Wellhead systems - PetroWiki

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Wellhead systems serve as the termination point of casing and tubing strings. As such, these systems control pressure and provide access to the main bore of the casing or tubing or to the annulus. This pressure-controlled access allows drilling and completion activities to take place safely with minimal environmental risk. Multiple barriers are used, such as primary and secondary seals, to reduce risk in case of equipment failure. Offshore wellhead systems are normally more sophisticated in design to handle ocean currents, bending loads, and other loads induced by the environment during the life of the well.