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)