Oil and gas customers demand quality construction that will incorporate the latest operational equipment for improved drilling efficiencies, generating time and cost savings while working in water depths of 122 m (400 ft) and beyond.

Since conditions for drilling in water depths of this kind are often critical, the goal is to design a jackup rig that experiences minimal difference between the operational variable loads and the variable load during a storm. It is crucial to strengthen the rig where necessary to meet these demands. For a jackup unit the obvious choice is to strengthen the legs.

With five shipyards based in Singapore, Sembcorp Marine carries out the in-house development of proprietary products that are not adapted from older rig designs. This gives the company the ability to provide custom-designed turnkey solutions to meet the requirements specified by both drilling contractors and field operators. The design solutions lead to standardization of the product, which eliminates changes and modifications during the manufacturing process.

PPL Pacific Class 400 features

The Pacific Class 400 design, developed by PPL Shipyard (a subsidiary of Sembcorp Marine), is a high-capacity, deepwater, self-contained, independent-leg, cantilever-type jackup drilling rig that is capable of operating in HP/HT wells to depths of 9,144 m (30,000 ft).

It is an enhanced version of the long-established PPL Pacific Class 375 design, featuring the same overall dimensions and leg centers (leg length including “spud can” is 162 m or 535 ft; leg center forward/aft is 44 m or 144 ft; leg center portside/starboard is 47 m or 155 ft).

The rig is equipped with full hotel services for a complement of 150 people on board in one-man and two-man cabins.

The design incorporates 72 high-jacking-capacity pinions, which allow jacking with a large preload of 58.6 MMlbf. The high-rating pinions also eliminate the need for a fixation system during a storm, while the robust leg design prevents severe structural damage during punch-through. The Pacific Class design commands a better leg-twisting and/or rotating resistance than other similar class rigs. As for individual chord twisting, any closed-section leg chord will have solid tensional resistance. The large-diameter leg chord of the Pacific Class design allows better resistance, especially during preloading.

There have been incidents of a sudden leg penetration into the seabed involving Pacific Class rigs, which reportedly had no significant damage to the leg chord, unlike other designs that needed substantial repairs in shipyards after experiencing such incidents.

For example, one Pacific Class 400 rig experienced a sudden penetration that resulted in a minor shear in one of the bracings. The leg chords, however, remained well intact. This allowed jacking of the hull and repair to be completed offshore.

The rig was put back into operation almost immediately without having to be towed back to a shipyard for costly leg repair work. Pacific Class 400 design rig legs are inherently strong and are highly resistant to sudden leg penetration or punch-through.

A large deck space for third-party equipment also is provided by the Pacific Class 400 design, promoting easy access and functionality. The drill floor is outfitted with a stand-building facility that enables tubular stands to be constructed away from the well center and works for standalone activities. The coring pipe is directly in line with the well center when the cantilever is fully retracted, which also promotes safety and less downtime.

The derrick stands at a height of 49 m (160 ft) with a base of 11 m by 11 m (35 ft by 35 ft) with a hookload capacity of 1.5 MMlb with 14 lines.

It is outfitted to permit the racking of casing, promoting continual well activity and less significant downtime. Two identical iron roughnecks are used for both the well center and the stand building. The stand-building iron roughneck acts as standby or interchange for the well center iron roughneck.

Additionally, the conductor tensioning platform has an extended longitudinal range from 4.5 m to 10 m (15 ft to 33 ft).

The drilling drive is built to a 24-pulse system configuration, with dual six-pulse rectifiers and 2 kv Amp by 5,000 kv Amp phase-shifted transformers. The total harmonic distortion in voltage waveform of the power system is less than 5%. The benefit of minimal harmonics includes a more efficient power system, fewer problems with heating (transformer, motor, and cable), and improved equipment lifetime.

A vessel management system (PLC-based) allows the operator centralized access to machinery alarms, tank levels, the ballast valve, pressure-tank monitoring information in the radio room, jacking control room, and electrician office work stations. The system will alert the operator to potentially hazardous conditions that may occur near the machinery spaces.

In terms of performance in action, the PPL Pacific Class 400 fleet experienced approximately 99% productive time for the first 48 months of operations, demonstrating that high-specification drilling units have proven operational efficiencies.

It also was the first mobile offshore drilling unit to receive the American Bureau of Shipping’s Habitability Plus notation for conformance. The PPL Pacific Class 400 design also was rig-safety approved by the National Offshore Petroleum Safety Authority for its best-in-class safety performance throughout 2008 in Australia.

There are currently four Pacific Class 400 rigs already delivered and in operation to date, with six more at various stages of construction. A total of 27 Pacific Class 375 units have been working around the world since the first rig of that design was delivered in May 2006.

Jurong Shipyard also has contributed to the building and delivery of a number of the Pacific Class 375 rigs, with Jurong also being a subsidiary of Sembcorp Marine.