A new workover rig has a modular design for quick rig up and rig down and easy transport between offshore platforms using field supply boats and platform cranes.
Pool Energy Services Co.'s new electric-powered platform workover rig recently left Houston bound for Australia's Bass Strait, where it began offshore operations for Esso Australia Ltd. in July (Fig. 1). This SCR (silicon controlled rectifier) rig is rated at 1,000 hp. A sister rig began operations offshore Malaysia for Esso Production Malaysia Inc. in late 1994.
The offshore platforms in Bass Strait are within close proximity of each other. The rig must be able to make quick moves from one location to another. The 427-ton rig has a modular configuration, allowing it to be rigged down, transported, and reassembled in this field in about 5-7 days, depending on the weather and supply boat schedule.
A typical rig move will consist of 32 major lifts and about 16 minor lifts, all of which can use the existing platform cranes. The maximum lift (mast crown section with the block) is 12 metric tons.
The rig has a Dreco model 1000E draw works powered by a General Electric 752 traction motor, specially designed for quick rig up without breaking any chains, according to Pool. The draw works assembly includes right angle rotary drive, Dretech model 7RD 150 electric brake, and hydraulic makeup and breakout cat-heads mounted in the lower mast end. Twin hydraulic winches are mounted on the draw works shelter. The power system consists of three 545-kw Caterpillar, diesel-powered generators and one SCR/MCC generator control building containing a Ross Hill model 1000 SCR system.
The Dreco triple mast telescopes vertically and is designed per American Petroleum Institute specification 4F Q1 for 428 kip static hook load, 115 mph wind, 84 knot wind with 260 kip setback, and dynamic conditions to suit most tension leg and guyed tower platforms, according to Pool. The clear height is 133 ft with a racking capacity of 19,530 ft of N-in. drill pipe and eight stands of 8-in. drill collars.
The pipe rack is an elevated 40 ft x 50 ft platform mounted on a support structure which pins to and skids with the rig. The pipe rack has a 300-kip capacity.
The rig substructure consists of two single girder strongback beams that span dual foundation boxes. The substructure has a clear height of more than 20 ft. The rig's lift and roll hydraulic skidding system can skid the rig assembly and integrated rig floor. The skidding assembly is unitized in the drill floor to move the rig laterally on the strongback beams.
The blowout prevention system consists of a Shaffer 11-in., 5M annular preventer; an 11-in., 5M double preventer; an 11-in., 5M single preventer; and an 11-in., 5M drilling spool with outlets for choke and kill valves.
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