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TRICERATOPS The Case for a New Deepwater Concept

Is there room for a new concept ? Principles and limitations of (TLP’s) What’s at the core of spar concepts? (risers) When is a spar not a spar? Reducing deepwater TLP costs. A Buoyant Leg Structure is an optimized tethered buoyant tower Clustering Towers to support big payloads

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TRICERATOPS The Case for a New Deepwater Concept

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  1. Is there room for a new concept? Principles and limitations of (TLP’s) What’s at the core of spar concepts? (risers) When is a spar not a spar? Reducing deepwater TLP costs A Buoyant Leg Structure is an optimized tethered buoyant tower Clustering Towers to support big payloads Triceratops (assembly) Triceratops in shallower waters TRICERATOPSThe Case for a New Deepwater Concept

  2. Is there room for a new concept? • Currently there are only 3 proven concepts for deepwater dry-tree platforms • Towers (steel - Bullwinkle, Lena; concrete - Troll, Draugen) • TLPs (& mini-TLPs) • Spars • Only TLPs and Spars have been proven for very deepwaters and large payloads • Large payload deepwater TLPs have very expensive hulls & mooring systems • Spars have very expensive hulls and riser systems • TLPs have great motion characteristics, but costs & dynamic response increase dramatically in ultra-deep waters

  3. Enter BLS & Triceratops • Buoyant Leg Structures are tethered spars (i.e., vertically restrained) • The BLS combines the qualities of spars and TLPs where its deep draft hull limits vertical excitation • The BLS can give better motions and more convenient riser systems/well access than spars with much smaller, simpler hulls than spars or TLPs • A Triceratops combines 3(or more) tethered spars to support very large production facility deck structures • Either one may support dry tree or subsea well risers • AND….BLS & Triceratops will be cheaper than TLPs & spars for competing payloads

  4. Water Depth Ranges for PLATFORM Concepts Dry Trees 10ft Caissons Wet Trees Posted Barge Jackets FPSO Tower Semi FPS TLP Mini-TLP Triceratops BLS BLS Spar Spar ? 10,000ft

  5. Tendons & Buoyant Legs TLP Tendons’ useful strength may be preserved by stepping wall thickness & partial buoyancy, but large steel cross-sections are still required to avoid vertical mode RESONANCE. Tendons become Heavier & ‘Stretchier’ with increasing WD => RESONANCE

  6. Reducing Ultra-deep TLP Costs $$$ TLP If a ‘buoyant tendon’ is extended through the surface, we might call it a ‘tethered buoyant tower’ Tendons are costly in deep waters, but rigid TLP ‘nodes’ are costly at ALL water depths

  7. Self-standing (buoyancy supported) Risers Tree Tree Multi-Function Barge Spar The ‘self-standing risers’ used in spar are simple ‘Tethered Buoyant Platforms’ With Trees as their payloads

  8. When is a Spar NOT a Spar? Spar Trees Tree When it’s Tethered and becomes a Buoyant Leg Structure Well & Riser

  9. Three (or more) tethered buoyant towers acting together can support “a lot”! Buoyant Columns Tension Legs (partially flooded) Hybrid Gravity/Suction Anchors Triceratops - a tethered buoyant platform structure

  10. Triceratops – a tethered buoyant tower structure Buoyant Columns Tensioned Restraining Legs (may be stepped in wall thickness, tapered in section, or partially flooded) CVAR Tubing Tieback Riser Hybrid Gravity/Suction Anchors Workover/Completion Rig Float-over Truss Frame Deck w/ Modules Contact “Hinge” Nodes The columns are installed and stand independently until the deck ties them together

  11. Triceratops – a tethered buoyant tower structure Buoyant Columns Tension Legs (partially flooded) Hybrid Gravity/Suction Anchors Workover/Completion Rig Contact “Hinge” Nodes • CONCEPT FEATURES/CHALLENGES- • Float-over Truss Frame Deck w/ Modules • Typical top-tensioned or Compliant Vertical Access Dry Tree Tieback risers can be used • Deck stays horizontal as platform offsets in wind, waves & currents (like a TLP) • Contact nodes between deck structure and buoyant columns allow angular deflections (acting as a bi-directional “hinge” joint) • Hinge points can face upward (to deck) or downward (to columns) • Hinges require careful design but loads and angles are well within limits for existing flex-joint designs • Columns are only about 450ft in draft (versus 700+ft for spars) and are relatively small diameter • Heave restraining leg allows column draft to be limited and still maintain great motions • Column vertical weight (mass) distribution optimized for stability and limited excitation to restraining legs • Restraining legs experience very little vertical resonant excitation due to column design/draft

  12. Triceratops –a Compliant Concept that is readily adapted to a wide range of water depths Deep Water Ultra-deep Water Moderate Water Depths

  13. Why Triceratops? Workover/Completion Rig Float-over Truss Frame Deck w/ Modules Contact “Hinge” Nodes • Payload & deck area virtually unlimited • Tethering costs minimized • Tethering loads minimized as with TBT/BLS • Concern about vertical mode resonance limited • Deck sees TLP-like motions • Lower cost deck fab/install • Small diameter columns cheaper to fabricate • Can be fab’d in GoM without long tow • Wells can be located beneath deck or well away from foundations Buoyant Columns Tension Legs (partially flooded) Hybrid Gravity/Suction Anchors

  14. Basic Comparisons

  15. Risks v. Benefits • Design/Safety Risks • Simple structures compared to TLP • Tethers see low dynamic loads • Wells can be located remote from foundations/anchors • Hulls float stably with restraining leg removed • Provides large deck area for safe distribution of hazardous area • Operational Risks • Limited inspection challenges • Easy maintenance of readily replaced components • Reservoir Risks • With tethers (ie., restraining leg) removed entire platform can be towed to new field as one unit or deck can be easily removed for upgrade inshore and re-installed at new field • Cost Risks • Replaces complex rigid nodes at deck & pontoons on TLPs with compliant compression bearing joints at deck • Reduces tethering steel/cost to minimum required for station-keeping • Avoids complex tendon porches • Avoids massive spar hull • Avoids complex riser systems & buoyancy on spar risers • Allows simple deck installation • Project Schedule Risks • Small, simple hull & tether structures easily fab’d locally (e.g., in US) • Towing column/tether as one unit with up-ending at field limits critical exposure periods for installation • Hook-up & pre-commissioning inshore can be maximized

  16. Apparent Cost Advantages Work-over + Completion Rig is leased =>Savings >30%

  17. Triceratops Introductory StudyUltra-deepwater Applications • Location & WD • Mission/Payload Characteristics • Definition of System Components • Performance Criteria & Safety Considerations • Global Analysis • Contact “Hinge/Node” loads and behavior • Installation Planning and Estimates • Costs • Schedule

  18. TriceraTOPS’emAll!! “A Triceratops horridus gallops”, a painting by Douglas Holgate

  19. “Triceratopshorridus charges through the forest” By, Frank DeNota

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