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Home , Aquitaine Basin, Limagne Graben, Martinique, Paris Basin, Paris metropolitan area

French geothermal resources

survey

BRGM contribution

to the market study in the LOW-BIN project

BRGM/RP - 57583 - FR August, 2009

French geothermal resources survey BRGM contribution to the market study in the LOW-BIN project

(TREN/05/FP6EN/S07.53962/518277)

BRGM/RP-57583-FR August, 2009

F. Jaudin With the collaboration of M. Le Brun, V.Bouchot, C. Dezaye

IM 003 ANG – April 05

Keywords: French geothermal resources, geothermal heat, geothermal electricity generation schemes, geothermal Rankine Cycle, cogeneration, geothermal binary plants

In bibliography, this report should be cited as follows: Jaudin F. , Le Brun M., Bouchot V., Dezaye C. (2009) - French geothermal resources survey, BRGM contribution to the market study in the LOW-BIN Project. BRGM/RP-57583 - FR

© BRGM, 2009. No part of this document be reproduced without the prior permission of BRGM

French geothermal resources survey

BRGM contribution to the market study in the LOW-BIN Project

BRGM, July 2009 F.JAUDIN M. LE BRUN, V. BOUCHOT, C. DEZAYE

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TABLE OF CONTENT

1. Introduction ...... 4 2. The sedimentary regions...... 5 2.1. The Basin ...... 5 2.1.1. An overview of the exploitation of the low enthalpy Dogger reservoir ...... 7 2.1.2. The geothermal potential of the different silicoclastic reservoirs in the Trias formation ……………………………………………………………………………………….10 2.1.3. Conclusion for the geothermal potential of the reservoirs in the …………………………………………………………………………………………….12 2.2. The Basin ...... 13 2.3. The Graben...... 14 2.3.1. The clastic reservoir (S1-DET)...... 16 2.3.2. The clastic reservoir (S2-DET) ...... 17 2.3.3. The Rupleian clastic reservoir (S3-DET) ...... 17 2.4. The Rhine Graben ()...... 19 2.4.1. Installed plants for electricity production ( > 120°C) ...... 19 2.4.2. Potential geothermal resources ...... 21 2.5. The Rhône Graben and the Valley...... 24 2.6. The Bresse Basin ...... 26 3. The volcanic region: the French Overseas Territories...... 28 3.1. ...... 28 3.2. ...... 29 3.3. La Réunion ...... 30 4. Conclusion ...... 31

Some references …………………………………………………………………………..32

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TABLE OF FIGURES

Fig 1: geological environment in ...... 4 Fig 2: location of the Paris Basin in France ...... 5 Fig 3: litho-stratigraphic log of the reservoirs in the Paris Basin...... 6 Fig 4: effective thickness (m) of the Dogger reservoir in the Ile de France region ...... 7 Fig 5: isotherms of the Dogger reservoir in the Paris (°C)...... 8 Fig 6: location of geothermal district heating plants in the vicinity of Paris ...... 8 Fig 7: depth of the top of the Donnemarie over the Paris basin...... 10 Fig 8: temperatures of the Donnemarie sandstone reservoir in the Paris basin ...... 11 Fig 9: temperatures at the top of the Marin Rhaetien reservoir in the Paris basin...... 12 Fig 10: location of the Aquitain basin on the France map ...... 13 Fig 11: location of the main geological formations in the Aquitain Basin ...... 14 Fig 12: location of the on the French territory ...... 15 Fig 13: geological map of the Limagne Graben...... 15 Fig 14: temperatures of the S1-DET reservoir in the Limagne graben...... 16 Fig 15 : temperatures of the top of the S2-DET reservoir in the Limagne graben...... 17 Fig 16: temperatures at the top of the S3-DET reservoir in the Limagne graben...... 18 Fig 17: location of the Rhine graben on the French territory...... 19 Fig 18 : Location of the EGS Soultz site and of the Upper Rhine Graben ...... 20 Fig 19 : schematic NW-SE geologic cross section, ...... 20 Fig 20 : Porosity and reservoir area of the Grande Oolithe ...... 22 Fig 21 : Map of temperature at the top of Buntsandstein in Rhine Graben ...... 23 Fig 22 : location of the Rhône Graben and the Provence valley on the French territory...... 24 Fig 23: location of the more interesting spot for the geothermal development ...... 25 Fig 24: location of the Bresse Basin on the French territory ...... 26 Fig 25: location of the French overseas department ...... 28 Fig 26: location of the Bouillante geothermal area in Guadeloupe (A)...... 28 Fig 27: location of the targets for geothermal development in Martinique ...... 29 Fig 28: location of the geothermal drillings in La Reunion ...... 30

LISTE OF TABLES

Table 1: characteristics of the heating plants in the Paris Basin ...... 9 Table 2: summary of the geothermal potential (in GJ/m²) in the Trias reservoirs...... 13 Table 3: temperatures of the and Jurassic formation in different regions ...... 14

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1. Introduction

France disposes of several very low-temperature to very high-temperature geothermal resources located at different depths, geographical locations and geological settings. The very low-temperature geothermal resources (below 30°C) are located in shallow layers and and are exploited with ground source heat pump or ground water heat pumps. These resources are scattered all over the territory but they represent a too low energy potential for the development of electricity production. They are not described in this report.

