转速突变对竖直井钻柱系统动力学特性的影响

钻井过程是一个非常复杂的瞬态响应过程。钻头突遇硬质岩石等突发状况使钻柱转速瞬时降低、随后经历一个加速过程恢复到正常转速。为了研究钻柱在这种情况下的动力学特性，应用有限元软件ANSYS分析了竖直井钻柱系统的恒转速和突遇硬质岩石后的加速过程，得到了两种工况的钻柱振动响应规律。结果表明，突遇硬质岩石后，由于钻头与岩石的撞击作用造成钻柱转速突变，钻柱与井壁发生碰撞，碰撞程度跟转速恢复时间有很大关系，转速恢复时间短，碰撞程度低，钻柱受力小；转速恢复的时间长，钻柱振动明显加剧，与井壁的碰撞频繁，受力增大。转速突变加剧了钻柱的振动响应。

Effect of Rotational Speeds Mutation on the Dynamic Characteristics of the Drill-String System in a Vertical Well

Drilling is a complex transient process. Speed will reduce instantly when drill-string hits a hard rock suddenly and an accelerate process follows it until the speed accelerates to normal value. To observe the dynamic characteristics of drillstring in this case, using the finite element software ＂ ANSYS＂ to analyze a constant speed process and accelerate processes of drillstring system in vertical well and gets the discipline of drillstring＇s vibration. The results show that after hitting hard rocks, the collision between drillstring and the borehole wall will happen for the hitting effect between rocks and bit, and the collision strength has a great relationship with acceleration time, if the acceleration time is short, the collision is slight and the force is small; if the acceleration time is long, the vibration will be exacerbated significantly, the collision is more serious and the force increases. In a word, the variable speed of drill-string exacerbates its vibration.