Global Marine Inc.'s Jack Ryan, one of the last drillships to be delivered from the current construction cycle, will utilize dynamic positioning, retractable thrusters, offline pipe-handling equipment, and a multiplex (MUX) blowout preventer (BOP) communication systems for future ultra-deepwater operations. The 759-ft long vessel departed Galveston, Tex., for Trinidad this month to begin a 3-year contract for ExxonMobil Corp. (Fig. 1).
The vessel utilizes a streamlined hull that allows transit speeds of up to 13.52 knots. While drilling, the drillship will maintain station within 1 m through the assistance of six fully retractable thrusters, a differential global positioning system (DGPS), and an acoustic backup.
A mirror DGPS, along with other redundant systems such as radar scopes, gyros, and echo sounders, will increase safety in the event of marine distress.
Jon Marshall, executive vice-president for Global Marine says downtime associated with maintenance and repairs will be minimized "as we can retract (the vessel's) thrusters into the hull and work on them without having to dry dock."
The vessel is similar in configuration to Global Marine's C.R. Luigs drillship (Fig. 2): Two thrusters are located on the stern, two forward, one aft centerline, and one on the bow in the centerline (see poster Glomar C.R. Luigs, OGJ, May 1, 2000). Thrusters 1 and 4, located along centerline, can be flexibly controlled from either one of two engine rooms, while the remaining thrusters are tied to specific engine rooms (OGJ, Aug. 23, 1999, p. 73).
This configuration will allow a turning motion of 16 degrees/min so that it can quickly react to changing weather conditions. Marshall says this thruster technology was not available on previous generations of drillships.
Currently equipped with 8,000 ft of riser, the ultra-deepwater drillship will be able to drill in 12,000 ft of water with additional riser. Rated drilling depth is 35,000 ft.
Pipe-handling capabilities include vertical and horizontal systems (Figs. 3 and 4). The vertical system will be used to make up bottomhole assemblies, landing strings, and casing strings offline.
The horizontal system, on the other hand, replaces traditional stand-it-back in the derrick pipe-racking technologies used by most drilling contractors (International Petroleum Encyclopedia 2000; PennWell Publishing Co., Tulsa; p. 221). This setup provides two advantages:
First, the permanent storage of drill pipe in a horizontal position provides a more-stable center of gravity. This is especially important during rough weather when wave, wind, and current motion produce a hazardous condition when the derrick is full of pipe.
Second, in an impending storm, crewmembers will not unnecessarily have to lay down vertical stands, a time-consuming procedure.
Linking both vertical and horizontal systems, drilling personnel will remotely operate the top drive, pipe-handling equipment, iron roughneck, and auxiliary mousehole from an automated driller's cabin actuated by programmable logic circuit control panels.
The 60-ft tall, 300-ton BOP module includes:
- Two 183/4-in., 15,000-psi, double ram BOPs.
- One 183/4-in., 15,000-psi, single-ram BOP.
- One 183/4-in., 15,000-psi wellhead connector.
- Two 183/4-in., 10,000-psi annular BOPs.
"A big leap in BOP technology occurred when we went to the MUX," says Charles Keaton, vice-president of engineering for Global Marine. "The system used to be hydraulic. Now we use electronic controls."
Essentially, MUX technology allows drillers to perform a riser disconnect within seconds in case well-control or drive-off conditions warrant a rapid well shut-in and riser disconnect. MUX responds faster than hydraulic systems because electronically coded commands travel faster through conductive cables than hydraulic signals do through hose bundles (OGJ, Dec. 1, 1997, p. 86).
And for vessels operating in thousands of feet of water, hose expansion along the umbilical further slows response time, extending the waiting time between initiation and completion of a functional command.
With a MUX system, however, there are no hydraulic fluid conduits in the communications cable. Instead, a separate supply line runs along the riser that ties in to a subsea accumulator bank.
Additionally, MUX cables have a distinct advantage over hydraulic bundles as a single MUX cable can simultaneously transmit several command signals. On the other hand, hydraulic cables only allow a single command.
Living quarters will accommodate 150 persons and amenities include a 60-seat movie theater (Fig. 2). Personnel safety is enhanced with a medic room, first-aid facilities, and four 75-person lifeboats.
With an optional addition of processing facilities on deck, operators may also be able to perform extended well testing (EWT) that provides information on reservoir flow characteristics and pressure data. To promote extended periods of well testing, the hull contains storage for more than 130 million bbl of fluid.
Global Marine will receive a dayrate of about $195,000 over the 3-year period for the Jack Ryan.