Abstract
With extreme complexity, the drilling process is a dynamic process which is severely influenced by longitudinal vibration. Longitudinal vibration, as one of the most important reason, is directly generated by the fatigue failure of the bottom hole assembly. In this paper, the natural frequencies of longitudinal vibration along the drillstring are analyzed by the finite element method. The deformed plot, stress nephogram, and displacement contour map under 1 to 4 ordered the natural frequency of the longitudinal vibration are obtained. The analysis results show that the maximum deformation always appears in the central part of the string so that some technological process on these positions is required to reduce the collision between the string and wellbore wall. Additionally, a time series of longitudinal vibration of a bottom rotating drillstring is extracted from real-time field data, which is measured while drilling near the drill bit. Then the time-frequency and energy spectrum analysis of the longitudinal vibration is carried out. The results of the statistical analysis show that, when the drillstring uniformly rotates, the longitudinal vibration can be considered as a kind of random vibration. However, if the stick-slip phenomenon occurs during the drilling process, the energy concentration will appear in the time series spectrum of the longitudinal vibration, by which means the vibration could be regarded as random no longer.
Highlights
In the field of oil and gas drilling engineering, drilling dynamics is one of the most important problems which is attracted the attention of engineers for more than half a century
It has been proved that drilling dynamics and its interactions with the surroundings is the essential reason of a lot of dangerous drilling accidents, such as the poor cementing quality induced by the deterioration of borehole quality and the failure of drilling tools caused by strong vibration [1]
Create a more accurate theoretical model of the drillstring vibration is difficult due to the impact of complex downhole conditions, but with the development of downhole measurement technology, it becomes possible to study the dynamic characteristics of drillstring by measuring the vibration signal while drilling
Summary
In the field of oil and gas drilling engineering, drilling dynamics is one of the most important problems which is attracted the attention of engineers for more than half a century. We use time series analysis method to further study the dynamics of longitudinal vibration on bottom drilling tools (BDT) with measurement data, by which new challenges appeared in the vibration modeling, like new drilling techniques such as directional and vibration-assisted rotary drilling, could be further explained comprehensively. When the drillstring appear stick-slip phenomenon, the energy concentration appeared in the spectrum of the longitudinal vibration time series, which should not be considered as random vibration any more. This is the mainly novelty and achievements of the work in this paper
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