Characterisation and rock typing of deep geothermal reservoirs in the Greater Geneva Basin (Switzerland & France)

(1)

Thesis

Reference

Characterisation and rock typing of deep geothermal reservoirs in the Greater Geneva Basin (Switzerland & France)

RUSILLON, Elme

Abstract

A first reservoir assessment was performed in the Greater Geneva Basin to develop geothermal resources of low to medium enthalpy (GEothermie 2020 program). A review of the entire basin sedimentary sequence ranging from Permo-Carboniferous to Lower Cretaceous units was first carried out, using data from wells and outcrops. Five promising units were identified and investigated, considering stratigraphic, sedimentological and petrophysical issues. The distribution and geometry of potential reservoir bodies were addressed through the identification of facies and lateral variations, integrated to previous regional studies. The Upper Jurassic Reef Complex unit was highlighted as the best reservoir in the area. Research focussed on this interval, aiming at characterizing its petrophysical properties, and providing new insights on their origin and distribution within this reservoir. A rock typing workflow was built, which aimed at defining petrophysical rock types and propagating reservoir properties vertically along the wells, and subsequently horizontally through the subsurface.

RUSILLON, Elme. Characterisation and rock typing of deep geothermal reservoirs in the Greater Geneva Basin (Switzerland & France). Thèse de doctorat : Univ. Genève, 2017, no. Sc. 5196

DOI : 10.13097/archive-ouverte/unige:105286 URN : urn:nbn:ch:unige-1052863

Available at:

http://archive-ouverte.unige.ch/unige:105286

Disclaimer: layout of this document may differ from the published version.

1 / 1

(2)

TERRE & ENVIRONNEMENT

Section des sciences de la Terre et de l’environnement, Université de Genève

Département F.-A. Forel des sciences de l’environnement et de l’eau

Département des sciences de la Terre

Characterisation and Rock Typing of Deep Geothermal Reservoirs

in the Greater Geneva Basin

(Switzerland & France)

Elme RUSillon

2018

Volume 141

(3)

Déjà paru /already published :

Previous volumes are listed under

http ://www.unige.ch/sciences/terre/mineral/publications/ter_env.html

Vol. 109 (2012) F. Mermoud, J. Khoury, B. Lachal : Suivi énergétique du bâtiment 40-42 de l’avenue du Gros- Chêne à Onex (GE), rénové selon le standard MINERGIE®. Aspects techniques et économiques.

(137 pages). ISBN 978-2-940472-09-3

Commande à : Institut F.-A. Forel, 10 route de Suisse, 1290 Versoix (Suisse) ; 30.– CHF

Vol. 110 (2012) F. Boekhout : Geochronological constraints on the Paleozoic to Early Mesozoic geodynamic evolution of Southern Coastal Peru. (176 pages). ISBN 978-2-940472-10-9

Commande à : Département de Minéralogie, 13 rue des Maraîchers, 1205 Genève ; 50.– CHF

Vol. 111 (2012) M. J. Reitsma : Reconstructing the Late Paleozoic –Early Mesozoic plutonic and sedimentary record of South-East Peru : orphaned back-arcs along the western margin of Gondwana. (226 pages).

ISBN 978-2-940472-11-6

Commande à : Département de Minéralogie, 13 rue des Maraîchers, 1205 Genève ; 50.– CHF

Vol. 112 (2012) M. Ndiaye : Etude sismostratigraphique et sédimentologique du bassin sénégalo-mauritanien dans le secteur de Diourbel et Thiès. (175 pages). ISBN 978-2-940472-12-3

Commande à : Département de Géologie, 13 rue des Maraîchers, 1205 Genève ; 30.– CHF

Vol. 113 (2012) Y. Fuchey : Sédimentologie comparée de systèmes contouritiques fossiles (Ultrahelvétique inférieur des Préalpes externes) et actuels (Holocène du golfe de Cadix). (200 pages).

ISBN 978-2-940472-13-0

Commande à : Département de Géologie, 13 rue des Maraîchers, 1205 Genève ; 30.– CHF

Vol. 114 (Erratum: première version parue par erreur sous 108/first version printed by mistake as 108) (2012) V. Rosset: Biodiversité des mares et étangs: impact du réchauffement climatique et de l’eutrophisation.

(245 pages). ISBN 978-2-940472-15-4 (new)

Commande à : Institut F.-A. Forel, 10 route de Suisse, 1290 Versoix (Suisse); 30.- CHF

Vol. 115 (2013) C. Recasens Vargas: Diatoms as indicators of hydrologic and climatic changes in Laguna Potrok Aike, Patagonia (PASADO). (171 pages). ISBN 978-2-940472-16-1

Commande à : Département de Géologie, 13 rue des Maraîchers, 1205 Genève; 30.- CHF

Vol. 116 (2013) K. Tsunematsu : New Numerical Solutions for the Description of Volcanic Particle Dispersal.

(269 pages). ISBN 978-2-940472-17-8

Disponible sur : http://archive-ouverte.unige.ch – Available at: http://archive-ouverte.unige.ch Vol. 117 (2013) M. Pirouz : The geometry and sedimentary record of tectonics in the Neogene Zagros foreland

basin. (152 pages). ISBN 978-2-940472-18-5

Disponible sur : http://archive-ouverte.unige.ch – Available at: http://archive-ouverte.unige.ch Vol. 118 (2013) R. Cochrane : U-Pb thermochronology, geochronology and geochemistry of NW South

America : Rift to drift transition, active margin dynamics and implications for the volume balance of continents. (202 pages). ISBN 978-2-940472-19-2

Disponible sur : http://archive-ouverte.unige.ch – Available at: http://archive-ouverte.unige.ch Vol. 119 (2013) A. Vuillemin : Characterizing the Subsurface Biosphere in Laguna Potrok Aike Sediments

(Argentina) : A Case Study. (153 pages). ISBN 978-2-940472-20-8

Disponible sur : http://archive-ouverte.unige.ch – Available at: http://archive-ouverte.unige.ch Vol. 120 (2013) J. Mederer : Regional setting, geological context and genetic aspects of polymetallic

hydrothermal ore deposits from the Kapan ore district, southern Armenia: a contribution to the Mesozoic island arc metallogeny of the Lesser Caucasus. (161 pages). ISBN 978-2-940472-21-5 Disponible sur : http://archive-ouverte.unige.ch – Available at: http://archive-ouverte.unige.ch

Vol. 121 (2013) R. van der Lelij : Reconstructing North-Western Gondwana with Implications for the Evolution of the Iapetus and Rheic Oceans: a Geochronological, Thermochronological and Geochemical Study.

(221 pages). ISBN 978-2-940472-22-2

Disponible sur : http://archive-ouverte.unige.ch – Available at: http://archive-ouverte.unige.ch

→ Suite page III de couverture

(4)

UNIVERSITÉ DE GENÈVE

Section des Sciences de la Terre et de l’environnement

FACULTÉ DES SCIENCES Prof. Andrea Moscariello

Characterisation and Rock Typing of Deep Geothermal Reservoirs

in the Greater Geneva Basin

(Switzerland & France)

THÈSE

présentée à la Faculté des Sciences de l’Université de Genève pour obtenir le grade de Docteur ès Sciences,

mention Sciences de la Terre et de l’environnement

par Elme Rusillon

de

Genève (Suisse)

Thèse n^◦5196

GENÈVE

Atelier de reprographie ReproMail 2018

(5)

UNIVERSITE DE GENÈVE

f:ê{U tTH trEË Ë,ilikC§§

DOCTORAT ÈS SCIENCES, MENTION SCIENCES DE LATERRE

Thèse de Madame Elme RUSILLON

intitulée ^:

«Characterisation and Rock Typing of

Deep Geothermal Reservoirs in the Greater Geneva Basin

(Switzerland & France))»

La Faculté des sciences, sur

le

^préavis

de

Monsieur

A.

