Loads calculation and strength analysis of landing string during deepwater drilling

Key words:  deepwater drilling  landing string  quasi-static analysis  loads calculation  strength analysis

Abstract:

In conductor and casing running operations during deepwater drilling, the exposed landing string in seawater can object very complicated loads with a risk of failure. A quasi-static mechanical model of the landing string in deepwater drilling without risers was established based on the Euler-Bernoulli theory. It was solved by a weighted residual method to analyze the effects of marine environmental loads, drilling vessel offset movement and the weight of casing strings on the deformation and strength safety of the landing string. The research results demonstrate that ocean currents and waves have a great effect on the lateral deformation and top bending moment of the landing string. The weight of the casing strings is a key factor on the strength design of the landing string. In different operations, the drilling vessel offset towards the negative direction of the ocean current is beneficial to the vertical jetting operation of the conductor, and the vessel offset towards the positive direction of the ocean current can decrease the top bending moment of the landing string efficiently. The Mises stresses at the top and bottom of the landing string can increase suddenly due to the effect of bending normal stress. A strength design method of the landing string based on the axial composite stress is proposed.