Rhino XS Underreams First Two-Phase Nitrogen Mud System Well in One Run

Increased wellbore quality and greater casing efficiency required

An operator attempting to drill and set casing for vertical borehole sections in northern Iraq was experiencing a number of formation-related challenges.

Beyond its sticky characteristics, the formation's instability was causing boreholes to collapse, and the boreholes that were completed were out of gauge. Additionally, wellbore pressure was causing severe mud losses. Although employing an underbalanced drilling (UBD) method using a nitrogen-charged mud system to counter this last condition, the operator was still forced to spend an inordinate amount of time running and setting casing. Before attempting to drill a 615-m, 14-in vertical section and set 13.375-in casing in this challenging formation, the operator sought a more efficient drilling assembly.

Proper reamer activation and performance in high-pressure conditions

To increase wellbore quality and casing efficiency, Schlumberger recommended using the 14250 Rhino XS hydraulically expandable reamer to underream the 14-in pilot-hole section. To ensure proper activation and performance of the Rhino XS reamer in a formation that produced such challenging wellbore pressure, it was essential that the reamer's hydraulic-up nozzles were correctly selected before attempting to enlarge the borehole below the casing ID restriction. Precise nozzle setup would require running the Rhino XS reamer with the selected BHA in simulations that matched the formation and drilling conditions previously experienced by the operator.