

Cited by 30 publications

(27 citation statements)

References 19 publications

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“…The magnitudes are then randomly drawn from a power‐law distribution with the assigned b ‐value for each failure occurrence. Using a linear diffusion model with homogeneous and isotropic hydraulic diffusivity is a strong simplification for two reasons: (i) the opening of fractures potentially modifies the diffusivity, creating non‐linearity [ Hummel and Müller , 2009] and (ii) actual pore‐pressure propagation can be highly anisotropic, occurring preferentially along zones of weakness [ Evans et al , 2005]. However, the model serves as a first‐order approximation and can explain some features of the observed seismicity well [ Goertz‐Allmann et al , 2011].…”

Section: Geomechanical Modelmentioning

confidence: 99%

Influence of pore‐pressure on the event‐size distribution of induced earthquakes

Bachmann

Wiemer

Goertz‐Allmann

et al. 2012

Geophysical Research Letters

226

187

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[1] During an Enhanced Geothermal System (EGS) experiment, fluid is injected at high pressure into crystalline rock, to enhance its permeability and thus create a reservoir from which geothermal heat can be extracted. The fracturing of the basement caused by these high pore-pressures is associated with microseismicity. However, the relationship between the magnitudes of these induced seismic events and the applied fluid injection rates, and thus pore-pressure, is unknown. Here we show how pore-pressure can be linked to the seismic frequency-magnitude distribution, described by its slope, the b-value. We evaluate the dataset of an EGS in Basel, Switzerland and compare the observed event-size distribution with the outcome of a minimalistic model of porepressure evolution that relates event-sizes to the differential stress s D . We observe that the decrease of b-values with increasing distance of the injection point is likely caused by a decrease in pore-pressure. This leads to an increase of the probability of a large magnitude event with distance and time.

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Section: Geomechanical Modelmentioning

confidence: 99%

Influence of pore‐pressure on the event‐size distribution of induced earthquakes

Bachmann

Wiemer

Goertz‐Allmann

et al. 2012

Geophysical Research Letters

226

187

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“…During the Ebreichsdorf 2013 sequence, inter-event distances of few hundred meters to one kilometer and inter-event periods of hours to days would be compatible with an ave-2 rage hydraulic diffusivity of about 1-10 m /s This would correspond to a highly permeable material (Roeloffs et al, 2003;Manga and Wang, 2007) and is few orders of magnitudes higher than values of hydraulic diffusivities found for fault -2 -7 2 gouges (10 -10 m /s; Wibberley, 2002;Doan et al, 2006). Fluid overpressure at depth could also be the cause of this high diffusivity, due to the non-linear relationship between pore pressure and hydraulic diffusivity (Miller et al, 2004;Hummel and Müller, 2009). If pore pressure diffusion is the driving mechanisms of this sequence, it could explain the position of the aftershocks above the main shocks with the propagation of fluids toward the surface.…”

Section: Discussionmentioning

confidence: 86%

Earthquake interactions during the 2013 Ebreichsdorf aftershock sequence (online appendix)

