| Abstract |
The New Energy and Industrial Technology Development Organization WEDO) has been conducting a research project named "Deep-seated Geothermal Resources Survey" since 1992 in order to evaluate the possibility of utilizing deep geothermal resources which exist beneath already-developed shallow reservoirs. A deep drillhole, WD-I, has been drilled in the Kakkonda geothermal field located in northern Honshu, Japan. WD-I, which is the deepest geothermal well in Japan, reached a depth of 3,729171 in I995 by applying innovative drilling techniques such as the top-drive drilling system (TDS) and a mud cooling system. Quaternary granite, considered to be a possible heat source, was encountered at depths of over 2,860 m. The borehole was drilled into the granite for a length of 870 m to determine the thermal structure and deep fracture systems. Temperature logging was carried-out up to a standing time of 1.59. hours using electric temperature tools, a kuster, and temperature melting tablets. We confirmed a temperature greater than 500 "c at the bottom of the well, but we did not encounter major lost circulations during drilling in the granite. This is the highest temperature recorded in a geothermal well in the world. Borehole fluids near the bottom of WD-1 were collected for geochemical investigation. The Cl content in the fluids was extremely high and the precipitation of halite occurred during the sampling. Side-track drilling of WD-I is now being conducted from a depth of 2,200 m, targeting productive fractures estimated near the boundary of the granite at a depth of about 3,000 m. |