Monitoring of the Bouillante Geothermal Exploitation (Guadeloupe, French West Indies) and the Impact on Its Immediate Environment

Abstract

The Bouillante high enthalpy geothermal field, 250-260°C, is located in the Guadeloupe volcanic Island (French West Indies). Since 2005, the new geothermal power plant has had an installed capacity of 15 MWe gross which represents about 8% of the annual electricity needs in the Island. It is supplied by 3 wells which can produce up to 120 tons/h of steam. No residual water is re-injected. Among the research efforts carried out by the BRGM group and partially funded by ADEME (French Environment and Energy Management Agency), different monitoring methods of the geothermal exploitation have been started, tested and developed in order to optimize and secure electricity production and to control its impact on the immediate environment of the power plant. This is especially important because the power plant is located inside the Bouillante town. These methods are: geochemical monitoring of the fluids collected from the geothermal wells and neighboring thermal springs in order to control the evolution of the fluid geochemistry and the Gas/Steam Ratio, surface soil thermometry monitoring, geophysical monitoring such as broadband seismology, microgravity and SAR interferometry to detect mass transfers or changes in the geothermal reservoir during its exploitation as well as vertical surface ground deformations. This paper presents the main results and conclusions obtained from these different monitoring techniques. On the whole, despite the pressure decrease observed in the geothermal reservoir due to an annual production estimated at about 4.5 millions of tons of fluid, no significant variation of the monitored parameters has been detected from these methods during four quasi-continuous years of geothermal exploitation. Most of these monitoring techniques will be continued and probably developed in the next few years, especially if the produced fluids are re-injected, in order to anticipate and/or quickly take into account problems such as issues related to chemical change of the reservoir fluid or induced microseismicity.