Abstract
An operational technique designed for safe and quick retrieval of deepwater drilling risers during an imminent threat from hurricane or typhoon is developed by proposing a new drilling riser model with disjointed sections for easier and faster disconnection as against the conventional practice of retrieving the whole length of the riser which is tedious, time-consuming and has a huge risk of untimely evacuation of personnel and facilities. A theoretical method is used to model the drilling riser in freestanding disconnected mode and the resulting differential equation is solved numerically. The mechanical behavior of the drilling riser is analyzed for its survivability in freestanding disconnected mode in order to ascertain its useability when the impending typhoon is over. Parametric studies are carried out on key influencing parameters such as buoyancy can upthrust ratio, buoyancy can (BC) position, and riser thickness to arrive at an optimum condition that will ensure the survivability of the drilling riser when disconnected in freestanding mode. Fifteen parametric case studies are presented. In the first five cases, with a varying buoyancy can upthrust ratio but a fixed BC position and riser thickness, it resulted to obtaining a suitable buoyancy can upthrust ratio which is used in subsequent cases. The next six case studies gave a suitable BC position, and finally the last four cases for riser thickness. Results obtained from the fifteen cases are used to get the optimum condition for survivability of the riser in freestanding disconnected mode. A deepwater drilling riser designed in conformity to the optimum configurational conditions as presented in the analysis can survive in the face of an emergency situation such as hurricane or typhoon.
