Numerical study of CO2-enhanced coalbed methane recovery

Fan, Yu; Deng, Cunbao; Zhang, Xun; Li, Fengqi; Wang, Xinyang; Qiao, Ling

doi:10.1016/j.ijggc.2018.06.016

Cited by 94 publications

(95 citation statements)

References 27 publications

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“…When the gas mixture is injected into the seam, the presence of multiple gases results in adsorption competition. The extended Langmuir equation describes the competitive adsorption characteristics of each component gas, which is as follows:

V_{sn} = \frac{V_{Ln} C_{normaln} b_{normaln} R T}{1 + {false\sum}_{n = 1}^{3} C_{n} b_{n} R T}

({, \begin{matrix} left V_{Ln} = V_{Ln 0} \exp (][, - \frac{d_{2}}{1 + d_{1} C_{n} R T} ()(, T - T_{t})) \\ left P_{Ln} = P_{Ln 0} \exp (][, \frac{C_{pn}}{R} ()(, \frac{1}{T} - \frac{1}{T_{normalt}})) \\ left b_{n} = \frac{1}{P_{Ln0}} \end{matrix})

where V Ln and P Ln represent the extended Langmuir volume constant (m 3 /kg) and pressure constant (Pa) for gas component n, respectively; b n is the Langmuir adsorption constant for gas component n and is equal to the reciprocal of the Langmuir pressure ( P Ln ); d 1 is the pressure correction (Pa −1 ); d 2 is the temperature correction (K −1 ); T t is the laboratory reference temperature (K); C pn is the specific heat capacity at constant pressure of gas component n (J/(mol·K)); and variables with a subscript “0” correspond to initial variable values.…”

Section: Fully Coupled Equations Of the Thm Fields For Gas Mixture Ecmentioning

confidence: 99%

“…Coal deformation causes shrinkage and swelling of the coal pore system, which results in porosity changes. The porosity is expressed as:

φ = \frac{V_{p}}{V_{b}} = \frac{V_{p0} + Δ V_{normalp}}{V_{b0} + Δ V_{normalb}} = 1 - \frac{V_{s0} + Δ V_{normals}}{V_{b0} + Δ V_{normalb}} = 1 - \frac{1 - φ_{0}}{1 + e} (1 + \frac{Δ V_{normals}}{V_{s0}})

where V b is the total coal volume; V p is the porosity volume of coal; e is the bulk strain, e = ( ε x + ε y + ε z )/3; φ 0 is the initial porosity; and V s is the solid skeleton volume of coal.…”

Section: Fully Coupled Equations Of the Thm Fields For Gas Mixture Ecmentioning

confidence: 99%

Section: Governing Equation Of Ternary Gas Transportmentioning

confidence: 99%

“…The extensive investigation involving the complex coupling responses during CO 2 injection is expected to be carried out. For CO 2 ‐ECBM numerical simulations, scholars have analyzed and discussed the distribution of pressure and temperature in coal reservoirs by coupling the stress and seepage fields, as well as the CH 4 production and CO 2 storage . However, the dynamic change of permeability under different reservoir pressures and temperatures was always ignored.…”

Section: Introductionmentioning

confidence: 99%

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Numerical study on enhancing coalbed methane recovery by injecting N₂/CO₂ mixtures and its geological significance

