Drilling is the cutting into sediment or rock layers (“the formation”) by using a drill bit located at the bottom tip of the drill pipe. The drill bit is usually rotated by turning the top portion of the drill pipe on the ship’s rig floor, and the contact pressure, or the weight-on-bit (WOB), that “pushes” the bit against the formation is well controlled by the driller. However, in deep drilling it is difficult to adequately maintain WOB and rotate the drill bit because of several kinds of complex drill pipe nonlinear dynamic motion. Therefore, we need to understand the motion of the drill pipe and the drill bit, and to control the drill bit motion as well as the WOB.
These dynamic motions include: drill pipe whirl, Magnus effect in riserless drilling, stick-slip, or torsional vibration on the drill bit, bit whirl, and others. Moreover, in deep drilling, vertical motion becomes much larger because the resonant frequency of the drill pipe matches that of the drilling vessel’s heave. This causes large variations in the WOB of the drill bit. These dynamic motions not only complicate the drilling operation but also generate or increase forces on the drill pipe resulting in cumulative fatigue. CDEX is using model experiments to understand the various complex nonlinear dynamic motions of the drill pipe and drill bit, creating numerical simulation models, and establishing a better fatigue evaluation methodology.
- Understanding nonlinear drill pipe and drill bit dynamic motion, including vortex induced vibration, whirl motion, Magnus effect, stick-slip, and vertical dynamic motion, and establishing numerical simulation models.
- Understanding fatigue strength of the actual drill pipe via full-scale fatigue tests, and establishing fatigue evaluation methods, applying cumulative fatigue and fracture mechanics.
- Developing technology to control or mitigate the motions of the drill pipe and the drill bit.
This research was partially supported by JSPS KAKENHI Grant Numbers JP16H04610, JP17H06458, JP26630457, JP24360368.