Petroleum Engineering 406 Floating Drilling

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Petroleum Engineering 406 Floating Drilling

• Lesson 10
• The Drilling Riser

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Lesson 10A - The Drilling Riser

• Riser Components
• Riser Tensioning
• Fatigue
• Kill/Choke Lines
• Inspection Maintenance
• Reentry

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Riser system for a floating drilling rig
RISER TENSION
SLIP JOINT OUTER BARREL
SLIP JOINT INNER BARREL
UPPER BALL JOINT
KILL AND CHOICE LINES
RISER JOINTS
LOWER BALL JOINT
BOP
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!
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MARINE RISER DIVERTER ASSEMBLY
FLEXIBLE JOINT
RISER TENSIONING LINES
TELESCOPIC JOINT
KILL AND CHOKE LINES
Upper Section Marine Riser System.
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Mud returns
L.P. Annular
Control valve
Vent line
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
MEAN WATER LEVEL
RISER ELEMENT
Schematic diagram of riser with imposed forces
Optimum riser tension to minimize damage to riser
and wear-and-tear on tensioners, sag
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Maximum stress
Mean tension
Stress in riser, kips
Minimum stress
Applied tension in riser, kips
Tension in riser must be not too low and not too
high. Set at 118 kips - will fluctuate 100-136
kips 15
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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)

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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 gt 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
• Butinadequate 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. Dont forget to limit tension to lt 1/3
of breaking strength.