Bouillante geothermal field (Guadeloupe, West Indies): Geochemical monitoring during a thermal stimulation operation.

Bernard Sanjuan (1) , Eric Lasne (2) , Michel Brach (1)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
2 CFG - Compagnie Française de Géothermie

In the geothermal Bouillante Field, only the well BO-2 is presently connected to a power plant. The now-closed well BO-4, located near BO-2 and producing around 10 t/h of steam in 1978, was considered as a potential candidate for a thermal stimulation test. During this operation (from 10th to 27th August 1998), around 8,000 m3 of cold sea water were injected into the fractured BO-4 reservoir. A chemical inhibitor was used to prevent anhydrite precipitation predicted by geochemical modelling. The two production tests, performed in BO-4 before and after the stimulation experiment (about 1,300 and 5,000 m3 of discharged brine), have shown a much higher productivity than the test carried out in 1978. An improvement in injectivity by 50% and in production stability has been observed after stimulation. Calculated well characteristic curves show that productivity has also been increased. An additional long time production test must be carried out to confirm the new data obtained from BO-4. During the stimulation operation, a multiple tracer test (MTT) was performed using 3 organic tracers (Na-naphtionate, Na-benzoate and isophtalic acid) injected into BO-4 with sea water and monitored during 45 days from BO-2 and 3 neighbouring thermal springs. The MTT has indicated and confirmed that no direct hydraulic connection exists between BO-4 and BO-2 and the 3 springs. A geochemical monitoring from BO-4 has been carried out during the two production tests. The production improvement by thermal cracking had no significant consequences on brine, steam condensate and non-condensable gases in terms of phase proportions and chemical, isotopic composition. According to the geochemical results, the injected sea water is never found at high proportions in the discharged fluid; it is rapidly mixed with the reservoir geothermal fluid. This can be explained by a relatively large interconnected reservoir volume and a high water-rock ratio, which is in agreement with the isotopic signature of the deep brine. Monitoring has shown that the chemical and physical characteristics of the deep geothermal fluid are similar in BO-4 and BO-2.

Domaines: Géochimie; Milieux et Changements globaux

Bernard Sanjuan, Eric Lasne, Michel Brach. Bouillante geothermal field (Guadeloupe, West Indies): Geochemical monitoring during a thermal stimulation operation.. Twenty-Fifth Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, Jan 2000, Stanford, United States. pp.215-222. ⟨hal-00773129⟩