MOSCARIELLO, professeur

ordinaire et directeur de thèse

(Département

des sciences de la

Terre), Monsieur G. E. GORIN, professeur honoraire (Département des sciences de la Terre),

Monsieur

E.

SAMANKASSOU, docteur (Département

des

sciences

de Ia

Terre), Madame

C.

HOLLIS, docteure (North

Africa

Research Group,

The

University of Manchester, United Kingdom), Monsieur J. BORGOMANO, professeur (Centre Européen

de

Recherche

et

d'Enseignement des Géosciences

de

l'Environnement, Aix-Marseille Université, Marseille, France), autorise I'impression de la présente thèse, sans exprimer d'opinion sur les propositions qui y sont énoncées"

Genève, le 19 mars 2018

Thèse - 5196 -

.--\

^I

( _lû-^-

Le Doyen

La thèse doit porter la déclaration précédente et remplir les conditions énumérées dans les "lnformations relatives aux thèses de doctorat à I'Université de Genève""

N.B.

(6)

3

Abstract

Since 2013, the State of Geneva (Switzerland) has initiated a multistage program named GEothermie 2020, which aims at developing the geothermal energy resources of the trans- border (Swiss-French) Greater Geneva basin (GGB). In order to assess the potential of medium to deep reservoirs, a review of the entire basin sedimentary sequence ranging from Permo-Carboniferous to Lower Cretaceous units has been carried out. Five promising units have been identified, and have been thoroughly investigated for reservoir assessment in the present study, considering stratigraphic, sedimentological and petrophysical issues.

The reservoir assessment has first consisted in describing both depositional and petrophysical characteristics of the sedimentary units ranging from the Permo-Carboniferous to the Lower Cretaceous. The material used includes both data from wells and outcrops: reports, cores and core samples (plugs, slices and cuttings), well logs and field rock samples (pieces and plugs). Microfacies and cathodoluminescence analyses have been performed on thin sections. Porosity, permeability and grain density have been measured on plug samples, and similar petrophysical measurements available in well reports have also been supple- mented to the database. In addition, modal mineralogy using Quantitative Evaluation of Mineral by SCANning electron microscopy (QEMSCAN) technology has been carried out, as well as P- and S-wave velocity measurements on selected samples. Finally, the pore network has been further investigated with Scanning Electron Microscopy (SEM) images, and Mercury Injection Capillary Pressure (MICP) measurements.

In order to apprehend vertically the entire sedimentary succession of the GGB, a selected, representative well, Humilly-2, has been thoroughly investigated. Existing data have been summarized and homogenized, and this background information has been completed with new measurements, in order to build a consistent and usable dataset for further integrated basin analysis. This full investigation provides calibration of vertical variations along the longest sedimentary subsurface record found in the GGB including lithology, log signature, facies and reservoir properties.

The distribution and geometry of potential reservoir bodies have then been addressed through the identification of facies and lateral variations identified on new outcrops and subsurface well data, integrated to previous regional studies (work co-authored with Maud Brentini). This information has been homogenized in a coherent stratigraphic framework at the basin scale, and represented with conceptual models of depositional environment developed during selected Mesozoic time. Structural aspects derived from 2D seismic data have also provided key constraints for facies distribution and unit thickness variations across

(7)

4

the basin (Clerc, in prep.). These integrated sedimentological observations have allowed the definition of a synthetic stratigraphic cross-section for the GGB, updated according to currently used regional nomenclature and age boundaries. In suitable units, correlations with terminology recently harmonized at national scale by the Swiss geological survey (swisstopo) (HARMOS) have also been attempted.

Sedimentological aspects developed previously have been integrated with new petrophysical measurements and analyses performed on the entire studied well dataset, specifically on the five potential reservoirs in the GGB (the Triassic Buntsandstein and Muschelkalk units, the Middle Jurassic Calcaires à entroques et polypiers and Calcaires terreux considered together, the Upper Jurassic Reef Complex unit and the Lower Cretaceous Calcaires urgoniens unit). The results are presented in summary sheet where information related to stratigraphy, sedimentology, petrophysical, thermal properties and fluid parameters of selected reservoir intervals are shown in table format and documented by microphotographs, mineralogy distribution and φ/K plots.

The Reef Complex unit has been highlighted as the best reservoir in the area. There- fore, research has finally focussed on this interval, aiming at characterizing its petrophysical properties, and providing new insights on their origin and distribution within this reservoir.

Results have been integrated into the sedimentological and stratigraphic analyses carried out previously on well and outcrop material. According to the available well dataset, a rock typing workflow has been built, which aims at defining petrophysical rock types and propagating reservoir properties vertically along the wells, and subsequently horizontally through the subsurface. Additional outcrop material has been integrated, in order to complement gaps in the well dataset, and better constrain the geometry of reservoir bodies. It has highlighted that the Reef Complex unit is highly heterogenous in terms of reservoir properties.

It should be considered as a dual porosity-permeability system, considering micropores and fracture networks as main pore network and permeability corridors. This investigation has focussed on static properties, and constitutes a solid basis to be complemented in the future with new thermal, fluid and fluid-rock interaction parameters.

This study, which has integrated quantified petrophysical measurements with sedimentological data and concepts, stratigraphically well constrained, has yielded a fundamental knowledge to apprehend the different reservoir units in the GGB. The specific reservoir rock typing analysis performed in the best potential reservoir has provided keys to understand the reservoir behaviour through the characterisation of the pore network, its interconnec- tivity, and clues to predict the distribution of conductive bodies. This study has provided key knowledge on potential reservoirs in the GGB, to assure the successful development of geothermal energy in the area.

(8)

5

Résumé

Le programme GEothermie 2020 a été initié en 2013 par le Canton de Genève (Suisse), et a pour but de développer les ressources géothermiques du bassin transfrontalier (Suisse et France) du Grand Genève (BGG). Afin d’évaluer le degré de développement des réservoirs à moyenne et grande profondeur, une révision complète de la série sédimentaire du bassin couvrant un intervalle daté du Carbonifère au Crétacé inférieur a été effectuée. Des propriétés réservoirs (porosité, perméabilité, fracturation) significatives ont été identifiées dans cinq intervalles du BGG (le Buntsandstein, le Muschelkalk, le Jurassique moyen et supérieur, le Crétacé inférieur). Ces unités ont été investiguées de manière détaillée d’un point de vue stratigraphique, sédimentologique et pétrophysique.

L’évaluation du degré de développement des réservoirs a été réalisée en plusieurs étapes permettant de décrire et comprendre les caractéristiques liées à l’environnement de dépôt et à la diagenèse, et l’impact de ces facteurs sur les propriétés pétrophysiques des unités étudiées. Le matériel utilisé inclut des données de forage et d’affleurement, i.e. des rap- ports, des carottes, des échantillons prélevés sur carottes (plugs, tranches, cuttings), des diagraphies (logs) et des échantillons prélevés à l’affleurement (blocs et plugs). L’analyse conventionnelle des microfaciès et l’étude diagénétique en cathodoluminescence ont été réal- isées sur lames minces. La porosité, la perméabilité ainsi que la densité de grain ont été mesurées sur plugs, et des mesures pétrophysiques supplémentaires disponibles dans les rap- ports de forage ont été ajoutées au set de données. De plus, la minéralogie a été quantifiée sur une sélection d’échantillons représentatifs de la série sédimentaire traversée à l’aide d’un outil technologique récent, le Quantitative Evaluation of Mineral by SCANning electron microscopy (QEMSCAN). Sur cette même sélection d’échantillons, des mesures de vitesse des ondes P et S ont aussi été réalisées. Finalement, le réseau poreux a été caractérisé en dé- tail par l’analyse d’images au microscope électronique à balayage (MEB), et au travers de mesures de pression capillaire (Mercury Injection Capillary Pressure, MICP).

