October 22, 2007
The Japan Agency for Marine-Earth Science and Technology
The Deep-sea Drilling Vessel "Chikyu" of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC: Mr. Yasuhiro Kato, President) had an incident where the bottom section of the drill pipe became disconnected in the borehole during drilling operations for the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) *1 in the Kumano basin off the Kii Peninsula, as her first expedition as part of the Integrated Ocean Drilling Program (IODP)*2.
Chikyu departed the port of Shingu on September 21, 2007. As of today, completed operations include a pilot hole at Site NT2-03 (drilling depth 1,000 meters below the seafloor, or mbsf) on September 28, LWD hole at Site NT2-03 (drilling depth 976mbsf) on October 7 and LWD hole at Site NT3-01 (drilling depth; 1,401.5mbsf) on October 18 and then, drilling at Site NT2-01 has been underway since October 20.
The Integrated Ocean Drilling Program (IODP) is an international marine research drilling program dedicated to advancing scientific understanding of Earth by monitoring and sampling subseafloor environments. Through multiple platforms, preeminent scientists explore IODP principal themes: the deep biosphere, environmental change, and solid earth cycles. IODP has started since October 2003 led by Japan and USA. IODP now has 21 member countries.
LWD is a technique to measure geological formation properties at the site while drilling, by attaching physical measurement sensor to near the top of the drill pipe.
Through continuous in-situ monitoring of drilling site, geological data can be obtained rather quickly. It is effective for the drilling at complex geological structure, especially in Nankai Trough, to acquire the scientific geological data and for the following coring operation to have data on borehole conditions for safety monitoring and risk aversion. Data planned to obtain by LWD are formation density, porosity, velocity of sound speed, natural gamma ray, resistivity and fluid pressure, etc.
A part of LWD uses americium-berylium (neutron source) and cesium 137 (gamma-ray source) as sealed radiation source. There will be no environmental impact since they are sealed in pressure resistant container.