Abstract
The wellhead is an important component in the context of well integrity and operational safety,as it serves as a link between well and riser in offshore oil wells.Wellheads,combined with the BOP and/or the Christinas tree,act as the final barrier element preventing leakage of oil from the well into the environment.The wellhead must sustain loads from the casings(soil reaction),which are hung into it through the casing hangers,as well as sustain loads from the riser(waves,current),which is connected at the top of the BOP(right above the wellhead)through the lower flex joint.In Part I of this work,we propose a deterministic methodology to evaluate wellhead motions,considering a mechanical system that couples the vessel,the riser,the wellhead itself,the conductor and surface casings,and their interaction with the soil.The limiting factor in this study is the excessive motions experienced by the wellhead,which can lead to well integrity problems such as dislodgment of the conductor casing or a poor cementing job.The simulation of this system provides the motions experienced by the wellhead,through simulation of some well design choices(use of jetting base,conductor casing size,and cemented conductor).Results have shown that modern 5-phase wells with cemented conductor confer higher integrity to the wellhead compared to old 4-phase wells with jetted conductors,while the jetting base has not affected the wellhead motions significantly.These results are extended in Part II,which incorporates a stochastic analysis.
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