The subsurface temperature gradually increases southward in the Sumikawa geothermal field and decreases sharply toward the north. The geothermal reservoir contains a two-phase zone between the cap rock and hot water zone. The target for production was designated in the deep zone, in the high temperature southern area. The production and reinjection areas have been separated to recover thermal energy efficiently during the recycling of reinjection fluid; the wells have been spaced as far apart as possible to reduce well interference. To improve productivity and injectivity, cold-water well stimulation was applied, and this experiment reduced the number of wells required for 50 MWe power generation. (C) 2000 CNR.