Discoverer Spirit, a drill ship operated by Transocean Inc., established the record for deepest offshore well, when in 2005 it drilled to a depth of 34,189 feet below the water’s surface in the U.S. Gulf of Mexico. (Photo courtesy Transocean Inc.)
The price tag to build the fourth Enterprise-class drill ship is expected to be $640 million.
The double-hull ship with an advanced dynamic positioning system is being built for Houston-based Transocean Inc. by Daewoo Shipbuilding and Marine Engineering Ltd. in South Korea. After delivery in the third quarter of 2010, the new ship will be used for drilling operations off Angola by a subsidiary of British Petroleum PLC.
Transocean, which announced the contract in June, said the ship will be equipped with an improved top-drive system for the derrick and expanded high-pressure mud-pump system and other features designed to allow the ship to drill wells up to 40,000 feet of total depth in waters up to 12,000 feet deep.
This vessel is the latest example of shipyard orders for larger and more technically sophisticated drill ships to meet the growing demand for oil and gas exploration in ultra-deep waters around the world. The latest drill ships have the potential to operate in waters 10,000 to 12,000 feet deep, a capability that only a few years ago was considered unreachable technically and too risky financially.
The newest Transocean drill ship will be equipped with “the most advanced drilling capabilities in the offshore drilling industry,” including Transocean’s dual-activity drilling technology, according to the company. The dual-activity drilling technology involves two drilling systems using a single derrick that permits simultaneous drilling of two wells.
It will have the capability of drilling in up to 7,500 feet of water and, with upgrading, in up to 12,000 feet, according to Transocean. The ship is expected to generate revenues of approximately $900 million for the first five years of drilling.
Until recently the search for offshore oil and natural gas fields took place in shallower waters. In this less demanding environment, the industry generally relied on two types of mobile drill rigs, jack-up and semi-submersible rigs.
Jack-up rigs capable of operating in water depths up to 400 feet are towed to the drill location and
|Discoverer Clear Leader is one of four Enterprise-class drill ships Tansocean has ordered from Daewoo Shipbuilding and Marine Engineering Ltd. in South Korea. The ships will be able to operate in waters up to 12,000 feet deep. (Photo courtesy Transocean Inc.)
their support legs are then lowered to the sea floor. The drilling structure can then be raised on the legs above the sea’s surface.
In deeper water up to approximately 5,000 feet, floating semi-submersible rigs are used. They are kept in position with multiple sea anchors or with dynamic positioning systems.
Drilling in ocean waters up to 5,000 feet deep was a challenge only a few years ago, but today those depths are now viewed as the “easy oil.” Exploration of ultra-deep locations is now possible because of technological advances in drill ship operations. They include improved on-board control systems and automation equipment, as well as new technologies to maintain the right weight of the mud used for drilling lubrication and the desired pressure in the drill string and hole. Perhaps the most important advances permitting today’s deep-water exploration involve dynamic positioning systems.
“Today’s DP technology can keep a 200-yard-long, 30-story-high drill ship within fifty feet of station, well within the tolerance needed for drilling,” according to the American Petroleum Institute.
A report by Siemens Energy & Automation, which supplies drill-ship automation and control systems, noted some of the challenges of working in waters up to 12,000 feet deep. The drill ships “must make critical positioning maneuvers relative to the drilling hole thousands of feet below the ocean surface. Satellite signals fed to sophisticated dynamic positioning systems provide the thruster motor responses to control the ship’s position within critical tolerances protecting the pipe string and ‘preserving the hole.’ Errors in positioning can be extremely costly in terms of equipment and cause a major setback to accomplishing the overall mission,” the report said.
The DP, GPS and automation systems aboard the 30,000-ton drill ship Pride of Africa control the ship’s two 50-ton tunnel thrusters and five propulsion pods that can rotate 360°. They permit the ship to stay within 6.5 feet of a specified position while operating in waters over 9,800 feet deep.
To avoid costly accidents to the wellhead and the thousands of feet of riser and drill string, drill ship systems are designed to factor in the effects of sea conditions. For example, GustoMSC’s 756-foot drill ship P10,000 can continue to operate in wave heights up to 19.7 feet, with wave periods of 22 to 29 feet per second and in winds of up to 56 mph. The ship can conduct drilling operations to a total depth of 31,500 feet.
