When a 6-in-long slickline fluted centralizer jammed in a nipple profile above the subsea safety valve of an injector well in the Irish Sea, Eni UK needed to have it milled out to access and retrieve the toolstring. Access to the fish was tight, in 4.79-ID tubing with a minimum restriction to 4.26 in.
A conventional bit hardfaced with tungsten carbide was deployed. However, it was highly inefficient, removing only 60% of the centralizer after 400 operating hours.
SLB collaborated with a custom bit manufacturer to design an annular bit with nine tips featuring three geometries for optimizing removal of the metal chips. The bit’s performance was tested on a similar centralizer with ReSOLVE instrumented wireline intervention service configured for milling in conjunction with a TuffTRAC cased hole services tractor. ReSOLVE service brings new efficiencies to milling operations by seamlessly integrating the tractor with the milling tool’s performance by using the MillOptimizer autonomous milling system.
The new bit design was efficiently advanced at 0.15 in/h in milling through the remaining centralizer in only 12 h. Eni UK was kept informed in real time of the rapid milling progress through ReSOLVE service’s continuous monitoring and control.
