4.7 Article

Diffusion characteristics of methane in various rank coals and the control mechanism

Journal

FUEL
Volume 283, Issue -, Pages -

Publisher

ELSEVIER SCI LTD
DOI: 10.1016/j.fuel.2020.118959

Keywords

Diffusion coefficient; Pore size distribution; Coal rank; Adsorption capacity; Controlling mechanism

Funding

  1. Shanxi Province Science and Technology Major Project, China [20201102001, 20191102001, 20181101013]
  2. Shanxi Provincial Basic Research Program Coalbed Methane Joint Research Foundation, China [2015012014]
  3. National Science and Technology Major Project of the Ministry of Science and Technology of China During 13th Five-Year Plan, China [2016ZX05067001-006, 2016ZX05043-001]
  4. Open Research Fund of the Key Laboratory of , ChinaTectonics and Petroleum Resources, Ministry of Education (China University of Geosciences Wuhan Grant), China [TP09 2014]

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The methane diffusion behavior in coals was investigated in this study, with experiments conducted on different rank coal samples to analyze pore size distribution and gas adsorption-diffusion behavior. The Langmuir effective diffusion coefficient and its influencing factors were studied, showing that the diffusion coefficient generally rises with pressure and the Langmuir volume increases with R-o, R-m values. Moisture content and coal rank affect gas diffusion differently, with a more significant influence in medium-rank coals.
The methane diffusion behavior is one of the key factors that influence the production potential of coalbed methane (CBM) reservoirs. In this study, low temperature nitrogen, carbon dioxide adsorption and methane isotherm adsorption experiments for various rank coal samples were carried out to investigate the characteristics of pore size distribution and gas adsorption-diffusion behavior. A mathematical model similar to the Langmuir equation was established to describe the methane diffusion in coals. The variation law of the Langmuir effective diffusion coefficient (Dr) with coal rank and its influencing factors, control mechanism were analyzed. With the increase of coal rank, the development degree of micropore rises, and both the specific pore volume and specific surface area first decrease and then increase. The diffusion coefficient of methane in coals generally rises with the rise of pressure. The Langmuir volume rises with the rise of R-o,R-m (maximum vitrinite reflectance with oil). The influence of moisture and coal molecular structure on gas diffusion varies with coal rank. The moisture content has a more significant influence on the gas diffusion in the medium-rank coals than in the low- and high-rank coals. The outcomes may deepen our understanding of gas transport in coals and benefit the exploration of CBM.

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