Mechanism of gas pressure action during the initial failure of coal containing gas and its application for an outburst inoculation

Faced with the continuous occurrence of coal and gas outburst(hereinafter referred to as“outburst”)disasters,as a main controlling factor in the evolution process of an outburst,for gas pressure,it is still unclear about the phased characteristics of the coupling process with in situ stress,which induce coal damage and instability.Therefore,in the work based on the mining stress paths induced by typical outburst accidents,the gradual and sudden change of three-dimensional stress is taken as the background for the mechanical reconstruction of the disaster process.Then the true triaxial physical experiments are conducted on the damage and instability of coal containing gas under multiple stress paths.Finally,the response characterization between coal damage and gas pressure has been clarified,revealing the mechanism of action of gas pressure during the initial failure of coals.And the main controlling mechanism during the outburst process is elucidated in the coupling process of in situ stress with gas pressure.The results show that during the process of stress loading and unloading,the original gas pressure enters the processes of strengthening and weakening the action ability successively.And the strengthening effect continues to the period of large-scale destruction of coals.The mechanical process of gas pressure during the initial failure of coals can be divided into three stages:the enhancement of strengthening action ability,the decrease of strengthening action ability,and the weakening action ability.The entire process is implemented by changing the dominant action of in situ stress into the dominant action of gas pressure.The failure strength of coals is not only affected by its original mechanical strength,but also by the stress loading and unloading paths,showing a particularly significant effect.Three stages can be divided during outburst inoculation process.That is,firstly,the coals suffer from initial damage through the dominant action of in situ stress with synergy of gas pressure;secondly,the coals with spallation of structural division are generated through the dominant action of gas pressure with synergy of in situ stress,accompanied by further fragmentation;and finally,the fractured coals suffer from fragmentation and pulverization with the gas pressure action.Accordingly,the final broken coals are ejected out with the gas action,initiating an outburst.The research results can provide a new perspective for deepening the understanding of coal and gas outburst mechanism,laying a theoretical foundation for the innovation of outburst prevention and control technologies.

Research on the pressure variation law and enhancing CBM extraction application effect of CO_(2) phase transition jet coal seam fracturing technology

Due to the limited permeability and high methane content of the majority of China’s coal seams,significant coal mining gas disasters frequently occur.There is an urgent need to artificially improve the permeability of coalbed methane(CBM)reservoirs,enhance the recovery efficiency of CBM and prevent mine gas accidents.As a novel coal rock fracture technology,the CO_(2) phase transition jet(CPTJ)has been widely used due to its advantages of safety and high fragmentation efficiency.In this study,to ascertain the effects of the pressure of CPTJ fracturing,the influence of its jet pressure on cracked coal rock was revealed,and its effect on CBM extraction was clarified.In this research,the law of CPTJ pressure decay with time was investigated using experimental and theoretical methods.Based on the results,the displacement and discrete fracture network law of CPTJ fracturing coal rock under different jet pressure conditions were studied using particle flow code numerical simulation.Finally,field experiments were conducted at the Shamushu coal mine to assess the efficiency of CPTJ in enhancing CBM drainage.The results showed that the pressure of the CPTJ decreased exponentially with time and significantly influenced the number and expansion size of cracks that broke coal rock but not their direction of development.CPTJ technology can effectively increase the number of connected microscopic pores and fractures in CBM reservoirs,strongly increase the CBM drainage flow rate by between 5.2 and 9.8 times,and significantly reduce the CBM drainage decay coefficient by between 73.58%and 88.24%.