HR: 16:30h
AN: V24B-03 INVITED     [Abstracts]
TI: Unzen Scientific Drilling Project: Challenging drilling operation into the magmatic conduit shortly after eruption
AU: * SAKUMA, S
EM: sakuma@geothermal.co.jp
AF: Japan Metals and Chemicals Co., Ltd., 101 Hosoyachi-Ukai, Takizawa,, Iwate, 020-0172 Japan
AU: NAKADA, S
EM: nakada@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, Univ. Tokyo, Yayoi, Bukyo-ku, Tokyo, 113-0032 Japan
AU: UTO, K
AF: Geological survey of Japan, AIST, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AB: Drilling operation was aimed at penetration into the core of the volcano 8 years after eruption of Unzen, including directional drilling in high temperature and with high inclination. The project started with fixing drilling site. Scientists and drilling engineers agreed to settle it at the northern slope of Mt. Unzen at 840 m asl, and the drilling target was set at sea level. Drilling operation was started in Feb. 2003. In the shallow section, frequent lost circulation and accidental side-track occurred due to the unconsolidated zone, and caused_@many troubles. Although the drilling was delayed, we succeeded in drilling down to 396m with the inclination of 25 degree in 17-1/2 inch hole and 13-3/8 inch casing section. 12-1/4 inch hole was drilled using TDS, EM-MWD, and DHM. When the inclination was built up to 75 degree at 795 m, we changed the drilling mode of trajectory control to keep the angle. A large fracture of total loss was encountered at 807m, and serious cuttings bed occurred. The latter made the drilling impossible to continue. Then, we inserted 9-5/8 inch casing down to 796 m. Trajectory correction runs was completed in 8-5/8 inch hole, and 7 inch casing was set down to 1550m. In 6-1/4 inch hole, though EM-MWD and DHM were not used, drilling inclination and azimuth were stable. Spot coring was started at 1582 m, the levels of spot coring depth were chosen based on the data of temperature measurement and cuttings observation. Though the drilling exceeded 1800m, the original target depth, drilling was continued, because we could not encounter the high temperature conduit at that time. Finally, the well reached the 1995 m, and succeeded in taking cores highly probable of magmatic conduit in July 2004. We could carry out geophysical logging mostly throughout the whole sections. Spot coring were done at 16 times; its total length was 75m. Although the highest measured temperature was 155 deg. C, the formation temperature may reach at least 200 deg. C. The reasons of smooth drilling after 9-5/8 inch casing installation were easy hole cleaning due to smaller diameter, least lost circulation, and no gas invasion.
DE: 8414 Eruption mechanisms
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting