Exploration is a key step for developing high-temperature deep geothermal and for assessing the geothermal potential. Relevancy and accuracy of the exploration depend closely on the deployed methods.
With the aim of increasing the Caribbean geothermal potential exploitation, the BRGM has focused its research efforts in reservoir localisation and characterisation for years, in particular, to overcome the specific Caribbean challenges due to:
- Uneven terrain and abundant vegetation, making it difficult to perform the observations, measurements and surveys,
- Complex geological structures, including strong heterogeneities at any scale, typical of active volcanic areas,
- Nearby sea, obstacle and discontinuity in the imagery and reservoir characterisation,
- Size of the deep targets, relatively small, associated with few surface indicators
In this WP, the BRGM develops two innovative methods (in geophysics and in geochemistry) to improve and adapt the geothermal exploration in this specific area. Both are applied on the well-known area of Bouillante (Guadeloupe) and on a green site (to be defined during the project).
Multidisciplinary data and knowlegde integration are required for a relevant exploration process. Among the central geosciences, fluid geochemistry and geophysics face directly the specific Caribbean challenges (heavy urbanisation, geological heterogeneities, nearby the sea, superficial and geothermal water mixing, water cooling…). Conventionally used methods appears non-relevant in such a context. To overcome these challenges, the BRGM tackles two issues:
Objectif 1: Develop innovative and well-adapted electromagnetic (EM) geophysical methods thanks to :
- (1) the coupled use of active (Controlled-Source EM), conventional passive (MagnetoTelluric MT) and aerial induced (Time-Domain EM) methods
- (2) the deployment of offshore and in-shore surveys.
Objectif 2: Develop new Caribbean-specificity-fitting chemical and isotopic geothermometers :
- Although geothermometers such as Ca-Mg, K-Mg, SiO2, δ18OH2O-SO4 have already been developed since the ’60s and are conventionally used, feedbacks from the field have sometimes been highlighted inconsistency with directly measured reservoir temperature. Similar observations can been applied to temperature prognostic based on geochemical and thermodynamic numerical modelling.
- In this WP, the BRGM addresses these issues by developing new thermometric relationships, such as Na-Cs, Na-Rb, K-Sr, K-Mn, KF ou KW, fitting the Caribbean specificities.
The well-known geothermal field of Bouillante, is Guadeloupe, have been selected to develop, test and validate the two innovative methods. In addition, the new surveys will be profitable for a better knowledge required for further exploitation of the area as planned by Geothermy Bouillante, the current company exploiting this field.
In addition, in the perspective of either characterizing a potential geothermal reservoir in new area(s) of interest, or of providing additional constraints on the location of the deep geothermal reservoir and its geometry in an area whose preliminary potential has already been characterised, other Caribbean territories (Saint Lucia, Saint Vincent, Grenada, etc region of interest for interregional cooperation and in agreement with the members of the consortium) could be also investigated.
Main planned steps:
- Offshore and in-shore geophysical survey in Bouillante, and coupled inversion processing (including all the EM surveys).
- Chemical and isotopic analysis of fluid samples (from selected wells and natural springs) accompanied by mineralogical and geochemical rock sample analysis for geothermometry relationship study.
Survey deployment in a new area (to be defined) for demonstrating the applicability of previously developed methods.