directional drilling in top hole (e.g. 26" hole)
02 December 2007
does anyone have experience/advice in what max build up dogleg is
advisable for kicking off in 26" top hole section?
also what limit inclination angle is recommended in big holes like
26" to succesfully run 20" casing in.
To find tools to give you the DLS is not really a problem.
However, I suggest you limit your design by the side forces and bending stresses you will be applying to your tubulars. To get Dog-Legs in a big hole is not (typically) a problem, however large diameter casing connections are not designed for high bending loads.
There is also the effect of the overall well design. Remember that surface hole dog-legs will see the worst case when drilling deeper in the hole from a perspective of pipe being in tension - casing wear may well become an issue.
This is a complex and multifaceted question. Answer is it depends upon.
1. Well profile and T&D to reach TD.
2. You need to carefully look at your casing design and resultant bending loads in large OD pipe. Bending stress will be significant and connections will likely limit your DLS. Typically design your well with half of what you want the pipe to see as a maximum.
3. Think the drilling systems available today will give much more than the pipe can take. Recommend RSS to keep well trajectory smooth. Avoid circulation and BR in one place. Avoid micro doglegs from sliding with MM.
4. Personally, the last time I did it I limited DLS to 1.5/100-ft and did it with a MM. All RL-4S connectors leaked with HP Seawater test till I used Seallube for the running dope.
Drilling Mgr, ENI Brasil
I support cervelo on the input parameters to determine the maximum buildup DLS, but the maximum inclination angle could be gotten from wellbore stability analysis.Also,you select a kick of point or depth that would minimize wellbore friction. Moreso, while running the casing you need a hole allowance that would prevent the casing from wear,etc.
Perhaps if you provide more information, like depth and formation
strength, the group will be able to help you better.
Having said that, have you considered doing a pilot hole and then
opening up to 26"
We have done a lot of 26" hole directional work outside 30"
conductors, mainly for collision avoidance against adjacent wells in a
multi-well platform situation. DLS are generally 1 to 2 deg/30m.
If you were drilling 26" hole and kick off, then to run surface
casing, have you considered casing wear of the surface casing?
Just some thoughts..........