Cause analysis on the rotation of riser during the operation of offshore oil and gas wells

The rotation of well in the service process of offshore production wells will bring potential safety hazard and serious operation risk to production tree, well manifold and oil & gas production. The rotation of well in a certain offshore oilfield which had been in service for many years was taken as the research object. Firstly, the influential factors in each stage of drilling and production process were analyzed with the stress analysis on the outer riser as the beginning point, and the mechanical model for the torque of the riser under the action of the ocean current was established. Then, considering that marine organisms will attach to the outside of the riser after long-term service of oil and gas wells and the attachment of marine organisms will produce greater torsion under the action of the ocean current, resulting in the rotation of the riser, the model for calculating the rotation force of the riser under different attachment conditions of marine organism was established by means of theoretical analysis and finite element calculation. Finally, the calculation model was used for case study to verify the correctness and accuracy of the theoretical model. The research results can provide theoretical basis for the buckle type design of offshore riser, the connection mode of riser and the well maintenance in the service process of oil and gas wells.