Casing stretch calculation
05 March 2010
Does anyone have a simple formula for working out the stretch of casing in a vertical well?
Is the formula given in the Haliburton book for tubing & small casing still valid for 13 3/8" casing, and if so, how do you calculate the value of the stretch constant?
Thanks in advance for your help.
The grade of steel doesn't affect Youngs Modulus, nor the coefficient of thermal expansion; so the results of strain due to stress or temperature should be the same for any grade of steel.
Does the Mathcad worksheet do what you need it to do?
Thanks for your various responses - I'll let you know how it works out in about 10 days or so!
One thing I see in common about the formulae proposed is that none of them reference the grade of steel involved and intuitively this does not seem right?
Or does this only matter when calculating when it starts to plastically deform?
BTW, Tim / Steve - doing fine, thanks, but I'm currrently in Sudan which does make life a little difficult in getting the info you need...
Attached is an excerpt from the Weatherford data handbook
included is stretch constants for larger casing
All - I've now created a "proper" Mathcad worksheet which calculates the change in length of a pipe due to a) own buoyant weight, b) additional axial load and c) temperature change.
Take a look at http://220.127.116.11/MCS/MathcadWorksheets/Public/PipeStretch.xmcd .
Comments welcome, hope you find it useful. I'll add it to the Mathcad worksheets on drillers.com.
I recently used the following formula when running a 22” string (with inner cementing string), it matched what was observed in running the casing.
Stretch = (Stretch due to landing string weight) + (Stretch from casing weight) = Sw + Sf
Sw = [(L^2)*(65.44-(1.44*MW))]/96,250,000
L = length of landing string
MW = mud weight
Sf = (F*L)/[1,963,500*(OD^2-ID^2)]
L = length of landing string
F = buoyed weight below landing string (lbs)
**NOTE: this had to be done for both the casing and inner string
OD/ID = landing string diameters
I hope this helps.
Good morning Scott,
Have just looked up my copy of Drilling Formulae etc. by Norton J Lapeyrouse, pages 69 thru 72, (copyright and acknowledgements to him).
Basic formula is:
Feet of free pipe = stretch (inches) x FPC / pull force in thousands of lbs.
FPC = As x 2500 where As is cross sectional area of the pipe wall.
You should be able to apply these to both DP and casing.
Hope this helps and that you're keeing well
Energy in Focus Limited
Scott, I may have made an error in the formula, am about to run with the Copenhagen Hash and will have another look when I get back.
Hi Scott, hope life is treating you well!
Using any length units, stretch due to own buoyant weight;
Stretch = length x 2.37 x 10^-5 x (7.85 - SG mud)
Assumes that steel SG = 7.85 and Youngs Modulus for steel = 30 x 10^6
Worked out from first principles; don't know what the Halliburton book says.