Abstract

Downhole drilling components are subjected to significant cyclic loading during drilling operations and these can result in fatigue damage. If undetected this can lead to downhole failure resulting in either twist off or washout. The threaded connections between the individual elements of the drillstring are particularly susceptible to fatigue and are routinely inspected to identify any damage that has occurred. Conventional inspection methods such as MPI and dye penetrant are widely used but are difficult to apply and rely very much on the skill of the operator. These methods have been found to be unreliable when used for inspection of threaded connections.

The Alternating Current Field Measurement (ACFM) technique is an electromagnetic method for detecting and sizing fatigue cracks. This has now successfully been applied to drillstring threaded connections. The system comprises a hand held probe which is swept around the thread. The system controller then collects the information, checks the data quality and makes an automated assessment of the threaded connection. This is presented as a simple GO/NO GO result to the operator. By de-skilling the inspection and improving control of the inspection process more reliable inspection is achieved. This, combined with reduced requirement for drillstring handling can lead to significant cost savings to a drilling operation.

The paper will describe the inspection technique, how it has been specially adapted to drillstring thread inspection and the way in which the system can be integrated into drillstring management systems.