高压水射流环形割缝深度理论模型及应用

Theoretical model of annular slotting depth for high pressure water jet and its application

我国煤层透气性系数普遍较低,尤其进入深部开采后,煤层表现出高地应力、高瓦斯压力和低渗透性等特征,采用高压水力割缝降低煤层地应力,增加煤体透气性,提高煤层瓦斯抽采效率是技术发展方向之一。针对不同煤层地质条件,煤层采用水力割缝的相关技术参数设计主要依据经验判断,可能导致煤层水力割缝钻孔控制不均匀存在空白带或两相邻钻孔割穿而影响瓦斯抽采及煤层防突效果。研究以高压水射流破煤冲击效应分析为基础,针对高压水射流冲击特征,结合高压水射流分区结构,通过边界层理论得出高压水射流速度分布函数,获得了高压水射流割缝过程中平均射流速度衰减规律;应用应力波在煤体中传播特性建立波动方程,然后结合高压水射流随距离变化的衰减规律及最大伸长线应变准则,综合建立了高压水射流环形割缝深度理论模型。通过试制高压水射流作用力采集装置,以喷嘴直径、射流压力和射流距离为条件,测试了不同参数下高压水射流打击力的变化规律,在理论上验证高压水射流平均速度衰减规律。采用研究获得的高压水射流环形割缝深度理论模型,结合新集二矿试验区1煤层力学参数,理论计算了不同射流压力条件下煤层割缝破煤深度,现场实际割缝深度与理论模型预测结果对比误差小于7%。研究表明高压水射流环形割缝模型能较好地预测煤层割缝深度,可用于指导煤层高压水力割缝参数的设计。

The permeability coefficient of coal in China is generally low,especially in deep mining,the coal shows the characteristics of high in-situ stress,high gas pressure and low permeability.Using high pressure water jet slotting to reduce the in-situ stress of coal seam,increase the permeability of coal seam and improve the gas extraction efficiency of coal seam is one of the technical development directions.According to the different geological conditions of coal seams,the design of technical parameters related to water jet slotting is mainly based on experience,which may lead to an uneven control of water jet slotting boreholes in coal seams and the existence of blank zones or two adjacent boreholes,thus affecting gas extraction and coal seam outburst prevention.Based on the analysis of the impact of high pressure water jet on coal slotting,considering the impact characteristics of high pressure water jet and the zonal structure of high pressure water jet,the velocity distribution function of high pressure water jet was obtained through the boundary layer theory,and the attenuation law of average jet velocity in the process of high pressure water jet slotting was also obtained.The wave equation was established according to the seeding characteristics,and then the theoretical model of annular slot depth of high-pressure water jet was synthetically established based on the attenuation law of high-pressure water jet varying with distance and the maximum elongation line strain criterion.By tri-al-manufactured high-pressure water jet force acquisition device,under the conditions of nozzle diameter,jet pressure and jet distance,the change law of impact force of high-pressure water jet under different parameters was tested,and the attenuation law of average velocity of high-pressure water jet was theoretically verified.Based on the theoretical model of annular slotting depth of high-pressure water jet and the mechanical parameters of coal in Xinji No.2 Coal Mine,the slotting depth of coal under different jet pressures was calculated theoretically.The comparison error between the actual slotting depth and the predicted results of theoretical model is less than 7%.The research shows that the annular slotting model of high pressure water jet can predict coal slotting depth well,and can be used to guide the design of coal slotting parameters under high pressure water jet.