The low-energy resources (between 65°C and 90°C) are located in aquifers contained in the major sedimentary basins, i.e the Paris Basin, the , the Upper Rhine Graben, the Limagne and Bresse region, the Rhone corridor and the Mediterranean region but also in faulted or folded regions. (Fig 1)

The geothermal resources with temperatures between 90°C and 150°C are in the course of evaluation. A very recent study, performed by BRGM and co-financed by ADEME1 , named CLASTIQ (CLAyed sandSTone In Question) explore new or poorly well-known deep silicoclastic geothermal reservoirs (Triassic reservoirs in Alsace and Paris Basin, reservoirs in Limagne) with fluids temperatures around 80°C and 120°C.

Fig 1: geological environment in France

1 French Agency for Environment and Energy Management

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The resources higher than 150°C. are located in the Overseas Departments (the volcanic of the - Guadeloupe and Martinique – and the Indian Ocean - Reunion) and in the crystalline basement where injection of water in fractures and production of heated fluid leads to the concept of EGS (Soultz-sous-Forêt scientific pilot plant).

This document focuses on the deep geothermal resources with temperatures between [65°C- 90°C] and [90°C-150°C} in the different regions in France and presents the available information about the thickness and the temperature of this potential geothermal reservoirs. The temperatures are those present at depth, they are different from the temperatures that will be encounter at surface. The difference between hole temperature and the wellhead temperature depends on the depth of the resource and the flow rate at which the fluid is extracted.

2. The sedimentary regions Low-energy resources, developed for thermal applications, are primarily located in the two major existing sedimentary basins: the Paris Basin and the Aquitaine. Other French regions have high potential for low-energy resources, but the geological structures are more complex and fields much more localized (Bresse basin, Limagne Graben, Rhône Graben/Provence valley).

2.1. The Paris Basin The Paris basin is a nearly circular large intracratonic which occupies a vast part of Northern France (110,000 km2) between crystalline areas (black contour on Fig 2). The central part of the basin, where the was the most important, is filled with about 3000 m of sediments (Guillocheau et al. 2000; Delmas, Houel, and Vially 2002).

Fig 2: location of the Paris Basin in France

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Several aquifers are found in the basin (stratigraphic log on the (Fig 3).

Fig 3: litho-stratigraphic log of the reservoirs in the Paris Basin (BRGM, Bouchot et al., 2008)

The Mid-Jurassic (Dogger) carbonate rocks were identified as the most promising geothermal development target below the urbanized Paris area (Ungemach et al., 2005). The geothermal reservoir formation stretches over 15,000 km2, covering a large part of the Paris and western distant suburbs where it lies between 1500 and 2000 m depth. Formation temperatures evaluated at the top of the productive layers are mostly comprised between 55°C and 80°C.

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2.1.1. An overview of the exploitation of the low enthalpy Dogger reservoir The Dogger is a carbonate reservoir with characteristics such as permeability and diffusivity highly variable horizontally and vertically. It comprises three series (, , from top to bottom) with the Bathonian layer being the most productive and exploited layer up to now. This aquifer is well described in the Ile de France region because of the high demand in energy in this area. The bottom of the reservoir in the Ile de France area is around 2000m deep and its effective thickness is comprised between 5m and 30m in this part of the basin (Fig 4).

Fig 4: effective thickness (m) of the Dogger reservoir in the Ile de France region

The fluid temperatures of the aquifer in the Ile de France area range between 45°C and 80°C with the highest temperatures located in the South East of Paris (Fig 5).

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Fig 5: isotherms of the Dogger reservoir in the Paris area (°C) ( BRGM, Aquifères et eaux souterraines en France, 2006)

Currently twenty nine geothermal heating networks (34 doublets or triplets) use low enthalpy geothermal energy from the water in the Dogger reservoir for heating 200 000 equivalent- dwellings (Fig 6).

Fig 6: location of geothermal district heating plants in the vicinity of Paris Details on the temperatures, the flow rates and the power produced by these heating plants are given in the following table.

