Abstract
The drilling riser is an important piece of equipment used to link the subsea wellhead with the drilling platform. Its operating environment is extremely complex because of the effects of ocean currents, which can cause riser overload, fatigue, leading to economic loss. Therefore, in order to improve design and prevent premature failure of drilling riser, it is important to research the mechanical response to ocean currents. The effects of tension ratio and platform deflection on the lateral displacement, bending moment, and the stress of the drilling riser are analyzed, under actual working conditions and shear flow. The results show that the bending moment and lateral displacement of the drilling riser decrease significantly and the stress of the riser increases with increasing tension ratio. There is an increase in the lateral displacement of the drilling riser and the bending moment at the lower end of the drilling riser, with an increase in the initial offset of the offshore drilling platform. However, the initial offset of the offshore drilling platform has little effect on the stress of the riser. Under shear flow conditions, the lateral displacement, bending moment, and stress initially increase, then decrease, and finally stabilize. These results can be used to improve the design of drilling riser.
Highlights
The drilling industry has gradually shifted marine oil and gas development from the continental shelf to deep water and ultra-deep water
The distribution of the lateral displacement, bending moment, and stress were investigated for a drilling riser, from the upper flex joint to the seabed
The results show that the lateral displacement, bending moment, and stress at any point on the riser gradually increase to the maximum value, decrease, and stabilize during the ocean current loading process
Summary
The drilling industry has gradually shifted marine oil and gas development from the continental shelf to deep water and ultra-deep water (sea depth ø 500 m). Actual ocean currents are shear flows, but in most studies, the current load is considered uniform.[20] In many models, the loads acting on the simulated riser are inconsistent with the actual conditions, leading to distorted results and loss of real-world applicability. A mechanical model of a riser was developed for a combination of wave and shear flow current loads, where the upper and lower ends were assumed to be hinged and the effect of drilling fluid was neglected. The distribution laws of the bending moment, stress, and lateral displacement of the riser and the related response variation during the process of loading were analyzed. These results will be useful in the engineering application of marine riser. Ð2Þ where Ka is the rotational stiffness of the lower flexible joint
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