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Collaborating Authors
Results
Abstract Transocean's 28-rig deepwater fleet has logged more than 375 years of service. Within that population, the 13 newbuild 5th-Generation rigs have accumulated more than 60 years of well-construction experience. On the depth and breadth of that experience, the company is uniquely positioned to assess the merits of various rig types and equipment suites in relation to different programs. In a paper presented at this forum two years ago, we introduced a performance modeling initiative grounded in the review of 80 exploration wells from 15 rigs. On that early work, we were able to predict relative timeline performance, and ultimately program cost for each of the rigs assessed. In the last two years, we have introduced a number of refinements, particularly in relation to completion activity. To date, we have modeled more than a dozen development programs with several operators, and are now able to make broad associations between rig specification and commercial advantage in relation to program attributes. It is evident that rig specification should factor significantly in preparing a subsea development strategy. Introduction - The Deepwater Rig Market We define deepwater rigs as capable of operation in 4,500 feet or more of water. On that definition, there are 70 deepwater rigs in the market. Important divides in that population are:Drillship vs Semisubmersible (28 vs 42 deepwater rigs) Harsh environment applications dictate specification for a semisubmersible. Column-stabilization yields better motion response and often better environmental transparency. The more challenging the environment, the narrower the field of candidate rigs. As the active population of deepwater drillships are all dynamically positioned, they have mitigating facility to weather-vane with the environment. Both transit speeds and variable deck loads are generally 2–3 times higher for drillships compared to semisubmersibles of like vintage. Moored vs DP (25 vs 45 deepwater rigs) Forty-five of the active deepwater rigs are dynamically positioned. About two-thirds of those are newbuilds, and with few exceptions, the balance date from the mid 70s. Moored vs DP can have significant implication in program cost. Consider for instance:Fuel costs are about twice as much for DP compared to moored operations, though there is often offsetting savings in relation to workboat specification. Field infrastructure may obligate preset moorings, imposing as much as $20 mil capex and nearly $100k per day in workboat and ROV services. (Also, vertically-loaded presets will not match the storm-loading potentials of a catenary system.) Loop currents may impede BOP handling on a moored rig, obstructing operations for weeks in circumstances where a DP rig might "drift" onto or off of location while running or pulling the BOP. Timeline impact of anchor handing in relation to DP may easily add 4 to 6 days per well. This might be mitigated in a clustered well development, or exacerbated in a harsh environment application where anchor-handling operations are often impaired. 5th Gen vs Earlier Builds & Upgrades (26 vs 44 rigs) On our definition, 5th-Generation rigs are 6,000 ft water depth capable newbuilds, with HP mud systems. These rigs are fundamentally different from anything before.Computer controls - In the 15–20 years since the last build cycle, computers have come of age. This is evident in the integration of drillfloor systems, power management, vessel management, DP systems and BOP controls. DP vs moored- All but two of the deepwater rigs built in recent years are dynamically-positioned.
- North America (0.28)
- Europe (0.28)
Performance Gains with 5th Generation Rigs
Keener, Chip (Transocean) | Keji-Ajayi, Ibukun (Transocean) | Allan, Rod (Transocean)
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 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.
- North America > United States (0.69)
- North America > Mexico (0.54)
- North America > Canada (0.54)
- (4 more...)
- Well Drilling > Drilling Operations (1.00)
- Well Drilling > Drilling Equipment (1.00)
- Well Drilling > Drillstring Design > Drill pipe selection (0.67)
- (2 more...)