Fan

Wang

Deng

et al. 2019

Energy Science & Engineering

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As an effective carbon utilization technology, the injection of N2/CO2 mixtures into coal seams has significant potential for improving coalbed methane recovery. Considering the technical barrier that injection of pure CO2 decreases the well injectivity index and pure N2 injection leads to the rapid methane recovery, a method of injecting N2‐enriched gas mixtures with a constant component is proposed. In this study, a thermo‐hydro‐mechanical (THM) coupling numerical model for enhanced coalbed methane (CBM) recovery by injecting N2/CO2 mixtures is established. This model includes complex interactions of coal deformation, competitive adsorption, ternary gas seepage, and heat transfer. The THM coupling model is first validated, and then applied to investigate the evolution of mixed gas concentrations, reservoir permeability, reservoir temperature, CH4 production, and N2/CO2 storage during N2/CO2 enhanced CBM recovery. The results show that the displacement radius and concentration of the mixed gas in the coal seam increased with gas injection pressure increase. The concentration of CH4 gradually decreased with time, and the early decline is faster than the later stage. The sweep of the N2 flow accelerates CH4 desorption and migration, promoting a reduction in reservoir temperature near the production well. Reservoir permeability evolution results from the combined effects of ternary gases (CH4, CO2, N2) competitive adsorption, gas pressure, and geostress on the coal seam within the THM fields. At the methane natural depletion stage (within 250 days), the permeability of coal reservoir first decreases and then increases. With the arrival of the N2/CO2 mixture, the permeability decreases dramatically. From the perspective of cumulative CH4 production, the optimal composition is dominated by the synergistic effect of maximizing breakthrough time and minimizing coal matrix swelling. For 30% CO2‐70% N2, the CH4 recovery ratio reached 71.76%, representing an increase of 16.67% compared to natural depletion.

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V_{sn} = \frac{V_{Ln} C_{normaln} b_{normaln} R T}{1 + {false\sum}_{n = 1}^{3} C_{n} b_{n} R T}

({, \begin{matrix} left V_{Ln} = V_{Ln 0} \exp (][, - \frac{d_{2}}{1 + d_{1} C_{n} R T} ()(, T - T_{t})) \\ left P_{Ln} = P_{Ln 0} \exp (][, \frac{C_{pn}}{R} ()(, \frac{1}{T} - \frac{1}{T_{normalt}})) \\ left b_{n} = \frac{1}{P_{Ln0}} \end{matrix})

Section: Fully Coupled Equations Of the Thm Fields For Gas Mixture Ecmentioning

confidence: 99%

“…Coal deformation causes shrinkage and swelling of the coal pore system, which results in porosity changes. The porosity is expressed as:

φ = \frac{V_{p}}{V_{b}} = \frac{V_{p0} + Δ V_{normalp}}{V_{b0} + Δ V_{normalb}} = 1 - \frac{V_{s0} + Δ V_{normals}}{V_{b0} + Δ V_{normalb}} = 1 - \frac{1 - φ_{0}}{1 + e} (1 + \frac{Δ V_{normals}}{V_{s0}})

Section: Fully Coupled Equations Of the Thm Fields For Gas Mixture Ecmentioning

confidence: 99%

Section: Governing Equation Of Ternary Gas Transportmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Numerical study on enhancing coalbed methane recovery by injecting N₂/CO₂ mixtures and its geological significance

Fan

Wang

Deng

et al. 2019

Energy Science & Engineering

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“…Injection of foreign gases into coal seam is considered an effective method to enhance gas drainage . This process expedites the gas transport by competitive sorption and sweeping effects and maintaining pressure gradient between coal seam and borehole .…”

Section: Introductionmentioning

confidence: 99%

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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State-Of-The-Art Overview of CO2 Conversions

Leonzio

2021

Advances in Science, Technology &Amp; Innovation

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Numerical study of CO2-enhanced coalbed methane recovery

Cited by 94 publications

References 27 publications

Numerical study on enhancing coalbed methane recovery by injecting N₂/CO₂ mixtures and its geological significance

Numerical study on enhancing coalbed methane recovery by injecting N₂/CO₂ mixtures and its geological significance

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

State-Of-The-Art Overview of CO2 Conversions

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Numerical study of CO2-enhanced coalbed methane recovery

Cited by 94 publications

References 27 publications

Numerical study on enhancing coalbed methane recovery by injecting N2/CO2 mixtures and its geological significance

Numerical study on enhancing coalbed methane recovery by injecting N2/CO2 mixtures and its geological significance

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

State-Of-The-Art Overview of CO2 Conversions

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Numerical study on enhancing coalbed methane recovery by injecting N₂/CO₂ mixtures and its geological significance

Numerical study on enhancing coalbed methane recovery by injecting N₂/CO₂ mixtures and its geological significance