Demanding application causes excessive NPT

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.

Greater wellbore integrity eliminates borehole collapse issues

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.