Title: A permeability model for gas flow in coal considering the water content and slippage effect

Authors: Jianhua Li; Bobo Li; Jiang Xu; Zhihe Wang; Zheng Gao; Yao Zhang

Addresses: College of Mining, Guizhou University, Guiyang, 550025, China ' College of Mining, Guizhou University, Guiyang, 550025, China; Guizhou Key Laboratory of Comprehensive Utilization of Non-metallic Mineral Resources, Guiyang, 550025, China; National and Local Joint Laboratory of Engineering for Effective Utilization of Regional Mineral Resources from Karst Areas, Guizhou University, Guiyang, 550025, China ' State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing, 400044, China ' School of Civil, Environmental and Mining Engineering, The University of Adelaide, Adelaide, 5005, Australia ' College of Mining, Guizhou University, Guiyang, 550025, China ' College of Mining, Guizhou University, Guiyang, 550025, China

Abstract: Coal seams are usually in a state of gas-water coexistence and for coal-bed methane (CBM) reservoirs, coal permeability is essential to the extraction process of CBM. The purpose of this study is to experimentally analyse the coal permeability characteristics under different water content conditions and to propose a permeability model for gas flow in coal seams. Experiment results show that when the pore pressure is fixed, the gas adsorption decreases with the increase of water content. Similar behaviour is also found for the adsorption deformation which can discourage the coal permeability. In the process of increasing pore pressure, under the control of sorption-induced deformation and slippage effect, the permeability of coal shows a trend of decreasing first and then tending to be gentle. In addition, based on gas flow experiments, an improved permeability model considering water content and slippage effect is established based on the classic matchstick model. We also proposed a calculation model of slip factor considering the influence of water content. Wherein, the slippage factor showed an increasing trend under the combined effect of water content and pore pressure.

Keywords: pore pressure; adsorption; water content; slippage effect; permeability.

DOI: 10.1504/IJPE.2020.116235

International Journal of Petroleum Engineering, 2020 Vol.3 No.4, pp.305 - 329

Received: 28 Nov 2020
Accepted: 14 May 2021
Published online: 13 Jul 2021 *