Methodology for Assessing Wellhead Integrity During its Life Cycle

Abstract

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 Christmas 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, which are hung into it through the casing hangers, as well as sustain loads from the riser, which is connected at the top of the BOP (right above the wellhead) through the lower flex joint. In this work, we propose a methodology for analyzing the wellhead, 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 simulation of this coupled system provides the loads that are transmitted to the wellhead due to its coupling with riser, vessel, casing, and soil. Then, these loads are converted into stresses and a criterion, such as yield, is applied to verify if they will cause wellhead failure. The objective of this work is to assess wellhead failure due to environmental loads (waves, currents) acting on the riser, by varying parameters such as significant wave height, peak period and current speed, as well as assess wellhead integrity during its lifecycle for operational and survival conditions. Results show that the wellhead may fail under certain environmental conditions, which would compromise well integrity and cause leakage from the well. The analysis performed here, which is deterministic, also provides a basis for a subsequent probabilistic analysis from which the wellhead reliability can be found, based on uncertainties such as the sea state parameters.