Dynamic Model of a Mobile Offshore Drilling Unit in Deep Water Environments for Drilling Simulation

In this study, a dynamic model of a Mobile Offshore Drilling Unit (MODU) is described that simulates drilling scenarios, imposed by the environmental factors in offshore drilling. The Response Amplitude Operators (RAOs) of an industry-recognized semi-submersible MODU are modeled for all six degrees of freedom. A stochastic modeling of waves in the North Sea is used and heave disturbance induced by elevation motion of sea surface is modeled using the JONSWAP spectrum. A bond graph model of a MODU predicts axial vibration, torsional vibration, and coupling between axial and torsional vibration due to bit-rock interaction. Axial and torsional submodels use a lumped-segment approach. The model can predict the expected coupling between Weight On Bit (WOB), bit speed, and bit-rock interface conditions. A series of sensitivity analyses were performed to investigate the significance of MODU motion on WOB fluctuations.