What is the minimum liner overlap that can be used???

[OldParr]

What is the minimum liner overlap that can be used???

I've asked this question many times, and I've never got neither a straight answer nor a calculation behind it...

When you ask someone about this, the usual answer is 150 m / 500 ft. But the reason behin this number seems to be no other than experience. However, some times due to operational reasons, the overlap needs to be way much smaller. I've heard that even some operators have placed a liner with only 15 m / 50 ft overlap.

Does anybody knows how to calculate the mentioned overlap?
If there is no such a calculation in place, can you please advice on the asumptions you've made or even if your company has a policy regarding this matter.

OldParr.

[haward_2006]

amigo,
permitame decirle que 500 pies es correcto.... debido al proceso de cementacion, por lo que se debe evitar que se contamine el cemento cercano a la empacadura del liner y garantizar por lo menos 100 pies de buen cemento....
siempre en el tope del liner exitira cemento contaminado y en relidad es imposible evitarlo lo que se trata es lograr al menos 100 pies de sello hidraulico---

saludos

[pankajbhavnani]

I think the answer would be that the hanger system and the cementing part, generally its 100m out of which 20-30 m is the hanger jt

[Yengineer]

Minimum? It can be as little as the liner hanger allows, also a couple of meters. However, you should keep in mind why you are running a liner, what are the formations characteristics, cementing quality, government regulations etc etc.

[scipiond]

Agree fully with Yengineer, minimum can be a few meters only with a liner top packer as the liner top seal will be achieved by the packer eventhough the quality of cement and its height in the liner by casing overlap do not achieve a seal. Without liner top, you usually want to keep a casing by liner overlap long enough for cement to achieve a seal, minimum will be in my experience 20 to 30 meters provided good spacer ahead of cement and some cement excess is pumped to place good quality cement in overlap.

[Dedy Tampubolon]

Other way to see "minimum liner overlap" is consider to set the Hanger and Liner Top Packer above previous casing Landing Collar (if you bumped the plug) or last known TOC of the previous casing (if you did not bump the Plug).

Cheers, Dedy Tampubolon

[muhammad abdulrehman]

I agree that there is no hard and fast rule to calculate liner length. it depends on the formation, cement quality, mud weight, and liner weight itself as with lesser weight in more depth (with high string weight), there may be no hanger setting indication at surface. My company's policy is 300 ft overlap. some times it is for overcoming depth errors in deep wells to make sure you are setting hanger within the casing, not in open hole.