Abstract

Transocean's fleet of newbuild, deepwater, 5th generation rigs have accumulated an aggregate 35 rig years work experience. Among the exceptional accomplishments:

  • deepest water depth (2,966 m / 9,727 ft - Unocal Discoverer Spirit)

  • deepest subsea completion (2,198 m / 7,209 ft - Unocal Discoverer Spirit)

  • deepest moored operation (2,442 m / 8,009 ft - Shell Deepwater Nautilus)

  • simultaneous well test / crude storage / offload - (BP Discoverer Enterprise)

The rigs are showing significant performance gains, some of this attributable to dual or off-line activity, and some in benefit of higher specification equipment (pump pressures, flow rates, etc). Many among the operator community are now factoring generous premiums for these efficiencies in their bid evaluations. In confirming and assessing the gains, Transocean have undertaken a modeling exercise, comparing the performance of 5th generation rigs with earlier builds. Representative performances have been distilled from the IADC Reports, such that well curves can be predicted and compared for each of the rig classes.

Introduction - The Legacy of Deepwater Drilling

Floating rig generations have been defined primarily on the time frame in which the units were conceived and built. The 3rd generation of the early 80s was the most dominant, producing a staggering 44(1) semi submersibles in an aggressive push into moderate water depths in particularly the Gulf of Mexico and the North Sea. These rigs were more robust than the generation that preceded them, with more reliable drilling packages and ancillaries.

In consequence of the overbuild of the early 80s, the 4th generation semi submersibles that followed numbered only 13, and they concentrated on demanding niche markets - deeper waters of the Gulf of Mexico (1,800 m / 6,000 ft), and year round operations in the extreme environments of Eastern Canada and the Atlantic fringe of Northern Europe. The 4th generation rigs are larger, displacing 30,000–53,000 mt, with much larger deck space and variable deck loads of 4,000–6,200 mt. Mud volumes increased to more than 3,000 bbls, pipe handling is automated, and multiplex or enhanced hydraulic BOP controls are standard.

The mid-90s thrust into frontier depths precipitated the upgrade of a number of units and conversion of vessels from different uses, stretching existing hulls and associated technology for program objectives in as much as 10,000 feet of water. Compromised efficiencies and constraints on space, variable load, and handling weights motivated the design and construction of a new generation of rigs with extreme water depth capability.

The 5th generation semi submersibles and drillships are large displacement new-builds, outfitted with high pressure pumps, generous high-flow solids control suites, big bore drill pipe, dual mud systems with upwards of 15,000 bbl pit capacities, and automated pipe handling. Most are dynamically positioned, drawing on upwards of 58,000 hp power plants, boasting 1,000 ton hook loads, and either dual activity or significant off-line activity. When the last of these rigs are delivered (mid-year 2004), the industry count will be 25 5th generation new builds, owned and / or operated by eight contractors.

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