Experimental Study On High Pressure Water Jet Broken Rock

High-pressure water jet (HPWJ) technology is renowned for its high drilling speed, low cost, no sparks during drilling process. Based on these advantages, it is a very good solution to the problems associated with coalbed methane(CBM) production, concerning high cost and reservoir damaging. In recent years, HPWJ has been widely applied to field coal drilling, but the research about the laws of drilling efficiency influenced by the jet parameters are still inadequate. As the coal seam has a strong heterogeneity, collapsing during the drilling is quite common. Thus the research of HPWJ drilling in the coal seam based on real coal by experiment is very few. Most physical simulation experiments are based on similar material such as a mixture of cement, sand, and coal dust, which can’t accurately characterize the real situation of drilling in the coal seam by HPWJ. Furthermore, the abrasive jet technology has been also applied to coal seam drilling, but few researches have focused on the influence of abrasive concentration.Featuring the above problems, on the basis of previous research results and basic theory of HPWJ, this paper analyzed the breaking coal process of HPWJ using comprehensive knowledge of oil and gas engineering, mechanical engineering, engineering fluid mechanics, rock mechanics. And the novel ex-mixing abrasive jetting system was developed and some experiments concerning multi-factor were made. The hole depth and aperture which were created by HPWJ were analyzed. The major achievements of this paper were as follows:(l)The evolving process of crushing hole was simulated and the crushing reason of coal was found.(2)A novel ex-mixing abrasive jetting experimental device which could be used to simulate HPWJ to drill in the coal was developed, and the accuracy of the abrasive supplying of the device was improved.(3)The characteristics of the drilling hole which provide a certain pioneering guiding of determining the parameters of the wall supporting tool in field application was made clear.(4)The rule of the efficiency of drilling in the coal by HPWJ concerning various factors was revealed. And drilling depth and drilling aperture are regarded as the objective function, a best group of jet parameters which provided a basis for the determining of the construction parameters of drilling in the coal seam by HPWJ was obtained.