Afin d’appréhender verticalement la succession sédimentaire du BGG, un puits de référence traversant la série sédimentaire complète, Humilly-2, a tout d’abord été étudié en détail. Les données existantes apparentées à ce puits on été résumées et homogénéisées, puis de nouvelles mesures ont été effectuées pour créer un set de données complet et cohérent, permettant une analyse subséquente approfondie à l’échelle du bassin. Cette étude a porté sur les carac- tères lithologiques, le (micro)faciès, la réponse diagraphique et les propriétés de réservoir des unités rencontrées, afin de pouvoir assurer un repère vertical représentatif le long de la série sédimentaire complète du bassin.

(9)

6

La distribution et la géométrie des corps réservoirs potentiels ont été évaluées en iden- tifiant les faciès et leur distribution latérale à l’affleurement et entre les forages (étude en collaboration avec Maud Brentini). Cette information a été intégrée dans un cadre stratigraphique homogénéisé à l’échelle du BGG, et a été représentée sur des modèles de dépôt conceptuels à différentes périodes clés de la série sédimentaire. L’interprétation structurale dérivée de l’interprétation de données de sismique 2D a aussi été intégrée (Clerc, in prep.), et amène des informations additionnelles contraignant la distribution des faciès et les variations latérales d’épaisseur à travers le bassin. Ces observations sédimentologiques ont permis de définir une coupe stratigraphique synthétique pour le BGG, mise à jour selon une nomenclature régionale révisée. Pour certaines unités présentant des corrélations appropriées, un lien avec la terminologie harmonisée à l’échelle de la Suisse (HARMOS) a été proposé.

Les caractéristiques sédimentologiques étudiées précédemment ont été intégrées avec de nouvelles mesures et analyses pétrophysiques réalisées sur tous les forages considérés, et plus spécifiquement dans les cinq intervalles présentant les propriétés de réservoir les plus in- téressantes. Ces résultats sont présentés sous forme de « fiches résumés » pour chacun de ces intervalles, comprenant les informations stratigraphiques, sédimentologiques, et pétro- physiques, ainsi que les propriétés thermiques de la roche et les caractéristiques des fluides retrouvés. Les faciès sont notamment illustrés par des micro-photographies, et par une représentation graphique de la distribution minéralogique et des valeurs de porosité et per- méabilité quantifiées.

L’unité du « Complexe récifal » datée du Jurassique supérieur (Kimméridgien-Tithonien) a présenté les meilleures valeurs de propriétés réservoirs dans le BGG. Des recherches spé- cifiques ont donc été ciblées dans cet intervalle, afin de caractériser l’origine des propriétés pétrophysiques et leur distribution au sein de l’unité. Les résultats de cette étude détaillée ont été intégrés à l’analyse stratigraphique et sédimentologique menée précédemment sur le matériel de forages et d’affleurements. Une étude (workflow) de rock typing a été menée, ayant pour but de définir des rock types pétrophysiques pouvant être propagés le long des puits selon les données diagraphiques, et corrélés horizontalement à travers la subsurface.

Afin de compléter les données parcellaires de forage et d’appréhender la géométrie des corps réservoirs, des échantillons d’affleurement ont été intégrés à ce workflow, qui a finalement permis de mettre en évidence deux types de porosité et perméabilité dominant le comportement du réservoir (microporosité et fracturation).

Cette étude intégrant des mesures pétrophysiques quantitatives à des données et concepts sédimentologiques et stratigraphiques, a apporté un savoir fondamental pour appréhender les différentes unités réservoirs du BGG. L’étude de rock typing réalisée sur l’unité montrant les meilleures caractéristiques de réservoir représente une étape clé pour comprendre le comportement du réservoir, de par la caractérisation du réseau poreux, et le moyen de prédire la distribution et l’interconnectivité des corps réservoirs. Finalement, cette étude a apporté un savoir essentiel sur les réservoirs potentiels du BGG, permettant d’assurer le développement futur de la géothermie dans la région.

(10)

7

Acknowledgments

Je voudrais tout d’abord remercier les Professeurs Eric Davaud et Georges Gorin de m’avoir donné goût à la géologie et plus particulièrement à la sédimentologie, dans une atmosphère scientifique, sincère et détendue. Merci aussi d’avoir été de bon conseil et soutenant tout au long de mes études aux Maraîchers, jusqu’au bout de ce doctorat, dix ans plus tard, finalement! Je remercie aussi le Pr Andrea Moscariello de m’avoir intégrée au projet GEothermie 2020 en me recrutant pour réaliser cette thèse, d’avoir eu confiance en mes compétences et idées géologiques sur le terrain comme au laboratoire. Un grand merci aussi au Dr Michel Meyer d’avoir initié ce projet, et pour toutes les intéressantes discussions genevo-géologiques qui m’ont bien aidées à avancer!

Une reconnaissance et gratitude infinie se portent à Nico et Maud, plus proches collègues de thèse, pour les bons moments passés sur le terrain, dans le cadre professionnel comme en dehors. Merci d’avoir été soutenants autant psychologiquement que dans la prolifération d’idées, dans la rédaction (écriture à 4 mains d’articles et d’un chapitre) au travers d’une collaboration constructive et en toute amitié. Grandes rencontres! Merci à Yasin et Damien pour leur grand soutien scientifique et moral aussi pendant ces années de thèse; à Roland Wernli, Jean Charollais et Bruno Mastrangelo, pour les excellents moments passés sur le terrain, et pour m’avoir transmis une part de leurs grandes connaissances en matière de géologie régionale! Merci à tous les autres collaborateurs du projet GEothermie 2020 qui m’ont aussi fait avancer: Cyril, Aurélie, Luca G., Aurore, Marion, Elias et Matteo à l’uni, l’équipe des SIG et du GESDEC.

Un grand merci à ceux qui m’ont entourée pendant les années de Bachelor et Master, voire même de doctorat ou simplement pendant ces dernières, pour la bonne ambiance et les supers moments partagés sur le terrains, au café, au bistrot, et aux Maraîchers évidemment:

Althéa, Aurore, la team desAnimaux -Aymeric, Gab, Romain, Vincent, Raphaël- mes deux collègues de bureau successifs qui ont réussi à me supporter même dans les moments de doute intense Camille P. et Giovan, la team du 3e et du 7e étage, joyeux et soutenant jusqu’au bout. Un spécial merci à Louis, pour son soutien particulier et pour m’avoir sauvée de la position foetale plus d’une fois dans le rush final!

Je remercie grandement tous les membres d’Hydro-Géo Environnement Sàrl de m’avoir accueillie et intégrée dans l’équipe, et de m’avoir apporté la motivation de terminer cette thèse de par leur soutien technique (aide pour les well summary sheets), moral, et amical.

Une sacrée chance pour moi de les avoir rencontré et de continuer l’aventure GEothermie 2020 et bien d’autres avec eux!

(11)

8

Enfin, j’adresse une immense reconnaissance à ma famille, mes amis hors géologie et mes collocataires, pour avoir toujours été présents et réconfortants, au quotidien. Merci!

(12)

9

5The writting of this Chapter has been co-authoted with Maud Brentini, PhD sponsored by the State of Geneva at the University of Geneva in the framework of the GEothermie 2020 program. Her PhD thesis has started in December 2014 and focuses on the integration of surface and subsurface data in the dynamic database linked to Geographical Information Systems (GIS), which is especially designed to fit with both archiving and operational objectives of the State of Geneva.