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Opération Temp Flowrate MWh Geo Comments °C m3/h 73 275 43 155 Blanc Mesnil 66 220 25 471 Bonneuil sur 79,3 280 25 579 70 360 49 028 Champigny 78 280 58 552 Coge* Chelles 69 280 16 917 Coge* Chevilly Larue – L’Hay les R. 72,6 580 72 580 2 doublets Coge* Clichy sous Bois 71 190 15 572 Coge* Coulommiers 85 230 24 752 Coge* Créteil 78,9 300 56 466 Coge* Epinay sous Sénart 72 250 49 874 Fresnes 73 230 32 335 Coge* Nord 58 200 21 666 Température<65°C La Courneuve Sud 56 180 12 472 Température<65°C A new well could be drilled soon Le Mée sur Seine 72 170 21 155 Maisons Alfort 1 73 300 36 673 Coge* Maisons Alfort 2 74 260 20 755 Coge* Beauval & Collinet 75 450 58 384 Coge* Meaux Hôpital 76 200 20 674 Coge* l’Almont 72 240 44 593 Coge* 72,5 220 16 881 1 & 2 75 355 62 046 A new doublet has been drilled in 2008 Ris Orangis 72 210 16 239 Coge* Sucy en Brie 78 180 25 167 A new well has been drilled in 2008, will operate as a tripet at end 2009 with increased heat production 76 250 43 539 Tremblay en France 73 275 45 562 Vigneux 73,2 260 33 579 Villeneuve Saint Georges 76 350 34 411 Coge* Villiers Le Bel 67 270 21 699 Coge*

2 new doublets are going to be drilled in 2009-2010 and several new operations could be launched in 2010 Coge*: geothermal plants operating with additional gas cogeneration (electricity and heat production from gas)

Table 1: characteristics of the heating plants in the Paris Basin Most of the geothermal district heating plants exploit the Dogger aquifer. The CLASTIQ scientific project highlights other potential resources in the Triassic silicoclastic aquifers.

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2.1.2. The geothermal potential of the different silicoclastic reservoirs in the Trias formation

In the Paris Basin, the Trias formation is formed by several silicoclastic reservoirs from the Rhaetien to the Buntsandstein. The five reservoirs studied in the CLASTIQ project are: The Donnemarie sandstone, The Chaunoy sandstone, The Boissy continental sandstone, The Sainte Colombe-Voulzie sandstone, The marine Rhaetien sandstone

The deepest reservoir is the Donnemarie sandstone and the depth of the top of this reservoir varies from 3000m to 1000m North to South.

Fig 7: depth of the top of the Donnemarie sandstone over the Paris basin (BRGM, Bouchot et al., 2008).

The four other reservoirs have almost the same geometry and the depth of their top can be recalculated from their thickness. The temperatures and the thickness of each reservoir have been calculated in the CLASTIQ project from petroleum well data intercepting the Trias formations and interpolation methods. They can rapidly be ordered according to their geothermal potential, which has been calculated according to a method described in the CLASTIQ report.

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i. The Donnemarie sandstone (Muschelkalk and Lower Keuper) It has been estimated to be between 0 m and 850 m thick across the whole Paris basin). The temperatures of this reservoir range from 10°C on on the East border of the basin to 120°C in the area of Sezanne (Fig 8).

Fig 8: temperatures of the Donnemarie sandstone reservoir in the Paris basin (BRGM Bouchot et al., 2008). The green points represent the geothermal plants tapping the Dogger reservoir, the black lines represent the isotherms

The calculated geothermal potential is around 25 GJ/m²

ii. The Chaunoy sandstone (Lower and Middle Keuper, Rhaetien) with almost the same geometry It has an estimated thickness varying between 0m and 200m.Its petrophysical characteristics are quite good with a porosity of 12,5% and a permeability of 360mD but they are very heterogeneous, a specificity of silicoclastic reservoir. The interpolated temperatures over the basin range between 10°C on the East border of the basin and 123°C near Sezanne (Fig 9).

The geothermal potential of the Chaunoy sandstone calculated with the CLASTIQ method is around 7,7GJ/m² in the region of Château-Thierry.

iii. The continental sandstone of Boissy (Upper Keuper and Rhaetien) Calculations give it a thickness comprised between 0m and 90m over the basin.

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The temperatures of the reservoir lie between 10°C and 121°C The Boissy reservoir has a maximal potential of 4 GJ/m² between Compiegne and Epernay. The petrophysical characteristics of the reservoir are unknown but the reservoir is superimposed on the Chanoy reservoir so its geothermal potential could be better.

iiii The sandstone of Sainte Colombe-Voulzie (Middle Keuper) and the sandstone of the marine Rhaetien (Upper Keuper and Rhaetien) The first reservoir has been estimated to be between 0m and 50m thick (the second one to be between 0m and 40m thick

Computations of the field data give calculated temperatures comprised between 10°C and 128°C for the Sainte Colombe sandstone reservoir and between 0°C and 119°C for the Marin Rhaetien reservoir (Fig 9)

Fig 9: temperatures at the top of the Marin Rhaetien reservoir in the Paris basin (Bouchot et al., 2008). The green points represent the geothermal plants tapping the Dogger reservoir,

Both of the reservoirs have an estimated geothermal potential between 3GJ/m² and 2GJ/m² between the Brie and Champagne regions The petrophysic characteristics of the Sainte Colombe reservoir are limited, those of the Marine Rhaetien reservoir are believed to be better but this reservoir is thin.

