偏心环空紊流场的发展规律及岩屑沉降特性

EVOLUTION OF TURBULENT FLOW IN ECCENTRIC ANNULUS AND SETTLING CHARACTERISTICS OF DRILLING CUTTINGS

实验结果表明环空紊流泥浆能有效地改善水平井的净化质量，然而对偏心环空紊流场的发展现律及岩屑颗粒的沉降特性的研究却很少。本文由确定偏心环空轴向流的当量直径出发，讨论了流态的转换条件；并以环空压降为自变量，流体稳定性参数为准则，描述了种空断面紊流的发展过程。用随机理论分析了局部紊流的强度及统一速度方程。其次，考虑紊动流场加速度的影响，以参数摄动小量，利用摄动法求解岩屑颗粒在紊动流场中的沉降运动，讨论流场性质对颗粒运动的影响。结果表明，脉动频率及紊动强度的增大，增大了颗粒的沉降阻力，降低了沉降速度。

Turbulent mud flow can effectively improve the cleanness of a horizontal well.Howev-er,little is know on the evolution of turbulent flow in eccentric annulus and the settlingcharacteristics of cuttings in a horizontal well.In this paper, the critical condition of flowstate transition is discussed.Taking pressure loss in annulus as a variable and stability num-ber of fluid element as criterion,an equation of turbulent evolution is established.Then theeffect of fluid acceleration is taken into consideration and the settling of cuttings in vortexflow is analyzed by perturbation theory, with as perturbation parameter.Theeffect of flow properties on cutting motion is discussed.The results show that greater tubu-lence frequency and strength help to decrease the settling velocity of cuttings by increasing resistance.