Posted on behalf of Nicola Jones
The Chikyu — the first research ship designed to drill far into the Earth in deep waters, using oil-rig-style risers — is running a bit behind schedule, thanks to high operating costs and some technical problems. At a poster presented at the American Geophysical Union meeting this week, Yuichi Shinmoto, an engineer with the Japan Agency for Marine-Earth Science and Technology, reported on how they have had to redesign the drill bit several times. The ship’s mission to drill into an underwater fault line in the Nankai Trough off the coast of Japan – originally planned for 2007 to 2012 – won’t be finished for at least another 5 years yet, he says. The ship spends several months a year being hired out to oil-drilling companies to help offset its costs (see story).
Drilling in the Nankai Trough, where one tectonic plate slides beneath another some 6-8km below the seafloor, has gone relatively well, if slowly. In 2008, researchers successfully pulled up about 38% of the cores that they drilled, reports Shinmoto. That’s about average for ocean-based drilling, but they decided to remodel the drill bit to do better – reshaping it so it has a single point instead of carving out a donut shape. With this bit in use in 2009, they achieved about 80% core recovery – but the drill teeth were completely worn out after only two cores. So they have redesigned it again, this time using a stronger material and two rows of teeth. They’re hoping for better results when they use this new bit for the first time at the end of this month. Such technical troubles aren’t unusual for an ocean drilling expedition.
So far the Chikyu has drilled 1600 meters below the seafloor (see story) – just a tiny portion of the 6-8km depth of the fault line in the Nankai Trough, and less than the more-than 2km that the JOIDES Resolution has reached (an older and smaller drill ship). The ultimate goal for the Chikyu is to try to drill straight through the Earth’s crust to get cores from the mantle underneath — that will also mean drilling about 7km down, at a site yet to be chosen from candidates near Hawaii, Mexico or Costa Rica, hopefully within a decade or so.
Image: JAMSTEC