Architecture, fracture system, mechanical properties and permeability structure of a fault zone in Lower Triassic sandstone, Upper Rhine Graben

Bauer, Johanna F.; Meier, Silke; Philipp, Sonja L.

doi:10.1016/j.tecto.2015.02.014

Cited by 58 publications

(34 citation statements)

References 47 publications

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“…The URG is part of a series of rifts in the "West European Palaeogene Rift System", which extends over 1000 km from Spain to the north of Holland into the North Sea (Illies 1967;Bergerat 1985;Brun and Wenzel 1991;Schumacher 2002;Ziegler and Dèzes 2005;Rotstein et al 2005;Edel et al 2007;Bauer et al 2015). The URG is located in north-eastern France (Fig.…”

Section: Geological Settingmentioning

confidence: 99%

New stratigraphic interpretation of the Soultz-sous-Forêts 30-year-old geothermal wells calibrated on the recent one from Rittershoffen (Upper Rhine Graben, France)

Aichholzer

Duringer

Orciani³

et al. 2016

Geotherm Energy

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The Soultz-sous-Forêts site (Alsace, France) is the first pilot geothermal project in the world that furnished the proof of concept of enhanced geothermal systems by producing energy from a deep-seated granite. The Alsace region, with its hundreds of previous drillings and seismic history related to both oil and potash exploitation, has been shown to have high subterranean temperatures. In the Soultz-sous-Forêts geothermal project, most attention has focused on the basement and the sedimentary cover/basement interface. Thus, the sedimentary portion of the well (approximately 1.4 km thick) has never been fully investigated. The only available data on the Soultzsous-Forêts sedimentary cover are from an old masterlog (GPK-1) with interpretations of the tops and bases of the main geological formations, and from some other less well-documented well logs (EPS-1 and GPK-2). The main challenge of this work is therefore to re-interpret the old well data to provide precise and detailed chronolithostratigraphic logs for GPK-1 and GPK-2, especially in their sedimentary portions. These new investigations of the GPK wells have been possible due to the new data collected in the recent geothermal wells at Rittershoffen (GRT-1 and GRT-2, located 6.5 km from Soultz-sous-Forêts), which are characterized by a quite complete stratigraphic succession. Both sites have been explored by deep drilling operations aiming to exploit the heat extracted from a deep granitic basement (Palaeozoic) covered by a stack of 1.4-and 2.2-km-thick sedimentary rocks (Mesozoic to Cenozoic) at Soultz-sous-Forêts and Rittershoffen, respectively. Thus, the Rittershoffen chrono-lithostratigraphic logs have been used as a baseline to interpret the sedimentary succession in GPK-1 and GPK-2. In conclusion, all the well logs are compared for stratigraphic comparisons. With approximately 1400 m of sedimentary cover at Soultz-sous-Forêts instead of 2200 m at Rittershoffen, the correlation between the two sites showed many differences exist in the sedimentary columns: layers missing due to erosion, lateral thickness variations in formations, and-above all-the occurrence of at least four major fracture zones affecting the units. In addition, a structural analysis was made to more precisely define the limits of the geological formations observed and to present more arguments for the presence of fracture zones or faults.

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Section: Geological Settingmentioning

confidence: 99%

New stratigraphic interpretation of the Soultz-sous-Forêts 30-year-old geothermal wells calibrated on the recent one from Rittershoffen (Upper Rhine Graben, France)

Aichholzer

Duringer

Orciani³

et al. 2016

Geotherm Energy

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“…In this way, damage evolution under various loading conditions was studied to investigate (1) changes in seismic velocity within a fault zone monitor before an earthquake [ Budiansky and O'Connell , ; Hadley , ], (2) acoustic emission associated with irreversible damage in rock subjected to cyclic loading and unloading (Kaiser effect) [ Hamiel et al ., ], (3) the development of the process zones, which is defined as a finite size region of high stress concentration at fault tip in which the intact rock is disintegrated and where the fault grows [ Katz and Reches , ], (4) the portion of elastic strain released during a seismic cycle [ Hamiel et al ., ], (5) the rotation of regional stress within the damage zone [ Faulkner et al ., ], and (6) the suitability of damage rheology models describing an earthquake cycle [ Alm et al ., ; Lyakhovsky et al ., ]. Laboratory experiments have also been done on rock samples taken along fault zones to investigate the role of mechanical heterogeneity on strain localization [ Heesakkers et al ., ] and the hydromechanical coupling within a fault zone [ Bauer et al ., ]. At the meter scale on outcrops with detailed structural description of fractures coupled to Schmidt hammer measurements to estimate the hydromechanical coupling within a fault zone [ Bauer et al ., ; Jeanne et al ., , ; Steer et al ., ] or in boreholes with geophysical logs to study seismic wave propagation within a fault zone [ Isaacs et al ., ]. At the kilometer scale (1) through the modeling of geodetic data where the rigidity of a compliant zone was determined to evaluate changes in the stress field induced by nearby earthquakes [ Fialko , ; Jolivet et al ., ] and to infer slip rate and locking depth [ Hamiel and Fialko , ] or (2) using seismic travel times, trapped waves, and interferometric synthetic aperture radar observations to estimate the fault zone width [ Cochran et al ., ]. In this last case the authors documented a 65% of reduction in shear moduli within the fault zone.…”