(14)

Contents 11

4.1.1 Aims . . . 84

4.1.2 Geographical setting . . . 86

4.2 Material and methods . . . 86

4.3 Sedimentology and stratigraphy . . . 88

4.3.1 Description of geological units . . . 90

4.4 Projects at the national scale . . . 112

4.5 Conclusion . . . 113

5 Regional reservoir assessment 115 5.1 Introduction . . . 115

5.2 Reservoir property summary sheets . . . 115

5.3 Results on reservoir facies and properties . . . 116

5.3.1 Triassic: Buntsandstein and Muschelkalk . . . 116

5.3.2 Middle Jurassic (Dogger) . . . 117

5.3.3 Upper Jurassic: The KimmeridgianComplexe récifal andCalcaires de Tabalcon units . . . 117

5.3.4 Lower Cretaceous: karstic reservoir . . . 118

5.4 Conclusion . . . 119

6 Rock typing of the Kimmeridgian - Tithonian Reef Complex unit 125 6.1 Introduction . . . 125

6.1.1 Aims . . . 125

6.1.2 Definition of the Reef Complex . . . 125

6.1.3 Historical background to the Reef Complex in the GGB . . . 126

6.1.4 Sequence stratigraphic framework . . . 128

6.1.5 Reef carbonate reservoirs . . . 132

6.2 Rock typing workflow . . . 132

6.3 Depositional rock types . . . 134

6.4 Diagenesis and fractures . . . 141

6.4.1 Paragenesis . . . 142

6.4.2 Microporosity . . . 150

6.4.3 Fractures . . . 157

6.5 Pore network . . . 164

6.6 Summary of rock types from core and outcrop data . . . 168

6.7 Electrical rock types . . . 169

6.8 Petrophysical rock types . . . 174

6.8.1 Comments on uncertainties and upscaling . . . 175

6.9 The South German Molasse Basin: a geothermal reservoir analogue? . . . 177

6.9.1 Geographical and geological settings . . . 177

6.9.2 Depositional environments . . . 177

6.9.3 Reservoir properties . . . 181

6.9.4 Karstification, fractures and faults . . . 182

6.9.5 Heat transfer . . . 183

(15)

12 Contents

6.9.6 Insights on the Reef Complex unit of the GGB . . . 184

6.10 Conclusions on the Reef Complex reservoir . . . 185

7 Conclusions and recommendations 188 References 191 Appendices 223 A Well summary 224 A.1 Well summary sheets . . . 224

A.2 Core plates . . . 224

A.3 Core description . . . 224

A.4 Log conversions and corrections . . . 224

A.5 Well database . . . 224

A.6 Well Log Interpretation procedure . . . 224

A.6.1 Identification of potential reservoir zones . . . 227

A.6.2 Water zones . . . 228

A.6.3 Mineralogy . . . 230

A.6.4 Porosity . . . 233

A.6.5 Saturation . . . 235

A.6.6 Pore network characterisation . . . 236

A.6.7 Permeability . . . 240

A.6.8 Borehole diameter and fracture identification . . . 241

A.6.9 Temperature . . . 243

B Microfacies analysis 246 C Petrophysics 247 C.1 Porosity, permeability and grain density measurements on plug samples . . . 247

C.2 Humilly-2 data . . . 247

C.2.1 Porosity, permeability, density data from report . . . 247

C.2.2 Mineralogical data from report . . . 247

C.2.3 Mineralogical measurements from QEMSCAN . . . 247

C.2.4 P-wave velocity measurements . . . 247

C.3 Mercury injection capillary pressure data . . . 247

D Abbreviations 248 E Publications 250 E.1 Peer review articles . . . 250

E.2 Conference proceedings . . . 250

E.3 Field trip guides . . . 250

E.4 Conference abstracts . . . 251

(16)

13

List of Figures

1.1 Stratigraphic column, situation map, and tectonic features . . . 22

1.2 Palaeogeographical maps, modified after Ziegler (1990) . . . 24

1.3 Geothermal systems and related geothermal infrastructures . . . 28

2.1 Situation of the Greater Geneva Basin and the wells studied . . . 34

2.2 Maps showing the location of unpublished M.Sc. field studies and well cores studied . . . 36

2.3 Number of core samples retrieved per chronostratigraphic unit. . . 37

2.4 Classification of carbonate rocks after Embry and Klovan (1971) . . . 39

2.5 Classification of porosity, modified after Choquette and Pray (1970) . . . 39

2.6 Artefacts on SEM samples, caused by the polishing . . . 41

2.7 Artefacts on SEM samples, caused by the glue . . . 42

2.8 Porosimeter-permeameter AP608 at the University of Geneva . . . 45

2.9 Map of outcrops studied . . . 50

3.1 Location of the Humilly-2 well in the Geneva Basin . . . 53

3.2 Humilly-2 well summary sheet . . . 56

3.3 Correlations between a synthetic stratigraphic column of the GGB and the reviewed stratigraphy in HU-2 . . . 57

3.4 Mineral associations after QEMSCAN measurements . . . 59

3.5 The Carboniferous unit in HU-2 . . . 60

3.6 The Buntsandstein unit in HU-2 . . . 61

3.7 The Muschelkalk and Lettenkohle units in HU-2 . . . 62

3.8 The Rhaetian unit in HU-2 . . . 63

3.9 The Bajocian unit in HU-2 . . . 65

3.10 The Bathonian unit in HU-2 . . . 66

3.11 The Oxfordian unit in HU-2 . . . 67

3.12 The Kimmeridgian unit in HU-2 . . . 69

3.13 Porosity-permeability plot . . . 72

3.14 The Bajocian stratigraphic and sequential subdivisions at the 3^rd order (?) scale . . . 73

3.15 The Kimmeridgian Reef Complex unit stratigraphic and sequential subdivisions at the 3^rd order (?) scale . . . 75

(17)

14 List of Figures

3.16 Boxplot of gamma-ray values per stratigraphic unit . . . 77

3.17 The Callovian condensed interval in cores . . . 79

4.1 Situation map: the Greater Geneva Basin, wells studied and M.Sc. studies included. Structural interpretation in the GGB after Clerc, (in prep.), and digitized geological map from Chantraine et al. (1996). . . 85

4.2 Geneva Basin stratigraphy 1.0 . . . 87

4.3 Microfacies illustrating depositional environments observed in GGB sedimentary succession. . . 88

4.4 Conceptual model of the depositional environment during the Carboniferous. 91 4.5 Triassic units, outcropping in the Jura Mountains and penetrated by Humilly-2 93 4.6 Conceptual model of the depositional environment during the accumulation of the Muschelkalk. . . 94

4.7 Lateral thickness variation of Liassic units in a NW-SE transect across the GGB. . . 95

4.8 Conceptual model of depositional environment during the early Upper Liassic. 96 4.9 Lateral thickness variation of Dogger units in a NW-SE transect across the GGB. . . 98

4.10 Conceptual model of depositional environment during the Bajocian. . . 99

4.11 Lateral thickness variation of Malm units across a broad NW-SE transect in the GGB. . . 102

4.12 Conceptual model of the depositional environment during the Upper Kim- meridgian, at the early stage of the reef sequence. . . 103

4.13 Lateral thickness variation of Lower Cretaceous units along a broad NW-SE transect across the GGB. . . 106

4.14 Conceptual model of the depositional environment during the Lower Berri- asian (Pierre Châtel Fm). . . 107

4.15 Lateral thickness variation of Tertiary units along a NW-SE transect across the GGB . . . 110

5.1 Porosity-permeability values measured on plug samples, from cores and outcrops116 5.2 Buntsandstein reservoir . . . 120

5.3 Muschelkalk reservoir . . . 121

5.4 Middle Dogger reservoir . . . 122

5.5 Middle-Upper Malm reservoir . . . 123

5.6 Lower Cretaceous reservoir . . . 124

6.1 Stratigraphic column of theReef Complex unit (modified after Donzeau et al. (1997)) . . . 126

6.2 Map of wells and outcrops where the Reef Complex unit has been studied . . 127

6.3 Sequence stratigraphic framework for the Kimmeridgian-Tithonian (simplified after Hardenbol et al. (1998)) . . . 129

(18)

