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Microstructural and petrophysical properties of the Permo-Triassic sandstones (Buntsandstein) from the Soultz-sous-Forêts geothermal site (France)
- Source :
- Geothermal Energy, Vol 5, Iss 1, Pp 1-37 (2017), Geothermal Energy, Geothermal Energy, Springer, 2017, 5 (1), ⟨10.1186/s40517-017-0085-9⟩, Geothermal energy, 2017, Vol.5(1), pp.26 [Peer Reviewed Journal]
- Publication Year :
- 2017
- Publisher :
- SpringerOpen, 2017.
-
Abstract
- International audience; 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 m2, 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 m2) 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.
- Subjects :
- 010504 meteorology & atmospheric sciences
Bedding
Renewable Energy, Sustainability and the Environment
[SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]
Petrophysics
lcsh:TJ807-830
lcsh:QE1-996.5
lcsh:Renewable energy sources
Mineralogy
15. Life on land
010502 geochemistry & geophysics
Geotechnical Engineering and Engineering Geology
01 natural sciences
Diagenesis
Graben
lcsh:Geology
Siderite
chemistry.chemical_compound
Permeability (earth sciences)
chemistry
Economic Geology
Sedimentary rock
Geothermal gradient
Geology
0105 earth and related environmental sciences
Subjects
Details
- Language :
- English
- ISSN :
- 21959706
- Volume :
- 5
- Issue :
- 1
- Database :
- OpenAIRE
- Journal :
- Geothermal Energy
- Accession number :
- edsair.doi.dedup.....c9e8098812ec04c63cfb3195d1ea95ef