Presentation on theme: "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?"— Presentation transcript:
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 Triceratops (assembly) Triceratops in shallower waters
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
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
Wet Trees Dry Trees Caissons Posted Barge Jackets Tower TLP Spar FPSO Semi FPS Spar Water Depth Ranges for PLATFORM Concepts BLS Mini-TLP BLS
Tendons & Buoyant Legs TLP Tendons become Heavier & ‘Stretchier’ with increasing WD => RESONANCE 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.
Reducing Ultra-deep TLP Costs TLP Tendons are costly in deep waters, but rigid TLP ‘nodes’ are costly at ALL water depths If a ‘buoyant tendon’ is extended through the surface, we might call it a ‘tethered buoyant tower’
Self-standing (buoyancy supported) Risers Spar Multi-Function Barge Tree The ‘self-standing risers’ used in spar are simple ‘Tethered Buoyant Platforms’ With Trees as their payloads
When is a Spar NOT a Spar? Spar Tree When it’s Tethered and becomes a Buoyant Leg Structure Trees Well & Riser
Triceratops - a tethered buoyant platform structure Buoyant Columns Tension Legs (partially flooded) Hybrid Gravity/Suction Anchors Three (or more) tethered buoyant towers acting together can support “a lot”!
Buoyant Columns Tensioned Restraining Legs (may be stepped in wall thickness, tapered in section, or partially flooded) Hybrid Gravity/Suction Anchors Float-over Truss Frame Deck w/ Modules Contact “Hinge” Nodes Workover/Completion Rig CVAR Tubing Tieback Riser Triceratops – a tethered buoyant tower structure The columns are installed and stand independently until the deck ties them together
Buoyant Columns Tension Legs (partially flooded) Hybrid Gravity/Suction Anchors 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 Contact “Hinge” Nodes Workover/Completion Rig Triceratops – a tethered buoyant tower structure
Ultra-deep Water Moderate Water Depths Deep Water Triceratops – a Compliant Concept that is readily adapted to a wide range of water depths
Buoyant Columns Tension Legs (partially flooded) Hybrid Gravity/Suction Anchors Float-over Truss Frame Deck w/ Modules Contact “Hinge” Nodes Workover/Completion Rig Why Triceratops? 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
Basic Comparisons TLPSparBLS/TBTT’tops WD range500- 5,000ft 1,500- 10,000ft 1,000- 8,000ft 500- 8,000ft Payload capacity 1,000- 60,000t 1,000- 30,000t 1,000- 20,000t 5,000- 60,000t Motions Vertical modes restrained; heave- pitch/roll cross- coupled All vertical modes minimized by design; surge/sway limited by size Heave restrained, roll/pitch minimized by design principles Heave restrained, roll/pitch & surge constrained by configuration High Cost elements Nodes at column tops & bottoms, tendons, installation Massive hull; spread mooring, deck installation, Restraining-leg (cheaper than tendons); deck installation Restraining-legs (cheaper than tendons) Risk Installation; Well hazards affect foundations Deck install & pitch/riser fatigue in well-bay Pitch angle at tension-leg New Ideas (see next slide)
Risks v. Benefits 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 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