围压条件下脉冲射流提高清岩效果数值模拟研究

脉冲射流钻井技术具有高效清岩能力,但其提速机制还不十分清楚。通过建立围压条件下单喷嘴脉冲射流井底清岩物理模型,对脉冲射流清岩过程进行了数值模拟研究,分析了影响脉冲射流清岩效果的主要因素。结果表明,非稳态旋流是脉冲射流提高清岩效果的主要原因之一,在相同排量条件下,脉冲射流清岩效率比连续射流平均提高约1~1.6倍。脉冲射流清岩效率随着喷嘴直径和入口流速的增大而增大;围压对脉冲射流清岩过程影响较小;低频率脉冲射流的清岩总体效果较好;随着岩屑粒径增大,井底冲击区域内岩屑分布非均匀性增强,脉冲射流清岩效率降低。研究结果对指导脉冲射流提速技术的工程实践具有一定的参考价值。

Numerical simulation research on improving cleaning cuttings effectiveness with pulsed jet under conifning pressure

The drilling technology with pulsed jet is highly capable of cleaning the cuttings, but its acceleration mechanism remains unknown. By establishing a physical model for bottom hole cleaning cuttings by pulsed jet with single-nozzle under confining pressure, the numerical simulation research was conducted on the whole process of cleaning cuttings by pulsed jet, and the main factors affecting the cleaning cuttings effect by pulsed jet was analyzed. The research finding shows that unsteady state rotational flow is one of the main reasons for improvement of cleaning cuttings effect by pulsed jet. Under the same flow rate, the cleaning cuttings efficiency by pulsed jet is about 1-1.6 times that of continuous jet in average. The efficiency of cleaning cuttings by pulsed jet increases with the increase of nozzle diameter and inlet flowrate. The confining pressure has small effect on the process of cleaning cuttings by pulsed jet. The overall effect of cleaning cuttings by low frequency pulsed jet is good, with the increase of particle sizes, the heterogeneity of cuttings distribution within the impact area at hole bottom is intensified and the efficiency of cleaning cuttings by pulsed jet is reduced. The resulting conclusions provide a theoretical guidance for research on acceleration technique by pulsed jet.