Research On Damaged Effect Of Coal Pore-fracture And Extracted Methane Mechanism By Liquid CO₂ Infiltrated

Coalbed methane(CBM)was treated as the potential new energy that can be considered as a substitute for natural gas and solve the problem of energy supply in China to some extent.China's coal seams generally exhibit high storage and low permeability characteristics,so artificially fractured to improve the permeability of coal seam have very important significance for gas drainage.This dissertation conducts experiments and field application studies under the support of the National Natural Science Foundation of China(51504186,51574193).Based on the low temperature and phase transition features of liquid CO2,the experiment of low temperature infiltrated coal bodies was proposed.Combined the low pressure nitrogen adsorption(LP-N2-Ad),micuery intrusion porosimetry(MIP)and sacning electron microscope(SEM)to investigate the damaged effect of pore and fracture structure was studied under the low temperature infiltrated by liquid CO2 meanwhile the simillarity physical experiment was used to simulate the efficiency of CO2 displacement CH4 in coal samples.Based on the study,the field application of injecting liquid CO2 into coal seam fracturing and displacing CH4 of coal bodies was conducted,the result indicated that injection liquid CO2 can effectively enhance the gas extraction efficiency.(1)After the coal samples are treated by LCO2,the pore structur parameters are commonly increased and the micropores were transformed into larger pores even microcracks in corresponding aperture section.Simitaneously the coal matrix suface become more roughness and irregularity,internal pore structure more complex for the treated coal specimens.(2)Some new apparent fractures are generated and the original fissures extended characteristics are obvious.Moreover the weak surface of coal body is exfoliated and the fissure-filled mineral components are eroded,therefore the penetration was increased during the coal sample are filtrated by liquid CO2.(3)The similar physical simulation experimental results indicated that injecting CO2 into coal seam can effectively displace CH4 gas commonent,and the displacement efficiency is beyond 94.0%.(4)Field application results proven that injecting liquid CO2 into coal seam greatly increased the indlucence radius and methane extraction efficiency.The number of drilling holes arranged on the working face is resuced and created greater economic benefits.