Paper No. OTC-26410-MS...Paper No. OTC-26410-MS Lightweight Drilling Riser Achieves 12 Years...

Paper No. OTC-26410-MS

Lightweight Drilling Riser Achieves 12 Years

Successful Operation in Offshore Brazil

Jeffry K Lehner, Alcoa Energy Systems, Ian Barker, Paragon Offshore, David Walters 2H Offshore, and Shreenaath Natarajan 2H Offshore

Learn more at www.2hoffshore.com

Project Justification Slide 2

Paper No. OTC-26410-MS Lightweight Drilling Riser Achieves 12 Years Successful Operation in Offshore Brazil Shreenaath Natarajan

PURPOSE

• Enable existing rigs to drill in deeper water with minimal rig upgrades

CONTEXT

• Trend is for drilling in deeper water

OBJECTIVES

• Capture new contracts without lengthy rig upgrades

• Capture operational learnings and optimize


Why Game Changer?

• Lighter weight eliminates rig deck tensioner upgrades

• Lighter weight eliminates the need for buoyancy

• Reduced buoyancy cross section means higher current operating window

• Reduced modulus results in smaller bending loads

• Light does not mean weak

• Engineer up instead of size up!



Advantages of Lightweight Risers

• ½ the buoyed weight of steel riser joint

• 1/3 lighter than steel riser joint

• 1/3 of joints require buoyancy vs. 95% of steel joints

• 46” versus 54” buoyancy diameter—reduced drag

• Easier maintenance—no descaling or painting

• Lower marine growth

• Easier to handle

• Allow floating rigs to increase depth 50% without extensive modifications



History of Light Weight Riser Development

• Major drilling contractor commissioned feasibility study in 1996

• Designed in Russia, by O&G experts, leveraging industrial knowledge in light metals

• Extensive mechanical testing conducted at Krylov Institute, Russia

• 2002 first 100 joints fabricated by Progress Facility (rockets), using tubes/flanges from then RUSAL, now Alcoa Samara facility

• Two semisubmersibles and two drillships outfitted

• 3 of those systems are still in service, in excellent condition with many years of useful life remaining


20,000 ton horizontal press Samara Russia

World’s Largest

80,000 ton vertical press Samara Russia

World’s Largest


Material, Geometry and Specifications • Main tube alloy—1980T1 Fusion weldable, YS=50ksi

• Aux line alloy—1953T1 Non-weldable, YS=73ksi

• Both are 7000 Zn alloyed, optimized for marine applications

Riser Body Specifications

Deep Water New Ultra Deep Water

Riser body ID 19.69 in. (500 mm) 19.69 in. (500mm)

Main wall thickness 1.378 in. (35 mm) 1.378 in. (35mm)

Welded wall thickness 1.378 in. (35mm) 2.165 in. (55mm)

Design temperature (max) (max) 248⁰F (120⁰C), (min) -4⁰F (-

20⁰C)

(max) 248⁰F (120⁰C), (min) -4⁰F (-

20⁰C)

Forged flanges 40.94 in (1040 mm) OD, steel bolts 40.94 in (1040 mm) OD, steel bolts

Yield Strength 50,750 psi 50,750 psi

Weld Yield Strength 29,000 psi 29,000 psi

Riser Tensile Capacity 1.5 million lb 2.7 million lb

Riser weight in air 17,000 lb 17,571

Riser weight, wet 11,200 lb 11,547

Maximum water depth 8,000 ft 12,000+ at 15ksi BOP



Reduced Need for Rig Modifications

• Variable deck load capacities—Avoid costly structural upgrades

• Aluminum joints 1/3 lighter in air

• Only 1/3 of joints require buoyancy, reducing weight further

• Avoid tensioning system upgrades

• Avoid rotary table and top drive on drawwork upgrades

• Avoids estimated ~$44M for equipment upgrades

• Avoids rig lost revenue out of service $200M-$300M



Operating Considerations • Handling is similar to steel, but easier due to light weight

• Running equipment is similar

• Stabbing procedures are similar because aux line pin & box are steel

• 2/3 of joints do not require buoyancy, can be run slick, with guards, or fins

• Anodes must be maintained, but none replaced to date

• Aluminum anode clamps are stout, ensure good electrical conductivity

• Switch over to completion brine saves 6 hours rig time, no rust and scale build up avoiding removal with riser brush

• Lower deck maintenance due to cleaner service condition

• Recommend inspection tear down each 365 wet days, to avoid threaded connections from seizing

• Maintenance of mechanical connections much simpler than steel, which require cutting and welding to replace connections

• Sacrificial pup joint at top recommended for interface for steel

Paper No. OTC-26410-MS*Lightweight Drilling Riser Achieves 12 Years Successful Operation in Offshore Brazil*Shreenaath Natarajan


Increased Environmental Operating Window • Installation window permits greater wave heights

• Typically driven by stresses at riser top

• Reduced bending stiffness results in smaller bending loads

• VIV fatigue damage is lower

• Aluminum is more compliant

• Lower fatigue damage induced by waves

• More dampening to excitation induced by vessel

• Hang off window increased by 20-35%

• Reduced flexjoint rotations

• Reduced buoyant drag diameter and length covered



Summary • The light weight Aluminum Drilling Riser allows existing drill ships & semis to

extend their drilling depths up to 50%

• Solution minimizes rig upgrade costs, and lengthy/costly out of service

• Extensions or hybrid mixed steel and aluminum strings minimize investment

• Not all joints need to be aluminum

• Field proven 14+ years with low maintenance and excellent performance

• Increased environmental operating window increases drilling days and saves money

• Next generation system capable of 12,000’+ at 15,000psi BOP



Acknowledgements / Thank You / Questions

Special thanks to Ian Barker at Paragon Offshore

Slide 11


Paper No. OTC-26410-MS...Paper No. OTC-26410-MS Lightweight Drilling Riser Achieves 12 Years...

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