Abstract
This study attempts to explain the motion behavior of the marine riser coupled to drill string when the vortex induced vibration is involved. Vibrations have been reported to have a major effect on drilling performance, affecting the Rate of Penetration (ROP), causing severe damage to drilling tools and also reduces the efficiency of the drilling process. There are two major components of drilling tools that are subjected to vibration, namely the marine riser and the drilling string. Analysis of vibration in the marine riser and drill string are two topical areas that have individually received considerable attention by researchers in the past. While these two subjects are interrelated, borne by the fact that the marine riser encapsulates and protects the drill pipe, they have been little attempt to investigate them together as an assembly. Due to the complexities of the models, simplifying assumptions were made in order to undertake the investigation. Using staggered approach, the results were compared with experimental and simulation data from the open literature. It was found that the maximum displacement with negative damping occurs at low frequency and rotation speed. The addition of vortex shedding forces caused the drill string to deform from its vertical axis and thus increased the risk of failure of drill string and riser.
Highlights
Drilling in deepwater presents a significant challenge, drill string failures like washout and twist-off can result in expensive non-productive time and loss of equipment
According to Eq (3) since the vortex shedding frequency is proportional to the current velocity and the load of intensity of riser is square of the current velocity, the magnitude of the drag force will be approximately constant (Sengupta, 1978)
The lateral vibration mode was analyzed at two conditions, with and without vortex shedding forces
Summary
Drilling in deepwater presents a significant challenge, drill string failures like washout and twist-off can result in expensive non-productive time and loss of equipment. Drill string vibrations are extremely complex because of the random nature of a multitude of factors such as: bit/formation interaction, drill string/wellbore interaction and hydraulics. In many cases, it becomes a main cause of premature failure of drill string components and drilling inefficiency. On the other hand in offshore operation, the presence of hydrodynamic pressure, sea current and tidal wave further complicate the analysis due to fatigue. A riser is needed to protect the drill pipe from the external environment and stabilize the drill pipe when the drilling is performed. Despite extensive research in the last four decades, questions remain unanswered because of the complexity in compounded parameters. (Bailey and Finnie, 1960; Aldushaishi, 2012)
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