Enhancement of multi-gas transport process in coalbed methane reservoir by oxidation treatment: Based on the change of the interaction force between coal matrix and gas molecules and knudsen number

摘要

Anthracite coal of Zhijin Block was taken as the coal samples and NaClO as the oxidants to investigate enhancement of multi-gas transport process in coalbed methane reservoir by oxidation treatment. Industrial microscope observation, SEM observation, low -temperature N2 sorption measurement and NMR test were used to comprehensively characterize the multiscale pore structure of coal. The change of macromolecular structure of coal before and after oxidation treatment was tested by 13C NMR test, and the force between coal matrix and gas molecules was estimated. Based on the pore size distribution of coal obtained by NMR analysis, the Knudsen number was calculated. Oxidation treat-ment effectively promoted the desorption of methane in coal, increased the content of free methane in coal. It also led to the CBM gas well entering the stable production period earlier, and shortens the gas breakthrough time of the gas well. Oxidation treatment improved micropores to larger pores by dissolving the coal matrix, and the porosity and permeability of coal were increased. Oxidation treatment led to the widening of pore diameter, and the effect of Knudsen diffusion on the core seepage of the matrix was gradually enhanced. Macroscopically, the gas slippage effect was more significant and the permeability was enhanced. The mechanism of oxidation treatment on multi-gas trans-port process was mainly reflected in two aspects: increasing the content of free methane and enhancing the gas supply capacity of coal. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. permeability was enhanced. The mechanism of oxidation treatment on multi-gas trans-port process was mainly reflected in two aspects: increasing the content of free methane and enhancing the gas supply capacity of coal. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.