The story goes that in Spring 1959, a brain storming session over breakfast at Dr. Walter Munk’s house resulted in Dr. Munk saying that he “wanted to drill to the Mantle”. This was the beginning of scientific ocean drilling. However, there still remained many technical hurdles and difficulties to overcome to make this a practical effort.
Great international collaborative science projects, like the International Space Station have been created over the years, but most of these have been led by the USA. As an island nation, Japan decided to contribute by designing and building the first scientific riser drilling vessel, D/V Chikyu, designed to reach the Mantle itself. Taking the lead in deep scientific ocean drilling, Chikyu uses state of the art technology to take scientific drilling into new directions. In this way, Japan hopes to make great contributions to Earth Science.
Japan is excited to take the lead with this new drilling ship, especially after so many years relying on the USA scientific drilling vessel. Working together is a great way to advance to goals of both countries. This special, purpose-built scientific drilling vessel will focus on drilling fewer, deeper, boreholes, to examine deep geological and geobiological processes.
Strictly speaking, the Mantle belongs to no single group or person; rather it “belongs” to everyone. If D/V Chikyu is successful in collecting samples from the Mantle material, then those samples would be curated by JAMSTEC. Much like the Moon, the lunar rock samples returned to Earth by the Apollo astronauts belong to NASA. These samples are available for science research, since they also “belong to the Earth”. However, the scientific priority goes to the onboard and shore-based scientists. If cores samples are collected, they, provide the experimental material necessary for various studies and are a genuine treasure for the world. One of the most important jobs is to ensure that these data and core samples are fairly distributed among researchers studying the mantle, and also collaborate on producing cutting edge science results, all made possible through the efforts of the supporting team members of Chikyu and JAMSTEC. We are confident that Chikyu will be able to support these efforts.
All the cores so far collected by Chikyu, along with other IODP cores, are preserved in special climate-controlled core repository at the Kochi Core Center. KCC holds about 120 km worth of core samples.
Registration of a ship harbor
All ships are required to register a nationality by law. Registering a ship’s documented nationality is like a legal domicile; since the JAMSTEC Headquarters is in Yokosuka, Japan, Chikyu is registered in Yokosuka.
The home port is the home base of a ship or a main anchoring harbor, and isn't required by law, so ship owners can freely choose a “home port”. Since D/V Chikyu cruises all over the world for long periods, there is no need for any particular home port. One reason is that when at sea, crew changes, fuel and resources re-supply are conducted on the ocean, and don’t require a port call.
The ship classification
Ship require periodical examination, much like automobile inspection for cars. Ship classification societies inspects ships and certifies that the ship meets the requirements of the inspecting society. The name of the certifying ship society is called “the ship order” of the ship. The ship order of Chikyu is NK (the Japanese society of maritime affairs). Other examples of famous ship order societies include: ABS (United States), LR (United Kingdom), and DNV (Norway), in addition to NK.
Chikyu’s ship number is "136960". This number is used to distinguish between ships, and by Japanese law is given to all Japanese ships of more than 20 tons gross tonnage. D/V Chikyu is a Japanese ship, and is registered in the City of Yokosuka, Kanagawa Prefecture, Japan, and therefore the ship number is regulated by the Kanto Transit Bureau, a government office.
The hull of D/V Chikyu was built in Tamano City, Okayama Prefecture (Mitsui Engineering & Shipbuilding Co. Ltd.) on 25 April 2001 (Heisei 13). The tall derrick was installed, as well as other equipment and laboratory area completion, in Nagasaki, Nagasaki Prefecture (Mitsubishi Heavy Industries Nagasaki Shipyard & Machinery Works, Koyagi Factory) and delivered to JAMSTEC on 29 July 2005.
In principle, Chikyu has accommodation and safety equipment for 200 people aboard. This includes the regular crew, stewards for cooking and cleaning, drillers and sub-contractors for drilling operation, researchers, marine technicians for data analyzing and maintain machine and instruments. What job do you want to do onboard Chikyu?
In case of emergency, there are 4 lifeboats (75 seats) and 1 lifeboat with 50 seats are equipped on starboard and port sides for a total of 200 per side. This is because Chikyu might list to one side, leaving only one side that can be used.
