Detailed descriptions of the lower-middle Triassic and Permian formations using cores and gamma-rays from the EPS-1 exploration geothermal borehole (Soultz-sous-Forêts, Upper Rhine Graben, France)

AbstractIn the 1950s, a petroleum well in Soultz-sous-Forêts (no 4589; Upper Rhine Graben, France) reached the Lettenkohle (Triassic) at 830 m depth. During the exploration phase at Soultz-sous-Forêts, the first enhanced geothermal system pilot project in the world, the well was core-deepened up to 2227 m into the granitic basement (then renamed EPS-1). The objectives of this deeper well were (i) to explore the granitic fractured reservoir and (ii) provide a precise geological characterization of the Soultz-sous-Forêts horst. This paper presents the first complete core analysis of the sedimentary formations observed in the EPS-1 cores (from the middle Muschelkalk to the Permian) in conjunction with the gamma-ray log description and field works. The detailed descriptions of the geological formations encountered in the well are presented with photo boards displaying the most characteristic facies of each formation, since the wells are rarely cored, especially in the Muschelkalk. This study also aims to describe the gamma-ray log to provide a strong baseline for future geothermal well exploration in this area (or old well reinterpretations). At this time, it is the only available reference for the complete section: Muschelkalk to Permian sedimentary formations.

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The complete lithostratigraphic section of the geothermal wells in Rittershoffen (Upper Rhine Graben, eastern France): a key for future geothermal wells

BSGF - Earth Sciences Bulletin ◽

10.1051/bsgf/2019012 ◽

2019 ◽

Vol 190 ◽

pp. 13 ◽

Cited By ~ 3

Author(s):

Philippe Duringer ◽

Coralie Aichholzer ◽

Sergio Orciani ◽

Albert Genter

Keyword(s):

Middle Jurassic ◽

Gamma Ray ◽

Upper Jurassic ◽

Upper Permian ◽

Upper Rhine Graben ◽

Rhine Graben ◽

Geothermal Wells ◽

The Subject ◽

Upper Rhine

Between 2012 and 2014, in Rittershoffen, in the Upper Rhine Graben, two geothermal boreholes (GRT-1 and GRT-2) reached the granitic basement at a depth of around 2150 m. The wells crossed about 1160 m of Cenozoic and 1050 m of Mesozoic. In the Cenozoic, these wells crossed the greatest part of the Eocene, the lower part of the Oligocene and a thinner Pliocene. The Quaternary is poorly represented (less than 10 m). In the Mesozoic, the wells crossed the Lower Dogger, the entire Lias and the entire Triassic. A reduced thickness of about 50 m of Upper Permian terminates the sedimentary column before entering into the granitic basement. A major erosional unconformity separates the Middle Jurassic from the Tertiary units (the Upper Jurassic, entire Cretaceous and Paleocene are absent). The Rittershoffen drilled doublets were the subject of particular attention concerning the acquisition of a very precise stratigraphic profile. In this paper, we give the recognition criteria for the fifty-seven formations crossed by the GRT-1 well and their upper and lower boundaries as well as their specific gamma ray signatures. The data are presented in four figures: a general complete log displaying the main sets and three detailed, precise logs showing the sedimentary formations overhanging the granitic basement: the Tertiary, the Jurassic, the Triassic, the Permian and the basement.

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Preliminary studies for an integrated assessment of the hydrothermal potential of the Pechelbronn Group in the northern Upper Rhine Graben

Advances in Geosciences ◽

10.5194/adgeo-45-251-2018 ◽

2018 ◽

Vol 45 ◽

pp. 251-258 ◽

Cited By ~ 2

Author(s):

Meike Hintze ◽

Barbara Plasse ◽

Kristian Bär ◽

Ingo Sass

Keyword(s):

Gamma Ray ◽

Joint Inversion ◽

Tectonic Setting ◽

Rock Properties ◽

Upper Rhine Graben ◽

Petrophysical Parameters ◽

Core Samples ◽

Rhine Graben ◽

Model Unit ◽

Upper Rhine

Abstract. The northern Upper Rhine Graben is due to its tectonic setting and the positive geothermal anomaly a key region for geothermal heat and power production in Europe. In this area the Upper Eocene to Lower Oligocene Pechelbronn Group reaches depths of up to 2800 m with temperatures of locally more than 130 ∘C. In order to assess the hydrothermal potential of the Pechelbronn Group a large dataset is compiled and evaluated. Petrophysical parameters are measured on core samples of eight boreholes (courtesy of Exxon Mobil). Additionally, 15 gamma-ray logs, 99 lithology logs as well as more than 2500 porosity and permeability measurements on cores of some of these boreholes are available. The Lower Pechelbronn Beds are composed of fluvial to lacustrine sediments, the Middle Pechelbronn Beds were deposited in a brackish to marine environment and the Upper Pechelbronn Beds consist of fluvial/alluvial to marine deposits. In between the western and eastern masterfaults of the Upper Rhine Graben several fault blocks exist, with fault orientation being sub-parallel to the graben shoulders. During the syntectonic deposition of the Pechelbronn Group these fault blocks acted as isolated depocenters, resulting in considerable thickness and depositional facies variations on the regional and local scale (few tens to several hundreds of meters). Laboratory measurements of sonic wave velocity, density, porosity, permeability, thermal conductivity and diffusivity are conducted on the core samples that are classified into lithofacies groups. Statistically evaluated petrophysical parameters are assigned to each group. The gamma-ray logs serve to verify the lithological classification and can further be used for correlation analysis or joint inversion with the petrophysical data. Well data, seismic sections, isolines and geological profiles are used to construct a geological 3-D model. It is planned to use the petrophysical, thermal and hydraulic rock properties at a later stage to parametrize the model unit and to determine, together with the temperature and thickness of the model unit, the expected flow rates and reservoir temperatures and thus the hydrothermal potential.

