Reservoir Simulation on the Kirishima Geothermal Field

Abstract

The Kirishima geothermal field is located in the southwestern part of the Kirishima volcano in ,Kagoshima Prefecture.

Nippon Steel Corporation(NSC) and Nittetsu Mining Company(NMC) joined to explore the geothermal resources of the field in 1978.Before then, the Government and NMC carried out surface surveys in the fields of geology,gravity,resistivity and surface temperature and three shallow structural wells were drilled. After considering their results, twenty-oneexploratory wells were drilled,and geological and geophysical loggings and well tests were carried out to obtain more detailed information on the geothermal reservoir in a 12 km area of the field. The results suggested that the predominant reservoir existed in the Ginyu area.On the basis of the information obtained,a simulation of the natural state was computed repeatedly using the simulator developed by NSC,and a geothermal structural model for the Ginyu area was established.Pressure change computed by this model for three years of actual' production/reinjection agreed with the observed data.We consider that the validity of this model is assured. The simulation of production indicated that steam production equivalent to 35 MW of electricity could be secured in the Ginyu area for more than 30 years.