Plugged gaswell tubing buckling due to hydrostatic pressure
Plugged gaswell tubing buckling due to hydrostatic pressure
(OP)
While running tubing (bull-plugged) into a gas-well I understand the tubing begins to 'buckle' as the hydrostatic increases. My question is; where does this buckling occur as the tubing starts to helix and if you were to anchor the tubing with a packer and open the tubing end (kobe sub or slickline plug) does the area of buckling or severity of it change after the packer is set and the kobe is opened and after the weight transfer has taken place? I have noticed during a TCP well completion with a double grip packer, that after the kobe sub was opened (broke) during the confirmation logging run the wireline was unable to get back out of the tubing, it got stuck just above the packer.
Dave Dalzell
Halliburton Energy Services
Red Deer, AB. Canada





RE: Plugged gaswell tubing buckling due to hydrostatic pressure
Or, if you run in open, land the hanger, then set a slick line plug and pressure set your packer, then the tubing will be in compression due to the internal pressure on it, which gets locked into the tubing as the packer sets. And then as it heats up due to production it may be in more compression (unless you've got a pre-spaced PBR...).
Usually, the point of maximum compression is just above the packer, (but the point of maximum buckling may be somewhere else, especially if you've got different tubing sizes, weights and connections!), but it may be different for different load cases (as run, pressure test tubing, production, bullhead kill for example) and the only way to find out is by doing a triaxial stress analysis. To do a tri-axial and helical buckling calculation by hand to account for all the different forces acting on tubing is very, very tedious, and it's better done using the various commercially available stress calculation packages- we use WS-Tube from Landmark where I am now, and I've used TDAS from Brother Blue in the past. I'm sure you can get hold of WS-Tube pretty easily at Halliburton!
RE: Plugged gaswell tubing buckling due to hydrostatic pressure