Model development and simulation study of the feasibility of enhancing gas drainage efficiency through nitrogen injection

Ren, Ting X; Wang, Gongda; Wang, Chenghao; Qi, Qingxin

doi:10.1016/j.fuel.2017.01.029

Cited by 62 publications

(38 citation statements)

References 39 publications

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“…Due to the complexity of the HM model, the following assumptions are adopted: (a) coal seam is assumed as a dual‐porosity (fractures and matrix pores) single‐permeability elastic medium; (b) the free gases conform to the ideal gas law, and they exist and migrate in the space of fractures and pores; (c) the adsorbed gas exists on the surface of pores, and water only migrates in fractures; (d) for the transport of methane, it first desorbs from the surface of matrix pores—Langmuir equation, then diffuses from the pores to the fractures—Fick's law, and finally seepages from fractures to drainage borehole—Darcy's law; while for the injected flue gas, the transport direction is opposite—gas mixture first seepages from the injection borehole to the fractures, then diffuses from the fractures to the matrix, followed by the competitive adsorption with CH 4 on pore surfaces. The mass transport of gas and water mixture in the process of flue gas enhanced drainage is shown in Figure .…”

Section: Mathematical Model For Flue Gas Enhanced Coal Seam Gas Drainagementioning

confidence: 99%

“…The gas content is defined as the adsorbed gas volume per unit mass. A modified Langmuir Equation is applied to calculate the gas content:

V_{sg i} = \frac{V_{L i} b_{L i} p_{mg i}}{1 + (b_{L 1} p_{mg 1} + b_{L 2} p_{mg 2} + b_{L 3} p_{mg 3})},

where p mg means the gas pressure in coal matrix, Pa; V L means the Langmuir volume constant, m 3 /kg; b L means the Langmuir pressure constant, 1/Pa.…”

Section: Mathematical Model For Flue Gas Enhanced Coal Seam Gas Drainagementioning

confidence: 99%

“…Other related parameters are listed in Table . These parameters are mainly recovered from field tests, laboratory experiments and recorded in the public literatures …”

Section: Simulation Of Flue Gas Enhanced Underground Coal Seam Gas Drmentioning

confidence: 99%

“…Hence, CO 2 injection is usually applied to coal seam with high permeability. Compared to CO 2 injection, N 2 injection may be more suitable for low permeability seam due to its lower sorption affinity on coal (approximately one‐fourth of CO 2 ) and thus smaller induced swelling . However, the small viscosity of N 2 may result in the early breakthrough of N 2 as well as a large amount of injection volume.…”

Section: Introductionmentioning

confidence: 99%

“…Wu et al numerically investigated CO 2 ‐ECBM recovery combining the infiltration and diffusion of binary gases (CO 2 , CH 4 ), competitive sorption and deformation. Ren et al proposed a binary gas transport model for N 2 injection enhanced gas drainage. Lin et al investigated the N 2 and CO 2 adsorption‐induced coal matrix swelling, and its impact on N 2 injection enhanced gas drainage in CO 2 ‐rich coal seam by conducting experiments.…”

Section: Introductionmentioning

confidence: 99%

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Numerical investigation of flue gas injection enhanced underground coal seam gas drainage

Huo

Jing

Fan

et al. 2019

Energy Science & Engineering

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Coal seam with low permeability is widely distributed in China. Injection of flue gas (N2:CO2 = 0.85:0.15) is an effective approach to improve coal seam gas drainage efficiency. This process relates complex responses among ternary gases (CH4, CO2, and N2) competitive sorption on coals, gas diffusion, gas‐water migration by means of two‐phase flow, and coal deformation. In this paper, an improved hydraulic‐mechanical model coupling above interactions is established for flue gas injection enhanced gas drainage. This model is used to simulate flue gas enhanced drainage by finite element method. The sensitivity analyses of key factors are made to recovery a better understanding on the processes controlling flue gas enhanced drainage. Results show that the flue gas enhanced drainage can indeed improve the efficiency of gas extraction and reduce the gas pressure to the required value in a shorter duration. Due to the competitive adsorption and gas sweeping effect of injected flue gas, CH4 is driven toward drainage borehole, and CH4 pressure and content near the injection borehole decrease faster than that near the drainage borehole. The peak CH4 pressure laterally moves from the injection borehole to the drainage borehole. Higher injection pressure, initial permeability, and smaller sorption affinity ratios may lead to greater CH4 production rate at early drainage stage, but smaller CH4 production rate at late stage. The factors controlling the behavior of flue gas enhanced drainage are initial permeability, injection pressure, and sorption affinity ratios in order. This work offers useful framework to investigate important technical challenges associated with enhanced mine gas drainage, as well as unconventional gas development.

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Section: Mathematical Model For Flue Gas Enhanced Coal Seam Gas Drainagementioning

confidence: 99%

“…The gas content is defined as the adsorbed gas volume per unit mass. A modified Langmuir Equation is applied to calculate the gas content:

V_{sg i} = \frac{V_{L i} b_{L i} p_{mg i}}{1 + (b_{L 1} p_{mg 1} + b_{L 2} p_{mg 2} + b_{L 3} p_{mg 3})},

where p mg means the gas pressure in coal matrix, Pa; V L means the Langmuir volume constant, m 3 /kg; b L means the Langmuir pressure constant, 1/Pa.…”

Section: Mathematical Model For Flue Gas Enhanced Coal Seam Gas Drainagementioning

confidence: 99%

“…Other related parameters are listed in Table . These parameters are mainly recovered from field tests, laboratory experiments and recorded in the public literatures …”

Section: Simulation Of Flue Gas Enhanced Underground Coal Seam Gas Drmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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