井底反向射流辅助破岩机理分析

MECHANISM ANALYSIS OF BOTTOM-HOLE REVERSE JET ASSIST ROCK FAILURE

采用有限元方法模拟分析了井底反向射流辅助破岩的机理,分析结果表明,反向射流抽汲井底流体,降低了作用于井底的压力,使得岩石易于破碎,岩屑的净化效果改善,而且抽汲作用在井底诱使流体定向流动,也强化了井底岩屑的启动,使新的岩石破坏面暴露,钻头的破岩钻进效率提高。随着反向射流速度、射流轴线速度与井底平面间夹角和喷嘴直径的增大、喷嘴数量的增多以及井眼直径的减小,反向射流对井底流体的抽汲作用逐渐增强,作用于井底负压的绝对值逐渐增大,也越有利于提高钻井速度。研究结果为实际应用提供了理论依据。

The mechanism for bottom-hole reverse jet assist rock failure is analyzed by the finite element method.Analytical results manifest that the pumping effect of reverse jet on bottom-hole fluids can lower bottom pressure and make it easier for rock failure,thus improved the cleanliness of cuttings.Furthermore,the pumping effect induces directional flow of bottom-hole fluids and enhances the start-up of bottom-hole cuttings,which can accordingly reveal the new rock damage interface and improve bit's drilling and rock-breaking efficiency.With the increase of reverse jet velocity,nozzle diameter and the angle between jet axial velocity and bottom-hole plane,accompanied with the rise of nozzle number and the reduction of borehole diameter,the pumping effect of reverse jet on bottom fluids will improve inch by inch,the absolute magnitude of negative pressure on bottom hole and the drilling speed will also grow gradually.Research results provide theoretical foundation for practical application.