A geochemical case history of the HGP-A well, 1976-1982

The Hawaii Geothermal Project Well-A, located on the Island of Hawaii, was completed in 1976 to a depth of 1966 meters. The bottomhole temperature, under shut-in conditions, is 360°C and at full discharge is capable of producing about 45,500 kg/hr of a mixed fluid composed of 48% steam and 52% liquid. The major element chemistry of the fluids suggests that recharge to the reservoir is largely fresh meteoric water with no more than 10% to 15% of the recharge being from sea water. Extensive water-rock equilibration has occurred; however neither Na-K-Ca nor silica geothermometry calculations have been able to yield reasonable reservoir temperatures. Isotopic data suggest that the circulation rate and residence times of fluids in the reservoir are on the order of a few thousand years. Helium isotopic data also indicate that the heat source for this reservoir is very young or very large