List of Figures 15 6.4 Cross-section along a W-E transect in the southern Jura Mountains (modified

after Meyer (2000a)) . . . 130

6.5 Sequence stratigraphic correlations between wells penetrating the Reef Com- plex unit . . . 131

6.6 Rock typing workflow. . . 135

6.7 Depositional model of the Reef Complex unit . . . 136

6.8 Illustration of DRTs microfacies . . . 138

6.9 The DRTs and their schematic distribution . . . 139

6.10 Porosity-permeability cross plot and DRT distribution . . . 140

6.11 Paragenesis of diagenetical sequences for the Reef Complex (Makhloufi et al., 2018) . . . 143

6.12 Examples of porosity remaining after diagenesis affected the original sediment 144 6.13 Occurrence of reef-related deposits and sucrosic dolomite in the GGB subsurface145 6.14 Occurrence of reef-related deposits and sucrosic dolomite in the GGB subsurface148 6.15 Occurrence of microporous micrite in the stratigraphic framework . . . 151

6.16 Micrite terminology used, after De Périère et al. (2011). . . 152

6.17 The different micrite morphologies observed in the Reef Complex . . . 154

6.18 DdRT represented on simplified 2D cross-section . . . 155

6.19 Porosity-permeability cross-plot and associated DdRT . . . 156

6.20 Different fracture patterns in outcrop of the Reef Complex . . . 158

6.21 Calcaires récifaux unit exhibiting different fracture patterns . . . 159

6.22 Fracturation related to poor core recovery . . . 160

6.23 Conceptual mechanical stratigraphy scheme . . . 161

6.24 DdfRT illustrated on 2D simplified cross-section . . . 163

6.25 MICP measurements performed on HU-2 samples . . . 165

6.26 Velocity-deviation logs calculated in Thônex-1 and Humilly-2 . . . 167

6.27 Summary of the successive rock types defined . . . 170

6.28 Electrical Rock Types interpreted along each well penetrating the Reef Com- plex unit. . . 172

6.29 ERT represented on 2D cross-section compared with ERT defined along well 173 6.30 PRT represented on smiplified 2D cross-section . . . 175

6.31 Porosity-permeability plot and related PRTs . . . 176

6.32 Stratigraphic framework of the South German Molasse Basin (SGMB) (Ho- muth et al., 2015a). . . 178

6.33 Model of the depositional environments for the Malm reservoir unit in the SGMB (Dirner and Steiner, 2015). . . 179

6.34 Distribution of palaeoenvironments in the Malm reservoir of the SGMB (Wolf- gramm et al., 2009). . . 180

6.35 Conceptual 2D cross-section of the Malm reservoir in the SGMB (Böhm et al., 2013). . . 182

A.1 Penetration depth of different logging tools . . . 225

A.2 Borehole environment and resistivity profile . . . 226

(19)

16 List of Figures A.3 Pickett plot . . . 230 A.4 Example of RHOB tool return in halite and gas effect on RHOB and NPHI log232 A.5 Electrical current flow in a residual gas/oil-bearing, water-wet pore network . 237 A.6 Porosity-Formation Factor plot: evaluation of "m" and "a" components . . . 239 A.7 Capillary pressure plots . . . 242 A.8 Examples of image logs (FMS, Caliper, OBI) . . . 243 A.9 Geothermal gradient for the Western Alpine Molasse Basin . . . 245

(20)

17

List of Tables

1.1 Compilation of properties for three deep geothermal reservoirs . . . 29 4.1 Comparative table of former and current stratigraphic designations . . . 101 6.1 Core recovery calculated for all cores penetrating the Reef Complex unit in

the GGB. . . 133 6.2 Values (range) attributed to each Electrical Rock Type (ERT). . . 171 6.3 Values (range) attributed to each Petrophysical Rock Type (PRT). . . 174 6.4 Petrophysical properties measured in the Malm aquifer, SGMB (Homuth

et al., 2014). . . 183

(21)

18

1 | Introduction

1.1 Aims

1.1.1 GEothermie 2020 program

During the last decades, an increased interest for the development of geothermal energy developed in Switzerland, not exclusively aimed at electricity generation, but also at heat/cold production to serve both industrial and domestic demand (e.g. heating/cooling of green- houses and buildings). The GEothermie 2020 geothermal exploration program, promoted by the State of Geneva and the Services Industriels de Genève (SIG, water and energy utility of the Geneva Canton), covers the Geneva Canton area and the surrounding French mu- nicipalities. This multi-phased program aims first at validating the results of a preliminary study (PGG, 2011) focussed on the geothermal potential of the trans-border Greater Geneva Basin (GGB), and secondly at further investigating the medium to deep subsurface. This until today is still poorly known and its understanding is an essential prerequisite in order to quantify the resources and ultimately lead to their development by 2020 (Moscariello, 2016).

1.1.2 Research orientations

As part of the GEothermie 2020 program, two PhD projects have been initiated in July 2013 financially supported by SIG. The main objectives of these projects are: (1) to build a homogenized dataset of available deep subsurface data, (2) to characterize potential reservoirs in the GGB, and (3) to provide integrated geological and petrophysical models of the subsurface, in order to support and further steer geothermal exploration at medium and great depth. These objectives have been divided in two main research axes according to the scale and data considered. First, it has been oriented towards a comprehensive regional scale study, using seismsic data to describe the basin structural configuration, the thickness variations of seismostratigraphic units and their specific seismo-facies. This has led to cre- ate a structural and geological framework, into which the petrophysical properties would be later implemented (Clerc, in prep.). In parallel, the second activity, which represents this study, has been focussed on the description and quantification of reservoir properties and their distribution. This project adresses reservoir property variability at any representative scale, with respect to sedimentological criteria in all reservoir units of the GGB. In the best reservoir unit specifically, it also explores the potential influence of property variability on

(22)

1.1. Aims 19 the fluid flow behaviour.

One of the main purpose of this PhD research is to respond to critical questions raised by the need to understand the subsurface of the Canton of Geneva in support of the on- going geothermal exploration activity. At the same time, this research addresses some key fundamental research questions involving key aspects such as the sedimentology, stratigraphy, diagenesis processes. Furthermore, the amount of data available nowadays is such that whatever the project considered, data compatibility and homogenization issues at different scales have become critical. The academic contribution is particularly important when using stratigraphic concepts in geological studies. With respect to these considerations, the following research orientations have been formulated:

• What is the palaeogeographic facies distribution and how this affects reservoir occurrence in the region of study?

• What are the primary (sedimentation) and post-depositional process (diagenesis/fractures) controlling reservoir properties distribution?

• Can we define a predictive model for reservoir quality?

The strategy established to answer these questions is developed below. It provides guide- lines for the reader to understand the organization of this manuscript and the structure of Chapters.

1.1.3 Organization of manuscript

In order to answer these interrogations, the following systematic approach has been carried out. It aims at investigating and conceptualising the reservoir distribution and quality in three dimensions across the region of study.

This study has generated a large dataset and used various methods. Chapter 2 presents these data and provides information on the methods used, in particular well log interpretation.

The well Humilly-2 penetrated a sedimentary record ranging from the Carboniferous to the Quaternary in the centre of the basin. For this reason, it has been used as a reference in this study. Chapter 3 presents the thorough investigations carried out on this well, which form a prime support for further multi-well study and time-depth conversions in seismic- based models.

Further to the investigation of the vertical succession of sedimentary units in Humilly- 2, the lateral distribution of the latter has been addressed. In Chapter 4, the different stratigraphic units present in the GGB as well as their specific compositional and textu- ral characteristics across the basin have been defined as the basis for a homogeneous and consistent stratigraphic framework. This substantial and comprehensive piece of work has been carried out jointly with another PhD research project (Maud Brentini). This Chapter offers a thorough review of the stratigraphy of the GGB by providing original information

(23)

20 Chapter 1. Introduction on horizontal extension and sedimentological characteristics, derived both from outcrop and subsurface data. It provides a completely revised stratigraphic framework for the study area.

