Permeable fracture zones in the hard rocks of the geothermal reservoir at Rittershoffen, France

Vidal, Jeanne; Genter, Albert; Chopin, Francis

doi:10.1002/2017jb014331

Cited by 56 publications

(29 citation statements)

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“…Certain facies types such as reef or reef detritus become less relevant for reservoir production while compaction and diagenesis come to control permeability variability with depth (Mraz et al 2019). The transmissivity data from the deepest geothermal well in the Molasse Basin, the well Geretsried GEN-1ST-A1 at 4.7 km depth, suggest that only faults and fractures constitute flow zones in tight rock, comparable with EGS sites in granite rock like Soultz (Kosack et al, 2011) and Rittershoffen (Vidal et al, 2017), although the Uppermost Jurassic (Kimmeridgian) contains reef detritus (Mraz et al, 2019).…”

Section: Discussionmentioning

confidence: 95%

Geothermal play typing in Germany, case study Molasse Basin: a modern concept to categorise geothermal resources related to crustal permeability

Moeck

Dussel

Weber

et al. 2019

Netherlands Journal of Geosciences

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The majority of running geothermal plants worldwide are located in geological settings with convection- or advection-dominant heat transport. In Germany as in most regions in Europe, conduction is the dominating heat transport mechanism, with a resulting average geothermal gradient. The geothermal play type concept is a modern methodology to group geothermal resources according to their geological setting, and characteristic heat transport mechanisms. In particular, the quantity of heat transport is related to fluid flow in natural or engineered geothermal reservoirs. Hence, the permeability structure is a key element for geothermal play typing. Following the existing geothermal play type catalogue, four major geothermal play types can be identified for Germany: intracratonic basins, foreland basins and basement/crystalline rock provinces as conduction-dominated play types, and extensional terrains as the convection-dominated play type. The installed capacity of geothermal facilities sums up to 397.1 MWth by the end of 2018. District heating plants accounted for the largest portion, with about 337.0 MWth. The majority of these installations are located in the play type ‘foreland basin’, namely the Molasse Basin in southern Germany. The stratigraphic unit for geothermal use is the Upper Jurassic, also known as ‘Malm’ formation, a carbonate reservoir with high variability in porosity and permeability. Recently drilled wells in the southernmost Molasse Basin indicate the Upper Jurassic as a tight, fracture-controlled reservoir, not usable for conventional hydrothermal well doublets. Our new data compilation including the recently drilled deep geothermal well Geretsried reveals the relation of porosity and permeability to depth. The results suggest that obviously diagenetic processes control permeability with depth in carbonate rock, diminishing the predictability of reservoir porosity and permeability. The play type concept helps to delineate these property variations in play type levels because it is based on geological constraints, common for exploration geology. Following the general idea of play typing, the results from this play analysis can be transferred to geological analogues as carbonate rock play levels in varying depth.

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Section: Discussionmentioning

confidence: 95%

Geothermal play typing in Germany, case study Molasse Basin: a modern concept to categorise geothermal resources related to crustal permeability

Moeck

Dussel

Weber

et al. 2019

Netherlands Journal of Geosciences

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“…Ledésert et al 1996;Aquilina et al 1997) and as a heat-exchanger, the majority of studies aimed at assessing or quantifying the permeability at the geothermal sites at Soultz-sous-Forêts and Rittershoffen, for example, have focussed on the granite basement (e.g. Genter and Traineau 1996;Shapiro et al 1999;Sausse et al 2006;Dezayes et al 2010;Ledésert et al 2010;Vogt et al 2012a, b;Vidal et al 2017). Few studies, especially laboratory studies that offer values of porosity and permeability, have targeted the overlying Permo-Triassic sedimentary units (e.g.…”

Section: Introductionmentioning

confidence: 99%

Microstructural and petrophysical properties of the Permo-Triassic sandstones (Buntsandstein) from the Soultz-sous-Forêts geothermal site (France)

et al. 2017

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Geothermal projects in the Upper Rhine Graben aim to harness thermal anomalies that have arisen due to hydrothermal circulation within the granitic basement and the overlying Permo-Triassic sedimentary units. We present here a systematic microstructural, mineralogical, and petrophysical characterisation of the lowermost unit of this Permo-Triassic sedimentary succession-the Buntsandstein-sampled from exploration well EPS-1 at the Soultz-sous-Forêts geothermal site (France). Twelve depths were sampled (from 1008 to 1414 m) and cylindrical cores were prepared perpendicular and parallel to bedding. These cores were described in terms of their microstructure, grain size and shape, specific surface area, pore size and pore throat size distribution, mineral content, porosity, P-wave velocity, and permeability. The Buntsandstein sandstones are predominantly feldspathic sandstones, often characterised by pores filled or partially filled (with clays (R3 illite-smectite), dolomite, siderite, and barite) as a consequence of diagenesis, tectonics, and the circulation of hydrothermal fluids. The porosity, dry P-wave velocity, and permeability of these sandstones vary from ~ 0.03 to 0.2, ~ 2.5 to 4.5 km s −1 , and ~ 10 −18 to 10 −13 m 2 , respectively. Our data show that P-wave velocity decreases and permeability increases as porosity increases. P-wave velocities are significantly higher when measured parallel to bedding (by about 10 to 25%), and that saturation with water increases P-wave velocity (by about 5 to 50%, depending on sample orientation). The pervasive pore-filling precipitation has significantly reduced the permeabilities of the Buntsandstein sandstones, which are orders of magnitude less permeable than similarly porous unaltered sandstone. We also find that their permeability can be up to an order of magnitude more permeable when measured parallel to bedding than perpendicular to bedding. Although Buntsandstein units with low matrix permeabilities (as low as ~ 10 −18 m 2 ) require macroscopic fractures to attain the high permeability required to sustain regional hydrothermal circulation, matrix permeability is important for units with low fracture densities and high matrix permeabilities. We anticipate that these data will aid future fluid flow modelling and seismic investigations at geothermal sites within the Upper Rhine Graben. Open Access© The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/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.

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“…2, 8). In GRT-2, temperature anomalies are consistently linked to the occurrence of permeable fracture zones, but they can extend spatially from 3 to 24 m in depth (MD) and vary from + 2 to − 3 °C (Baujard et al 2017a;Vidal et al 2017). In addition, there is an evident correlation among the lengths of a temperature anomaly, the fractured zone sampled with the caliper and the resistivity anomaly zone in the electrical logs.…”

Section: Resistivity Signature Of Permeable Fracture Zonesmentioning

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.

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Permeable fracture zones in the hard rocks of the geothermal reservoir at Rittershoffen, France

Cited by 56 publications

References 52 publications

Geothermal play typing in Germany, case study Molasse Basin: a modern concept to categorise geothermal resources related to crustal permeability

Geothermal play typing in Germany, case study Molasse Basin: a modern concept to categorise geothermal resources related to crustal permeability

Microstructural and petrophysical properties of the Permo-Triassic sandstones (Buntsandstein) from the Soultz-sous-Forêts geothermal site (France)

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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