The growing use of under-reamed well-bores and the ever decreasing annular clearance between tubulars has increased the demands placed on centraliser design and construction.
Poor centralisation can result in channelling, poor zonal isolation and even lead to an expensive squeeze job.
Centraliser failure, a position nobody wants to be in, can require the withdrawal of casings, casings getting stuck, side-tracking or in the worst case even losing the well.
Either way these are risks which can and should be minimised with no great expense and crucially no downtime.
Multi-part bow spring centralisers have gained a bad reputation for unreliability and the more robust fixed dimension centralisers are not suitable for under-reamed bores as they totally inflexible in under-gauge conditions and are under-sized to begin with.
Putting such a unit in an over-gauge borehole will not help any critical cement job.
In addition the preload of traditional bow spring centralisers, created by being oversize, results in a cumulative resistance that can prevent the passage of the tubular to final depth.
Centek manufactures its bow spring centralisers from a single piece of steel alloy which is fully heat-treated to give greatly reduced torque and drag figures.
Outer diameters do not need to be oversize to the borehole to achieve reactive force, and performance is substantially in excess of industry standard ANSI/API 10D/ISO 10427-1&2.
Full compression of the bow-spring’s outer diameter allows the centraliser to pass through narrow tubulars and afterwards expand fully to centralise effectively in an under-reamed bore.
Finally, the centralisers offer exceptionally high fatigue strength for radial side loads on bows, for example during rotation of the tubular.
Centek has pioneered this design since 2001 and the company says they are now recognised as the market leader for centralisers in under-reamed well sections.
Centek’s centralisers have been used in thousands of applications worldwide without, says the company, a single centraliser failure.
The Centek S2 centraliser offers: maximised stand off; maximum flexibility when tight spots are encountered; maximum flow by area thus improving well clean out; pipe rotation with reduced effect on torque; optimum cementation operations.

Centek Ltd is based in Newton Abbot, England. www.centekltd.com