1. Evaluation of the geophysical exploration methods through analysis of experiences in Europe and overseas H. Fabriol, A. Manzella, JM Baltassat
dimanche 9 juin 2019

2. Engine, Launching conference, Orléans 13-15 February 2006
Summary
State of the art
Comparison of methods exploration vs. exploitation
Examples
Advantages, disadvantages
New perspectives : I-GET
Engine, Launching conference, Orléans February 2006

3. Four types of reservoirs
High and medium enthalpy resources
Metamorphic/plutonic beneath thick sedimentary cover
Larderello-Travale (It.)
Volcanic
Hengill (Ic.),
Guadeloupe and Martinique (Fr.)
others
Deep sediments
Paris Basin (Fr.)
EGS Soultz-ss-Forêts (Fr.)
Engine, Launching conference, Orléans February 2006

4. Comparative table of methods for Exploration
Volcanic
Metamorphic
Deep sediments
Soultz-ss-Forêts
Gravity
Regional/local scale
Regional scale No
Magnetism
Heat source
Electric DC
Local scale, 2D and 3D resistivity imaging
Local scale
TDEM
Local scale (penetration depth down to 1000 m) MT
Local scale: 2 D and 3 D resistivity imaging
Idem
To be used in
I-GET
Active seismic
Local scale: 2D and 3 D images of reservoirs
Exploration for deep reservoirs beneath sedimentary cover
Oil exploration seismic, to be used in I-GET
Oil exploration seismic profiles + well seismic
Passive seismic
Local scale: Active faults, seismic velocities anomalies
see exploitation
Engine, Launching conference, Orléans February 2006

5. Comparative table of methods for Exploitation
Volcanic
Metamorphic
Deep sediments
Soultz-ss-Forêts
Gravity
Time lapse (4D) microgravity
idem
Magnetism
Electric DC
Monitoring: repeated mise à la masse and SP (experimental)
Monitoring:
Self potential (experimental)
TDEM MT
Repeated MT (Coso)
Active seismic
Repeated active seismic (Japan)
Exploitation of deep reservoir
Passive seismic
Monitoring Induced seismicity: steam/liquid limit, stress regime, seismic hazard
Idem
Monitoring seismicity induced by hydraulic fracturing: location of events, stress regime, seismic hazard
Engine, Launching conference, Orléans February 2006

6. Engine, Launching conference, Orléans 13-15 February 2006
Gravity/Magnetism
Generally used for structural studies at regional scale
Local scale: high density/demagnetization anomalies linked to hydrothermal alterations
Sedimentary basins: tool to detect anomalous areas (high heat flow) in basement beneath sedimentary basins (coupling of both methods)
Improvements in data interpretation: Euler decomposition, probabilistic tomography etc.
Repeated microgravity surveys: evaluation of extracted volumes & assessment of recharge
Engine, Launching conference, Orléans February 2006

7. Gravity local scale, Le Diamant (Martinique Island), BRGM 2003
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8. Coupled Interpretation Le Diamant (Martinique), BRGM 2003
Engine, Launching conference, Orléans February 2006

9. DC electrical resistivity impaging
Low resistivities linked to the caprock/upper part of the reservoir (illite-smectite-zeolite alterations), higher resistivities to the reservoir (chlorite, > °C)
Long electric arrays (Schlumberger and dipole-dipole) used in the 70’s and 80’s for resistivity imaging
2 D and 3 D inversion softwares available “off the shelf”
Advantages : source controlled, resolution < 100 m down to 1 or 2 km
Disadvantages : Heavy implementation compared with MT, equivalences (non unique solution),
“Blackbox” software could drive to erroneous interpretations
Engine, Launching conference, Orléans February 2006

10. 2D resistivity imaging at Bouillante (BRGM, 2004)
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11. Engine, Launching conference, Orléans 13-15 February 2006
TDEM (Hengill, ISOR 2004)
Advantages: penetration beneath resistive shallow layers, better resolution than DC Schlumberger soundings
Disadvantages: size of the transmitter for deep penetration, generally 1 D inversion, 2 D modelling at research stage
Engine, Launching conference, Orléans February 2006

12. Engine, Launching conference, Orléans 13-15 February 2006
MT trends
Resistivity method most used since the 80’s
Research always supported by geothermal exploration but also by oil exploration (coupled with seismic to distinguish water or gas from oil)
Reliable equipment, processing and interpretation (2D inversion) softwares available “off the shell”
3 D Inversion available (research stage)
Teams able to carry high density surveys
Disadvantage: resolution at depth function of EM signal periods, industrial noise (remote reference, but how far?)
Engine, Launching conference, Orléans February 2006

13. Example of 3D Inversion of MT data, Ogiri field, Japan (Uchida, 2005)
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14. Seismic reflection trends
Seismic velocities, Vp & Vs, related to
Fracture system
Lithology
Fluid/gas content (vapour/liquid limit)
Temperature
Traditionally used for geothermal reservoirs located beneath a sedimentary cover
High resolution 3 D imaging of the reservoir
Improvements in data acquisition and processing (developments issued from oil industry) allows to work in volcanic areas
Difficult to implement overseas (cost)
Marine seismic could be useful for off shore geothermal fields
Engine, Launching conference, Orléans February 2006

15. Seismic reflection example (Larderello), Fiordelisi et al. 2005
Engine, Launching conference, Orléans February 2006

16. Offshore high resolution seismic at Bouillante (BRGM, 2004)
Easy to implement
Depth of penetration < 200 m
High resolution mapping of faults
Help to understand the tectonic framework of the geothermal reservoirs on land
Engine, Launching conference, Orléans February 2006

17. Passive seismic trends
More useful for exploitation monitoring, than for exploration
Relatively “low cost” method but needs at least 6 month to 1 year recording
Benefits from EGS (and oil fields monitoring) improvements
Use of broadband seismology to hydrothermal systems characterization (research stage)
Engine, Launching conference, Orléans February 2006

18. Engine, Launching conference, Orléans 13-15 February 2006
Conclusion
Existing gravity and magnetism data reinterpretation could be a powerful tool to localize deep heat source in sedimentary basins
Coupling of methods (joint inversion, fusion of data, etc.) and integration with geology and geochemistry are compulsory
MT-seismic improvements: I-GET
Further developments in exploration should be linked to monitoring of exploited fields (4D geophysics)
Engine, Launching conference, Orléans February 2006

19. Engine, Launching conference, Orléans 13-15 February 2006
Merci pour votre attention
Profils de sismique réflexion haute résolution et levé magnétique face au champ géothrmique de Bouillante (Ouest Guadeloupe)
Engine, Launching conference, Orléans February 2006