Geothermal implications for fracture-filling hydrothermal precipitation

Griffiths, Luke; Heap, Michael; Wang, F.; Daval, Damien; Gilg, H. Albert; Baud, Patrick; Schmittbuhl, Jean; Genter, Albert

doi:10.1016/j.geothermics.2016.06.006

Cited by 58 publications

(56 citation statements)

References 33 publications

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“…12). Our permeability data are in agreement with recently published permeability data for Buntsandstein sandstones from EPS-1 (Griffiths et al 2016;Fig. 17).…”

Section: Matrix Permeability Of the Buntsandsteinsupporting

confidence: 92%

“…17). However, we highlight that permeability measurements of the EPS-1 cores performed using a TinyPerm II field permeameter suggest that the permeability of the Buntsandstein varies from ~ 10 −15 to ~ 10 −12 m 2 (Haffen et al 2013), much higher than the values measured herein and by Griffiths et al (2016). We note that the lowest permeability measurable using the TinyPerm II is 6.92 × 10 −16 m 2 (Farquharson et al 2015), highlighting that the TinyPerm II field permeameter may not be an appropriate tool for measuring the permeability of several units of the Buntsandstein, especially the Voltzia, Annweiler, and Anté-Annweiler units (Fig.…”

Section: Matrix Permeability Of the Buntsandsteincontrasting

confidence: 64%

“…For example, Haffen et al (2013) estimated the permeability of the Buntsandstein sandstones of EPS-1 using a portable TinyPerm II permeameter and found that their permeability ranges from 10 −15 to 10 −13 m 2 . However, the laboratory measurements of Griffiths et al (2016) highlight that the permeability of Buntsandstein sandstones from EPS-1 can be lower than 10 −18 m 2 .…”

Section: Introductionmentioning

confidence: 96%

“…Few studies, especially laboratory studies that offer values of porosity and permeability, have targeted the overlying Permo-Triassic sedimentary units (e.g. Haffen et al 2013;Stober and Bucher 2015;Vidal et al 2015;Griffiths et al 2016). For example, Haffen et al (2013) estimated the permeability of the Buntsandstein sandstones of EPS-1 using a portable TinyPerm II permeameter and found that their permeability ranges from 10 −15 to 10 −13 m 2 .…”

Section: Introductionmentioning

confidence: 99%

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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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“…12). Our permeability data are in agreement with recently published permeability data for Buntsandstein sandstones from EPS-1 (Griffiths et al 2016;Fig. 17).…”

Section: Matrix Permeability Of the Buntsandsteinsupporting

confidence: 92%

Section: Matrix Permeability Of the Buntsandsteincontrasting

confidence: 64%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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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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“…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). However, integrated field examples are lacking (Faulkner et al 2010).…”

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.

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

Vidal

Genter²,

Chopin

2017

JGR Solid Earth

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Fluid circulation in zones of fractures are a key challenge to exploit deep geothermal heat from natural reservoir. At Rittershoffen (Upper Rhine Graben, France), two geothermal boreholes, GRT‐1 and GRT‐2, were drilled in 2012 and 2014, respectively. They targeted the local Rittershoffen normal fault, which strikes N‐S and dips westward. In this study, major natural fractures were observed in the open holes of both wells from acoustic image logs correlated with other standard geophysical logs (gamma ray, neutron porosity, and caliper). Their permeability was evaluated at the borehole scale from temperature logs, mud losses, and gas surveys. One originally permeable (OP) fracture zone was observed in the granite of GRT‐1. In GRT‐2, four OP fracture zones were observed in the granite and two in sandstones. In GRT‐2, fracture zones are composed by several fluid pathways that could explain the higher natural permeability than in GRT‐1. All OP fractures are associated with positive temperature anomaly, interpreted as circulation of hot geothermal water through the permeable fracture, or negative one, interpreted as the cooling of a porous, altered and fractured zone around the permeable fracture after drilling operations. Permeability of natural fracture oriented N170° seems to be intimately linked to the secondary mineral deposits resulting from paleocirculations. The geometrical fracture model along the wellbore suggests that the inclined trajectory of GRT‐2 increases the connection between the borehole and the nearly vertical fracture network associated to the local fault. A good characterization of zones of fractures in a targeted natural reservoir allows an optimal exploitation of geothermal resource.

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Geothermal implications for fracture-filling hydrothermal precipitation

Cited by 58 publications

References 33 publications

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

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)

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

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