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Study identifies strong geothermal potential at Petite-Terre in French African territory Mayotte

View of Mbouzi islet and Grande-Terre from a height of Petite-Terre, Mayotte (source: flickr/ Jean-Pierre Dalbéra, creative commons)
Alexander Richter 26 Oct 2020

Studies by the French geological survey BRGM identify strong geothermal resources of high temperature at Petite-Terre in the French overseas territory of Mayotte in the Indian Ocean. Depending on fossil fuel for power generation, this could provide the opportunity to cost effective and cleaner power generation for the island territory.

In an article already published in September 2020, Yann Le Bigot, Energy Engineer, at French climate change agency ADEME, shared details on exploration work to determine the geothermal potential of Petite-Terre, Mayotte. Mayotte is an archipelago in the Indian Ocean between Madagascar and the coast of Mozambique off the coast of southeastern Africa. It’s a department and region of France. Comoros Islands is another island in that region but further west and closer to the continental coast.

Since 2005, BRGM – the French geological survey – has been carrying out an exploration program on the island. The latest study, carried out in 2019, concluded that there is strong potential at Petite Terre. An additional study is planned for 2020, in order to prepare exploration drilling and confirm the presence of this resource.

Demand

In 2017, the electricity mix of the Mayotte department included 5% photovoltaic production, spread over more than 70 installations on the island, and 95% diesel thermal production, provided by the two power plants operated by Electricité de Mayotte. In order to diversify its sources of electricity supply, the Departmental Collectivity of Mayotte has implemented since 2005 a vast program to develop renewable energies, including the evaluation of the geothermal potential of Mayotte in order to produce electricity.

As part of this program, the geothermal exploration study carried out by the BRGM, between 2005 and 2008, in Mayotte, made it possible to identify the Petite Terre area as the sector showing signs of a potential active geothermal resource. deep (> 1,000 m) of high temperature (> 200 degrees Celsius), likely to be used for power generation. Following this first study, in order to establish the existence of an area of ??geothermal interest and to locate it with precision, it was necessary to implement a deep exploration program, including in particular the drilling of exploration. Given the cost and complexity of such a program, a preliminary step was carried out by the BRGM with the support of ADEME Mayotte from June 2018 to December 2019, in order to define and size the campaign as best as possible. exploration with regard to the objectives and uncertainties specific to Petite Terre.

Results

As part of this project, the new geoscientific data (in particular geophysical) that were collected made it possible to confirm the strong deep geothermal potential at Petite Terre, but also the need to carry out several deep exploration holes (up to 2,000 m deep) in order to:

  • characterize the nature of geological formations;
  • identify the different water inlets, their temperature and their physico-chemical characteristics;
  • determine the permeability of the reservoir;
  • estimate the electricity production capacity of the latter.

To achieve this, and before any exploration by drilling, it is recommended to carry out, as a first step, an additional study which will define the location of the wells and assess their probability of success. This study could be based on geoscientific work (eg geological, geophysical, geochemical and hydro-thermal) targeted on Petite Terre, but also on the valuation of data acquired by the Mayotte Volcanological and Seismological Monitoring Network (REVOSIMA), put in place due to the exceptional seismic-volcanic activity observed since May 2018 off Mayotte, probably linked to the presence of a high-temperature geothermal resource.

Utilization

The additional exploration drilling siting study, which is expected to begin in the second half of 2020, will bring together the geoscientific elements necessary for any decision to invest in exploration drilling. Depending on the results, boreholes should be carried out in order to confirm the presence of an exploitable geothermal resource and to estimate it quantitatively. This information will constitute one of the key elements in order to be able to move on to the next phase of exploitation of the Petite Terre geothermal resource to produce electricity, and thus potentially significantly increase the share of renewable energy in Mayotte’s energy mix ( several tens of percent of total production).

“Geothermal energy is a controllable renewable energy that represents a viable solution to meet our need for energy autonomy. Thanks to the support of BRGM, the study confirmed the existence of a deep geothermal potential on Petite Terre. From now on, these results must be specified with a more in-depth exploratory phase. It will confirm the possibility of exploiting a geothermal resource to produce electricity and thus increase the share of renewable energy in Mayotte’s energy mix. “, so Yann Le Bigot, Energy Engineer, ADEME

Source: BRGM