Tension Variation and Limiting Wave Height of a Deep Sea Drilling Riser in Hang-Off Mode

Abstract

The wave spectral analysis technique is applied to predict the limiting wave conditions for a deep sea drilling riser in the hang-off mode. In this mode, the riser is disconnected from the subsea BOP stack, hangs from the riser tensioner wires, and the top of the riser moves with the drilling vessel. The limiting wave height then, is the highest wave which does not cause compression in the top of the riser. Calculation results are presented showing the limiting wave height as a function of averaged wave period for a 2, 000 m long deep sea riser. This method is then verified through comparisons with results of calculations performed using the time domain method in response to a random sea. Additionally, the influences of internal fluid mass in the riser and the associated fluid friction on the limiting wave height are discussed. Finally, applications of the method to the analysis and design of deep sea drilling risers are presented.