柳津西山地熱発電所の探査・開発経緯と蒸気供給の現状

抄録

The Yanaizu-Nishiyama geothermal field is located on the western part of the Aizu district, Fukushima prefecture, northeast Japan. Geothermal investigation in the area were commenced by Mitsui Mining and Smelting Co., Ltd. (MMS) in 1974. Advanced surveys were also carried out by Ministry of International Trade and Industry and New Energy and Industrial Technology Development Organization (NEDO). In the earliest model, the geothermal reservoir was thought as a horizontally spread porous media beneath the Miyashita mudstone member which acts as a cap rock. But later surveys, such as structural well drilling in NEDO's survey during 1982-1983, indicated that the reservoir was strongly controlled by vertical faultzones. And Okuaizu Geothermal Co., Ltd. examined the detail fissure structure. Okuaizu Geothermal Co., Ltd. planned the steam production facilities with next characteristics. (1) A single flash method has been applied. (2) Two phase fluid from each production well is transported to two steam separation facilities. (3) In order to prevent silica scaling in the re-injection wells, brine is dilutedwith waste water from the power station and river water. (4) Concentrated operation monitoring system using DCS (Distributed Controll System) has been applied. Construction work has been undertaken between 1993-1994, and steam production has been started in December 1994 for rehearsing plant. Commercial operation beganon May 25, 1995. Large amount of steam decline was observed, mainly because of carbonate scalinginside of several production wells. Although this trouble was dissolved using scale inhibitor injecting system, steam decline problem still remains. It is necessary to investigate the problem.