The Otake geothermal water has been injected into two injection wells for up to 656 days. The injection and two other observation wells range in depth from 365 to 450 m. The average silica concentration in the water was in a range from 541 to 587 mg/1. The water was injected at 80, 60, and 50 °C to change the degree of supersaturation with silica. Both the falloff test and the maximum injectivity test were repeated to examine the decrease of injectivity. A tracer test, caliper log, and borehole televiewer survey were also conducted. The permeability-thickness product(kh) of Injection Well R-2 has reduced from 91 darcy-m down to 4 darcy-m after injecting 5.49×105 m3 water. In the case of Well R-1, its injectivity was nearly eliminated after injecting a total of 4.59×105 m3 water:its kh value of 224 darcy-m decreased to 0.79 darcy-m, and the water level rose up over the wellhead.
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