58 PRODUCTION/PROCESSING/HANDLING
The importance of optimal tubular alignment in the wellbore O
f 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
Pigging and SPL development
iscovered deepwater fields may have oil recovery not large enough for independent hub development. The solution to tie back this marginal field to an existing host through a Single Production Line (SPL) is an economic development. SPL looped with one service line (smaller diameter) or SPL equipped with an electrical
D
heating system have been
identified as frontrunners but create some operability issues. One concern is the line inspection with intelligent pigging.
Such operations are complex with specific issues related to deepwater conditions, such as hydrate formation and pig velocity control. Subsea pig launcher, injection hoses and one multi purpose vessel will have to be mobilised for days. Production will also be stopped during days. Even
with the best preparation, the risk to abort such inspection operations will always exist.
For all these reasons, the benefit of pigging must be precisely evaluated during the early stage of SPL
development. All operational and logistical issues will be identified, and the subsea system design adapted
accordingly. Pending risks associated to subsea
pigging, the solution to provide a looped SPL (service line with diameter continuity) will also have to be considered as a serious alternative to allow round trip pigging from the existing host. More details are available in paper 19941 presented by ADC during OTC 2009. o
Enter 58A or ✔ at
www.engineerlive.com/iog
Doris Engineering is based in Paris, France.
www.doris-engineering.com
www.engineerlive.com
underreamed hole to provide any effective centralisation. 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 centraliser flexibility requirements. o
Enter 58 or ✔ at
www.engineerlive.com/iog
Centek Limited is based in Newton Abbot, Devon, UK. www.
Centekltd.co.uk
Rupture discs: videos clarify installation
ressure management specialist Elfab has become the first member of the rupture disc industry to offer installation videos to its customers.
P
The three-minute films detail the entire rupture disc installation process, from removing the old disc, through handling and fitting its replacement, to finally correctly tightening the pipework. Separate films have been made for Elfab’s forward- and reverse-acting rupture disc ranges, while a third covers the company’s graphite rupture disc, Universal Arma-Gard.
Elfab is keen to underline the importance of its products being correctly installed. It is vital that, as safety devices, they are fitted carefully and as advised by the manufacturer. If rupture discs are damaged, misaligned or wrongly fitted, they risk operating incorrectly, with potentially serious consequences for the organisations concerned. o
For more information, visit
www.elfab.com
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