Chikyu - Drillship

The Chikyu is a scientific drillship which was designed to operate in water depths in excess of 2500m. It incorporates a range of facilities that enable it to drill up to 7000m below the sea bed. This makes it one of the world’s deepest drilling vessels. By comparison, the US deep-sea research ship Joides Resolution achieved a hole of 2111m.

Its mission is to drill into the tectonic plates and potentially into the earth's mantle. It is anticipated that research will play an important role in understanding the principles of tectonic movement and earthquake prediction.

Chikyu means 'Earth' in Japanese. It was built by Mitsubishi Heavy Industries for the Japanese Agency for Marine Earth Science and Technology (JAMSTEC).

The Chikyu was delivered to its owners in 2005, but since then it has been carrying out a range of system integration tests. These were followed by a shakedown cruise, undertaking test drilling off the Shimokita Peninsula to ensure that everything is working satisfactorily before it commences full operations in 2007. It is anticipated that future operations will be carried out off Kenya as well as off Australia.

DESIGN

The drill ship has an overall length of 210m and a breadth of 38m. It has a 16.2m depth and a 9.2m draught. The gross tonnage is 57,000gt. The ship has a complement of 150 people, which includes the drilling and support personnel as well as the laboratory staff.

At its centre lies the drilling derrick. This stands 70.1m high and has a deck footprint of 18.3m by 21.9m. It is large enough to accommodate a string of up to 10,000m and has a hookload capacity of 1250t. The drawworks, which moves the string in and out of the hole, is rated at 5,000 horsepower (3,728kW).

The drillpipe, riser and casing are stored in the pipe rack which is located next to the V-door. They enter the derrick by an automated pipe transfer system. This is based on a rail-mounted Hydratracker. Once the pipes are introduced and stored in the derrick, an iron roughneck is then used to connect them onto the drillstring.

Drilling is carried out by means of a top drive system. The drillstring enters the water through a 12m by 22m moonpool. In order to allow for the vertical and lateral movement of the drillship in the ocean, the ship includes a crown-mounted heave compensator.

When drilling, to prevent reservoir pressure suddenly forcing its way back up the drillpipe, there is a blowout preventer system. This weighs 380t, stands 14.5m high and can withstand a pressure of 103MPa. Because of the water depths, the drillship has a riser drilling and a riserless drilling option.

To facilitate well operations, there is an electric hydraulic knuckle boom crane system. Its principal operation is to load and unload stores from the support vessels, mainly the drill pipe, casing and other tubulars.

PROPULSION

The main propulsion is by a series of thrusters, which are also responsible for the dynamic positioning that is fundamental to deep water operations. These enable the drillship to maintain position in conditions of up to 23m/s wind speeds, a surface current of 3–4 knots and wave heights of up to 4.5m.

The system includes a 2550kW tunnel thruster in the bow, three 4100kW thrusters located forward and another three 4100kW thrusters aft. The diameter of the thruster propellers is 3.8m. This also gives a 12 knot cruising speed and gives the ship a range of around 14,800 nautical miles (full load condition, 10 knots).

The power is provided by six generators with an output of 5000kW each. There are also two auxiliary generators with an output of 2,500kW each.