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How Can Deep Geothermal Projects Provide Information on the Temperature Distribution in the Upper Rhine Graben? The Example of the Soultz-Sous-Forêts-Enhanced Geothermal System

Geosciences ◽

10.3390/geosciences10110459 ◽

2020 ◽

Vol 10 (11) ◽

pp. 459

Author(s):

Béatrice A. Ledésert ◽

Ronan L. Hébert

Keyword(s):

Temperature Distribution ◽

Source Rocks ◽

Geothermal System ◽

Upper Rhine Graben ◽

Fluid Temperature ◽

Thermal Anomalies ◽

Rhine Graben ◽

Mature Type ◽

Oil Source ◽

Upper Rhine

The Upper Rhine Graben (URG) hosts thermal anomalies that account for the development of oil fields. Recently, a geothermal power plant has been installed in this area. Data obtained in this framework provide an insight into the temperature distribution in the URG. The present thermal gradient at Soultz-sous-Forêts is not linear: nearly 90 °C/km down to 1400 m depth, then about 12 °C/km from that depth down to 5000 m. The combination of temperature conditions and natural fluid circulation in fracture networks has led to the hydrothermal alteration of the granite into mineral assemblages such as those including illite, quartz and calcite. Illite is locally impregnated with organic matter of two kinds: a mature type derived from oil source rocks and a less mature type derived from surficial sedimentary layers indicating the km-scale of transfer. Newly formed crystals of quartz and calcite from around 2000 m depth record a fluid temperature range of 130 to 170 °C, consistent with modelling and the temperatures measured at present in the drill-holes at this depth. In such hydrothermally altered zones, local variations of temperature are encountered indicating current fluid flows that are being sought for geothermal purposes.

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Fracture reactivation for permeability enhancement in geothermal systems

10.5194/egusphere-egu2020-7273 ◽

2020 ◽

Author(s):

Alexandra Kushnir ◽

Michael Heap ◽

Patrick Baud ◽

Thierry Reuschlé

Keyword(s):

Initial Permeability ◽

Natural Fracture ◽

Geothermal System ◽

Upper Rhine Graben ◽

Geothermal Systems ◽

Permeability Enhancement ◽

Rhine Graben ◽

Angle Fracture ◽

Fracture Reactivation ◽

Upper Rhine

While the deep granitic basement in the Upper Rhine Graben is currently being exploited as a geothermal reservoir at numerous geothermal sites, the Permo-Triassic sandstones that lie directly above the granite are critical to continued regional hydrothermal convection. Here we investigate the propensity for variably sealed fractures to be reactivated during deformation and the role this fracture reactivation plays on permeability enhancement in geothermal reservoirs. We source un-fractured, bedded sandstones and the same bedded sandstones containing a single, variably-sealed fracture from a 400 m-thick unit of Permo-Triassic sandstone sampled from the EPS-1 exploration well near Soultz-sous-For&#234;ts (France) in the Upper Rhine Graben.31 cylindrical samples (20 mm in diameter and 40 mm long) were cored such that their dominant structural feature (i.e. bedding or natural fracture) was oriented parallel, perpendicular, or at 30&#176; to the sample axis. The initial permeability of the un-fractured samples ranged between 2.5&#215;10-17 and 5.6&#215;10-16 m2 and between 3.6&#215;10-16 and 3.3&#215;10-14 m2 for naturally fractured samples. In un-fractured samples, permeability decreases as a function of increased bedding angle; fracture orientation, however, does not appear to have a discernable influence on permeability. Samples were water-saturated and deformed until failure under pressure conditions appropriate to the Soultz-sous-For&#234;ts geothermal system - Peff of 14.5 MPa - and at a strain rate of 10-6 s-1. All samples developed through-going shear fractures, however, only in samples containing partially sealed fractures did the experimentally produced fractures take advantage of the pre-existing features. In samples containing a fully-sealed fracture, the experimentally induced fracture developed in a previously undeformed part of the sandstone matrix. Further, post-deformation permeability measurements indicate that while sample permeability increased by up to one order of magnitude for a given sample, this increase is generally independent of feature orientation.Therefore, formations containing sealed fractures may not necessarily be weaker and, as a consequence, may not be more apt to significant permeability increases during stimulation than un-fractured formations. These data can contribute to the development and optimization of stimulation techniques used in the Upper Rhine Graben.

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