Overview of Production at the Mori Geothermal Field, Japan

Abstract

Mori geothermal field is located in Hokkaido, northern part of Japan and has a liquid dominated reservoir. This field is characterized by its caldera, Nigorikawa Caldera, of an angular funnel shape. It was formed 12,000 years ago with a series of violent eruptions. Heat sources of the field are related to the volcanic activities. Also, major permeability of the reservoir is related to fractures associated with the formation of the caldera. Geothermal exploration in the caldera began in 1972. A 50 MWe double-flash power generation started in 1982, with 4 production wells and 4 reinjection wells.
Stable steam production in this field has not been very easy. This field has experienced many types of troubles since its start of operation, e.g. CaCO3 and CaSO4 scaling in production wells, stevensite scaling in hot water pipelines and reinjection wells, return of reinjected water to producers, down flow of shallow ground water into the reservoir, resulting enthalpy decrease of the produced fluid, and resulting decline of steam production. Some of them have been solved but some of them are still not. Reassessment of the reservoir suggests that sustainable steam production from the reservoir is about 250 t/h. Current output is 20 to 25 MWe with 10 production wells and 10 reinjection wells.