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Petroleum Engineering 406 Floating Drilling

Lesson 10

The Drilling Riser

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Lesson 10A - The Drilling Riser

Riser ComponentsRiser TensioningFatigueKill/Choke LinesInspection & MaintenanceReentry

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Riser system for a floating drilling rig

BOP

RISER JOINTSKILL AND CHOICE LINES

SLIP JOINT OUTER BARRELUPPER BALL JOINT

SLIP JOINT INNER BARREL

RISER TENSION

LOWER BALL JOINT

Mudline

Marine riser = drilling riser, get returns to surface, well control, communications link

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Integral Marine Riser Joints

Choke and kill lines are integral with the marine riser , flanged connections; clamp, etc

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Integral Marine Riser Connector

Flanged connection - 6 bolts

NOTE: Choke and Kill Lines

O-ring type seals- inspect when running

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Integral Marine Riser Connector

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Marine Riser

Flexible Joint

Flexible joint, binding from high tensile forces, inject lubricant, up to 1,500,000 lbf!

8Upper Section Marine Riser System.

MARINE RISER DIVERTER ASSEMBLY

RISER TENSIONING

LINESTELESCOPIC JOINT

KILL AND CHOKE LINES

FLEXIBLE JOINT

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Control valve

Vent line

Mud returns

L.P. Annular

A diverter system.Re-directs flow from rig floor to blooey line (10”+), downwind, do not shut in, erosion -10E8

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Figure 6-6. Vertical steel loops used for kill / choke line transition around the ball joint.

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The Drilling Riser

Schematic diagram of riser with imposed forces

MEAN WATER LEVEL

RISER ELEMENT

Optimum riser tension to minimize damage to riser and wear-and-tear on tensioners, sag

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Str

ess

in r

iser

, ki

ps

Applied tension in riser, kips

Maximum stress

Minimum stress

Tension in riser must be not too low and not too high. Set at 118 kips - will fluctuate 100-136 kips ~ 15%

Mean tension

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Riser Considerations:

Riser Metallurgy is very important. Correct heat treatment is

essential. 80,000 psi min. yield strength and

good toughness is preferred. Preheating, welding & normalizing

after welding is critical for riser integrity & long life.

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Riser Considerations:

No Field Welding on Riser!

Fatigue of riser cannot be measured prior to some indication of failure.

Routine inspection required.

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Riser Considerations:

Fatigue is an embrittlement of the metal. It often starts in the vicinity of welds or other places of high stress concentration.

Fatigue is caused by cyclic loading.

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Riser Inspection:

Visual Inspection of the riser should occur every time the riser is run.

Check all the seals Check all the sealing areas

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Riser Inspection:

A complete inspection should be made annually.

Dyes: Will detect cracks. To use dyes, paint must be removed.Magnetic Particle Inspection: Sand blast areas around welds prior to magnetic particle inspection.

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Riser Inspection:

Ultra-Sonic Inspection: May detect cracks below the surface. This test is run inside pipe. Paint removal is not necessary.

X-Ray Inspection: Is for cracks inside the metal. It may miss surface cracks.

*No one technique will find all the cracks.

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Riser Instrumentation:

Heavy Gauge: Pointer attached to guide line moving in front of graduated board.

Riser Angle Indicator (at ball joint):

2/1y

2x

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2/12y

2x

tantantan

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Riser Instrumentation:

Accurate Positioning System: For detecting and monitoring vessel

position.

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Ball Joint:

A Ball Joint Angle > 4 degrees is an indication that something is wrong!

Vessel is offset Riser tension is inadequate

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Ball Joint:

Must decrease ball joint angle before operations are resumed.

Remedial Action:

Decrease Offset

Increase Riser Tension

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Vessel to Seafloor Guidance System

Guidelines are used for guiding equipment from the vessel to the seafloor.

Selection and care of guidelines is critical.

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Vessel to Seafloor Guidance System

Guidelines should not be tensioned beyond 1/3 of breaking capacity

But…inadequate tension is the most common cause of failure in guidelines

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Vessel to Seafloor Guidance System

Tension should be maximum when landing the BOP stack, or when landing the riser onto the stack.

When the guidelines are not being used to run equipment, tension may be slacked off to ~ twice the weight of the line in seawater.

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Table 6-1. Recommendations for

Conventionally Used Guidelines

As water depth increases, larger diameter guidelines must be used.

Higher tensioning is required.

Don’t forget to limit tension to < 1/3 of breaking strength.