Preventing Casing Collapse During Floatation What parameters matter? Stephen Mann MSc Drilling and Well Engineering Project Supervisor: Ian Cowe
Preventing Casing Collapse During Floatation
What parameters matter?
Stephen MannMSc Drilling and Well EngineeringProject Supervisor: Ian Cowe
What sparked my interest?
“The risk is too great - There’s no way we are
going to float this liner!”
Why Investigate Floatation?
Better understanding of factors that
increase load or reduce resistance
Highlight pertinent factors
Improved Design Review and Risk
Assessment
Why Investigate Floatation?
• Drilling success must be
complimented by casing running
success
• Extend life of existing North Sea
infrastructure
• Reach small pool accumulations /
satellite fields from a central location
Why Investigate Floatation?
Mota, M.O., 2012. Near Field Developments With an Upgraded Brownfield
Platform Rig. SPE 151193
When is Floatation Required?
• Friction significant in inclined wells
• Negative weight
• Buoyancy
• Reduced normal force
• Reduced friction
• INCREASED Reach
Summary of Floatation Methods?
• Several methods
• Air Filled
• Light Fluid Filled
• Mud over Air – SFC
• Air Cavity
• Concerns
• Increased Collapse Risk
• Well Control
My Investigation
• Literature search
• SPE Papers and Industry Journals
• Discussions with casing suppliers and
Specialist ER Drilling Engineers
suggested
• Static design acceptable
• Runnings loads neglected!
My Investigation
• Using Landmark Wellplan, Compass
and Stress-Check software packages
• Along with manual methods including
Biaxial collapse resistance
calculation from API recommended
practices
• Investigated the sensitivity of casing
to collapse for various running loads
and conditions
My Investigation
The Parameters I Think Matter
• In summary I found that:
• Bending stress
• Actual vs Planned Trajectory
• Frictional Heating
• Can be significant if no
reciprocation
• Shock Load - Did not vary greatly
The Parameters I Think Matter
• Surge Pressure
• Unsurprisingly, faster running speed
increased collapse load
• Smaller hole size more susceptible to gauge
reduction
• Mud rheology – YP important
• String rotation - Minimal reduction of collapse
load
Final Thoughts
• Decommissioning need not be the (only)
future of the North Sea
• Techniques exist but must be leveraged to
allow us to extend the life of existing
platforms
• Casing floatation is such a technique
• My project identified parameters that can
provide the vital edge when engineering a
floatation operation
Questions?
Bending Stress
• Passing through
a curve will
impart a bending
stress
• Stress can be
converted to an
equivalent axial
load
• Using Landmark “StressCheck” bending stress was
calculated for a range of DLS
• A biaxial calculation was manually completed and the
reduction in collapse resistance determined
Shock Load
• Imparted when string comes to an abrupt halt• Hole bridged over / Ledge – Hole condition
deterioration• Slips set while pipe moving – Poor procedure
• Magnitude increases with casing weight and running speed
• Investigated additional axial load / reduction in collapse resistance
Surge Pressure
• Greater attention to running speed is necessary as by-pass area decreases
• PV doesn’t appear to have a significant effect on surge pressure
• YP can have a significant effect
• Density – magnitude difference is due to HSP
String Rotation
• It is generally accepted that string rotation increases annular pressure – high rpm
• It had earlier been argued • Rotating pipe in a shear thinning fluid
• Lower effective viscosity
• Reduced annular pressure drop
• After calculation it was found that pressure drop was insignificant (2%) at the expected rotary speed
• Luo, Y. and Peden, J.M., 1990.
Frictional Heat
• ARMSTRONG, N.R. and EVANS, A.M., 2011.• “5 Minutes of rotation was followed by a 5 minutes cooling
period”
• Drillstring failures have been attributed to frictional heating
• Could we be close to this occurring with Casing?
• Greater consequences of failure!
• This situation may occur during periods of off bottom rotation
• Preparing for cement job / percolating air from floated string
Frictional Heat
• Constructed three test trajectories using Compass
• Using Wellplan calculated side force
• Using the method experimentally validated by Eaton (1993) friction energy was calculated and converted to an expected temperature change
• Maximum side force depth – greatest temperature increase
• It was found that temperature could be significantly increased during 5 minutes of rotation
Frictional Heat
• Standard ERD profile• Side force of 1640 lb/ft. , 5 minutes rotation,
15rpm
• Fluid CoF: 0.15
• Temperature increase • 515 °F
• Potential 10% - 25%
reduction in yield
strength dependent upon
grade
• Effect on collapse
resistance dependent
upon D/t regime
Yield Strength Changes against Temperature
Goetzen (1986) cited by Rahman and
Chilingarian (1995)
Frictional Heat
• To investigate the required cooling period • A form of Newton’s Law of Heat Transfer• Bellarby (2009) – Completion engineering context• Plot shows temperature reduction due to Radial
Convection• Much of the cooling
does occur in the
initial 5 minutes
• Cooling slows as
temperature
approaches ambient
• Little advantage to
waiting over 15
minutes (in this case)