| Title | Abnormally High-Pressure Geothermal Field |
|---|---|
| Authors | M. Nonaka, Y. Sugiyama, K. Akaku, Y. Yamada, H. Okada |
| Year | 2016 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Musadake geothermal field, Abnormally high-pressure reservoir, Intrusion, Boiling, Fluid inclusion |
| Abstract | The Musadake geothermal field located in the eastern part of Hokkaido is an unusual field associated with abnormally high pressure. In 2014, an exploration well, SMMG-2D, was drilled in the Musadake area and produced 26 t/h of steam and 16 t/h of hot water at atmospheric pressure almost stably during a short-term discharge test over two weeks. The well SMMG-2D recorded a maximum temperature of 333°C and a pressure about 5 MPa higher than hydrostatic pressure. It was drilled through a dacite intrusive body below impermeable mudstone, and Pressure Temperature Spinner logging data indicated that fractures in and around the dacite served as feed zones. We analysed an assemblage of hydrothermal alteration minerals and performed fluid inclusion microthermometry of SMMG-2D. Wairakite, sulphide minerals such as sphalerite and galena, epidote, and platy calcite were identified as hydrothermal alteration minerals in the vicinity of the feed zones. The platy or saw-tooth appearance of the calcite observed in the intervals of the feed zones indicates boiling conditions. The homogenisation temperature was in the range of 325–380°C, which exceeds the static temperature of the feed zones (320°C). The Musadake geothermal field is an unusual field with abnormally high pressure. The logging data, occurrence of hydrothermal alteration minerals, and fluid inclusion microthermometry for well SMMG-2D revealed hydrothermal activity near production zones. Although this high temperature and pressure well produced steam and hot water stably, the evaluation of this high-pressure reservoir remains problematic. In this report, we describe the geological setting, drilling data, logging data, and mineralogy of well SMMG-2D. |