The Mixing of the Cooling Waste Water Reinjected with the Production Fluid at the Uenotai Geothermal Power Station

Abstract

At the Uenotai geothermal power station, the cooling waste water had been reinjected into underground through the reinjection Well F-1. Reinjection into Well F-1 started in February, 1993. After one and a half years (June,1995), the production well T-44, which was originally producing only steam from the feed zone located 250 meters away from the reinjection zone of Well F-1, started producing steam-water mixtures as the fluid enthalpy decreased, and the injection capacity of Well F-1 coincidentally increased about four times. These phenomena suggest subsurface interference between the two wells. On the basis of monitoring of stable isotopic ratios, fluid chemistry, and production history of Well T-44, a quantitative interpretation was made.