P10,000’s systems will allow it to maintain position with the riser disconnected in waves up to 33 feet with wave periods of 49 to 59 feet per second and in winds of up to 67 mph.
Drill ship systems also monitor the currents between the surface and sea floor to determine their effects on the riser or drill string on their way down to the sea floor and the wellhead as much as 12,000 feet below the ship’s moonpool.
Propulsion systems perform the dual functions of moving the ship from point to point and maintaining a stationary position for extended periods over a drill site. The 689-foot-long scientific drill ship Chikyu, built by Mitsubishi Heavy Industries in Japan, has 12.5-foot-diameter propellers on each of its seven thrusters.
It has a 2,550-kW thruster in the bow, three 4,100-kW thrusters forward and three 4,100-kW thrusters aft. The thrusters, controlled by the automation and DP systems, give the 57,000-gross-ton ship a cruising speed of 12 knots. Chikyu is also able to maintain a stationary position in waves up to 14.8 feet high with a surface current up to 4 knots and in winds up to 52 mph.
The drill ship Peregrine II is one of the Pelican class of drill ships designed by GustoMSC in Houston. The first of this class entered service in 1972. When Peregrine II’s current upgrading work is completed in January 2008, the 90,000-ton, 756-foot-long, 117-foot-wide ship will be able to operate in waters up to 9,000 feet deep. During the upgrade at the Keppel FELS Shipyard in Singapore, the ship is receiving six larger diesel engines, a new DP system meeting DNV requirements, accommodations for 115 persons, a new drilling derrick, new drill floor, new heliport, and sponsons for additional payload capability and stability enhancement. Before entering service with Frontier Drilling USA, the ship will be renamed Frontier Deepwater.
Transocean Inc.’s 835-foot-long Discoverer Enterprise was the first ultra-deep-water drill ship equipped with its proprietary dual-activity drilling technology. The two separate full-capability drilling stations under the single 418-foot-high derrick allow simultaneous drilling operations in water depths up to 10,000 feet. Discoverer Enterprise’s technology allows drilling “a well more than 6.5 miles beneath its drill floor” and “aims to reduce the cost of an ultra deepwater development project by up to 40 percent,” according to a company fact sheet.
Under construction at Samsung Heavy Industries in South Korea is the Stena Drill MAX I for Stena Drilling of Aberdeen, Scotland. Wärtsilä will supply six 16-cylinder Wärtsilä 32 diesel engines each with a rated output of 7,290 kW at 720 rpm.
They will drive the vessel’s main generators, which will provide power for the drilling equipment, hotel demands and the propulsion motors. Stena Drill MAX I is designed to operate in any environment but is expected initially to do drilling in the North Sea. The ship will have special wind walls and equipment to flush decks with warm water for operations and safety in harsh, cold weather operations.
|The 835-foot-long Discoverer Enterprise is a sistership of Discoverer Deep Seas, which owns the record for a deep-water well. Enterprise was the first of Transocean’s ships with the ability to drill two wells simultaneously in water up to 10,000 feet deep. (Photo courtesy Transocean Inc.)
Drill ships are built in part around the derricks, which are designed to handle the drilling operations, as well as the installation of the marine riser and the piping-handling equipment to assemble the riser.
Drilling mud carried aboard the ships lubricates the drill bits. Technicians on the drill ships vary the mud composition pumped down to the well during drilling to precisely control its pressure to prevent oil or water from forcing its way upward through the drilled hole. As the water depths increase, the composition of the mud becomes more critical to avoid drilling problems, such as damaging blowouts of gas or oil resulting from fracturing rock or sediment around the drill hole. The deeper the drill goes, the greater the problems from low temperatures and higher pressures.
Drilling through the sea floor rock, the drill bits can encounter relatively small gas bubbles under great pressure that can grow significantly in size as they meet lower pressure as they rise toward the surface. Control devices known as riser diverters and blowout preventers are increasingly important as drill depths grow longer and deeper.
Exploration in environmentally difficult ocean areas requires the use of increasingly sophisticated exploration and navigational technologies.
Recent prices of crude oil in the range of $60 to $80 per barrel provide the incentive for the billions of dollars in investments needed to locate and develop new oil and gas sources in deep waters.
As long as oil prices remain in this range or higher, the oil industry will continue to spend the hundreds of millions of dollars it costs to design and build highly capable drill ships.