Effects of Liquid CO2Phase Transition Fracturing on Mesopores and Micropores in Coal
Energy and Fuels
In this study, we conduct laboratory experiments on coal with liquid CO2 phase transition fracturing (L-CO2-PTF) treatment under the fracturing pressures of 120 and 185 MPa. The variations of structure and fractal characteristics for mesopores (2-50 nm) and micropores (<2 nm) are studied by employing the low-temperature N2/CO2 adsorption measurements and the fractal theory. The results indicate that the effects of pore enlarging and fractal dimension reducing of L-CO2-PTF are visible for mesopores, while these effects are underperformed for micropores. The connectivity of mesopores is improved due to the transformation of semi-open pores (type II) and thin-necked bottle pores (type III) into open pores (type I). The size of mesopores is increased, while the pore volume, pore specific area, and fractal dimension are reduced. All these performances are conducive to enhancing the capacity of coalbed methane (CBM) desorption and diffusion. It should adopt different fracturing pressures for coals with different metamorphic degrees. Primarily, it is significant to explore a novel L-CO2-PTF device with considerable energy, high fracturing pressure, and long action time for improving the nanoscale channel connectivity of CBM transport. This study further reveals the effects of L-CO2-PTF on mesopores, micropores, and CBM transport, which proposes theoretical guidance for the improvement and optimization of the L-CO2-PTF technique.
Open Access Status
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National Natural Science Foundation of China