2.1.3. Conclusion for the geothermal potential of the Triassic reservoirs in the Paris basin The potential of each tertiary silicoclastic reservoir in the Paris basin is summarised in the Table 2. In the end, a global geothermal potential for the Triassic formation is calculated for

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the central region of the Parisian Basin (2GJ/m² to 6 GJ/m²) and for the eastern region of the Parisian Basin (around 12 GJ/m²).

Table 2: summary of the geothermal potential (in GJ/m²) in the Trias reservoirs located under the exploited zones in the Dogger formation (BRGM, Bouchot et al., 2008).

2.2. The Aquitaine Basin Located in the Southwest of France, the Aquitaine basin is surrounded by the to the North, the Central massif to the East, the Pyrenean mountains to the South (Erreur ! Source du renvoi introuvable.).

Fig 10: location of the Aquitain basin on the France map

The basin is filled with Liasic, Triassic and Cretaceous formations lying on a crystalline basement (Fig 11). ).

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Ah

Fig 11: location of the main geological formations in the Aquitain Basin

Liassic and Triassic reservoirs are formed by thick detrital series and Liassic . The temperatures can reach 90°C but these reservoirs have not yet been exploited.

The temperatures of the reservoirs in Cretaceous and Jurassic formations are between 65°C up to 100°C. Three regions show a good geothermal potential with relatively high temperatures (Table 3).

REGION FORMATION TEMPERATURE (°C) Lower Cretaceous 65-70 Mont de Marsan Upper Jurassic 75-95 Lower Cretaceous 80-100 axis Pau- Upper Jurassic 90-115 Lower Cretaceous 70 Upper Jurassic 85

Table 3: temperatures of the Cretaceous and Jurassic formation in different regions

The Jurassic aquifer holds the high enthalpy geothermal potential, especially in the Pau region. The total energy stocked in the Jurassic is estimated to 3342 TWh and is quite similar to the energy stocked in the Buntsandstein.

Among 18 operations which have been realized in the Aquitan Basin only 5 operations display a temperature over 60°C.

2.3. The Limagne Graben The Limagne graben is located in the Northern part of the French Central Massif and is partly filled with tertiary silicoclastic formations (Fig 12).

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Clermont-Ferrand & Chatelguyon

Fig 12: location of the Limagne Graben on the French territory

The potential reservoirs are named S1-DET, S2-DET and S3-DET and are pointed on the lithostratigraphic column below (Fig 13).

A

B

Fig 13: geological map of the Limagne Graben (A); lithostratigraphic column of the geological formations in the Aquitain Basin (B) (Bouchot et al., 2008)

For the CLASTIQ project, GEOWATT AG has evaluated the temperatures and the thickness of the different reservoir and deduced their geothermal potential following a method they explain in their final report. Nevertheless, it has to be noticed that the calibration process during the modelling revealed some differences between the temperatures given by the model and those measured on the field.

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2.3.1. The Lutetian clastic reservoir (S1-DET) The Lutetian reservoir is located at the base of the basin and is the principal target for a geothermal exploitation. In the Western and Northwestern zones of the Graben, the reservoir is up to 1000 m thick and up tu 1 200 m deep.

The S1-DET displays temperatures around 100°C (Fig 14) with the highest temperatures comprised between 70°C and 100°C in the area of Châtelguyon.

Châtelguyon

Clermont- Ferrand

Fig 14: temperatures of the S1-DET reservoir in the Limagne graben (Bouchot et al., 2008)

The Northwest and West regions present the best values for the geothermal potential. The area of Châtelguyon represents the best target with a geothermal potential between 20 Gj/m² and 30 Gj/m². Toward the South of Châtelguyon, the geothermal potential decreases as it is becoming thinner and shallower.

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2.3.2. The Bartonian clastic reservoir (S2-DET)

The shallower the reservoir, the lower the geothermal potential. The thickness of the S2-DET reservoir is up to 500m and its temperatures are estimated up to 80 °C (Fig 15).

Châtelguyo

Clermon t - Fd

Fig 15 : temperatures of the top of the S2-DET reservoir in the Limagne graben (Bouchot et al., 2008)

Nevertheless, the Lutetian reservoir S1-DET is locally connected to the S2-DET. The association of these two reservoirs builds a virtual thicker reservoir around 1200m thick, which is good for the geothermal potential. Thus, the geothermal potential of the S2-DET is still high (5 GJ/m² to 15 GJ/m).

2.3.3. The Rupleian clastic reservoir (S3-DET)

The computations of the thickness and the temperatures of the S3-DET lead to a maximal thickness of 450 m and a maximal temperature of 60°C (Fig 16 ).