Within this stratigraphic framework, different potential reservoir units highlighted in the literature have been investigated in terms of reservoir characteristics and properties.

Chapter 5 presents the results of petrophysical measurements obtained in these units. This Chapter meant to be a preliminary operational document, in which the different reservoir units can be observed "at a glance". It presents brief explanations which have been published in the proceeding of European Geothermal Congress 2016 (Appendix E). The integration of petrophysical and microfacies analyses have resulted in the characterisation of potential reservoirs in the GGB, and highlighted the best potential target unit for geothermal purposes, i.e., the Kimmeridgian-TithonianReef Complex .

Chapter 6 thoroughly describes the Kimmeridgian-Tithonian Reef Complex, following an integrated rock typing methodology. Categories of reservoir properties, which can be propagated along wells and in the inter-well space are here defined based on sound conceptual geological thinking. The methodology has been organized to highlight the different factors influencing reservoir properties, and to understand which of them predominates. It has provided first insights on the reservoir morphology, heterogeneity, and property distribution.

This methodology has been applied integrating the sparse subsurface data with samples from outcrop. It has also been designed to allow the integration of new subsurface data and to improve the current understanding of rock types. This Chapter therefore offers the first concrete constraints on which reservoir properties could be modelled across the GGB.

Moreover, the results of this Chapter can be considered as the basis for future reservoir modelling approach (i.e., MPS training images), which is the logical, next step for geothermal exploration.

1.1.4 Collaborations

This PhD project benefited from several collaborations within the framework of the GEother- mie 2020 program. As mentioned above, this work has been initiated jointly with a different PhD research project focussing on basin-cale structural model, essentially based on 2D- seismic data (Clerc, in prep.). The results of the present study have been organized so as to be integrated in such subsurface models. Stratigraphic and sedimentological information (revised stratigraphic well tops, insights for seismic facies) has been implemented in seismic data interpretation and seismic horizon definition. Inversely, information from seismic interpretation has allowed a better understanding of unit variability within the basin.

Stratigraphic and sedimentological issues have been discussed in the framework of another PhD project (Brentini, in prep.), where the results have been integrated constructively with seismic data input on the structural framework. The genesis and evolution of dolomite occurring in theReef Complex unit intially described in this study has also been addressed by a post-doctoral research project (Makhloufi et al., 2018), thereby helping interpretations on diagenesis in the present study.

Several other research projects have followed from the extensive data collection phase carried out at the beginning of this study. A large, formatted and usable well dataset

(24)

1.2. Geographical setting 21 has been created, which still contributes to improve the knowledge of the GGB subsurface (Appendix E).

1.2 Geographical setting

The GGB covers a Swiss-French transnational zone located at the southernmost extremity of the North Alpine foreland Molasse basin (Figure 1.1). It is limited to the northwest by the internal chain of the Jura Mountains and to the southeast by the thrusting front of the Alpine units. The study area (about 2200 Km²) extends from the city of Nyon, Switzerland, up to the city of Rumilly, France.

1.3 Geological setting

1.3.1 Palaeogeographical and palaeoenvironmental settings

¹

The sedimentary succession in the Geneva Basin overlies a crystalline basement which formed during the Variscan (Hercynian) orogeny (basement sensu stricto). This oldest unit results from the collision between the Gondwana (South) and Laurasia (North) continents (Debrand- Passard et al., 1984 ; Ziegler, 1990 ; Dercourt and Vrielynck, 1993). From the end of the Carboniferous until the Triassic, the development of the North Atlantic and Tethys ocean rift systems caused crustal thinning and extensional features in the basement of Western and Central Europe (Van Wees et al., 2000 ; Ziegler, 2001 ; Wilson et al., 2004 ; Ziegler and Dèzes, 2006). In the studied area, it created SW-NE trending, low angle normal faults and half grabens in the basement (McCann et al., 2006). In the GGB, these depressions were filled by continental siliciclastic material eroded from the surrounding topographic highs (Massif Central, Vosges, Serre, Morvan, Bohemian Massif). Coal seams intercalated in these deposits testify to a vegetation thriving in a humid environment during Carboniferous times. The crystalline basement and these mainly continental deposits form the basement sensu lato, and the contact between this unit and the overlying Triassic sediments is marked by an angular unconformity (Sommaruga, 1999 ; Signer and Gorin, 1995 ; Guellec et al., 1990, and references therein).

At the beginning of the Mesozoic, a large part of the Pangea megacontinent started to break up (Golonka, 2007). In the Lower Triassic (unit and age called "Buntsandstein" according to German nomenclature, Figure 1.2a), continental sedimentation was progressively replaced by carbonates and evaporites deposited in a shallow epicontinental sea coming from the North and the East (marine transgression until the Middle Triassic Muschelkalk), whose depocenter was located in the Northern Germany domain (Sommaruga, 1997)(Figure 1.2b).

Sedimentation along the northwestern Tethys margin was partially isolated from the open sea by the Alemanic-Vindelician High acting as a barrier. Consequently, a thick anhydrite

(25)

22 Chapter 1. Introduction

1

Geneva

Salèv Vuache e

Bornes P lateau Rumilly Basin

Nyon

Rumilly

Geological units Legend

Subalpine un its Jura Mountains

City Quaternary Neogene Paleogene Lower Cretaceous Upper Cretaceous

Upper Jurassic

Triassic

Permo-Carboniferous

Granite and gneiss, external crystalline massifs Fault

Wrench fault in the GGB, interpreted from seismic data Thrust

Studied area

Middle Jurassic Lower Jurassic Quaternary

TertiaryCretaceousMalmDogger

Liassic

Keuper

Buntsandstein

Muschelkalk

Permo-Carb.

Basement OSM

OMM

USM Eocence Barremian Hauterivian

Valanginian - Berriasian

Thitonian

Callovian - Bajocian

Aalenian

Upper

Middle Early

Kimmeridgian - Oxfordian

lower

A

B

Figure 1.1: The Greater Geneva Basin, A) stratigraphic units, B) situation, geological units and tectonic features (structural interpretation in the GGB from Clerc, (in prep.), and simplified geological map (1:1000000) after Chantraine et al. (1996)). The studied area is outlined by the black dashed line.

(26)

1.3. Geological setting 23 and dolomite unit developed from the Northern Jura domain towards the Geneva area (Pao- lacci, 2013). Similar palaeoenvironmental conditions lasted until the Late Triassic (Keuper) and then evolved into more restricted environments (anhydrite, salt and shale deposits).

Another phase of transgression occurred during the Rhaetian and Lower Jurassic (Lias- sic) times on the NW European platform (Figure 1.2c). At this time, the Alemanic High (individualized from the Vindelician High) was still active and partially disconnected the epicontinental platform from the Tethyan ocean realm. Although the Alemanic High was flooded during the Middle Jurassic (Dogger), it still formed as a "submarine swell" (McCann, 2008) influencing and compartmentalizing the marine sedimentation. The part of the platform corresponding to the present-day Jura relief was then progressively tilted towards the SE (Rigassi, 1962 ; Mangold, 1984). This movement continued throughout the Late Juras- sic (Malm), during which the Alemanic High subsided accordingly. The boundary between the shallow platform and external and deeper environments following a general NE-SW axis Geneva-Bern was therefore shifted to the SE (Sommaruga, 1997). During the Upper Malm (Kimmeridgian-Tithonian, Figure 1.2d), this shift is indicated by the southward and south- eastward progradation of patch reefs and oolithic bars developing on inherited topographic highs in the carbonate platform of the Jura domain (Meyer, 2000a). Overall, the Jurassic period is characterized by two transgressive-regressive cycles, ending in the Lower Berriasian (locally known as "Purbeckian"). The top of the latter sequence is marked by typical emersion features well documented in the studied area (Deconinck and Strasser, 1987 ; Strasser and Davaud, 1982, 1983 ; Müller, 1986).