If you want to sail as a scientist belonging to a research institute in a IODP signatory partner organization (J-DESC, ESSAC, USSSP), you can apply to sail. You could also sail as a lab technician or as a third party specialist engineer. You can also write a drilling proposal for the bi-annual submission period and apply via the International Ocean Discovery Program (IODP) web site. Please follow the instructions there. A science proposal is required to develop the scientific background, purpose, goals to drill, basic hypothesis, and site survey data, what tools and equipment are required, and to develop a drilling expedition. Once the proposal passes a peer and safety review, the onboard science leaders or co-Chief scientists, start recruitment through the IODP member organizations. A secretariat of coordination of Japanese drilling science consortium (J-DESC) is for Japan-based research scientists. A call to apply to sail is announced on the IODP website and member organizations about 6 months to 1 year before actual sailing. Apply, and if you are selected, it's possible to sail on Chikyu!
In general, wind by itself is no problem. One exception would be typhoons, which can be dangerous, so for those storms and for low pressure storm cells, Chikyu suspends operations for safety. In these cases, Chikyu may decide to evacuate and leave the drill site.
Chikyu is designed to endure strong winds and waves and continue working. However, the safety of the crew and passengers is the first priority, therefore, Chikyu always careful pays close attention to weather and hydrographic conditions forecasts. Once a typhoon and low pressure is observed approaching, we obey all safety procedures (e.g. close the BOP) for the borehole. After separating the riser from the LMRP (Lower Marine Riser Package), the upper part of the BOP and the riser pipes are recovered on the ship, while the Chikyu seeks refuge in sheltered waters.
There are three kinds of pipes required for deep drilling.
- Riser pipe: Connects the ship to the seabed. Drilling mud is recovered from the bottom hole to the ship through the riser pipe. Drill pipe also passes through the riser pipe.
- Drill pipe: Drills the hole, with special bits attached at the bottom of the pipe to drill below the ocean floor.
- Casing pipe: Protects the inside wall of the borehole.
You can access the following web site to find in more detail drilling method.
Chikyu has 10 km of drill pipe (10,000 meters) onboard. This means it is possible to drill from the ship to 10,000 meters deep from the ship. To do this requires riser pipe, therefore, the water depth can be a maximum of 2,500 meters, to support the heavy weight of the riser system above. 10 km minus 2.5 km gives us 7.5 km (7,500 meters), which is the length of the longest possible drilling depth under the seafloor.
This all depends on the toughness/firmness of the submarine mud, soil, and rock. For example, it is easy to get a 10 meter core sample in soft sediments, but when it's firm, it takes a long time to drill. Usually, Chikyu encounters soft mud from the seafloor, and this gradually hardens into solid rock as you drill deeper and deeper. When soft, about 300 meters a day can be drilled; when firmer, it takes a day to drill 50 meters!
The speed of drilling into the formation is called the rate of penetration (ROP). When drilling into the seafloor around Japan, the general guide is:
Shallow portion (0 – 1,000 m below sea floor [mbsf]) about 300 m/day (15 m per hour),
Middle portion (1,000 – 2,000 mbsf) about 150 m/day (8 m per hour) and
Deeper portion (2,000 – 3,000 mbsf) about 70 m/day (3 m per hour).
If the bit needs to be changed, at 4,000 mbsf depth for example, it takes about 6 hours to recover all the drill pipe back to the deck of Chikyu, or about 600 m per hour.
Of course! However, over time, drill pipe and riser pipe become fatigued and can develop cracks, etc., so they are all periodically examined and replaced as needed.
Casing pipe, on the other hand, will be deployed downhole and left in place. Casing pipe is used to protect the borehole from collapse, and they are cemented into place.
A drill pipe and a riser pipe are all assigned serial numbers, and their usage and status are checked regularly and replaced with new pipe before they become worn out..
When D/V Chikyu is engaged in riser drilling operations, these can last for at least 5-6 months, sometimes longer. During this time, Chikyu needs to remain on site, secured to the ocean floor. Therefore, all staff changes and resupply must take place by supply boat and helicopter. Some of Chikyu’s crew change every 4 weeks, so this is handled on a staggered rotation schedule. Because crew change by boat is dangerous, it’s preferred o change crew via helicopter.