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Fig 16: temperatures at the top of the S3-DET reservoir in the Limagne graben (Bouchot et al., 2008)

Compare to the S2-DET reservoir, the geothermal potential of the S3-DET reservoir is less interesting (5GJ/m²). But, the favourable zones of the S2-DET and S3-DET reservoirs are superimposed and sometimes connected.

As the petrophysical characteristics of these zones are better than the S1-DET characteristics (good hydraulic conductivity, especially for the S3-DET), it is recommended to consider the graben as a multi layers reservoirs and to think about drilling through the three reservoirs.

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2.4. The Rhine Graben (Alsace) The Rhine Graben is located in the North East part of France with its western part and in Germany for its eastern part (Fig 17)

Fig 17: location of the Rhine graben on the French territory

2.4.1. Installed plants for electricity production ( > 120°C)

Soultz-sous-Forêts (Alsace) The Soultz site is located in the northern part of France, within the Rhine Graben, but near the western border (Fig 18). This site was initially chosen in a region characterized by a high geothermal anomaly based on extensive well data collected in the Upper Rhine Graben thanks to a former petroleum field exploration (Kappelmeyer et al., 1991). A of sub- surface information was available in the sediments: seismic profiles, thousands of wells of various depth, and temperature measurements at 500 m depth.

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Fig 18 : Location of the EGS Soultz site and geology of the Upper Rhine Graben (Dezayes et al., 1995). (1) sediments (2) Cenozoic volcanism (3) Jurassic (4) Trias (5) Hercynian basement (6) Border faults (7) Faults (8) Temperature distribution in °C at 1500m depth (Haenel et al., 1979). (9) Local thermal anomalies (Haenel et al., 1979). (a) Cenozoic filling sediments (b) sediments (c) granite basement under 1400m of sediments.

The EGS target is a Paleozoic altered and fractured granite overlain by a thick sedimentary cover made of , Triassic, Jurassic and Tertiary sedimentary formations. The wells reach into the naturally fractured granite basement at a depth around 1200m (Fig 19) each of them with a particular trajectory.

Fig 19 : schematic NW-SE geologic cross section, with the three fractured zone clusters in the Soultz wells (Sanjuan et al., 2008).

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Three wells (GPK2, GPK3 and GPK4) were drilled at 5km depth and one well (EPS1) was a fully exploratory cored well at 2.2 km depth. Temperatures at 5km depth are over 200°C and the temperature profile is not linear but shows a typical convective response related to large- scale fluid circulations occurring within the fault network. At depth, large-scale faults developing hydrothermal alteration (illite, quartz, calcite, secondary porosity) are naturally permeable and support high salinity fluids (brines, 100 g/l). The concept of Enhanced Geothermal Systems (EGS) applied to a low permeability pre-fractured granite was born at Soultz. The natural permeability is estimated to less than 1m3/h. This faulted granitic reservoir was reactivated by Termo-Hydro-Mechanical stimulations generating microseismicity events as well as by chemical stimulations in order to dissolve the hydrothermal products sealing the natural fractures in the near-well domain. Two short-term circulation tests were done in 1997 and in 2005 at 3.7 and 5 km depth respectively (Baumgärtner et al., 1998; Sanjuan et al., 2006). The hydraulic and thermal performances of this deep non conventional reservoir are encouraging and showed that a large proportion of geothermal brines is produced avoiding fluid losses (Sanjuan et al., 2006). After injectivity/productivity enhancement, fluid circulations between the injecting well, GPK3 and the producing wells (GPK2, GPK4) are operating. In 2006, a 1.5MWe Organic Ranking Cycle (ORC) power unit (manufactured by Cryostar in association with Turboden) was constructed. Since the end of 2008, it started to produce 5MW to 6MW of electricity from two productor wells and one injector well with a flowrate around 90m3/h using a geothermal fluid between 130°C and 160°C.

2.4.2. Potential geothermal resources The main geothermal resources are embedded in four aquifers (Munck et al., 1979 ; Haenel, 1989 ; Hurtig et al., 1992): three of them are embedded in calcareous formation, the last one is hold by a silicoclastic formation.

• The Lusitanien limestone is mainly represented South of the Graben at a depth between 500m and 1750m. This aquifer is scattered with a poor porosity but it is highly fracturated. The temperatures vary between 20°C and 90°C and the salinity is comprised between 5 and 50 g/l.

