| Title | A Large Wellfield Steam Explosion at the Onikobe Geothermal Power Station |
|---|---|
| Authors | Akasaka, Chitoshi; Shimizu, Isao; Nakanishi, Shigetaka; Tezuka, Shigeo |
| Year | 2011 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Steam explosion; thermal activity; wellfield; power plant; Onikobe; Japan |
| Abstract | The Onikobe single-flash steam turbine geothermal power plant has been supplying electricity to the grid for 36 years. Power station output has gradually increased over the years and reached 15 MWe (gross) in February 2010. Numerous natural geothermal surface manifestations were present in the field prior to development. New fumaroles accompanied by hot liquid discharges spontaneously appeared near Well 128 on 8 September 2010. Such spontaneous features had frequently appeared in the past. The new features were monitored carefully – the manifestations intensified abruptly on 8 October, and the resulting crater engulfed Well 128 the same day. Cold water was pumped into the well in an unsuccessful attempt to reduce the wellhead pressure. The fumaroles continued to grow until a large scale steam explosion occurred on 17 October 2010. A large steam cloud with entrained solid explosion products rose high into the air. A crater formed and the Well 128 wellhead became submerged in hot water. Large quantities of erupted material fell in the vicinity. One project worker was killed and another was severely burned. Steam and hot water are still discharging. This paper describes the sequence of events, the probable causes, and the present situation at Onikobe since the explosion. |