Design concept for a subsea wellhead subject to iceberg contact for marginal field development - Grand Banks of Newfoundland (2007)

With the key drivers of rising energy demand and increasing prices, major operators are expanding their search for new hydrocarbon reserves, moving into deeper water, more hostile environments and targeting smaller pools and more remote reserves. -- Thus, other type of challenges rise ahead, which require developing of new innovative, cost effective, and safe technology to put these fields into production. -- One of Canada's important offshore areas that is expected to feed into the continental energy market is the East Coast offshore fields located on the Grand Banks of Newfoundland and Labrador. In addition to the conventional challenges that accompany any offshore field development activity, wellhead protection from icebergs remains one of the most important challenges and takes the priority in any intended development on the Grand Banks. So far, several design strategies for iceberg risk mitigation have been suggested, and some are being already adopted, such as the glory hole concept which proved to be an efficient protection measure but at a high capital cost. -- The thesis work gives a general overview of the oil and gas industry on the Grand Banks with a focus on the various strategies and concepts for the protection of the wellheads on the Grand Banks, and their application for marginal fields' development. -- The present study favors the use of a shear link wellhead as a protection mechanism against floating and gouging icebergs, and accordingly an evaluation study was done for this system. -- A detailed structural analysis was conducted, by performing a study to determine the wellhead section stresses generated due to a floating /gouging iceberg wellhead accidental interaction. The response of the well upper section (conductor and wellhead) to ice gouges and to floating icebergs events was analyzed by a 3-D finite element numerical model using ABAQUS software. The parametric computations and creation of the ABAQUS input file employed a MATLAB code. The result was a better understanding of the interaction mechanism between floating/ gouging icebergs, soil mechanics and the subsea wellhead sections, where not much detailed engineering, structural and analytical work has been done previously. -- The calculated stresses and their distribution along the wellhead sections were used to address the structural reliability and integrity of the well by highlighting the stress levels and loads on: the down-hole safety valves, the isolation valve on top of the hanger, the conductor stress limit (buckling), completion tubing stress limits (buckling and rupture), the shear key and the wellhead components. Another purpose for this analysis was to present a guide for the detailed engineering, which is not addressed in this thesis, of the shear link and the suggested isolation valve on top of the tubing hanger. -- A detailed overview of well structure (Casing and Completion) and sealing barriers failure modes leading to leak paths and loss of well integrity is presented in the work where the probability of a leak occurrence in the event of X-mas tree displacement in the suggested system is done. Suggested intervention and work-over sequence to put the well into production following the event of an iceberg impact to the wellhead leading to the loss of the X-mas tree and the upper part of the well was discussed taking into consideration the safety of the operation and highlighting the practicality of the shear link wellhead system.