固井前置液冲洗效率评价方法——改进的旋转黏度计法

冲洗效率是评价固井前置液性能的关键指标，直接影响着前置液优选、用量与排量设计，进而影响固井质量。为了克服评价前置液冲洗效率的传统旋转黏度计法存在的结果误差大、重复性差等方面的不足，改进了转筒结构和残留钻井液质量确定方法，实验分析了改进措施的有效性和适用性，并利用改进后的评价方法对Y井区页岩气水平井固井前置液洗油剂类型进行了优选，优化了前置液冲洗时间。研究结果表明：①改进后的方法避免了转筒内壁无法被有效冲洗与转筒上残留冲洗液或清水的影响，大幅度提高了实验结果的准确性和可重复性，多次平行实验结果的标准偏差均在3%以内；②准确性和可重复性的提高，使得不同实验条件下的实验结果具有可对比性；③对Y井区页岩气水平井固井而言，S80洗油剂具有最高的冲洗效率，前置液用量按照冲洗时间8～10 min时设计具有较高的冲洗效率和经济性。结论认为，改进后的旋转黏度计法能够准确评价前置液冲洗效率，可以为前置液优选和应用工艺参数优化提供依据。

A method for evaluating the flushing efficiency of cementing preflush: an improved rotary viscometer method

Flushing efficiency is a key index to evaluate the performance of cementing preflush, and it has direct influence on the optimization, dosage and displacement design of preflush and eventually impacts the cementing quality. Aiming at the shortcomings of the traditional rotary viscometer method in evaluating the flushing efficiency of preflush, such as large error and poor repeatability, this paper improves rotary drum's structure and residual drilling fluidmass determination method. Then, the effectiveness and applicability of the improvement measures are analyzed experimentally. Finally, the improved evaluation method is applied to select the oil-washing agent and optimize the flushing time of cementing preflush in the shale gas horizontal well of Wellblock Y. And the following research results were obtained. First, by virtue of the improved method, the influence that the inner wall of the rotary drum cannot be effectively washed and there is residual washing fluid or clear water on the rotary drum can be avoided, so the accuracy and repeatability of the experimental results are greatly improved. The standard deviation of the results of multiple parallel experiments is within 3%. Second, the improvement of accuracy and repeatability makes the experimental results under different experimental conditions comparable. Third, for the cementing of the shale-gas horizontal well in Wellblock Y, oil-washing agent S80 is the highest in flushing efficiency, and flushing efficiency and economy are higher when the preflush volume is designed based on the flushing time of 8–10 min. In conclusion, the improved rotary viscosimeter method can accurately evaluate the flushing efficiency of preflush and provide a basis for the selection of preflush and the optimization of application technological parameters.