While working in Australia's North West Shelf, Apache Energy encountered wellbore instability while drilling development wells, which caused hole problems and the loss of a wellbore. During the operation, greater-than-normal NPT resulted from controlling circulation losses, making wiper trips, tripping in and out, and running casing. Apache wanted to reduce NPT-related costs and improve performance by reducing off-bottom risks when drilling the 12 1/4-in sections.
To help Apache reduce NPT and minimize operational risk, the Allegro CD directional casing-while-drilling service with a retrievable BHA was used. The 12 1/4-in section was directionally drilled from the 13 3/8-in shoe to TD in a single run, using 9 5/8-in casing instead of a conventional drillstring. Casing the wellbore while drilling eliminated the danger of borehole collapse before casing could be run.
The Allegro CD service retrievable BHA included an RSS to drill a pilot hole and an underreamer to enlarge the borehole to 12 1/4 in. The BHA was actively steered to avoid unstable regions and wellbore collision risks using real-time MWD measurements. The resulting wellbore inclination increased from 27° to 90°, holding angle to section TD at 2,197-m MD and 723-m TVD. Once TD was reached, the underreamer's cutters were retracted, the BHA was unlocked from the 9 5/8-in casing and retrieved on drillpipe, and the casing was cemented.
Compared with nearly 13 days to drill the offset well by conventional means, the Allegro CD service ran casing to TD while drilling in 5.88 days, saving approximately 7 rig days.
In addition to reducing Apache’s NPT-related costs and drilling time, the run eliminated the need for a long liner run on the next section. The operation also resulted in three Allegro CD service world records for
