UK-based Centek Ltd. and US-based Protech have introduced the Centek CT (Close Tolerance) centralizer to operators in the Gulf of Mexico. The centralizer has proven to reduce deepwater drilling costs based on a six-month trial by BHP Billiton and Chevron on the Tahiti project.
The Centek CT centralizer saves through its single-piece construction and low friction, low drag design. Deepwater wells have reduced tolerances because operators must run line through an existing casing. The centralizer has to be flexible enough to compress fully to pass through the tight restriction, yet in the open hole, it must expand back to gauge with no permanent set occurring.
“The CT Centralizer reduces run-in-hole time because you have less drag as it is pulled into the well and time is further saved by one less make-up,” says Cliff Berry, sales and marketing manager, Centek Ltd. “This product brings new technology to the problem of close tolerance centralization in deepwater operations, producing a cost saving of up to two-thirds when compared to a centralizer sub.”
Because of the close tolerances, the centralizer does not use conventional steel stop collars on the outside of the liner casing. Instead, the end-bands are notched to allow low-friction, composite-limiting blocks to be inserted, thereby ensuring the centralizer is pulled into the well rather than pushed. As a result, drag is reduced.
Centek normally manufactures centralizers from 4 mm (0.16 in.) sheet steel, but to reduce clearances with the CT this can go down to 2.5 mm (0.1 in.). A ring gauge on all fitted components also has to pass over the end-band.
Conventional inline centralizers, or centralizer subs, are expensive to produce mainly because of the cost of threading both pin and box ends. By comparison, the CT Centralizer is slipped onto the pipe and the limiting blocks attached.
The Centek CT centralizer uses Protech Centerform’s CRB Carbon Fiber/Ceramic Composite material for the limiting blocks, which are molded directly to the casing to form a permanent stop that will not slip. This allows the centralizer to be positioned on the casing joint to accommodate automated pipe handling systems. It also is installed in the pipe yard before shipping to the rig. Speedy installation makes for quick turn around and eliminates the need to maintain expensive stocks of centralizer subs.
