THE BOUILLANTE GEOTHERMAL FIELD (F.W .I.) REVISITED :NEW DATA ON THE FRACTURED GEOTHERMAL RESERVOIR IN LIGHT OF A FUTURE STIMULATION EXPERIMENT IN A LOW PRODUCTIVE WELL.S

Abstract

Four geothermal wells were drilled in the Bouillante geothermal fractured reservoir in the 70's. They revealed high temperature conditions at shallow depth (240?C at 350m) but only Well BO-2 showed a significant productivity, certainly due to highly contrasted values of permeability throughout the
reservoir. New data on the local fracture system, the origin of geothermal fluids and well interferences have been collected. They point out the influence of fracturing on the development of the geothermal reservoir and the observed permeability anisotropy. Recharge of surface cold water (sea water, meteoric water), fluid mixing and heating, and discharge of hot fluids appear to be controlled by extensional highly-dipping faulted zones striking N100- 120o, organized into one or several, independant fractured reservoirs. Geothermal fluids result from mixture of sea water and fresh water, as indicated by their chemical and isotopic compositions. According to new temperature profiles, the low productive Well BO-4 probably intersected fluid circulations along natural fractures and layer contacts, corresponding to lateral fluid outflows. Future experiments will be devoted to stimulate these permeable zones.