Numerical assessment of the effect of equilibration time on coal permeability evolution characteristics

Liu, Qingquan; Wang, Chenghao; Wang, Haifeng; Zhang, Hongxing; Wang, Liang; Li, Wenyuan; Liu, Hongyong

doi:10.1016/j.fuel.2014.09.099

Cited by 87 publications

(30 citation statements)

References 29 publications

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“…In-situ CBM is in a dynamic equilibrium in which the gas pressure in the matrix is equal to the reservoir pressure in fractures-with this equilibrium disturbed by the dewatering [45]. The mass flux may be defined as [46,47]:…”

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confidence: 99%

Evolution of Production and Transport Characteristics of Steeply-Dipping Ultra-Thick Coalbed Methane Reservoirs

et al. 2020

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The large spatial variability of in-situ stress and initial reservoir pressure in steeply-dipping ultra-thick coalbed methane (UTCBM) reservoirs exert strong control on the initial distribution of stress-sensitive permeability. This results in significant differences in the propagation of reservoir depressurization, gas production characteristics, distribution of fluid saturation, and evolution of permeability relative to flat-lying and thin counterpart coalbed methane (CBM) reservoirs. We contrast these responses using the Fukang mining area of the Junggar Basin, Xinjiang, China, as a type-example using coupled hydro-mechanical modeling. Production response indicates: (1) Dual peaks in CBM production rate, due to the asynchronous changes in the gas production rate in each the upper and lower sections of the reservoir; (2) higher depressurization and water saturation levels in the lower section of the reservoir relative to the upper at any given distance from the production well that ameliorate with time to be similar to those of standard horizontal reservoirs; (3) the heterogeneity in effective stress is further amplified by the asymmetry of the initial pressure drawdown distribution of the reservoir to exert extreme control on the down-dip evolution of absolute permeability—with implications for production. Field drainage data and simulation results obtained in this study more accurately reflect the drainage characteristics of the steeply-dipping UTCBM reservoirs. For ultra-thick low-rank coal seams, permeability anisotropy plays an important role in determining the utility of horizontal wells and hydraulic fracturing to maximize rates and yields CBM production, and requiring further study.

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mentioning

confidence: 99%

Evolution of Production and Transport Characteristics of Steeply-Dipping Ultra-Thick Coalbed Methane Reservoirs

et al. 2020

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“…

P_{b}

is defined as the "virtual" pressure in the matrix pores because the gas pressure in the matrix pores is difficult to be discussed clearly. Most of the analysis models assume that the system has reached the equilibrium state in the initial state, that is, the gas pressure in the matrix pore and the gas pressure in the fracture are equal to the gas pressure in the coal reservoir 37 . Therefore, the initial pore gas pressure and fracture gas pressure of the model are both 0.8 MPa.…”

Section: Numerical Simulation Of Gas Seepagementioning

confidence: 99%

Gas seepage laws based on dual porosity and dual permeability: Numerical simulation and coalbed methane extraction practice

Qin

Wang

et al. 2021

Energy Science & Engineering

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Coalbed methane (CBM) is the very important unconventional energy resource. Enhancing extraction is the main method to improve the utilization of CBM and prevent coal mine gas disasters. To reveal the laws of gas migration during the underground gas extraction, the paper established the solid‐gas coupling model, regarding coal as the homogeneous elastic medium with dual pore‐fracture structure and dual permeability and considering the gas dynamic diffusion coefficient. Then, the regulations of gas migration in the in‐seam borehole were simulated by the COMSOL Multiphysics software and verified via the field trials of gas extraction. The results revealed that the permeability increased with time due to the coupling of matrix shrinkage and volume compression of coal, in which the matrix shrinkage played a leading role. The gas seepage velocity at the observation points can be divided into three stages: the rapid rise stage, the stable decline stage, and the stable and invariant stage. The gas extraction rate continued decreasing with time and finally tended to a fixed value. In the coal seam #4 of Zhongxing coal mine, the measured flow rates of three in‐seam drilling holes were in good agreement with the simulation results, which verified the correctness of the theoretical coupling model.

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“…where M c is the molar mass of methane, kg/mol; ρ g is the gas density under standard state, kg/m 3 ; V M is the molar volume of methane under standard conditions, m 3 /mol; V L is the maximum adsorption capacity of coal, mL/g; P L is the Langmuir pressure constant of coal, Pa; ϕ m is the porosity in coal matrix, %; R is the universal gas constant, J/(mol•K); and T is the temperature, K. Gas diffusion in coal matrix and fractures is caused by concentration gradient, which is considered as unsteady diffusion and can be expressed by the following equation [25]:…”

Section: The Governing Equation Of Gas Diffusion In Coal Matrixmentioning

confidence: 99%

Gas Expansion Energy Model and Numerical Simulation of Outburst Coal Seam under Multifield Coupling

Cao¹,

Hu²,

Yong-liang³

et al. 2021

Geofluids

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Due to the insufficient understanding of the outburst mechanism, the coal and gas outburst disasters in China are more serious. Gas expansion energy is the main source of energy that causes outburst. In order to explore the distribution law of gas expansion energy in outburst coal seams, a gas-solid coupling equation of outburst coal seams was established. The distribution law of coal stress field, deformation field, gas flow field, and gas expansion energy were simulated and analyzed by using COMSOL Multiphysics. The results showed that from the excavation face to the deep part of coal seam, the stress presented unloading zone, stress concentration zone, and original stress zone. The volumetric strain and permeability reached the minimum, while the gas pressure reached the maximum at the peak value of vertical stress. As time goes on, the gas pressure in the fracture near the working face gradually decreased and was less than the pressure in coal matrix. The total gas expansion energy consists of free gas and desorption gas expansion energy. Affected by the excavation, free gas expansion energy maintained a constant value in the original coal seam and gradually decreased in the area close to the working face. The expansion energy provided by desorption gas was zero in the original coal seam. And it first increased and then decreased rapidly near the working face. Compared with stress and coal seam thickness, gas pressure and initial diffusion coefficient had significant influence on gas expansion energy of coal seam. When the diffusion coefficient was greater than 1e-9 m2/s, the gas expansion energy of the coal seam near the working face was significantly higher than that of the original coal seam, which had the risk of inducing outburst.

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Numerical assessment of the effect of equilibration time on coal permeability evolution characteristics

Cited by 87 publications

References 29 publications

Evolution of Production and Transport Characteristics of Steeply-Dipping Ultra-Thick Coalbed Methane Reservoirs

Evolution of Production and Transport Characteristics of Steeply-Dipping Ultra-Thick Coalbed Methane Reservoirs

Gas seepage laws based on dual porosity and dual permeability: Numerical simulation and coalbed methane extraction practice

Gas Expansion Energy Model and Numerical Simulation of Outburst Coal Seam under Multifield Coupling

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