考虑钻具屈曲的环空流动仿真研究

摘要

在小井眼定向井和水平井钻井过程中,钻具屈曲会对环空流场、压力场产生较大影响.文中借助流体动力学计算软件ANSYS FLUENT开展了考虑钻具正弦、螺旋屈曲的环空流动仿真模拟,系统地研究了不同环空偏心距、不同转速等因素对环空流场和流动压降的影响规律.研究发现:同心环空中,流体流速沿径向对称分布,偏心、屈曲环空中偏离对称分布;环空间隙越大,环空流速就越大;当考虑钻柱旋转时,钻柱旋转对环空窄间隙处流速的影响比对环空宽间隙处的影响要大,可明显提高环空窄间隙处的流速;同心环空、偏心环空压降值沿井深呈线性增加,偏心度越大,压降越小;屈曲环空压降值沿井深呈非线性增加,转速越大,压降越小.仿真结果与实验结果相比,具有较高的准确性,对真实钻井条件下环空压降的计算具有一定的指导意义.%During the process of slim-hole directional well and horizontal well drilling,the buckling of drilling tools can affect not only the mechanical properties of the drilling tool assembly,but also the annulus flow field and pressure field greatly.In this paper,the simulations of annular flow about the sinusoidal and helical buckling were carried out by ANSYS Fluent software,and the effects of different annular eccentricity and rotational speed on annular flow velocity field and flow pressure drop were studied systematically.The results show that the flow velocity is distributed symmetrically in the radial direction in the concentric annulus,however,the flow velocity distribution is deviated from the radial direction in the eccentric and buckling annulus;without considering rotation,the larger the annular clearance is,the higher the velocity is;the influence of drill string rotation on the flow velocity at the narrow gap is larger than that at the wide gap;the concentric annulus and eccentric annulus pressure drops increase linearly along the depth of the well,and the larger the eccentricity is,the smaller the pressure drop is;as the depth of well increases,the pressure drop of buckled annulus will also increase nonlinearly,the faster the speed of pipe rotation is,the smaller the pressure drop will be.The simulation results agree well with the experimental results,which has some guidance to the calculation of annular pressure drop under real drilling conditions.