Fuel, food, and other bulk supplies are delivered from shore supply bases by a large supply boat. Some items, like equipment that is no longer needed, or drilling cuttings, are brought to land for delivery and or disposal. Chikyu has an automatic navigation system, the DPS (DPS: Dynamic Positioning System), can maintain and adjusted ship position automatically. When the supply boats approach Chikyu, some automatic navigation system have errors; therefore, separate DPS systems on Chikyu and the supply boat are used to calculate each ships’ positioning separately. While Chikyu and the supply boat are simultaneously maintaining their positioning relative to each other, loading and backloading or supplies and materials are carried out.
Torque is created while Chikyu is rotating the drill pipe while drilling. It could be imagined that this is enough to make the ship spin, but this is not the case. The top drive, which is the motor in the derrick, which actually spins the drill pipe can produce about 17.4 t-m of maximum torque. This far exceeds the possible downhole torque of the drill pipe. Additionally, natural forces acting on the ship (sea currents, wind, etc.) can be resisted using the ships DPS ability.
Riser drilling technology was introduced to scientific drilling by D/V Chikyu for the first time to allow deep drilling. The seafloor and the riser ship are connected by a Blow Out Preventer (BOP) and riser pipe; inside the riser pipe is where the drill pipe is used to drill deep below the seafloor.
Small diameter drill pipe is run down inside the riser pipe; a special fluid, drilling mud, which is a blend of chemicals and materials is used to protect the borehole, maintain constant pressure with depth, and clean the borehole of drilling cuttings.
The drilling mud is pumped down the drill pipe, and jets out of the drilling bit, where is cools and cleans the borehole. The drilling mud then passes up the space between the borehole wall and the outside of the drill pipe and returns to the ship. The chemicals in the drilling mud also penetrate the borehole wall and create a protective “mud pack” that helps stabilize the borehole wall from collapse. This allows drilling to depths never before possible in scientific drilling. The BOP on the well head on the seafloor protects the ship from bursts of gas and pressure from the formation, by closing valves to prevent these bursts from reaching the ship.
If you dig a big hole in a sandbox, you end up with a big pile of sand that needs to go somewhere. In the same way, as Chikyu drills deeper and deeper, all the rock fragments, or “cuttings”, are returned to the ship, and removed from the drilling mud by “shale shakers”, big vibrating sieves. Some cuttings are used for scientific research, but not all of it, and the remaining portion needs to be properly disposed of. This helps reduce the environmental impact Chikyu could make while drilling.
The effect of the riser drilling system is enormous. For example, the system prevents the geological formation in the hole from collapsing by the drilling mud circulation which circulates through the riser system. This also cools the drill pipe and the bit which are being heated from friction from drilling. After cooling and cleaning the borehole, the hole is drilled deeper.
In January, 2014 in the Nankai Trough off of southwestern Honshu, Japan, Chikyu reached a new scientific drilling record, record, 3058.5 meters below the sea floor. The water depth at this location is 1,939 meters, so the total pipe length was 5,026 meters was connected from Chikyu down to the bottom of the borehole..
As with anything, the key is preparation. This includes not only collecting and gathering the materials and equipment you’ll need aboard, but also to think about the possible risks related to living and working at sea. CDEX considers safety from every angle, and tries to manage risk as much as possible. Time management is also important, but the greatest thing is that no one can predict what will happen, weather-wise, at sea. The stormy weather, typhoons, low pressure fronts all can interfere with, or stop, operations, so a wait on weather (WOW) time margin is calculated and added to the operation plans.
How do scientists know where significant and fascinating areas are to to drill from a scientific point of view? The International Ocean Discovery Program (IODP) has four big areas of scientific interest: deep biosphere life, tectonic activity and geodynamics, global climate change, and the history of the Earth, all as part of the IODP Initial Science Plan. This plan is revisited and revised every 10 years. Any scientist with an interest in a specific area and theme can create an original drilling proposal. These proposals select an area of scientific interest, and are reviewed by special committees of scientists; there are some environmental and safety aspects to consider as well. A complete drilling proposal includes discussion on the drilling plan and scientific goals, environment, safety operation, but also site survey data. Twice a year (April and October) proposals can be submitted through the IODP web site. Once the science evaluation panel committee approves the proposal, it becomes closer to becoming reality. At this point the operators of the various drill ships review the proposal and work with the principal investigators to develop a complete drilling plan and expedition. In the case of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), the original pre-proposal was submitted in 2001, while drilling didn’t begin until September 2007.
