小井眼钻井环空压耗计算与分析

环空水力学是小井眼钻井的关键技术，通过对钻井水力参数的分析和研究，结合小井眼钻井的实际情况，采用合适的流变模式来描述小间隙环空中的流动规律．并应用非牛顿流体力学的基本原理建立偏心环空螺旋流模型，对小井眼情况下的环空压耗进行了计算，进一步对小井眼环空中的压力损失进行了研究．所选择的模型层流时为偏心环空螺旋流模型，紊流时为考虑广义雷诺数、范宁摩阻系数、水力直径的模型．分别运用当量直径和水力直径，层流时通过迭代、积分，紊流时通过修正系数进行了求解，并与实验和现场数据相比较，经验证，此模型基本上满足现场需要．结果表明：①在小井眼钻井中，环空中的压力损失远大于常规井；②钻杆偏心及高转速对环空压耗的影响很明显；③在窄的环空间隙，需要建立准确的环空压耗模型来调整泥浆密度及钻井液的流变性能．

Calculation and Analysis of the Pressure Loss in Narrow Annular in Slim Hole Drilling

By studying the hydraulics in the narrow annulus, power law rheological model is chosen to describe the behavior of the fluid flowing in the narrow annulus. The model is a spiral flow model in eccentric annulus when the flow is laminar flow. Based on the principle of non Newtonian fluid mechanics, the spiral flow model is established when the flow is turbulent flow,and general Reynolds number, Fanning friction factor and hydraulic diameter are all considered in the model. Comparing the calculated pressure loss by the model with the measured data in field, it is shown that, (1) the accuracy of the model can meet the requirements of the calculation; (2) the pressure loss in a slim hole is much greater than that in a conventional well; (3) the offcenter of drilling rod from well bore and the high rotary speed of drilling rod have great effects on the pressure loss; (4) it is neccesary to establish the accurate pressure loss model for adjusting the density and rheological behavior of drilling fluid.