Page 16: of Maritime Reporter Magazine (September 15, 1985)

OUTSTANDING

RIG DESIGNS (continued) contoured pontoon concept. Sumi- tomo of Japan and MSC of Holland teamed together to provide the

DSS-40 semisubmersible, a four- column, two horizontal bracing de- sign which also happens to be fully winterized.

Of the new or enhanced semisub- merisble designs, Aker Engineering of Norway continues to stand by its tried and true six-column design. Its latest unit is called the D-6, a six- column, harsh environment, fully winterized unit. However, like most of the new designs, the D-6 is fitted with the two horizontal cross brac- ings that have become so popular, eliminating the support bracings from the pontoons to the underside of the deck. The mooring equipment and chains are housed inside each of the four corner columns down to the fairleads. The rig also can be config- ured so that drilling can be carried out through one of the middle col- umns or through the center of the unit.

Marine Structure Consultants (MSC) and Neddrill teamed to- gether to develop the DSS-10,000 semisubmersible designed to drill in up to 10,000 ft. of water with a max- imum payload of 10,000 tons in harsh and Arctic conditions. The four-column unit features a com- pletely enclosed derrick and moon- pool and a central drilling column which serves also as a vertical riser storage area. The vessel can operate in up to 10,000 ft. of water with dynamic positioning equipment, and up to 1,500 ft. with an eight- point conventional mooring system.

Blohm & Voss of West Germany has the P-099 semisubmersible de- sign rated for drilling in up to 6,600 ft. of water with dynamic position- ing equipment. Blohm & Voss claim the rig qualifies for operation in

Arctic and subarctic areas with ice drift because of structural reinforce- ments in the waterline areas. The work area also is protected to permit operation in Arctic conditions. To- tal payload is 11,000 metric tons.

The unit is an eight-column design with the two inside columns on the port and starboard sides inclined toward the center of the deck, pro- viding for greater strength and en- abling the use of lighter weight steel during construction.

BOTTOM-SUPPORTED

ARCTIC DRILLING

STRUCTURES:

With the anticipated rush of oil companies to drill in the Beaufort

Sea a few years ago, several marine architects introduced new bottom- supported structures for the area.

Of the various designs introduced several years ago and the more re- cent designs, only three have so far been built.

The first two units were ordered in 1981 by Gulf Canada specifically for its Arctic Drilling program. The

MOLIKPAQ, a mobile caisson with an octagonal shaped base, is rated for 60 ft. of water sitting on the sea- floor, but also can drill in deeper waters if it is set on a berm. Gulf

Canada also ordered the KULLUK in 1981, which is a conical shaped floating barge unit rated for 200 ft. of water. The KULLUK was part of a package Gulf Canada designed for

Arctic exploration, including the

MOLIKPAQ, two icebreakers and two supply boats.

The third such Arctic unit was ordered by Global Marine Develop- ment. The unit is a submersible of its own design dubbed the Concrete

Island Drilling System, or CIDs.

The structure consists of three sec- tions, a steel mud base which sits on the seafloor, a concrete mid-section which rests on the base and upper steel deck barges for drilling equip- ment and quarters. The rig is rated for about 50 ft. of water but the water depth can be increased by fit- ting an extra concrete midsection to the unit. The rig was built under contract for Exxon in the U.S. Beau- fort Sea and already has drilled sev- eral wells for the oil company.

Other firms with bottom-sup- ported Arctic designs which have not been built include Pool Arctic

Alaska, which has a mono-leg jack- up concept. Arctic Alaska Drilling originally was working in conjunc- tion with Friede & Goldman on the design before it merged with the

Pool Company. The upper hull of the unit measures 200 ft. square and 30 ft. deep, with the lower hull mea- suring 300 ft. square and 30 ft. deep.

The single 40 ft. diameter leg is raised and lowered by a rack and pinion jacking system. The leg is raised above the upper deck during transit, with the rig package slid to one side. When the lower hull is jacked down, the rig is moved over the column where it has the capacity to drill up to four wells. The unit is rated for 100 ft. of water. To keep the unit on location over soft bot- toms, the lower hull has 20 spuds with a maximum 50 ft. penetration.

The rig has a total variable deckload capacity of about 17,000 tons, in- cluding about 500 days' worth of fuel which can be stored in the lower hull, enabling the rig to work for one year without resupply.

