Of all the components involved in running tubulars the least appreciated is the casing centraliser. Unappreciated that is until a centralisation problem occurs.
The purpose of a casing centraliser is twofold, to act as a mechanical aid on RIH and to support and centre the casing in the wellbore, so as to allow cement to be pumped up the annulus with least resistance around the tubular and produce a robust cement seal, ensuring zonal isolation. If the centraliser is not strong enough to centre the pipe, or if it breaks, the consequences can be very expensive. If it breaks in a deviated well, centralisation is usually completely lost rendering effective cementation impossible added to which the centraliser may jam the pipe down hole.
Stuck drill strings are one of the major contributors to drilling downtime, and a common cause of a pipe stuck down hole is a failed centralizer. A very conservative estimate is that annually, 400 wells worldwide are affected by centraliser problems, at an average cost per well of around $1.5M producing a total annual loss of $0.6B. This is a loss which is largely preventable.
A major problem in under-reamed wells is getting effective casing centralisation in the enlarged open-hole section. Conventional bow-spring centralisers that are wide enough to fit the under-reamed section accurately, often get damaged or set in passing though narrower casings. Solid centralisers are less prone to damage but are too small in the underreamed hole to provide any effective centralization.
Centek centralisers are manufactured from a single piece of heat-treated steel and despite being fully compressed during passage through the casings, these unitary construction centralisers offer exceptional restoring force with a very high stand-off ratio once in the open hole.
Before choosing a centraliser, consideration should be given to running forces, stand-off, zonal isolation and centralizer flexibility requirements.
Enter X at www.engineerlive.com/iog
Centek Limited is based in Newton Abbot, eveon, UK. www.Centekltd.co.uk
