Experimental Study on CH4 Displacement from Coal Seam Fractured by Liquid CO2

Abstract

In order to improve the gas drainage efficiency of low permeability coal seams, based on the theoretical analysis of liquid CO2's phase change permeability improvement, negative temperature damage, extrusion stress damage, and displacement effects on coal seams, this paper researches and develops a process system for liquid CO2 fracturing coal seam CH4 displacement, and carries out industrial tests on the 17246 coalface of B6 coal seam in Zhangji Coal Mine. The test results show that, in the injection process, liquid CO2 first fills in the cracking holes and visible cracks with larger opening degree, then it enters the original weak plane areas, and finally penetrates into the coal matrix pores, the pressure at the orifice of the injection borehole presents fluctuation characteristics; when CO2 flows into the coal mass cracks, and diffuses into the pores of the coal matrices, it's affected by flow resistance and adsorption, and the coal mass permeability in the fracture zone, plastic zone and elastic zone decreases in turn; the effective influence radius after liquid CO2 is injected in the coal seams for permeability improvement displacement is more than 30 meters. The average single-hole gas concentration is increased by 2.15 times, the average single-hole pure gas drainage flow volume is increased by 2.27 times, and the average single-hole pure gas flow attenuation coefficient is reduced by 80.76%, which improves the gas drainage efficiency.

Enhancing Methane Recovery with Cryogenic Liquid CO2 Cyclic Injection: Determination of Cyclic Injection Parameters

“…In addition, according to the China National Code for Coal Mine Gas Drainage AQ 1027-2006 [ 42 , 43 ], the gas drainage attenuation coefficient could be used as an index to evaluate the degree of difficulty of pre-drainage in the coal seam, which could be calculated using Equation (8): where Q 0 is the initial flow of the drainage hole, t is the drainage time, Q t is the gas drainage flow at time t , and β is the attenuation coefficient of the borehole gas flow. According to Equation (8), the attenuation coefficient could be obtained by fitting the average gas drainage flow of a single borehole.…”

Coal and rock dynamic disasters: Advances of physical and numerical simulation in monitoring, early warning, and prevention

“…There are many kinds of complex mine disasters. coal spontaneous combustion is one of the most serious mine disasters Zheng et al, 2019;Jin et al, 2021;Kuai, 2021), which can easily cause casualties, environmental pollution, and property loss . According to the data, fire accidents caused by coal spontaneous combustion account for more than 90% of the total mine fires , and coal spontaneous combustion in goafs comprise over 60% of total mine spontaneous combustion .…”

Numerical simulation study on the influence of air leakage on oxygen concentration in goafs of fully mechanized caving mining with shallow buried and large mining height

“…There are many kinds of complex mine disasters. coal spontaneous combustion is one of the most serious mine disasters (Querol et al, 2011;Liu et al, 2019;Zheng et al, 2019;Liu et al, 2020;Onifade and Genc, 2020;Jin et al, 2021;Kuai, 2021), which can easily cause casualties, environmental pollution, and property loss (Deng et al, 2017;Wu et al, 2018;Song et al, 2020). According to the data, fire accidents caused by coal spontaneous combustion account for more than 90% of the total mine fires (Ma et al, 2022), and coal spontaneous combustion in goafs comprise over 60% of total mine spontaneous combustion (Su et al, 2016;Wen et al, 2017).…”