Global Marine Development also has a mono-leg jackup design simi- lar to the above mentioned Pool

Arctic Alaska unit. Global Marine's unit features a 254 ft. square base which is ballasted to the seafloor and an octagonal shaped upper hull which measures 100 ft. across flats.

The base is ballasted until it just reaches the seafloor and then is low- ered further via four legs, which are used to jack the upper hull above the water. The four legs then are jacked above the upper hull during drilling operations. This design also features a rig package that is moved to one side during transit and then is placed over the center during drilling.

Sonat Offshore Drilling has a sub- mersible concept called the Sonat

Hybrid Arctic Drilling Structure (SHADS) which combines concrete and steel to create a unit similar to

Global Marine's CIDS unit. The

SHADS consists of a 430 ft. square steel base mated to a concrete mid- section and a steel deck. The unit can work in up to 65 ft. of water sitting on the seafloor, and deeper water if set on a berm. The unit can drill up to five wells without resup- ply-

Zapata Offshore and Brian Watt

Associates developed the Brian

Watt Arctic Steel Pyramid (BWASP) for operations in up to 65 ft. of water or 120 ft. of water, depending on the configuration.

The unit is a one-piece octagonal design which utilizes a steel and concrete sandwich panel for the out- er shell and structural bulkheads. In the 65 ft. water depth version, the structure is built with a base width of 480 ft. across flats, with a 430 ft. base width across flats in the 120 ft. water depth version. The unit has a storage capacity to enable it to oper- ate for nine months without resup- ply- .

Brian Watt Associates also has a design of its own called the Arctic

Cone Exploration Structure (ACES) which features a 550 ft. diameter base of prestressed, lightweight con- crete which is fitted with a floating steel deck. The design is rated for 50-110 ft. water depths. The unit would have the capacity to carry 270 days of supplies or the duration of three 16,000 ft. wells. Brian Watt is the prime contractor for the design, while Zapata Offshore has provided the drilling system design.

CBI Industries also designed an

Arctic drilling structure designated the Portable Arctic Drilling Struc- ture (PADS) with a 400 ft. diameter base. The unit is rated for 20-50 ft. of water. The PADS has the capac- ity to operate for 270 days without resupply and can be used for explo- ration and development operations.

The structure, which was designed for Parker Drilling, utilizes a land rig.

Bouygues Offshore is marketing the "Zee-Star 120" for use in the

Beaufort Sea. The unit would be capable of year around drilling in 40-120 ft. of water. Other versions of the structure, the "Zee-Star 60" and "Zee-Star 80" are available for shal- lower water depths. The "Zee-Star 120" would be able to drill three 15,000 ft. wells during a 270 day period without resupply. The struc- ture features an internal concrete space frame, eliminating the need for internal walls or bulkheads.

When Bouygues first introduced the structure in 1984, it envisioned building the unit at Bos-Kaiser Off- shore at Ensenada, Mexico, which was formed by Bouygues and Kaiser

Steel. Bouygues had all its market- ing and equipment suppliers in place for any forthcoming order.

Zeeland Resources, a Netherlands

Antilles-based company, was formed to enter into the leasing or charter of the rig. Bouygues also formed Zeeland Parker with Parker

Drilling to operate the unit, which would utilize a Parker Drilling Com- pany Arctic land rig.

More recently, Odeco introduced its all-steel Arctic Mobile Drilling

Platform (AMDP), a 16-sided cone- shaped and multi-sloped hull struc- ture with a 662 ft. base. The unit is rated for up to 200 ft. of water. The

AMDP would be outfitted with two enclosed drilling rigs and a moon- pool large enough to accommodate up to 48 wells. The AMDP also can be used as a production platform at the same drill site. The unit would be capable of operating up to one year without resupply, equivalent to eight 15,000 ft. wells. The helicopter deck features an enclosed hanger designed to accommodate a Boeing

Chinook 234 or Sikorsky S61. The upper hull also provides covered storage for drill pipe and supplies.

Finally, several years ago, Bow

Valley Industries and Canarctic

Ventures Ltd., both of Canada, de- veloped a concept of a mobile year around drilling structure utilizing surplus supertankers. The firms formed a joint venture known as

Bow Arctic Resources to market the 18 Maritime Reporter/Engineering News