油井中卡森流体稳态波动压力研究

Steady Surge Pressure of Casson's Fluid in Oil Wells

波动压力是影响井眼稳定的主要因素。其大小是制定泥浆附加密度的主要依据。因此要求对实际波动压力的预测有较高的精度，而多年来常用的波动压力计算模式多为近似模式，存在较大的误差。卡森流变模式形式简单，但精度高，近年来国内外多用其描述钻井液的流变性。文中以该模式为基础，理论上推导了定向井同心环空中起下钻或下套管过程中，稳定层流条件下钻井液粘性产生的波动压力精确模式。为便于现场应用，绘制了不同情况下波动压力系数的变化规律。并给出了算例。对现场施工时控制起下钻速度及设计钻井液性能提供了理论依据。

Surge pressure is a major factor which affects borehole stability.It is important for the calculation of additional mud density, therefore predicting pressure surges accuractely is needed. While the tranditional models usually are approximate, thus have many errors. Being simple form and higher accuracy, Casson's rheological model has been used to describe drilling mud properties in recent years. Calculation method of surge pressure caused by mud viscosity during drilling pipes or casings moving through Casson's fluid in a concentric annulus of directional wells under laminar condition is given.For convenience, the coefficients of surge pressure under different conditions are plotted. These results are useful in the controlling of trip velocity and the designing of mud properties.