Tary¹,

Apoloner²,

Bokelmann³

2015

AJES

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The Vienna Basin Fault System (VBFS) is one of the most seismically active regions of Austria, delineating the southern part of the Vienna Basin. This sinistral, strike slip fault system, accommodates part of the deformation due to the northward push of the Adriatic microplate. In 2000 and 2013, two pairs of main shocks followed by a few tens of aftershocks occurred in the region of Ebreichsdorf, one of the clusters of seismicity along the VBFS. The main shocks seem to be located closely in both cases, even though high-resolution double-difference locations are available only for the sequence in 2013. Focusing on this sequence, we investigate the interactions between the two main shocks and their 18 aftershocks. The two main shocks are located almost at the same place, at a depth of 10.5 km, while the aftershocks constitute a shallower ellipsoid with its long axis parallel to the main trace of the VBFS. We use two Coulomb failure stress models to study possible static stress transfer between the main shocks and the aftershocks of this sequence, the apparent friction model and the isotropic poroelastic model. Both models yield Coulomb failure stress changes below 0.01 MPa at the aftershocks locations. Static stress transfer seems then unlikely to explain their occurrence, even though interactions between aftershocks could play a role in their triggering. Two other mechanisms are considered, 2 namely pore pressure diffusion along an idealized fault plane, and aseismic creep. A high hydraulic diffusivity of about 1-10 m /s would be however required to account for the spatial extent of the possible interactions (~0.5-1 km) and the inter-event times (hours to days). The shallower location of the aftershocks compared to both main shocks could also point to the migration of fluids toward the surface. The occurrence of collocated events of comparable sizes and focal mechanisms, also named seismic repeaters, is often attributed to the presence of aseismic creep. But without further observations it would be difficult to support or rule out this hypothesis. Either the presence of high pore pressure or aseismic slip has important implications for the presentday earthquake potential of the VBFS to produce large earthquakes.Das Wiener-Becken-Störungssystem (VBFS) ist eine der seismisch aktivsten Regionen Österreich. Das VBFS ist eine sinistrale Blattverschiebung, welche den südlichen Teil des Wiener Beckens durchzieht. Damit ist es Teil eines größeren Systems von Verwerfungen, welches die Nordbewegung der adriatischen Mikroplatte begleitet. Im Jahr 2000 und 2013 gab es jeweils zwei Erdbebenpaare an der VBFS, die von einer Serie an Nachbeben begleitet wurden. Die Hauptbeben ereigneten sich rund um Ebreichsdorf, einem Ort an dem schon mehrere Erdbebenserien aufgezeichnet wurden. Jedes der beiden Bebenpaare scheint praktisch am gleichen Ort stattgefunden zu haben, auch wenn hochauflösende « double-difference » Hypozentrem nur für die Beben von 2013 zur Verfügung stehen. Diese Arbeit konzentriert sich daher auf die Serie ...

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“…As a consequence of the coupling between pressure, fracture compliance and permanent fracture aperture changes, the pressure field does not propagate through the reservoir as a linear diffusive field, but rather as a pressure front (Murphy et al, 2004). The fracture normal and shear dilation that occurs in response to elevated fluid pressure thus has a major influence on the magnitude and profile of the propagating pressure perturbation in the rock mass during hydraulic stimulations (Evans et al, 1999;Hummel and Müller, 2009). As a consequence, fracture compliance and normal or shear dilation characteristics have an impact on the size and geometry of the reservoir created during hydraulic stimulation.…”

Section: Stimulation By Hydraulic Shearingmentioning

confidence: 99%

The seismo-hydromechanical behavior during deep geothermal reservoir stimulations: open questions tackled in a decameter-scale in situ stimulation experiment

et al. 2018

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Abstract. In this contribution, we present a review of scientific research results that address seismo-hydromechanically coupled processes relevant for the development of a sustainable heat exchanger in low-permeability crystalline rock and introduce the design of the In situ Stimulation and Circulation (ISC) experiment at the Grimsel Test Site dedicated to studying such processes under controlled conditions. The review shows that research on reservoir stimulation for deep geothermal energy exploitation has been largely based on laboratory observations, large-scale projects and numerical models. Observations of full-scale reservoir stimulations have yielded important results. However, the limited access to the reservoir and limitations in the control on the experimental conditions during deep reservoir stimulations is insufficient to resolve the details of the hydromechanical processes that would enhance process understanding in a way that aids future stimulation design. Small-scale laboratory experiments provide fundamental insights into various processes relevant for enhanced geothermal energy, but suffer from (1) difficulties and uncertainties in upscaling the results to the field scale and (2) relatively homogeneous material and stress conditions that lead to an oversimplistic fracture flow and/or hydraulic fracture propagation behavior that is not representative of a heterogeneous reservoir. Thus, there is a need for intermediate-scale hydraulic stimulation experiments with high experimental control that bridge the various scales and for which access to the target rock mass with a comprehensive monitoring system is possible. The ISC experiment is designed to address open research questions in a naturally fractured and faulted crystalline rock mass at the Grimsel Test Site (Switzerland). Two hydraulic injection phases were executed to enhance the permeability of the rock mass. During the injection phases the rock mass deformation across fractures and within intact rock, the pore pressure distribution and propagation, and the microseismic response were monitored at a high spatial and temporal resolution.

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Microseismic signatures of non-linear pore-fluid pressure diffusion

Cited by 30 publications

References 19 publications

Influence of pore‐pressure on the event‐size distribution of induced earthquakes

Influence of pore‐pressure on the event‐size distribution of induced earthquakes

Earthquake interactions during the 2013 Ebreichsdorf aftershock sequence (online appendix)

The seismo-hydromechanical behavior during deep geothermal reservoir stimulations: open questions tackled in a decameter-scale in situ stimulation experiment

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