• Grande Oolithe aquifer The lower geothermal aquifer in the Rhine Graben is constituted by the Bajocian- Bathonian formation, namely the Grande Oolithe. This aquifer is well-known by numerous oil exploration studies because it was an important petroleum goal too. This formation is constituted by massive oolithic in thick bed, presents under the whole Rhine Graben, except beyond Haguenau. Two reservoirs could be distinguished within the Grande Oolithe: - the upper part very compact with fractures filled by calcite; - the lower part, real reservoir, but with heterogenic porosity (Fig 20). The best values (around 10%) are located between and . Fractures are present in this formation and could increase the reservoir potential in the southern part of the Rhine Graben. The depth of the top of the reservoir is around 1000-1500m. However, in the southern part of the graben, the top of the formation is higher, about 500-700m whereas in the

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north the depth could reach 2000-2500m (Munck et al., 1979). The thickness of the bed decreases regularly from south to north, between 120m and 30m respectively. The temperature at the top of the aquifer could reach 100°C near Mulhouse and Strasbourg. In this last case, this temperature is due to the depth of the aquifer, whereas near Mulhouse, there is a real geothermal anomaly in relation with the oil field of Staffelfelden (Munck et al., 1979) (C.DEZAYS, 2008). The value of the salinity can reach 100g/l where thre are connected with salt layers.

______

Fig 20 : Porosity and reservoir area of the Grande Oolithe (Munck et al., 1979)

• The Upper Muschelkalk is made of limestone up to 100m thick in the central part of the Graben. This formation is less porous. However, it exits numerous fractures which allow the circulation of a fluid whose salinity is close to 50 g/l. The depth of the top of the Muschelkalk vary from 1200m in the South part of the graben to 3000m in the North, and reach 4300m in the Rastatt basin in the NE. The thickness of the aquifer is around 60m and 100m (Munck et al., 1979). The temperature of this reservoir is rather high, between 80°C and 130°C in the Mulhouse-Colmar area and in the northern part of the graben, where the temperature could reach 150°C in the Rastatt

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basin (where the layer is deeper) (Dezayes, 2008). The geothermal electrical potential of the Muschelkalk reservoir for the whole Alsace region could reach 596 TWh (Champel, unpublished).

• The Buntsandstein is a clastic formation of the lower Triassic unit. It is a sandstone more or less coarse. This homogeneous formation is present within the whole Rhine Graben and well-known in outcrop and quarry, where it is exploited as Vosgian Sandstone for example. This aquifer is also intensely fractured and could be consider as a fractured reservoir. The depth of the top of the formation increase from the southern part of the graben to the northern part, where the depth is 2000m to more than 3000m respectively. The top of the Buntsandstein could reach 4000m in the Rastatt basin (Munck et al., 1979). The thickness of the aquifer increase also from the south to the north. In the southern part, the thickness is less than 100m. Between Colmar and Strasbourg, the thickness varies between 200m and 300m, whereas in the north of Strasbourg, the thickness reaches 500-600m. The temperature of the top of the Buntsandstein is around 100°C, less in the southern part where the depth top is higher (Fig 21). In the northern part, where the aquifer is deeper, the temperature could reach 150°C. The potential map, which combine temperature data and Buntsandstein thickness, shows that the northern part of the graben, beyond Erstein, is the most favourable area for geothermal exploitation. In this area, the exploitable potential of the Buntsandstein is between 20GJ/m2 and 40GJ/m2. For the whole Rhine Graben, the thermal exploitable potential is about 330.106TG (Dezayes et al., 2007).

Fig 21 : Map of temperature at the top of Buntsandstein in Rhine Graben (Dezayes et al., 2007)

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2.5. The Rhône Graben and the Provence Valley The Rhône Graben and the Provence Valley are located South East of France (black outline on the (Fig 22).

Fig 22 : location of the Rhône Graben and the Provence valley on the French territory

The Jurassic formations lie under a relatively constant thickness of Tertiary formations. A North-South cross section through the Graben shows numerous faults connecting the Jurassic and Tertiary formation on the edge of the Graben. A NW-SE cross section shows the Jurassic layer thickness growing toward the centre of the Graben and two main faults which shift the Jurassic and Tertiary formations. In the Rhone Graben, near Valence and Montélimar, the Upper Jurassic displays temperatures above 80°C. Then, South of the town of Nîmes, the Upper Jurassic formations host water at 200°C at 5km deep in fractured area. The temperatures in the Upper Jurassic around Uzes, Nîmes and Sommieres, are above 65°C and increase to 90°C going North (Fig 23).

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Fig 23: location of the more interesting spot for the geothermal development (Genter et al., 2004)

The formation (Dogger) is around 2500m deep and exceeds 100m in thickness. The temperatures exceed 100°C like in the area near Orange and Valence, where the water is around 140°C and 150°C at depth 2700m and 3200m respectively.

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2.6. The Bresse Basin In the Northern part of the Rhône Graben (black outline on the Fig 24), the Bresse Basin hosts several deep and shallow geothermal reservoirs.

Fig 24: location of the Bresse Basin on the French territory

The deep reservoirs correspond to the Bundsandstein (Lower Trias), other targets are hold by the Jurassic formations and Tertiary formations.