The Early Cretaceous is characterized by an intense tectonic and volcanic activity linked to the break-up of Pangea, which affected the climate, sea level and sedimentary dynamics (Föllmi, 2012). At this stage, despite another marine incursion flooded the platform of the Jura domain, near-emersion conditions prevailed until the end of the Barremian (Fig- ure 1.2e). The Aptian to Albian period is characterized by intensified greenhouse climate conditions (Föllmi, 2012). Several successive emersion and drowning episodes together with coeval tectonic structuration resulted in an intricate topography. Topographic depressions were filled with lacustrine to marine sediments rich in siliciclastic material and marked by numerous hiatuses and condensed beds (Pictet et al., 2016). Finally, pelagic chalk and lime- stones associated with a wide transgressive phase deposited over the entire area. The latter sediments were later eroded, and are today only found in karst pockets, which formed during the subsequent subaerial exposure of the Cretaceous sequence (see later). In the same area, Aptian-Albian deposits are well preserved in inherited topographic depressions, but seem to disappear eastwards of Bienne (Sommaruga, 1997 ; Pictet, 2016)(Figure 1.2f).

In the Early Cenozoic, convergence of African and Eurasian plates, together with basement uplift linked to the Vosges-Black Forest mantle dome, exhumed the Mesozoic strata (Trümpy, 1980 ; Karner and Watts, 1983). The sub-equatorial climate accelerated the erosion of the Cretaceous units and created a major unconformity at the top of the Mesozoic sequence. Lateritic sediments of Eocene age (Hooker and Weidmann, 2007 ; Becker et al., 2013) with reworked Aptian-Albian material filled karsts and fractures.

The overlying Oligocene Molasse (Figure 1.2g), covering the entire Swiss Plateau from

(27)

1. Bundsandstein

3. Rhaetien-Hettangien

4. Kimmeridgian-Oxfordian

5.Berriasien-Valanginien

6. Aptian-Albian

7. Oligocene 2. Carnien-Norien

Sand and conglomerate Sand

Sand and shale Carbonate and sand Carbonate Carbonate and shales Shale, some carbonate Shale

Organic shale Halite Sulphate Volcanic local Continental, lacustrine

Deltaic, coastal and shallow-marine clastics Shallow-marine, mainly shales Deeper-marine, mainly shales Deeper-marine clastics Carbonates, mainly shallow-marine Evaporite

Uninterpreted area Cratonic, mainly low relief

Depositional environments Lithological symbols

Areas of non-deposition

Tectonic symbols Others symbols

Inactive fold belts, moderate to high relief Active fold belts, high relief

Normal fault Transcurrentfault Active deformation

front of bold belt 0 Km 100

Direction of clastic influx Direction of marine incursion Direction of inta-basinal clastic

Figure 1.2: Palaeogeographical maps, modified after Ziegler (1990)

(28)

1.3. Geological setting 25 Geneva to Lake Constance and continuing to the east until the Pannonian region, in the GGB is divided in three palaeogeographical domains: the Bornes Plateau, the Geneva Basin and the Rumilly Basin (Berger, 1996 ; Morend, 2000 ; Charollais et al., 2007). The Bornes Plateau contains the Lower Marine Molasse (UMM according to the German nomenclature, see Strunck and Matter (2002, and references therein)) and Lower Freshwater Molasse (USM (Strunck and Matter, 2002)) units which were thrusted and folded during the Alpine orogeny to form the Subalpine Molasse. In the Geneva and Rumilly basins, the USM directly onlaps the eroded Cretaceous units or the Eocene lateritic sediments where present. In the Rumilly basin, the USM is overlain by the Upper Marine Molasse (OMM, (Strunck and Matter, 2002)) which transgressed from the SW and is to date present only in this domain. According to Schegg et al. (1997) more than 2000 m of USM and OMM are missing in the Geneva Basin and Bornes Plateau because of erosion.

The Quaternary period is characterized by several glaciations, and the resulting sediments record different progradation and retreat episodes of the Rhône Glacier and its related glacial, glacio-lacustrine and lacustrine environments (Moscariello et al., 1998 ; Fiore et al., 2011 ; Wildi et al., 2014). During the last glacial maximum, the Geneva Basin was covered by about 1000 m of ice (Rhône and Arve Glacier) as indicated by erratic blocs found on the Jura Mountains and near the top of Mount Salève (Moscariello, 2018).

1.3.2 Tectonic setting

²

The GGB sedimentary cover described above consists of a thick Mesozoic and Cenozoic succession (3000-5000 m), which overlays a crystalline Variscan basement dipping gently to the S-SE, locally affected by paleo-graben or half-graben structures filled with siliciclastic Permo-Carboniferous sediments (Signer and Gorin, 1995 ; Paolacci, 2013 ; Clerc et al., 2015).

In response to the alpine compression, the GGB Mesozoic and Cenozoic sedimentary cover underwent some shortening possibly associated with a rotational motion, which decoupled the sedimentary succession from the basement by a decollement surface occurring in Middle and Upper Triassic evaporites at the base of the Mesozoic sequence (Guellec et al., 1990 ; Affolter, 2004 ; Arn et al., 2005). This shortening was absorbed through the structuration of the fold and thrust reliefs of the Jura arc mountains during the late Miocene and Early Pliocene (Meyer, 2000a ; Homberg et al., 2002 ; Affolter, 2004). This deformation was laterally accommodated by a set of strike-slip faults. Among them, the most important has a prominent morphotectonic expression in the landscape represented by the NW-SE oriented Vuache mountain (Vuache fault, (Charollais et al., 2013b), Figure 1.1). The Vuache fault, inherited from former tectonic deformation phases (Blondel et al., 1988), crosscuts the entire basin and played an important role in the structuration of the GGB and distribution of Tertiary sediments.

According to the “thin-skin” (or “distance push”) dynamic tectonic model proposed in the early years of the century to explain the Jura deformation (Buxtorf, 1907, 1916), where the Molasse basin and the Jura developed over a moving basal decollement layer (Sommaruga,

2In collaboration with Nicolas Clerc and extracted after Rusillon et al. (2016)

(29)

26 Chapter 1. Introduction 1999, and references therein), no direct morphogenetic connection should be expected between the basement faults and those observed in the overlying Mesozoic-Cenozoic overbur- den. However, inherited basement reliefs and normal faults bounding Permo-Carboniferous troughs might have played a role in the nucleation of the Mesozoic northwestward thrusts present in the SE sector of the Geneva Basin and Bornes Plateau (Gorin et al., 1993 ; Signer and Gorin, 1995).

As a result of this structuration, the GGB can be subdivided into three main structural compartments, which correspond to Cenozoic paleogeographical domains (see paragraph 1.3.1): (1) the Geneva basin sensu stricto, bounded by the Mount Salève, Mount Vuache and the Jura Mountains, or “cuvette”, in the sense used by Gorin et al. (1993) (2) the Bornes Plateau and (3) the northern part of the Rumilly Basin, also called “Albanais” Basin (Charollais et al., 1983 ; Muralt, 1999 ; Berger et al., 2005 ; Morend, 2000 ; Charollais et al., 2007, 2013b).

A complete seismic dataset including reprocessed old 2D lines and newly acquired high- resolution 2D seismic data have enabled Clerc (in prep.) to perform a complete detailed structural analysis of the Greater Geneva Basin aimed at building a 3D-geological subsurface model. The interpretation of this new dataset add new knowledge while allows the fine- tuning of existing interpretations (e.g., location of main fault zones (Gorin et al., 1993)), as well as better delineating their continuations across the study area. In the Geneva Basin sensu stricto (Clerc, in prep.), current interpretation reveals that apart from the regional Vuache fault described above, series of smaller-scale NW-SE striking left-lateral wrench faults affect the southwestern part of the Geneva Basin. They are known, from SW to NE, as the Cruseilles fault zone, Le Coin fault and the presumed Arve fault zones respectively.

