The focus of this paper is to illustrate how a first-principles model of the well hydraulics can be utilised to assess the magnitude of heave-induced pressure oscillations while drilling offshore from floating rigs. Such pressure oscillations are important to consider, as they can violate tight pressure margins.
Based on numerical simulations, we identify situations in which significant downhole pressure oscillations must be expected. We discuss parameters that affect the pressure amplitudes, and illustrate how the simulator is set up to predict the to-be expected pressure oscillations. Such predictions are essential for making an educated decision on whether drilling is possible under given wave conditions and drilling parameters, both when planning a well and in real-time while drilling. We also illustrate how uncertain downhole parameters affect the pressure oscillations, and propose ways to handle the uncertainty in the predictions.
Finally, practical issues such as the estimation of downhole pressure oscillations from on-site measurements, calibration of model parameters, ways to reduce the pressure oscillations via the choke, and the limitations thereof, are discussed.