Stimulation test of a high-enthalpy geothermal well by cold water injection.
Résumé
Initially, the low steam output of exploration well BO-4 in the Bouillante geothermal area of the island of Guadeloupe, Lesser Antilles, did not justify its connection to the existing power plant. Production decline in well BO-2, the only one sending steam to the power plant, raised in 1997 the question about the possible utilisation of BO-4 as a makeup well, if its output could be improved. Between August 10 and 27, 1998, an experimental stimulation program by thermal cracking induced through cold seawater injection was performed. Production tests before and after the experiment were used to evaluate the effects of the stimulation. During the BO-4 stimulation, a Multiple Tracer Test was carried out using three different organic tracers. For 45 days, tracer breakthrough was monitored in well BO-2 and three neighbouring thermal springs. The results indicated that they had no evident hydraulic connection with BO-4. The samples of separated brine, steam condensate and non-condensable gases collected before and after the stimulation experiment showed no noticeable changes in the chemical and isotopic composition of the geothermal fluid produced by BO-4. Microseismic monitoring studies did not detect any events that could be related to hydrofracturing related to the injection into BO-4. It is inferred that the productivity enhancement showed by the well is due to an increase in permeability caused by a thermal cracking mechanism.