Investigation on the influence of the macropores in coal on CBM recovery

Xudong Liu; Shuxun Sang; Xiaozhi Zhou; Shiqi Liu; Ziliang Wang; Youxin Mo

Heliyon (Sep 2023)

Investigation on the influence of the macropores in coal on CBM recovery

Xudong Liu,
Shuxun Sang,
Xiaozhi Zhou,
Shiqi Liu,
Ziliang Wang,
Youxin Mo

Affiliations

Xudong Liu: School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China; Key Laboratory of Coalbed Methane Resources & Reservior Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou 221116, China
Shuxun Sang: School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China; Key Laboratory of Coalbed Methane Resources & Reservior Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou 221116, China; Carbon Neutrality Institute, China University of Mining and Technology, Xuzhou 221116, China; Jiangsu Key Laboratory of Coal-based Greenhouse Gas Control and Utilization, China University of Mining and Technology, Xuzhou, 221116, China; Corresponding author. School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China.
Xiaozhi Zhou: School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China; Key Laboratory of Coalbed Methane Resources & Reservior Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou 221116, China
Shiqi Liu: Carbon Neutrality Institute, China University of Mining and Technology, Xuzhou 221116, China; Jiangsu Key Laboratory of Coal-based Greenhouse Gas Control and Utilization, China University of Mining and Technology, Xuzhou, 221116, China
Ziliang Wang: School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China; Key Laboratory of Coalbed Methane Resources & Reservior Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou 221116, China
Youxin Mo: School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China; Key Laboratory of Coalbed Methane Resources & Reservior Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou 221116, China

Journal volume & issue: Vol. 9, no. 9
p. e19558

Abstract

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As an important component of coal structure, the macropores have a great influence on CBM recovery. In this paper, the macropores characteristic of two coal samples collected from 3# coal seam in the south of Qinshui Basin, China was analyzed on the basic of mercury intrusion porosimetry, and a fully coupled triple-porosity/double permeability mathematical model for CBM recovery was established according to the physical structure of coal and the non-Darcy flow of methane in macropores. Then, the various factors affecting the macropores permeability were discussed and the influence of size distribution and connectivity of macropores on CBM recovery was investigated. The following conclusions have been drawn from these efforts: (1) in 3# coal seam of the south of Qinshui Basin, the macropores have an extremely heterogeneous pore size distribution with the high variation, and their connectivity is not good because they are mainly composed of the conical and cylindrical pores with one dead end and the open pores, the structure characteristics of macropores are not conducive to CBM recovery; (2) the fully coupled triple-porosity/double permeability mathematical model containing the non-Darcy flow of methane in the macropores includes the methane occurrence-migration field, hydraulic field, thermal field and stress field as well as the complex intercoupling between them, and the model was verified by the fitting of methane production history, with an average error of 3.24%; (3) the macropores permeability is closely related to the Knudsen number controlled by methane pressure and temperature in macropores and the intrinsic permeability which is an internal attribute of macropores affected by size distribution and connectivity of pore; (4) the pressure drop of reservoir plays a major role in the macropores permeability, which promotes the increase of macropores permeability with time, and the high intrinsic permeability of macropores corresponding to the good pore size distribution and connectivity is more conducive to the improvement of fracture permeability and methane production rate of coal reservoir during CBM recovery. It is recommended that coal seams including the macropores with uniform size distribution and good connectivity should be preferentially used for the development of CBM.

Published in Heliyon

ISSN: 2405-8440 (Online)
Publisher: Elsevier
Country of publisher: United Kingdom
LCC subjects: Science: Science (General); Social Sciences: Social sciences (General)
Website: https://www.cell.com/heliyon/home

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