Section: Introductionmentioning

confidence: 99%

“…In this way, damage evolution under various loading conditions was studied to investigate (1) changes in seismic velocity within a fault zone monitor before an earthquake [Budiansky and O'Connell, 1976;Hadley, unloading (Kaiser effect) [Hamiel et al, 2004], (3) the development of the process zones, which is defined as a finite size region of high stress concentration at fault tip in which the intact rock is disintegrated and where the fault grows [Katz and Reches, 2004], (4) the portion of elastic strain released during a seismic cycle [Hamiel et al, 2006], (5) the rotation of regional stress within the damage zone [Faulkner et al, 2006], and (6) the suitability of damage rheology models describing an earthquake cycle [Alm et al, 1985;Lyakhovsky et al, 1997]. Laboratory experiments have also been done on rock samples taken along fault zones to investigate the role of mechanical heterogeneity on strain localization [Heesakkers et al, 2011] and the hydromechanical coupling within a fault zone [Bauer et al, 2015]. 2.…”

Section: Introductionmentioning

confidence: 99%

Field characterization of elastic properties across a fault zone reactivated by fluid injection

et al. 2017

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We studied the elastic properties of a fault zone intersecting the Opalinus Clay formation at 300 m depth in the Mont Terri Underground Research Laboratory (Switzerland). Four controlled water injection experiments were performed in borehole straddle intervals set at successive locations across the fault zone. A three‐component displacement sensor, which allowed capturing the borehole wall movements during injection, was used to estimate the elastic properties of representative locations across the fault zone, from the host rock to the damage zone to the fault core. Young's moduli were estimated by both an analytical approach and numerical finite difference modeling. Results show a decrease in Young's modulus from the host rock to the damage zone by a factor of 5 and from the damage zone to the fault core by a factor of 2. In the host rock, our results are in reasonable agreement with laboratory data showing a strong elastic anisotropy characterized by the direction of the plane of isotropy parallel to the laminar structure of the shale formation. In the fault zone, strong rotations of the direction of anisotropy can be observed. The plane of isotropy can be oriented either parallel to bedding (when few discontinuities are present), parallel to the direction of the main fracture family intersecting the zone, and possibly oriented parallel or perpendicular to the fractures critically oriented for shear reactivation (when repeated past rupture along this plane has created a zone).

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“…In a volcanic geothermal context, fault zones are also main pathways for fluids (Gailler et al 2014;Gudmundsson et al 2002). Fault zones have also been widely studied in outcrops for geothermal applications (Bauer et al 2015) or at the well or basin scale for oil and gas exploration in sedimentary formations. Deep fracture zones in crystalline rocks have been largely studied with laboratory experiments (Griffiths et al 2016).…”

Section: Introductionmentioning

confidence: 99%

How do the geological and geophysical signatures of permeable fractures in granitic basement evolve after long periods of natural circulation? Insights from the Rittershoffen geothermal wells (France)

Glaas

Genter²,

Girard

et al. 2018

Geotherm Energy

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Two deep wells were drilled at Rittershoffen (Alsace, France) to produce high-temperature fluids to supply heat to a biorefinery. The GRT-2 production well was drilled to a depth of 3196 m MD and was deviated to target a permeable local fault in the granitic basement buried beneath a thick sedimentary cover. The objective of this study is to better understand the permeability of fractured reservoirs within crystalline rocks, focusing on the production well GRT-2. Based on a petrographic and mineralogical analysis of cutting samples, several granitic facies associated with hydrothermal alteration were identified on the basis of the amounts of illite, chlorite, anhydrite, secondary geodic quartz, and oxides. These observations were correlated with various geological and geophysical datasets (gamma ray, porosity, density, electrical resistivity, caliper, borehole image logs, temperature, rate of penetration, and mud losses) to localize and identify permeable fracture zones. In sections where acoustic image logs were not available, such as in the deepest part of the well, the geometries of the fracture zones were interpreted from an oriented caliper log. The caliper log interpretation detected one-third of the fractures detected by acoustic image logs. However, two major fracture sets striking N-S and dipping eastward or westward were observed. Furthermore, a synthetic resistivity log that fits the measured resistivity log relatively well was built using the Archie and Waxman and Smits models. This approach is a proxy for estimating the porosity and the mineralogical changes based on the cation exchange capacity, which is controlled by the chlorite/illite ratio, derived from electrical logs in granitic formations. The correlation of all these results allowed the identification of a resistivity signature of a permeable fracture zone that spatially fits with the temperature signature. The major contribution of this study is the identification of a hierarchy of permeable fractures based on petrophysical signatures. The geophysical signature of fracture zones with low residual permeability exhibits a broad depth extent, whereas the geophysical signature of a highly permeable fracture zone is more localized. Past hydrothermal circulation has enlarged the altered and porous zones around open Open Access© The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

show abstract

Architecture, fracture system, mechanical properties and permeability structure of a fault zone in Lower Triassic sandstone, Upper Rhine Graben

Cited by 58 publications

References 47 publications

New stratigraphic interpretation of the Soultz-sous-Forêts 30-year-old geothermal wells calibrated on the recent one from Rittershoffen (Upper Rhine Graben, France)

New stratigraphic interpretation of the Soultz-sous-Forêts 30-year-old geothermal wells calibrated on the recent one from Rittershoffen (Upper Rhine Graben, France)

Field characterization of elastic properties across a fault zone reactivated by fluid injection

How do the geological and geophysical signatures of permeable fractures in granitic basement evolve after long periods of natural circulation? Insights from the Rittershoffen geothermal wells (France)

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