• The Bundsandstein formation The reservoir is thicker on the east zone of the Bresse basin (45 m) than on the west zone with values close to 90m. For depths between 2000m and 3000m, the temperatures can reach 130°C and thus make the Bundsandstein reservoir a good target for the production of heat and electricity but the thickness of the reservoir is low (< 50 m).

By combining maps of the temperatures and thickness of the Bundsandstein, the amount of heat and then the exploitable heat have been calculated. The area with a maximal geothermal potential superimposes to the deepest and thickest zones inside the Basin but these are only 50m thick, which lead to a geothermal potential of only 2 GJ/m². The more favourable area draws an arc along the eastern border of the Basin. The reservoir below Bourg en Bresse displays temperatures between 100°C and 140°C at depths comprised between 2000m and 3200m. The thickness of the formation (30m to 50m) leads to a geothermal potential of around 1,5GJ/m². The lack of data about the permeability and the porosity of the Bundsandstein make it hard to estimate if the relatively thin silicoclastic layer will provide sufficient water flow rate.

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• Other targets in the and Jurassic formations Near Bourg-en-Bresse, some sandy lenses are located at the basement of the Eocene formation. The temperatures at this depth (1900m) are around 75°C and could provide a good geothermal potential if the lenses are thick enough. The upper Jurassic in the same area displays temperatures which can reach 80°C.

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3. The volcanic region: the French Overseas Territories.

France also possesses high-energy resources that are potentially exploitable for electricity production. These are located essentially in its Overseas Departments: the volcanic islands of the Antilles - Guadeloupe and Martinique – and of the Indian Ocean – Reunion (Fig 25).).

Fig 25: location of the French overseas department

3.1. Guadeloupe

At present, the exploitation of high temperature geothermal resources (250-260°C) is limited in Guadeloupe and particularly to the area of Bouillante (red star on the Fig 26)

B

A

Fig 26: location of the Bouillante geothermal area in Guadeloupe (A) and view of one drilling site (B)

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In Bouillante, 40 years after starting the exploration work, the two turbines of the geothermal plant, with 15 MWe total capacity, supply around 8% of Guadeloupe’s electricity requirement. For the moment, the residual production fluids are directly discharged into the sea, after mixing with the seawater used for the cooling system of the geothermal plant. Presently, reinjection of the residual water is also envisaged in order to maintain production rate and pressure within the reservoir. Other developments are expected in the Northern and Southern parts of Bouillante Bay and should allow a considerable increase of the present electricity production.

3.2. Martinique

Three areas of interest had been identified: Lamentin , Montagne Pelée-Morne Rouge and the Diamant area (red stars on the Fig 27).

Fig 27: location of the targets for geothermal development in Martinique

An exploratory borehole drilled in 1970 within the Lamentin prospect evidenced a shallow- low temperature aquifer (around 93°C) which could be used for direct-use application. Three new deep exploratory wells (1000m) drilled in 2001 in confirmed the existence of the shollow low temperature aquifer but showed no evidence of the presence of high temperature resources. The Montagne Pelée-Morne Rouge prospect is located in the vicinity of the Montagne Pelee . The more recent geothermal exploration studies were carried out by BRGM IN 2003. A hydrothermal reservoir associated with this volcano is suspected to contain fluids displaying temperatures around 200°C. The extent of the reservoir is badly constrained and the threat of a new explosion of the volcano limit the development of this area for the geothermal energy. A geothermal reservoir at about 180°C is supposed to be located in the Diamant area, in the South of Martinique but the drilling of deep exploration wells should validate this result obtained after geochemical and geophysical studies.

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3.3. La Réunion

The recent age of the volcanism and the existence of surface hydrothermal manifestations pointed out the possible development of high temperature geothermal resources suitable for electricity generation. Two exploration wells were drilled in 1985 around 2000-3000 m deep in the areas of the Piton des Neiges and Piton de la Fournaise (Fig 28).

Salazie area (Piton des Neiges) 1 dry drilling, T=180°C

New site

Grand Brûlé area (Piton de la Fournaise) 1 drilling, good flowrate, low temperature

Fig 28: location of the geothermal drillings in La Reunion

Only one (Salazie area) evidenced high temperature conditions suitable for electricity generation but the permeability of the formation was too low to sustain the production of high temperature fluids at a suitable flowrate.

Exploration of such a large volcanic pile is not obvious and requires numerous surface investigations and cvalidation by the drilling of exploration wells. Additional exploration studies were carried out between 2001 and 2005 in the area of the Piton des Neiges and Piton de la Fournaise. The active volcano of the Reunion , Piton de la Fournaise, is among Earth’s most active volcanoes. The regional Council of La Reunion has taken the decision to drill 2 or 3 geothermal reconnaissance (1200-1300m deep) wells on Piton de la Fournaise near Plaine des Sables. It has also expressed a strong willingness to open the drillings to the scientific community. The drilling operations could start in 2010.

