A three-month circulation test was conducted in 1991 at the Hijiori hot dry rock test site. During the test, pressure, temperature, and spinner survey (PTS survey) was periodically conducted in three production wells, HDR-1, HDR-2, and HDR-3. Flow impeadance in pathes between a injection well SKG-2 and the production wells was calculated from pressure and flow data obtained by the PTS survey. Flow regime in fractures is estimated by impeadance difference in each path and impeadance changes during the circulation test.
The injected and produced fluid was collected during tracer tests to monitor water-rock interaction in the reservoir. Increase of dissolved species concentration in produced fluid shows that waterrock interaction in the fractures took place in a very short residence time; less than 6 hours.