During the winter season, rig movements will quickly pick up in response to a passing weather system and not subside until long after the system has gone. It was in such a situation that Statoil was drilling a subsea producer towards a tight ERD target in the Njord field.
The 12 ½” PDC bit and the optimized RSS system had been performing well until it was found that the system was subjected to increasing stick-slip and orientation problems in a historically “easy” formation. A 9″ HD-AST tool was called out and made up to go in hole on the fly without any other changes to the BHA.
The stick-slip immediately fell to a low level and directional performance was regained along with a steadier torque and a boost in ROP. The AST service was maintained throughout the program as the weather remained unstable.