Failure Costs

An Industry Insight with Centek

Cliff Berry outlines how single-piece centralizers have brought an end to regular failures and high downtime losses in the drilling sector.

“Centralizer failure costs a fortune. Why is it that some operators seem reluctant to spend on risk reduction up front, but are prepared to pay for downtime in millions of dollars later?”
-Cliff Berry, Centek

Annual downtime during drilling, or running casing, is only marginally better than it was 20 years ago. Estimates from North Sea operators suggest drilling efficiency is still only around the 50% mark, considered across all rig activities from spud to completion, including running casing tubing.

Downtime attributed to centralization problems is reaching sums in excess of $0.5 billion per year. Spiraling rig costs, of all types, including $1 million per day drill ships, mean downtime is becoming prohibitively expensive. Centralizers in real terms are cheap, but when they fail due to damage, breakages or simply getting stuck in hole due to fitting insufficient centralizers at the correct intervals, then they assume a consequential cost out of all proportion to their price.  Centralizer failure costs a fortune. Why is it that some operators seem reluctant to spend on risk reduction up front, but are prepared to pay for downtime in millions of dollars later?

Most centraliser failures are due to choosing an incorrect unit for the job. Everyday someone, somewhere, is pulling casing and leaving debris in the hole for the simple reason that the wrong type of centralizer was used. A second and equally disturbing fact is that the industry always seems to reward failure. If unit failures cause massive overspend, then a 'so what?' attitude becomes common, and the easy answer is to buy some more of the same and hope they work better next time.

Since the early 1950s, centralizers have been of a multipart design and construction, being either welded or interlocked and having hinges and pins to hold them together. That design remains largely unchanged to this day. When wells were vertical this type was ideal as the string is in tension and no radial loads are being applied. However, these units were oversized to the borehole, had high start and high drag forces and were weak as far as restoring force is concerned. These centralizer types are still a regular choice in the industry but they are also the single largest contributor to downtime and overspend. Modern wells have extremely close tolerance casings, some are under-reamed and many are horizontal, making radial and axial forces critical. Solid-body centralizers provide strength and are often used in these wells, but they are inflexible, have low stand-off and restrict annular flow impeding the formation of a good cement bond.

The introduction, by Centek, of a single-piece, non-welded, inherently reliable centralizer, has finally addressed the engineering failings of traditional centralizers. First used in the North Sea in 2002 these single-piece centralizers have brought an end to regular failures and high downtime losses.

Key characteristics such as zero start force and zero running force reduce drag significantly. Reducing torque ensures that casings can be rotated without wear, in both cased and open holes, at a deeper level than before. The low profile of the single-piece centralizer improves the flow by area. Robustness of the centralizer was a paramount design and manufacturing criterion. Flexibility too was a key area as units must be able to pass well tight spots, squeeze down, and then expand back to the original outer hole size.

Pack-off was vastly reduced due to the increased flow by area of these low profile centralizers. Units must have a high restoring force to allow for radial compression, weight of pipe and well geometry, yet get to the bottom and give the stand-off required to achieve the best possible cement job.

Downtime due to centralizer failure is not an acceptable industry norm, when available technology has greatly improved the chances of drilling successfully to depth with reliable cementation.

For an engineered solution for your well that reduces torque and drag, gets to bottom and offers good zonal isolation it is time to investigate change. Call or email sales@centekltd.co.uk and start looking at where saving money protects better than wasting it. The choice, as they say, is yours.