摘要
在窄环空间隙中下套管、小井眼钻进、深水钻进和大位移井钻进等作业中,精确的波动压力计算模型是准确预测井底压力的前提。以往利用CFD软件模拟赫-巴流体在偏心环空中流动的波动压力计算方法不仅对计算机性能要求高,而且时间成本高,导致现场应用受限。用窄槽流动模型模拟偏心环空建立了流体流动的物理模型,在稳态层流条件下,结合流体流动的控制方程和赫-巴流体的流变方程,建立了波动压力数学模型和基于自适应辛普森积分与黄金分割理论的数值求解方法,利用室内试验结果对模型的合理性进行了对比验证。结果表明:建立的赫-巴流体在偏心环空中的波动压力数学模型结果准确;采用的数值求解方法精度高、速度快,与室内试验数据对比误差在10%以内,满足现场精度需求;分析了波动压力的影响因素,在管柱处于完全偏心的情况下,波动压力梯度降低为同心环空的50%左右,在窄环空间隙中作业时,应严格限制起下钻的速度。
A precise computational model for surge pressure is the prerequisite to accurately predict the bottom-hole pressure in various drilling operations,including casing in narrow annular space,as well as drilling in slim holes,deep-water and extended-reach wells.Traditional computational methods for surge pressure,which use Calculation Fluids Dynamics(CFD)software to simulate the flow of Herschel-Bulkley fluid in eccentric annuli,require high computer performance and is time costing,resulting in limited field application.A physical model of fluid motion is established using narrow slot flow model to simulate eccentric annulus.Under the condition of steady laminar flow,a mathematical model of surge and swab pressure and analytical solution method based on the golden section method and self-adaptive Simpson integral method are obtained by combining the governing equations of fluid motion and rheology equation of Herschel-Bulkley fluid.The rationality of this model is verified by laboratory test data.The mathematical model for the surge-swab pressure of Herschel-Bulkley fluid in eccentric annulus shows high accuracy and fast computational velocity in terms of numerical method.Compared with the laboratory test data,the error is within the range of±10%,indicating that the model is sufficiently accurate to meet the requirements of field operations.The influence factors of the surge-swab pressure are analyzed.Under the condition of totally eccentric annulus,the gradient of surge pressure decreases to around 50% of that for concentric annulus.The tripping velocity should be strictly limited for operations in the narrow annular space.
引文
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