The surface expression of Cruseilles and Le Coin faults can be recognised in outcropping Mesozoic units in Mount Salève (Charollais et al., 1988). Unlike the Vuache fault, which can be traced geomorphologically for several kilometres from the Annecy region up to the Jura Mountains, no obvious connections between the Cruseilles, Le Coin and Arve systems and the Jura Mountain can be drawn across the Geneva Basin as suggested in previous interpretations (Signer and Gorin, 1995 ; Paolacci, 2013). The work carried out in this study phase associated with the GEothermie 2020 program (Clerc, in prep) suggest that the latter structural features are part of smaller-scale fault segments, which altogether crosscut the Salève thrusted anticline from the Borne Plateau towards the Geneva Basin. Towards the northeast of the basin, the structural configuration is dominated by E-W striking faults.

NW-SE and E-W strike slip faults occur as series of subvertical individual faults often affecting most of the Mesozoic sequence (down to the Triassic decollement surface) with associated smaller-scale sets of conjugates. Upward extension through the Cenozoic interval of the most important faults often appears as flower structures as already outlined by Signer and Gorin (1995) and Paolacci (2013) based on examination of 2D seismic line. This shallow subsurface expression is consistent with fault geometries observed in some outcrops of Tertiary Molasse (Charollais et al., 2007 ; Angelillo, 1987).

(30)

1.4. State-of-the-Art 27

1.3.3 Stratigraphic framework

³

A thorough revision of the stratigraphic framework has turned out to be necessary when confronting outcrop and well data interpreted and published by several authors. The rele- vance of this work was also increased considering the long time lapse between the first and last study used in this work, which resulted in a very heterogeneous and inconsistent way of describing and referring to individual or complexes of stratigraphic units. Local homonyms, facies appellation instead of formation name, or obsolete definition of chronostratigraphic intervals are typical puzzling inconsistencies found in the dataset. Homogenization of the stratigraphy in terms of chronology and names has been required not only to ensure consis- tency of interpretations at the basin scale, but also to respond to cantonal demand concerning the collection, inventory and management of geological data in a consistent and up-to-date database (Brentini, in prep.; Favre, in prep.). Subsequently, correlations with HARMOS nomenclature (Morard, 2014) developed by the Swiss geological survey (Swisstopo) have been attempted considering the limitation of extending the GGB stratigraphic units to the NE and correlating them with the rest of Switzerland.

The review of the stratigraphy is based on the last investigations on regional geology (Donzeau et al., 1997 ; Charollais et al., 2013b), and also includes an expanded literature on specific chronostratigraphic intervals and geological cross-sections (see Chapter 4 for more details).

1.4 State-of-the-Art

1.4.1 Geothermal reservoirs

Geothermal projects aim at using heat produced from the earth, which is carried by fluids. A geothermal reservoir is thus defined as a heat conducting, permeable rock, and requires water which can circulate through it and transmit heat. Main intrinsik rock properties to consider to evaluate a geothermal reservoir are porosity, permeability, heat conductivity and capacity (defintion in Chapter 2 and Appendix A.6). Parameters including fluid properties such as hydraulic conductivity and transmissivity are also important. Temperature (geothermal gradient) and flow rate are also parameters which cannot be ignored, because they influence the type of infrastructure which would be possible to install at the surface.

Geothermal systems can be separated in three categories according to the depth considered: "shallow" at depth < 400 m, "medium" at depth between 400 - 3000 m, and "deep"

at depth > 3000 m (www.geothermie2020.ch). The present study has focused on the two last systems, which mainly consider Mesozoic sedimentary units is the GGB, and whose capacity for reservoir potential has been poorly studied compared to the shallow subsurface one.

Infrastructures designed for these medium and deep systems are open (Figure 1.3).

In order to appreciate and compare further the quality of potential reservoirs in the GGB, reservoir properties of three different geothermal reservoirs have been compiled in

(31)

Figure 1.3: Geothermal systems and related geothermal infrastructures (modified after www.geothermie2020.ch)

Table 1.1 (Bavarian Basin, Paris Basin, Alberta Basin). These producing geothermal fields are found at medium to deep depth in carbonate-dominant lithologies, in foreland basin settings, equivalent to the GGB. The values reported show large variations, which highlight the heterogeneity of reservoir properties, of their distribution, and the complexity of reservoir architectures according to depositional, diagenetical, and structural factors (Lopez et al., 2010 ; Casteleyn et al., 2010 ; Makhloufi et al., 2013 ; Böhm et al., 2013 ; Birner, 2013 ; Moeck, 2014 ; Moeck et al., 2015 ; Homuth and Sass, 2014 ; Homuth et al., 2015b).

1.4.2 Previous studies on potential geothermal reservoirs of the GGB

This paragraph briefly presents relevant background studies and reference papers, which specifically deal with occurrence, extension and properties of reservoir units in the GGB.

Indeed, the GGB and surrounding massifs have been the subject of several publications, dealing with the regional geological framework (sedimentology, palaeontology, stratigraphy) and structure of the Jura and subalpine realms. Despite the new interest generated in the last six years thanks to the intense geothermal exploitation effort in the area and the recent debate on shale gas exploitation (Gorin and Moscariello, 2013), in the past only few authors focussed on reservoir characterisation, especially on deep reservoirs.

The shallow Quaternary and Tertiary units have been extensively studied, because of their implications on societal and human concerns such as drinking-water resource managment (de Los Cobos, 2012), or hydrocarbon exploration (Olmari, 1983), and because of their accessibility. The numerous wells penetrating Quaternary and Tertiary units (more than

(32)

1.4. State-of-the-Art 29

Table 1.1: Compilation of properties for three deep geothermal reservoirs, according to different sources. Note the wide range of values for each property considered, revealing that these reservoirs, which have been producing geothermal energy since decades, are heterogeneous in terms of reservoir quality.

Characterisation and rock typing of deep geothermal reservoirs in the Greater Geneva Basin (Switzerland & France)

Thesis

Reference

Characterisation and rock typing of deep geothermal reservoirs in the Greater Geneva Basin (Switzerland & France)

TERRE & ENVIRONNEMENT

Section des sciences de la Terre et de l’environnement, Université de Genève

Characterisation and Rock Typing of Deep Geothermal Reservoirs

in the Greater Geneva Basin

(Switzerland & France)

Elme RUSillon

2018

Volume 141

Characterisation and Rock Typing of Deep Geothermal Reservoirs

in the Greater Geneva Basin

(Switzerland & France)

THÈSE

UNIVERSITE DE GENÈVE

DOCTORAT ÈS SCIENCES, MENTION SCIENCES DE LATERRE

Thèse de Madame Elme RUSILLON

«Characterisation and Rock Typing of

Deep Geothermal Reservoirs in the Greater Geneva Basin

le

de

A.

ordinaire et directeur de thèse

des sciences de la

E.

des

de Ia

C.

Africa

The

de

et

de

.--\

( lû-^-

Abstract

Résumé

Acknowledgments

Contents

List of Figures

List of Tables

1 | Introduction

1.1 Aims

1.1.1 GEothermie 2020 program

1.1.2 Research orientations

1.1.3 Organization of manuscript

1.1.4 Collaborations

1.2 Geographical setting

1.3 Geological setting

1.3.1 Palaeogeographical and palaeoenvironmental settings

1.3.2 Tectonic setting

1.3.3 Stratigraphic framework

1.4 State-of-the-Art

1.4.1 Geothermal reservoirs

1.4.2 Previous studies on potential geothermal reservoirs of the GGB

( _lû-^-