Abstract
The landing string is an important component of deepwater riserless drilling systems. Determination of the dynamic characteristics of the landing string plays an essential role in its design for ensuring its safe operation. In this paper, a dynamic model is developed to investigate the dynamic response characteristics of a landing string, where a landing string in a marine environment is modeled as a flexible slender tube undergoing coupled transverse and axial motions. The heaving motion of the drilling platform is taken as the upper boundary condition and the motion of the drilling bit caused by the interaction between the rock and the bit as the lower boundary condition. A semiempirical Morison equation is used to simulate the effect of the load imposed by the marine environment. The dynamic model, which is nonlinearly coupled and multibody, is discretized by a finite element method and solved by the Newmark technique. Using the proposed model, the dynamic responses of the displacement, axial force, and moment in the landing string are investigated in detail to find out the influences of driving depth of surface catheter, platform motion, bit movement, and marine environment on the dynamical characteristics of the landing string.
Highlights
Riserless drilling is a new deepwater drilling technology in which the drilling platform no longer bears the interaction load induced by the ocean waves and the ocean currents which are imposed on the riser and the mass buoyancy block
Due to the lacking of protection from riser as well as the exposure to the ocean environment directly, the landing string bears very complex patterns of external loads, such as working load, marine environmental load, drilling platform movement, and their combinations. erefore, the internal force and deformation of the landing string are often complex and changeable, making the pipe string prone to be instability, fracture, and fatigue failure and causing serious accidents and economic loss [2]. us, in order to ensure the safety and reliability of deepwater riserless drilling operation, it is very necessary to find out the dynamic characteristics of the landing string, including vibration modes, critical speed of the bit, deformation, and internal load response under the actions of environmental load and platform movement [3,4,5]
Many works, using theoretical analyses [6, 7], numerical simulations [8], and experimental investigations [9, 10], have been conducted to investigate the dynamics behaviour of on-land drilling string to determine the change regulations of the friction, torsion, and axial force under various working conditions. ese research results guided the operation of on-land drilling operation
Summary
Riserless drilling is a new deepwater drilling technology in which the drilling platform no longer bears the interaction load induced by the ocean waves and the ocean currents which are imposed on the riser and the mass buoyancy block. Liu et al [37] established a LTCV model to investigate the effects of the main parameters such as marine load, platform motion, and suspending length on the dynamic behaviour of a deepwater hard suspension riser under emergency evacuation conditions. Besides the effect caused by the nonlinear LTCV of a pipe string or a beam discussed by Han and Benaroya [32]; Zhao and Wu [36]; and Liu et al [37], the landing string in riserless drilling is affected simultaneously by the combined actions of the platform, drilling bit, ocean environment, driving depth, and so on. Is paper presents a nonlinear dynamic model of a deepwater landing string under the combined action of platform movement, drill movement, and marine load, taking into account the LTCV and driving depth effects. The nonlinear vibration modes and mechanical response mechanism of a landing string are investigated in detail, aimed at providing a theoretical basis for the design, construction, and operation of deepwater landing strings in riserless drilling
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