钻井液对钻柱纵向振动影响分析

Analysis of the influence of drilling fluid on axial vibration of drill string

钻柱纵向振动严重时造成钻头损坏、钻杆磨损加剧和迅速的疲劳破坏,使钻井成本大大增加。利用ANSYS软件建立钻柱振动有限元模型,采用Block Lanczos法进行固有振动特性分析,然后在钻头处施加干扰力,采用完全矩阵法进行动力响应分析,得出钻井液密度对钻柱纵向振动的影响规律。钻井液密度降低,导致固有振动频率升高,振幅增大;钻柱响应力的变化趋势与响应位移基本一致;钻井液密度降低引起钻柱的响应位移和响应力增大,进而造成von Mises等效应力增大,疲劳寿命降低。

The axial vibration of drill string can cause the drill bit failure, drill pipe wear and increase the cost of drilling. The paper created the finite element model of drill string axial vibration by ANSYS. Then the natural vibration characteristic and dynamic response are analyzed by Block Lanczos method and Full Matrix method, so the relationship between drilling fluid and drill string vibration frequency was known. The natural vibration frequency and amplitude of drill string increase with the decreasing of drilling fluid density. The change trend of drill string response force is the same with response displacement. When the density of drilling fluid is decreasing, both of response displacement and force are increasing which cause rising of the von Mises stress and reduction of fatigue life.