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4. Conclusion

In , the most promising sedimentary formations for the geothermal potential above 100°C (15 GJ/m² to 30 GJ/m²) are the Bundsandstein of the Rhine Graben (Northern part) and the Tertiary formations of the Limagne Graben. Then, the Trias formation of the Paris Basin holds two main reservoirs with a good geothermal potential: the Donnemarie reservoir (up to 25 GJ/m²) and the Chaunoy reservoir (up to 7,7 GJ/m²). The Bundsandstein in the Bresse Basin displays a poorer geothermal potential (2 GJ/m²) because of the thin sandstone layers. The deep granite in the Rhin Graben is an EGS target, as shone with the Soultz Pilote. France also possesses high-energy resources that are potentially exploitable for electricity production. These are located essentially in its Overseas Departments: the volcanic islands of the Antilles - Guadeloupe and Martinique – and of the Indian Ocean – La Reunion. For the instant, the exploitation of the geothermal resources is limited to Guadeloupe and particularly to the area of Bouillante. Deep high- temperature aquifers suitable for electricity generation are suspected in La Martinique and La Reunion but have not been discovered so far.

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Some references

Baumgärtner J., Gerard A., Baria R., Jung R., Tran-Viet T., Gandy T., Aquilina L., Garnish J. (1998), Circulating the HDR reservoir at Soultz: maintaining production and injection flow in complete balance. Proceedings of the 23rd Workshop on Geothermal reservoir Engineering, Stanford University, California, USA.

Bouchot V. et collaborateurs (2008) - Projet CLASTIQ : CLAyed sandSTone In Question. Rapport final BRGM/RP-56626-FR.

Dezayes C., Thinon I., Courrioux G., Tourlière B., Genter A., (2007). Estimation du potentiel géothermique des réservoirs clastiques du Trias dans le Fossé Rhénan, Rapport final, BRGM/RP-55729-FR, 70 p.

Dezayes C., Villemin T., Genter A., Traineau H. & Angelier J. (1995) - Analysis of fractures in boreholes of the Hot Dry Rock project at Soultz-sous-Forêts (Rhine graben, France). Scientific Drilling , 5, p. 31-41.

Dezayes Ch., Genter A., (2008). Large-scale fracture network based on Soultz borehole data. EHDRA Scientific Conference, Proceedings of the EHDRA scientific conference 24-25 September 2008, Soultz-sous-Forêts, France.

A.Genter et al (2004) -Typologie des systemes HDR/HFR en ,. BRGM/RP-53452-FR.,

Haenel R. (1979) - Atlas géothermique de l'Europe, 1980. CCE EUR 6578 EN, Ed. R. Haenel

Haenel R. (1989) – Atlas of geothermal resources in the European Community, and . In: International Seminar on the Results of EC Geothermal Energy Research and Demonstration, vol. 4 (edited by Louwrier K., Staroste E., Garnish J.D., Karkoulias V.). Kluwer Academic Publishers, Dordrecht, Boston, 482-489.

Kappelmeyer O., Gérard A., Schloemer W., Ferrandes R., Rummel F., Benderitter Y. (1991), European HDR project at Soultz-sous-Forêts, general presentation, Geothermal Science and Technology, 2, 263-289.

Munck F., Walgenwitz F., Maget P., Sauer K, Tietze R. (1979) - Synthèse géothermique du Fossé Rhénan Supérieur. Commission of the European Communities. BRGM Service Géologique Régional d’Alsace – Geologishes Landesamt Baden-Württemberg.

Sanjuan B., Pinault J.-L., Rose P., Gérard A., Brach M., Braibant G., Crouzet C., Foucher J.- C., Gautier A., Touzelet S. (2006), Tracer testing of the geothermal heat exchanger at Soultz-sous-Forêts (France) between 2000 and 2005, Geothermics, Vol. 35, 622-653.

European Commission (1999) - Geothermal Atlas of Europe.

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European Commission (2002) - Atlas of Geothermal Resources in Europe.

Vathaire, J.C. Boissavy, C. Gérard. A. (2006) – Géothermie. Aquifères et eaux souterraines en France, Editions BRGM , p.906-917, 2006

Munck F., Walgenwitz F., Maget P., Sauer K, Tietze R. (1979) - Synthèse géothermique du Fossé Rhénan Supérieur. Commission of the European Communities. BRGM Service Géologique Régional d’Alsace – Geologishes Landesamt Baden-Württemberg.

Fritsch D., Gerard A. (2006), Current status of the EGS Soultz project: main achievements, results and targets, From Ledru P. & Genter A. (eds.) 2006, in Actes/Proceedings of the Engine Launching Conference, 12-15 February 2006, Orléans, France, p. 21-23.

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Scientific and Technical Centre Geothermal Energy Department 3, avenue Claude-Guillemin - BP 36009 45060 Orléans Cedex 2 – France – Tel.: +33 (0)2 38 64 34 34