| Title | The Geothermal Resource in the Roseau Valley in Dominica, West-Indies. Drilling of Three Exploration Wells; Lithology, Alteration, thermal Conditions and Chemistry |
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| Authors | Sigurður S. JONSSON, Thorsteinn EGILSON, Dadi THORBJORNSSON, Bjarni RICHTER, Alexis V. GEORGE |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Dominica, Laudat, Wotten Waven, resource exploration. |
| Abstract | An exploration project aimed at studying the geothermal activity in the Caribbean region was funded by the Organization of American states (OAS) in 2005. It provided a preliminary conceptual model of parts of the reservoir in the Roseau valley. The “Géothermie Caraïbes†project, initiated by the EU, the Commonwealth of Dominica and France, further focused on the Wotten Waven area and a report was published in 2008 with proposals and site-selection for the drilling of three exploratory wells. The drilling project was funded by the EU development fund, the French development fund and the Government of the Commonwealth of Dominica. Resistivity surveys had indicated the presence of a geothermal reservoir, up to 15 km2 in size, and chemical geothermometers estimated the reservoir temperatures to be in the range of 210-230°C. Drilling of the first well started in November 2011, and the third well was completed in May 2012. The formations drilled through were mostly ignimbrites/welded tuffs and other pyroclastic materials, intercalated with dacitic lava domes and intermediate/basaltic intrusions. Alteration was quite high and indicated fairly high formation temperature with the appearance of epidote at 900-1000 m. Clay-minerals also show progressive increase in alteration from smectite-zeolite zone near surface succeeded by a chlorite-epidote zone below 900-1000 m. Subsequent flow-testing was successful and all three wells did flow without aid. Highest temperature values recorded during flow-test after short heat-up period were ~246°C. Total flow of each well was 6-25 kg/s with enthalpy of around 1000 kJ/kg. The reservoir liquid is relatively dilute and the gas content of the steam was acceptable for electricity production in two of the three exploration wells. Quartz and alkali geothermometers matched the reservoir temperature in all the wells. Environmental monitoring was initiated prior to the drilling operation, during the drilling and three months from the testing of the last well. The results do not indicate any negative effect of the drilling and testing of the three wells on the aquatic environment in the Roseau Valley. |