淹没条件下超高压水射流破岩影响因素与机制分析

INFLUENTIAL FACTORS AND MECHANISM ANALYSIS OF ROCK BREAKAGE BY ULTRA-HIGH PRESSURE WATER JET UNDER SUBMERGED CONDITION

超高压水射流辅助破岩是提高机械钻速的有效途径,水射流破岩效果影响因素及机制研究是其关键之一。选取100～200 MPa共5档驱动压力和3种岩样,实验研究淹没条件下水射流驱动压力、喷距、作用时间和喷射角4个因素对冲蚀切割破岩效果的宏观影响规律。采用全解耦流固耦合数值分析方法,对超高压射流破岩过程中耦合系统应力场进行计算,建立岩石宏观断裂规律与微观破坏机制间的联系。研究表明,淹没条件下超高压水射流冲蚀切割破岩存在最优喷距和喷射角:100 MPa时最优喷距约为15倍喷嘴直径,200 MPa时约为20倍喷嘴直径,随压力的增加而增加;最优喷射角为12°～14°。超高压水射流作用下岩石的破坏发生在毫秒量级,主要是拉伸和剪切破坏作用,是由射流冲击应力所造成。研究可为超高压射流辅助钻井技术中水力参数优选及钻头设计提供参考依据。

Ultra-high pressure jet assisted drilling is an affective approach for improving penetration speed; and influential factors and mechanism of rock breakage are key technologies. Experiments of rock breakage by ultra-high pressure water jets under submerged condition are conducted to investigate the effect rules of driven pressure, standoff distance, jet acting time and impact angle on rocks. In the experiments, five kinds of driven pressures from 100 MPa to 200 MPa, and three types of rock samples are selected. Thereafter, numerical simulation with fluid-structure interaction（FSI） method for stress distribution in the coupling system is utilized to analyze rock macrofailure mechanism by jets cutting. The study shows that there exists optimum standoff distance for different driven pressures. Under the experimental condition, the optimum standoff distance is approximately 15 times of the nozzle diameter when the driven pressure is 100 MPa and 20 times for driven pressure of 200 MPa. The optimum standoff distance increases as driven pressure increases. The maximum rock broken volume can be obtained when the jet impact angle is between 12° to 14°. Meanwhile, numerical simulation shows that the micro-mechanism of rock failure due to water jets impingement is a brittle fracture mainly destructed in a few milliseconds. It constructs in the condition of tensile and shear stress. The rocks are a bridge between the micro-failure and macro-breaking mechanism of rocks with water jets impact. The study can offer some rules for optimizing hydraulic parameters and designing drill bit in the ultra-high pressure jet assisted drilling technology.