Abstract
As a useful technology, the horizontal drilling for underground coalmine has been applied in many fields such as gas drainage, water control, exploration and accurate drilling borehole engineering. In this paper, the annulus tubes are used to simulate the fluid transportation process between drilling rod and casing tube when drilling horizontally. The main goal of this research is to analyze the effects of eccentricity, fluid velocity, outer tube length and volume fraction on dynamic characteristics of partially liquid-filled annulus tube in a drillstring system. According to the Euler-Bernoulli beam model, the partially liquid-filled inner tube model and outer tube model are established respectively when considering the effect of transport fluid inside the annulus tubes. Based on the vibration characteristics of the tube, the added mass coefficient is proposed to calculate the natural frequencies of the outer tubes. And natural frequency is the frequency at which a system tends to oscillate in the absence of any driving or damping force. According to the compared results of experiments and simulations, the natural characteristics of outer tube depend on the tube design parameter (outer tube length) and the volume fraction of liquid filled in the outer tube. Furthermore, experiments have verified that the natural frequencies of the outer tubes can be directly calculated from the length of outer tubes. Therefore, it is feasible to propose the method of attaching liquid mass to tube mass to obtain the natural frequencies of outer tubes. According to the results, it can be concluded that: (i) The natural frequencies of tube decrease as the length of the tube increases; (ii) The increase of volume fraction of liquid in the tube can significantly reduce the natural frequencies of tube; (iii) The fluid velocity and eccentricity have less effects on the natural frequencies of tube; (ⅳ) The added mass coefficient of outer tubes can be calculated and it is not a fixed value, it varies with the volume fraction of fluid in annulus tubes. In this work, the inner and outer tube models are established respectively for fluid transportation process between a horizontal drilling rod and casing tube. The effects of four factors on the natural frequencies are compared, and the concept of added mass coefficient is proposed to obtain reasonable tube natural frequencies.
Highlights
The losses caused by tube vibration in a drilling system amounted to almost tens of billions of dollars each year in advanced industrialized countries
Dynamic characteristics analysis of partially liquid-filled tubes in a drillstring system was investigated through the added mass method
The annular tubes are divided into an inner tube and an outer tube, and both are modeled by the Euler-Bernoulli theory
Summary
The losses caused by tube vibration in a drilling system amounted to almost tens of billions of dollars each year in advanced industrialized countries. The sudden change of load and strong vibration are inevitable in the process of mechanical work, which will cause strong disturbance to the transmission tubes and lead to instable work situation [1]. It is very important to study the vibration of tube transportation during drilling. It is necessary to reduce the vibration of the annulus tube so as to avoid the resonance. When the level of liquid is different, the vibration characteristics of the annulus tubes can be affected. This problem leads to the increasing difficulty of the fluid transportation. The research on the dynamic characteristics of the annulus tubes is very necessary
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