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Wellbore temperature assessment for generic deepwater well in Blacksea and mitigation of hydrate dissociation risk

Öztürk, M Tarık
Drilling operation expanded through deep water environments starting from mid-1980. As water depth increased, hydrate bearing formation in the shallow ocean floor is observed and that started to cause problems during drilling and production operations. Problems due to hydrate dissociation and forming during operations are also reported by the companies working in those environments many times. Although there are several factors affect the dissociation of shallow hydrate bearing sediments, heat flux from deeper sections of the well through shallower section during the operation is the major one. In order to mitigate that risk in this study, Black Sea is taken as a reference drilling environment. Hydrate phase boundary of the region is calculated via using actual temperature and pressure data gathered during drilling operations. Generic wellbore is defined and common drilling operation sequence is simulated in this defined wellbore. Heat transfer from section target depths to the shallow wellbore section is observed during simulations. Reducing effect of low inlet temperatures and a low circulation rate on wellbore temperatures are determined. In addition positive effect of riser boosting on depressing wellbore temperature in the well head is determined. Black Sea deep water hydrate stability zone is determined between 2210-2275m. Target depth limitation for generic well designed in drilling operations is determined as 4600m.