Experimental Study On Carbon Dioxide Fracturing In Coal Rock

Compared with traditional fracturing technology,CO₂ dry fracturing has the advantages of high flowback,low damage to the reservoir,and a large increase in production rate.It has a broad application prospect in the development of coalbed methane.In order to study the expansion law of coal-rock fractures when liquid CO₂ is used as a fracturing fluid,a physical simulation experiment of CO₂ dry fracturing for coal and rock was carried out.The factors such as horizontal principal stress difference,CO₂ temperature,and CO₂ displacement were analyzed.The effects of splitting and spreading,and verifying the results by numerical simulation.The experimental results show that when the horizontal principal stress difference of the specimen is small,the natural cracks in the coal rock have a great influence on the crack propagation and easily generate complex multiple cracks.With the increase of the horizontal principal stress difference,the control effect of the in-situ stress on the crack propagation is gradually enhanced,and the cracks mainly extend in the direction of the vertical minimum principal stress,and the fracture morphology is relatively single and straight.When the temperature of CO₂ decreases,the elastic modulus of the coal rock increases,the Poisson's ratio decreases,and the mechanical properties of the rock transition from plastic to elastic,and the crack morphology after pressing is single.The CO₂ emission has a certain influence on the complexity of the fracture,and increasing the CO₂ emission makes the crack more complicated.The numerical simulation study of crack propagation in coal and rock confirms the conclusion of the model experiment.This paper studies the law of crack initiation and extension of cracks in CO₂ dry fracturing of coal and provides a certain reference for the construction of CO₂ fracturing on site.