Scientific ocean drilling provides a lot of important and interesting scientific results, all over the world. In the case of the Nankai Trough, off Southwestern Honshu, drilling sites were selected based on the 1944 Tonankai Earthquake deformation area, with the idea that the plate boundary could be reached with Chikyu’s capabilities. In the Tohoku region, drilling sites were also chosen to reach the plate boundary, which is where the slip that caused the disaster itself was believed to happen. Coring in situ and long-term measuring & monitoring of frictional heat profile in the fault plane soon after the earthquake struck were top priorities for scientists. The Shimokita Deep Biosphere drilling targets were to reveal the hydrocarbon circulation process in carbon formations and methane inside ancient coal beds.
Earthquakes are caused by fault movements, but the energy behind the fault movement comes from the accumulation of the distortion (or frictional strain) in the tectonic plate where it suddenly breaks, or releases, this energy. The place where the strain accumulates between two plates, or where the movement of the two plates is “locked”, is called an "Asperity" (Asperity translates as "Bulge"). When the stress or strain in the asperity overcomes the frictional strength, there is slip, and an earthquake occurs. These locations may be small, tens of kilometers, compared to the overall length of a subduction zone, which could be hundreds of kilometers long. The typical borehole is about 20 centimeters in diameter, and while we have drilled through many faults in scientific drilling, we have not yet drilled through an asperity. Even so, the impact of a 20 cm hole on a system that covers hundreds of square kilometers should be negligible. We also do not drill randomly – for example, on Chikyu, we work with scientists who have developed a drilling project designed to investigate a specific series of questions, and we work together to ensure we do this safely, while getting the greatest possible scientific results.
To put this another way, this is like pushing a needle into a thick rubber sheet the size of a basketball court – you may understand why there is such an extremely low level of risk.
The Earth’s mantle is a solid and not a liquid, like magma. The mantle to a depth of about 600 km is regarded as peridotite (that is, the gem stone peridot: see photo 1). In general, it’s thought to be stable rock due to the high pressure on minerals with the same chemical composition as a peridotite deeper than about 600 km underground. It’s believed that the mantle moves very slowly, driven by convection from the outer core. These peridotites are slowly rising from deep underground by convection, out at the mid-Atlantic ridge.
When temperature rises and pressure falls, peridotite can be transformed into magma. In the liquid phase it is more buoyant than the solid phase, so the liquefied rock will rise throught the mantle and crust. After spilling out onto the ocean floor, it cools into basalt.
We have a rough image of the internal structure of the Earth, but no one has ever gone down to the mantle and sampled from it directly. Even though from the same mantle peridotite source, differences in temperature and pressure, as well as differences in chemical composition affect changes in evolutional processes over time. Therefore, studying material directly from the upper mantle show the greatest promise of new discoveries.
Our planet, the Earth is somewhat like a watermelon; the green colored skin on the outside could represent the crust, and the inner white and red parts can refer to the mantle and core, as temperature and pressure gradually increase as one moves towards the center.
If mantle rock is kept at a constant temperature, a sudden pressure drop will cause it to melt in “adiabatic melting”. This is also called decompression melting. When drilling, however, the bit is constantly being cooled by drilling mud, so there is no sudden temperature drop, nor is there a sudden pressure drop, as the mud is formulated to match the formation lithostatic pressure, to preserve the borehole. Therefore, these conditions do not support the possibility of having decompression melting.
Chikyu is a big ship, but you may feel stress building up after being onboard for a long period. The ship might even start feeling “small”. During long cruises, there can be stress from living in close quarters with your colleagues. Some people may try to “eat their way out of stress”, but this is really unhealthy and should be avoided. Instead, using the ships’ gymnasium, walking on the helideck in mild breezes, watching the ocean view outside, looking for sealife, seeing sunsets, and other kinds of recreation are better ways to relieve stress. Expeditions often have ping-pong matches, calligraphy lessons (see photo), dance parties, Xmas and New Year celebrations and dinners, Halloween, Easter and Hump-day parties, other events! These are great opportunities to make friends and build relationships with scientists from many different countries and cultures, languages, etc.. Imagine what you would do onboard!