Evaluation of the Hijiori HDR geothermal resource continued in 1996 with a 31-day flow-enhancement circulation test to characterize the improvement in connectivity of the two production wells. In this last of a series of short-term circulation tests to improve reservoir performance, analysis of the thermal energy extracted was added to the accumulated data from previous tests to predict the thermal energy production capability in a planned long-term circulation test. In contrast to prior short-term circulation tests, the injection flowrate was maintained essentially constant over the 31-day period. The test consisted of two production periods, the first for 23 days to stimulate flow to production well HDR-3 (with well HDR-2a shut-in), and the second for 8 days with flow to production wells HDR-2a and HDR-3. For analysis of thermal energy extracted, the test data for both production periods were treated as flow through independent zonal sectors similar to the technique used for the prior Hijiori short-term circulation tests. The thermal output was estimated by the two heat-sweep methods of calculated temperature cooldown at the production well and calculated thermal-front velocity at abandonment temperature from temperature cross-sections across each zonal sector. The two methods provide estimates of thermal energy extracted from the two zonal sectors during the circulation periods and the reservoir lifetime to the selected abandonment temperature.

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