Modeling of gas migration in a dual-porosity coal seam around a borehole: the effects of three types of driving forces in coal matrix

Wei Liu, Dongyang Han, Hao Xu, Xiangyu Chu and Yueping Qin

Energy, 2023, vol. 264, issue C

Abstract: Migration behaviors of coalbed methane (CBM) are the core issue for gas extraction, but in terms of coal seams considered as a dual-porosity medium, gas migration investigations have rarely been addressed. This work developed three gas migration models in the dual-porosity coal seam around a borehole, in which gas flow in coal matrix was driven by the pressure gradient (PG model), concentration gradient (MCFP model) and free gas density gradient (MDFP model), respectively. The numerical solutions of these models were compared with field measurements to determine the optimal one. The results show that (i) the simulation results of the MDFP model are in better agreement with the observed data, and its maximum relative error is less than 5%, which is much smaller than that of the PG model and MCFP model, so the MDFP model can reflect the gas migration behaviors in dual-porosity coal seams more effectively; (ii) the gas seepage in fractures controls the initial gas emission rate, and the gas diffusion in coal matrix then gradually dominates gas emission in the later stage, where diffusion behavior in the matrix is more consistent with the driver of the free gas density gradient; (iii) sensitivity analysis indicates gas emission rates of the borehole are positively correlated with original gas pressure and fracture permeability coefficient, but negatively correlated with matrix radius. This research contributes to providing a theoretical basis for CBM production prediction.

Keywords: Coal seam; Gas migration; Dual-porosity model; Density gradient; Gas emission rate (search for similar items in EconPapers)
Date: 2023
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Citations: View citations in EconPapers (3)

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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:264:y:2023:i:c:s0360544222030675

DOI: 10.1016/j.energy.2022.126181

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