Petroleum Engineering 406
Floating Drilling
Lesson 10
The Drilling Riser
1
Lesson 10A - The Drilling Riser
Riser Components
Riser Tensioning
Fatigue
Kill/Choke Lines
Inspection & Maintenance
Reentry
2
RISER TENSION
SLIP JOINT INNER BARREL
KILL AND CHOICE LINES
SLIP JOINT OUTER
BARREL
UPPER BALL JOINT
RISER JOINTS
LOWER BALL JOINT
BOP
Mudline
Riser system for a floating drilling rig
3
Marine riser = drilling riser, get returns to surface, well control, communications link
Integral Marine Riser Joints
4
Choke and kill lines are integral with the marine riser , flanged connections; clamp, etc
Integral Marine
Riser Connector
Flanged connection - 6 bolts
NOTE: Choke and Kill Lines
O-ring type seals
- inspect when running
5
Integral Marine
Riser Connector
6
Marine
Riser
Flexible
Joint
7
Flexible joint, binding from high tensile forces, inject lubricant, up to 1,500,000 lbf!
FLEXIBLE
JOINT
TELESCOPIC
JOINT
MARINE RISER
DIVERTER
ASSEMBLY
RISER
TENSIONING
LINES
KILL AND
CHOKE LINES
Upper Section Marine Riser System. 8
Mud returns
L.P. Annular
Control valve
Vent line
A diverter system.
9
Re-directs flow from rig floor to blooey line (10”+), downwind, do not shut in, erosion -10E8
Figure 6-6. Vertical steel
loops used for kill / choke
line transition around the
ball joint.
10
The Drilling Riser
MEAN WATER LEVEL
RISER ELEMENT
Schematic diagram of
riser with imposed forces
11
Optimum riser tension to minimize damage to riser and wear-and-tear on tensioners, sag
Maximum stress
Mean
tension
Minimum stress
Applied tension in riser, kips
12
Tension in riser must be not too low and not too high. Set at 118 kips - will fluctuate 100-136 kips ~ 15%
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.
13
Riser Considerations:
No Field Welding on Riser!
Fatigue of riser cannot be measured
prior to some indication of failure.
Routine inspection required.
14
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.
15
Riser Inspection:
Visual Inspection of the riser should
occur every time the riser is run.
 Check all the seals
 Check all the sealing areas
16
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.
17
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.
18
Riser Instrumentation:
 Heavy Gauge: Pointer attached to
guide line moving in front of
graduated board.
Riser Angle Indicator (at ball joint):
  
2
x


2
y

1/ 2
  tan 1 tan 2  x  tan 2  y

1/ 2
19
Riser Instrumentation:
 Accurate Positioning System:
 For detecting and monitoring vessel
position.
20
Ball Joint:
 A Ball Joint Angle > 4 degrees is an
indication that something is wrong!
 Vessel is offset
 Riser tension is inadequate
21
Ball Joint:
Must decrease ball joint angle
before operations are
resumed.
Remedial Action:
Decrease Offset
Increase Riser Tension
22
Vessel to Seafloor
Guidance System
Guidelines are used for guiding
equipment from the vessel to the
seafloor.
Selection and care of guidelines is
critical.
23
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
24
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.
25
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.
26