Geothermal resource assessment of the Wotten Waven geothermal field – Dominica, West Indies

Abstract

Geothermal resource assessment involves the estimation of the geothermal energy that can be extracted from a reservoir and utilized economically for a specified time period. It is based on the evaluation of surface discharge, well logs and other geoscientific information obtained via geological, geophysical and geochemical measurements. This report is aimed at conducting a geothermal resource assessment of the Wotten Waven geothermal field in Dominica, based on available surface exploration data and data obtained from three exploratory wells: WW-01, WW-02 and WW-03, by establishing a simple natural-state numerical model of the Wotten Waven field and through the determination of the field’s resource potential. The success of recent exploratory work resulted in the proposed installation of a 10-15 MWe plant for domestic consumption with plans to extend the capacity to 120 MWe by 2020.

Available downhole temperatures indicate the presence of a 234-250°C high-temperature reservoir of 600-2000 m thickness at depths greater than 100 m b.s.l. A conservative volumetric analysis confirms with a 90% probability that the current Wotten Waven field should be able to sustain a capacity of 10-15 MWe for up to 100 years. A natural-state numerical model modelled over an area of 5 km2 requires 80 kg/s of fluid with an enthalpy of approximately 3300 kJ/kg to be injected into three pre-determined heat sources giving a thermal input of approximately 260 MWt. A more detailed numerical model is needed to cater for a greater reservoir surface area to accurately model the reservoir conditions of the Wotten Waven field, including data from the newly drilled production and injection wells. Once the wells are put into production, a production model should be set up to simulate the response of the reservoir (pressure, enthalpy, etc.) to utilization and to assist in optimizing the power production during future utilization.