新型固井冲洗液评价装置适用性分析

Applicability of a New Device for Cementing Flushing Fluid Evaluation

为了明确新型固井冲洗液评价装置的适用范围,根据评价装置内筒外壁面处与固井环空壁面剪切速率相等的原理,结合罗伯逊-斯蒂夫流变模式推导了冲洗液为牛顿、宾汉和幂律流体时其在内筒外壁处剪切速率的计算公式,并分析了不同流变模式冲洗液内筒外壁面处剪切速率与固井环空壁面剪切速率的误差。分析结果为:当冲洗液为牛顿流体时,评价装置在内筒外壁面处的剪切速率与固井界面处相等,不存在理论误差;当冲洗液为宾汉和幂律流体时,评价装置内筒外壁面处的剪切速率大于固井界面处,且剪切速率增量与内外筒间隙和冲洗液流变性质有关;当评价装置外内筒半径比限定在1.04~1.20时,冲洗液为幂律流体且流性指数大于0.6或为宾汉流体且动塑比小于1Pa/(mPa·s)时,剪切速率相对误差在10%以内。研究结果表明,评价装置外内筒半径比越小,相对误差越小,其适用范围越大。

To clarify the application scope of an innovative evaluation device for cementing flushing fluid,a calculation model for shear rates of Newtonian,Bingham and power-law fluids on external wall of the inner barrel was established in accordance with the Robertson-Stiff rheological model and with consideration to the equivalent shear rate on external wall of the inner barrel and on annular sidewall in cementing.In addition,errors between the shear rate of the external sidewall of inner barrel and that of cementing annual sidewall under different rheological modes was analyzed.Research results showed that the shear rate at the inner wall of the device is equal to that at the cementing interface with no theoretical error for Newtonian fluids,while the shear rate of the inner cylinder wall is higher than that on the cementing interface,and the increase in shear rates is related to the inner and outer cylinder gap and rheological properties of the flushing fluids for Bingham and the power-law fluids.When the diameter ratio between the outer and inner barrel is 1.04-1.20 and the flushing power-law fluid flow indexes over 0.6,or plastic viscosity below 1.0Pa/（mPa·s）for Bingham fluid,their relative error in the shear rate can be maintained less than 10%.Research results show the smaller ratio between external and internal barrels diameter would cause less relative error,and the application scope of the device would be more extensive.