Effects of the Injection Temperature on Injectivity of Geothermal Wells.

概要

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High temperature reinjection scheme is applied to many recently constructed geothermal power stations to prevent wells and reservoirs from silica scaling and to make an effective thermal recovery. At Sumikawa, Northeast Japan, production and reinjection started in November 1994 to supply steam for the geothermal power station. The injectivity has progressively decreased with time. To clear the effect of water temperature on the injectivity, injection tests were carried out for SD-1 at Sumikawa in 1995, where borehole pressures were monitored with changes in injection temperature and flow rate. The temperature of the injected water was controlled to be approximately 50°C and 150°C at wellhead. The results show that the pressure differences between different injection flow rates and the borehole pressures at the depth a pressure gage was located are smaller and lower respectively, for low temperature water than those for high temperature water. This means that the transmissivity and the injection flow rate at low injection temperature become larger than those at high injection temperature. In conclusion, it can be said that water temperature affects the permeability-thickness and the injection flow rate, due to the changes in fracture aperture and reservoir pressure around the injection well, changing the injectivity.
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