The stress field at Soultz-sous-Forêts from focal mechanisms of induced seismic events: Cases of the wells GPK2 and GPK3

Dorbath, L.; Evans, Keith F.; Cuenot, Nicolas; Valley, Benoît; Charléty, Jean; Frogneux, M.

doi:10.1016/j.crte.2009.12.003

Cited by 27 publications

(24 citation statements)

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“…MD: measured depth; when boreholes are inclined, it is different from true vertical depth (TVD). After Dorbath et al () and references therein.…”

Section: The Soultz Reservoir: Review Of Geology Tectonic Setting Hmentioning

confidence: 99%

“…According to Dorbath et al (), the maximum horizontal principal stress (SH max ) orientation ranges between N170° and N180° down to 5 km depth (Table ), but it shows strong heterogeneities in several depth intervals, because it is perturbed by major fracture zones (Hettkamp et al, ; Valley & Evans, ). Sh min is clockwise rotated by about 10° in GPK3 compared to GPK2 (Dorbath et al, ), and SH max is between 0.9 and 1.05 times the value of the vertical principal stress Sv , which indicates a quasi‐uniaxial extensive stress regime (Valley & Evans, ). The present‐day stress field is favorable to the opening of the fracture network and was the crucial factor for the N‐S alignment of the boreholes at depth (Figure ).…”

Section: The Soultz Reservoir: Review Of Geology Tectonic Setting Hmentioning

confidence: 99%

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Is There a Link Between Mineralogy, Petrophysics, and the Hydraulic and Seismic Behaviors of the Soultz‐sous‐Forêts Granite During Stimulation? A Review and Reinterpretation of Petro‐Hydromechanical Data Toward a Better Understanding of Induced Seismicity and Fluid Flow

Meller

Ledésert

2017

JGR Solid Earth

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In the framework of the European Soultz‐sous‐Forêts enhanced geothermal system (EGS) in Alsace, France, 20 years of scientific and preindustrial tests had to be performed before the site began production of electricity in 2008. Stimulation tests were designed to enhance the permeability because most of the numerous natural fractures that crosscut the granite body were sealed by secondary minerals that crystallized as an effect of the circulation of local hot brines. The deep‐seated granitic reservoir is located between 4,500 and 5,000 m depths. Hydraulic stimulations were conducted in the four deep wells (GPK1, GPK2, GPK3, and GPK4) inducing different microseismic event patterns, which cannot be explained by tectonic structures alone. In the present work, we provide a review of the hydraulic tests and reinterpret them in the light of mineralogical data obtained along the boreholes. A clear relationship appears between mineralogy (mainly clay and calcite content) and the petrophysical, mechanical, and hydraulic behaviors of the rock mass. High calcite contents are correlated with an abundance of clay minerals, low Young's modulus, low magnetic susceptibility, and variation in spectral gamma ray. Microearthquakes are generated in the fresh granite zones, while clay and calcite‐rich zones, linked with hydrothermal alteration, might behave aseismically during hydraulic stimulations. These findings highlight the importance of a detailed knowledge of the petrography of a reservoir to conduct an effective stimulation while keeping the seismic hazard at a minimum.

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“…MD: measured depth; when boreholes are inclined, it is different from true vertical depth (TVD). After Dorbath et al () and references therein.…”

Section: The Soultz Reservoir: Review Of Geology Tectonic Setting Hmentioning

confidence: 99%

Section: The Soultz Reservoir: Review Of Geology Tectonic Setting Hmentioning

confidence: 99%

Is There a Link Between Mineralogy, Petrophysics, and the Hydraulic and Seismic Behaviors of the Soultz‐sous‐Forêts Granite During Stimulation? A Review and Reinterpretation of Petro‐Hydromechanical Data Toward a Better Understanding of Induced Seismicity and Fluid Flow

Meller

Ledésert

2017

JGR Solid Earth

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“…, 2008). Fracturing induced by high pressure fluids injected into deep boreholes (Dorbath et al. , 2010) and also reservoir‐induced seismicity (El Hariri et al , 2010) and seasonal variations in seismicity due to natural piezometric (Christiansen et al.…”

mentioning

confidence: 99%

The fracture permeability of Hard Rock Aquifers is due neither to tectonics, nor to unloading, but to weathering processes

Lachassagne

Wyns

Dewandel³

2011

Terra Nova

201

152

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Terra Nova, 23, 145–161, 2011 Abstract The hydrogeology of superficial (∼0–100 m b.g.l.) Hard Rock Aquifers (HRA; i.e. plutonic and metamorphic rocks) has so far been dominated by a few concepts considered to be relevant by a large majority of the HRA community. One of the most fundamental of these concepts is that their (secondary, fissure/fracture) permeability is either of tectonic origin or related to unloading processes. We will show that these genetic concepts are erroneous. We will demonstrate how the hydraulic conductivity of HRAs is a consequence of the (palaeo) weathering processes, with a stratiform fissured layer located immediately below the unconsolidated saprolite and, to a lesser extent, a verticalized fissured layer at the periphery of (or within) pre‐existing discontinuities (veins, joints, ancient faults, lithological contacts, etc.). This result opens up large perspectives in terms of applied hydrogeology and applied geology. A specifically dedicated methodological toolkit well adapted to the operational survey, management and protection of HRAs is briefly presented.

