Crack Form And Influencing Factors Of Liquid Carbon Dioxide Phase Transition Fracturing

As a new technique of fracturing,liquid carbon dioxide phase transition has many advantages such as non-spark,easy control of pressure,easy storage and transportation,safety and efficiency.This paper adopts the physical simulation experiment,theoretical analysis and field verification experiment and computer simulation,the CO₂ phase change the mechanism of the crack,fracture morphology and its influencing factors such as the further research,to guide the liquid carbon dioxide phase change crack technology application in the engineering practice is of great significance.Application of large size true triaxial stress loading system of liquid CO₂ phase change crack experiment,combined with soil and no stress condition of physical experiment,by means of acoustic emission system for monitoring,compared to conventional hydraulic crack and traditional explosive blasting experiment,the spatial distribution of cracks in crack after the basic form of study.The results show that there is a pulverized zone in the center of the borehole causing fracture,and the main fracture is produced in the direction of the gas outlet polymerization,and the development is further extended,with the characteristic of directional crack.Affecting the liquid carbon dioxide phase change after crack related influence factors of coal and rock fracture morphology was studied,mastered the confining pressure effect,the principal stress difference,such as your key factors on the phase transition of crack fracture morphology and the influence on the effect of crack.The confining stress state changes the propagation law of the stress wave,and it has a certain guiding effect on the further extension and expansion of the crack.The fissures formed after the phase transition are mainly extended along the vent orifice to form an advantage fracture and inhibit the expansion of cracks in other directions.The difference of ground stress has a significant effect on the expansion of the crack.When the horizontal principal stress is equal,the direction of the fracture expansion is in line with the direction of the outlet.When the horizontal principal stress is unequal,it produces an advantage crack in the direction of the exhaust outlet,and also produces a number of radial fractures perpendicular to the direction of the exhaust outlet.The more the gas,the more cracks,the higher the degree of fragmentation,the wider and more uniform the fragmentation distribution.Based on the theory of elasticity,fracture mechanics and rock mechanics,the mechanism of liquid phase transformation induced by CO₂ is analyzed and compared.The destruction of coal rock mass caused by phase transition is accomplished under the joint action of high energy gas jet,shock wave,stress wave and high pressure gas produced after CO₂ phase change.CO₂ phase change produced by the shock wave and stress wave in the borehole wall damage form the initial fracture of coal or rock,then high pressure carbon dioxide gas into the initial crack,in the role of quasi static pressure,formed in the crack tip stress concentration,initial crack extended further.Through the field verification experiment,the fracture morphology and spatial distribution of the carbon dioxide in the granite chamber were analyzed.Cracks in the main direction extending along the vent,until with other borehole fissure,formation fracture surface smooth level off,will fly from peeling off a cliff and threw the rock and form a"wedge"phase change crack profile section,verify the CO₂ phase change crack the possibility of the technology applied in the cavern excavation.