An Experimental Study on the Conductivity Changes in Coal during Methane Adsorption-Desorption and their Influencing Factors
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This work was financially supported by the Independent Projects of the Key Lab. of Coal Resources Exploration and Comprehensive Utilization, Ministry of Land and Resources of China (grants No. KF2019-2, ZKF2018-1, KF2018-4, ZP2018-2), the Major National Science and Technology Special Projects (grant No. 2016ZX05042-004), the Projects Funded by China Postdoctoral Science Foundation (grant No. 2019M653873XB), the Natural Science Foundation Research Projects of Shaanxi Province (grant No. 2019JQ-245), the Doctoral Research Starting Foundation of Xi’an University of Science and Technology (grant No. 2016QDJ041) and the Research Projects of the Geological Research Institute for Coal Green Mining of Xi’an University of Science and Technology (grant No. MTy2019-04).

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    Abstract:

    During the processes of methane adsorption and desorption, the internal structure of coal changes, accordingly leading to changes in electrical conductivity. In this paper, using low rank coal seams of the Yan’an Formation in the Dafosi field as the research subject, the relationship between coal resistivity, methane adsorption quantity, and equilibrium pressure is analyzed through proximate analysis, mercury injection tests, low temperature liquid nitrogen adsorption tests, and coal resistivity measurements during methane adsorption and desorption. The results show that during the process of pressure rise and methane adsorption, the conductivity of coal increases, resulting from heat release from methane adsorption, coal matrix swelling and adsorbed water molecules replaced by methane, but the resistivity reduction gradually decreases. The relationship between coal resistivity and methane adsorption quantity and equilibrium pressure can be described by a quadratic function. During the processes of depressurization and desorption, the resistivity of coal rebounds slightly, due to decalescence of methane desorption, coal matrix shrinkage and water-gas displacement, and the relationship coincides with a linear function. Methane adsorption leads to irreversible changes in coal internal structure and enhances the coal conductivity, and resistivity cannot be restored to the initial level even after methane desorption. The resistivity and reduction rate of durain are higher than those of vitrain, with relatively greater homogeneous pore throat structure and fewer charged particles in the double electric layer. In addition, moisture can enhance the conductivity of coal and makes it change more complexly during methane adsorption and desorption.

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CHEN Yue, MA Dongmin, GUO Chen, YANG Fu, MU Tian, GAO Zheng.2019. An Experimental Study on the Conductivity Changes in Coal during Methane Adsorption-Desorption and their Influencing Factors[J]. Acta Geologica Sinica(),93(3):704-717

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History
  • Received:October 30,2018
  • Revised:December 20,2018
  • Online: June 26,2019
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