Abstract
The Appi area was selected as one of fields to be investigated under NEDO' s project “Geothermal Development Promotion Survey”. Drilling of 6 wells, various investigations and integrated analyses were conducted on the Appi area between 2000 and 2003 fiscal years. The geothermal system is located around the stepped faults at the south edge of the Appi collapsed structure. The heat source is originated from a magma chamber at great depth of Mt. Appi-dake which lies to the south of the investigation area. The geothermal fluids ascend the fractures around the faults at the south edge of the Appi collapsed structure zone. The fracture system is mainly composed of the northward steeply inclined fractures trending east-west, and the southward gently inclined fractures trending east-west corresponding to the bedding plane. The geothermal system is characterized as a liquid dominated reservoir to some extent. On the other hand, a vaporstatic pressure gradient is recognized at the southwestern part, which indicates presence of a vapor phase. The chemistry of the discharge fluid from the Appi investigation wells indicates a steamheated water with a weak alkaline Na-SO4-HCO3 type. Based on the numerical simulation, it is estimated that the geothermal reservoir in the Appi area is capable of generating 20 MWe for 30years.
