Page last updated at 01:16 GMT, Thursday, 28 May 2009 02:16 UK

Ocean monster shows hidden depths

By Richard Black
Environment correspondent, BBC News, Japan

Chikyu ship (Jamstec)
The Chikyu carries the tallest ship-borne rig in the world

For a while during its design, Asahiko Taira told me, the ship became known as "Godzilla-maru", so unusual and top-heavy were its projected lines.

"We started planning the Chikyu about 15 years ago, and there were some people who thought we were too ambitious," he recalled.

"But now we can see that the ship is doing what it is designed to do and is opening up new possibilities."

As director-general of the Center for Deep Earth Exploration (CDex), an arm of Japan's Agency for Marine-Earth Science and Technology (Jamstec), Dr Taira played a key role in steering the Chikyu from vague concept to steel reality.

The idea was simple. Scientists wanted to drill down into the Earth's crust - and even through the crust - to get samples from the key zones 6 or 7km down where earthquakes and lots of other interesting geological processes begin; but that was impossible with existing ships.

Solution: find six hundred million dollars, and design and build a new one.

Chikyu explainer graphic

The first thing that strikes you when the Chikyu comes into view is the drill derrick, which stands 100m above the deck - the tallest ship-borne rig in the world.

Festooned from it are cables a handspan thick, and huge pieces of yellow machinery, all connected with the core business of sending a drill bit deeper into the Earth than has ever been done at sea.

"There is far more to drilling a hole in the ground than just drilling a hole in the ground," Steve Krukowski tells me as we look down from the deck outside the ship's onboard laboratory, home of the scientists waiting for the samples that the drillers will provide.

"In days gone by, rigs were manual, whereby you had a guy stuck up on the derrick running the drill pipe on a rope. All the rigs coming out nowadays are automatic, reducing the interface between man and machine."

Steve is the Chikyu's offshore installation manager, and runs the entire operation when the ship is stationary and drilling.

Although men are still needed on the drill floor, most of the heavy work is done by programmed machines that extract and replace lengths of the drill shaft - or "drillstring" as the professionals call it - or that screw lengths of pipe together, or bring lengths of casing that will line the drill hole.

A robot submarine is deployed near the sea floor, monitoring the shaft as it goes into the ground.

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Jason Dow is in charge of the ROV on board the state of the art drilling ship Chikyu.

But you might find all this on any scientific drilling ship. What allows Chikyu to reach the subterranean depths of a subduction zone is a large pipe that goes around the drillstring - the riser.

The riser extends from the bottom of the ship to the bottom of the ocean, effectively connecting the two.

The drill is lowered inside the pipe. Viscous drilling mud can now be pumped down inside the drillstring, returning to the ship inside the riser.

Common as mud might be, it is the key to penetrating down more than one or two kilometres. Without it, there is no way of extracting all the chippings and loose material thrown out by the drill bit, or of keeping enough pressure in the hole to prevent collapse.

Chikyu is currently the only scientific research ship in the world equipped with a riser drilling system, so it is the only ship able to do the work that its onboard scientists are attempting - to drill right into one of the Earth's major subduction zones, where one tectonic plate slides roughly under another one, with periodic catastrophic consequences.

Water feature

Currently, Chikyu is drilling in water about 1.6km deep; but one of the further scheduled holes will see a drop of 4km from ship to bottom.

So here is the challenge. Your ship is connected to the ocean floor by a drillstring and a riser, so it has to remain still; yet the water is too deep for anchoring.

The solution lies in technologies on the water and in space that combine into a dynamic positioning (DP) system.

The ship is continuously receiving information from global positioning satellites and from acoustic beacons on the sea floor around the drill site. Special equipment monitors the strength of the wind.

The DP software monitors these streams of data and issues commands to the six azimuth thrusters (variable-direction propellers) and one side thruster in the bow, telling them where to point and how hard to push.

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Animated graphic explaining how the Chikyu research vessel drills deep beneath the seabed

"Of course, it depends on the weather conditions, but usually we keep the ship's position to within five metres," says the Chikyu's captain Yasushi Minoura.

"If the weather is good, our position is like a dot."

Inner quest

The Chikyu's third hi-tech element is the onboard laboratory. Rock cores are scanned and cut and probed and scanned again as soon as they come up from the ocean floor.

"First we cut the core section into 1.5m lengths, and then we scan with an X-ray CT scanner," explains Toshikatsu Kuramoto, who is in charge of the core laboratory.

Riser pipes
Getting down to the sea-floor one pipe at a time

"Then it goes through a gamma ray attenuation sensor, measuring the rock density. Then we have a p-wave velocity sensor, measuring the speed of sound through the rock, we sense electrical resistance, susceptibility to magnetism, and the flux of gamma rays coming from the rock itself."

Only after these tests are the cores sawn down the middle - one half destined for further, possibly destructive testing, and the other for a core archive kept in the Japanese city of Kochi.

The current project, NanTroSEIZE, is concerned with the Earth's crust and the mechanisms that cause earthquakes.

But Asahiko Taira sees other possibilities for a ship whose drill can reach depths of six, seven or even possibly 10 kilometres under the surface.

"One of the most exciting new ventures could be the first penetration into the mantle," he says.

"You know the Earth has three layers - crust, mantle and core - and no-one has ever been down into the mantle before."

The mantle is much closer to the surface under the sea than on land, so the idea does make sense.

But such an operation cannot be conceived overnight. Applications would have to be made - at least in triplicate, one presumes - through the Integrated Ocean Drilling Program (IODP), the international venture that brings together scientists from all over the world and raises money for projects such as NanTroSEIZE.

The company that Jamstec contracts to run the ship is already planning for the operation if its name - Mantle Quest Japan - is anything to go by.

The cost of these operations is formidable - NanTroSEIZE comes in at several hundred thousand dollars per day - but in terms of a project that truly breaks new ground, what could be more appropriate for a vessel that has already re-written the rulebook of the possible?

Chikyu explainer graphic

Richard.Black-INTERNET@bbc.co.uk



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