Fracturing Mechanisms And Functions Of Improvement Of Gas Drainage Of Highly Pressurized Carbon Dioxide Gas System

Recently,a number of applications,related to the highly pressurized carbon dioxide system for coal seam stimulation and improvement of coal seam gas drainage efficiency,can be found in Chinese coal mining industry.However,according to literature review,it is rarely found that the studies on the mechanisms of coal seam fracture stimulation,relevant theories and functions of gas drainage improvement of this technique.In this thesis,therefore,a systematical investigation about the highly pressurized carbon dioxide system has been conducted to study: 1)Fundamental characteristics of the system,2)Coal seam fracturing stimulation mechanisms,3)Functions of gas drainage efficiency improvement provided by this technique.According to the research results,the outcomes can be provided as follows.Firstly,the fundamental characteristics.In this part,the energy and TNT equivalence of the system.TNT equivalence calculation and verification,in which,three methods obtained from previous literatures have been used for calculating the TNT equivalence of CO2 system,and the results are verified by the blasting tests;the comparison of the high pressure gas volumes generated with that of dynamite explosion.Secondly,the fracturing stimulation mechanisms.Stimulation mechanisms of the highly pressurized gas system have been proposed,including: 1)shaped charge and slotting mechanism,2)thermal expansion mechanism of liquid carbon dioxide and 3)destress mechanism.Based on these mechanisms,the crushing and fracturing radii created by the highly pressurized gas have been calculated and corroborated well with the field monitoring data.Thirdly,the functions of gas drainage efficiency improvement.According to the data collected from field application,there are three functions provided by the system which may beneficial for the improvement of coal seam gas drainage efficiency,such as: 1)Changing the trend of gas concentration and/or pure gas quantity over time,2)Maintaining the uptrend of gas concentration and/or pure gas quantity in a relatively long time period,which,in the current case,is ninety days and counting and 3)Elevating gas drainage to a higher level.