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“…This direction is roughly parallel to the maximum horizontal stress orientation estimated to be 158°by Dorbath et al (2010) from the inversion of well-constrained focal mechanisms.…”

Section: Shear-wave Splittingmentioning

confidence: 70%

Crack Features and Shear-Wave Splitting Associated with Fracture Extension during Hydraulic Stimulation of the Geothermal Reservoir in Soultz-sous-Forêts

Adelinet

Dorbath

Calò

et al. 2015

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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-The recent tomography results obtained within the scope of the Enhanced Geothermal System (EGS) European Soultz project led us to revisit the meso-fracturing properties of Soultz test site. In this paper, we develop a novel approach coupling effective medium modeling and shear-wave splitting to characterize the evolution of crack properties throughout the hydraulic stimulation process. The stimulation experiment performed in 2000 consisted of 3 successive injection steps spanning over 6 days. An accurate 4-D tomographic image was first carried out based upon the travel-times measured for the induced seismicity [Calò M., Dorbath C., Cornet F.H., Cuenot N. (2011) Large-scale aseismic motion identified through 4-D P-wave tomography, Geophys. J. Int. 186, 1295Int. 186, -1314. The current study shows how to take advantage of the resulting compressional wave (Calò et al., 2011) and shear-wave velocity models. These are given as input data to an anisotropic effective medium model and converted into crack properties. In short, the effective medium model aims to estimate the impact of cracks on velocities. It refers to a crack-free matrix and 2 families of penny-shaped cracks with orientations in agreement with the main observed geological features: North-South strike and dip of 65°East and 65°West [Genter A., Traineau H. (1996) Analysis of macroscopic fractures in granite in the HDR geothermal well EPS-1, Soultz-sousForêts, France, J. Vol. Geoth. Res. 72, 121-141], respectively. The resulting output data are the spatial distributions of crack features (lengths and apertures) within the 3-D geological formation. We point out that a flow rate increase results in a crack shortening in the area imaged by both compressional and shear waves, especially in the upper part of the reservoir. Conversely, the crack length, estimated during continuous injection rate phases, is higher than during the increasing injection rate phases. A possible explanation for this is that cracks remain large because the system has time to relax. We also calculate the extension and opening rates during all hydraulic stimulation sets. While the opening rate is unchanged, the extension rate varies depending on the stimulation phase. It is also shown to be higher around and above the open-hole section than below. This can indicate a potential upward path that makes fluid percolation easier within the granite formation, this path being induced by the temperature gradient. We also compare the evolution of crack extension during injection with shear-wave splitting. Split shear waves were recorded at 2 stations during hydraulic stimulation and processed in terms of splitting parameters. The fast shear-wave polarization remains constant and parallel to the maximum horizontal stress orientation while the amplitude of splitting varies with time. We observe a good agreement between travel-time differences and crack extension rates during the first 4 days of the stimulation experiment. Afterwards, these two parameters depart from each other. This stud...

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The stress field at Soultz-sous-Forêts from focal mechanisms of induced seismic events: Cases of the wells GPK2 and GPK3

Cited by 27 publications

References 10 publications

Is There a Link Between Mineralogy, Petrophysics, and the Hydraulic and Seismic Behaviors of the Soultz‐sous‐Forêts Granite During Stimulation? A Review and Reinterpretation of Petro‐Hydromechanical Data Toward a Better Understanding of Induced Seismicity and Fluid Flow

Is There a Link Between Mineralogy, Petrophysics, and the Hydraulic and Seismic Behaviors of the Soultz‐sous‐Forêts Granite During Stimulation? A Review and Reinterpretation of Petro‐Hydromechanical Data Toward a Better Understanding of Induced Seismicity and Fluid Flow

The fracture permeability of Hard Rock Aquifers is due neither to tectonics, nor to unloading, but to weathering processes

Crack Features and Shear-Wave Splitting Associated with Fracture Extension during Hydraulic Stimulation of the Geothermal Reservoir in Soultz-sous-Forêts

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