SPECIAL REPORT: NEXT GENERATION CENTRALIZER SOLUTIONS
The Centek design is a proven tool to reduce both torque and drag. Drag will occur when centralizers are oversized to the wellbore or when smaller solid UROS CENTRALIZER SIDE VIEW
units push debris in front of them, like a piston
compressed to such an extent that they lose their elasticity and can’t expand to the correct diameter of the under-reamed hole – a condition known as permanent set. The latest generation of centralizers from Centek is manufactured from a single piece of heattreated steel giving a hardened and tempered surface that results in greatly reduced torque and drag losses, so abrasive wear caused by running to depth and rotating the tubular is virtually eliminated. These centralizers offer exceptionally high fatigue strength for axial forces and radial side loads on bows during tubular rotation. Reducing torque ensures that casings can be rotated without wear, in both cased and open holes, at a deeper level than before. Despite being fully compressed during passage through the casings, these one piece construction centralizers offer exceptional restoring force with a very high stand-off ratio once in the open hole. As low profile units they take up less annular space, so the ECD (Equivalent Circulating Density) signature is low allowing the operator to pump at a slightly higher rate improving well clean out. When running casing, losses can result from not getting to bottom due to friction or mechanical interference, getting packed off or stuck, while extra trips and side-tracks, all add to well costs. In addition, poor cementation due to inadequate stand-off causes improper cement placement resulting in production delays and early water entry directly attributable to incorrect tubular placement in the well-bore. All these problems can be resolved by ensuring correct centralization.
The UROS Centralizer In 2010 the Centek Group introduced its UROS centralizer, embodying a radical new design 6 | WWW.OFFSHORETECHNOLOGYREPORTS.COM
targeted specifically on under-reamed well sections, which optimises the balance between drag resistive loads and the performance required once in final position. The UROS, or Under-Reamed Offset centralizer, is the answer to the oil industry’s need to reduce drag forces on run-in-hole through previously set casing before continuing into an under-reamed well section. The UROS significantly reduces initial insertion forces, a characteristic of bow type centralizers, and additionally delivers a substantial reduction in running forces when passing through previously set casings. Once through the compressed stage, the UROS reverts to normal centralizer operation in the open hole with the bows regaining their nominal outer diameter to maximise stand off. The UROS achieves a reduction in drag by its unique, patented bow design, in which the high points of the bows are offset alternately. This produces significant drag force reduction without reducing the strength of the unit or its capacity to centralize the casing once in the open hole. In the open hole the UROS’s characteristics are those of a gauge hole centralizer so maximising stand-off. UROS centralizers are now increasingly being used in South American and Norwegian offshore operations. Many of the Norwegian wells have a high risk of wash-out sections (i.e. open-hole sections larger than the original hole size), generally caused by soft or unconsolidated formations. Centek centralizers have proved remarkably resilient when casing has had to be pulled. On one occasion casing was pulled twice and each time the UROS centralizers were undamaged and the rig team could simply rerun the same centralizers. These centralizers are individually
Defence Industry – Special Report on Next Centralizer Solutions