Push-and-Twist Drillstring Assemblies

Deep drilling using a rigid drillstring requires the assembly and disassembly of multiple drill pipes. The interfaces between these pipes provide a challenge for automation because they must transmit large drilling forces and movements while, at the same time, minimise the actions and forces that are needed to make or break the interface.\ud A geometry which can address these requirements has been suggested by the authors. This approach would use a push-and-twist bayonet system to engage drill pipes, with torque transmission through the bayonet studs. A variety of L-shaped and T-shaped bayonet paths have been proposed to ensure that separation of specific drill pipes can be achieved through a combination of clockwise and counter-clockwise rotation and single-point clamping. Sustained drills into a variety of media are used to show that percussive impulses are transmitted across the interface, whilst ensuring that the drill interface is able to withstand the shock loading associated with hammer-drilling. These tests are repeated and contrasted to control experiments using a single-piece control drillstring, which allows the performance of the interface and any degradation over time to be quantified. Results suggest that the bayonet-style connection performs well with no significant performances losses encountered or structural degradation noted.