Time-dependent coal permeability: Impact of gas transport from coal cleats to matrices

Wang, Chunguang; Zhang, Jidong; Zang, Yuxiao; Zhong, Ruizhi; Wang, Jianguo; Wu, Yu; Jiang, Yujing; Chen, Zhongwei

doi:10.1016/j.jngse.2021.103806

Cited by 37 publications

(14 citation statements)

References 59 publications

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“…It is difficult to obtain the diffusion coefficient of gas in the pores of coal due to the complexity of the internal pore structure. Through experiments, Li et al [36] and Wang et al [37] pointed out that in the case of the same initial adsorption amount, during the process of heating diffusion at different temperatures, the diffusion amount at high temperature is always greater than that at low temperature, but the diffusion process at low temperature can reach the diffusion equilibrium more quickly. A rise in temperature will give methane molecules higher energy, enabling more molecules to be…”

Section: The Influence Of Temperature On the Gas Diffusion Processmentioning

confidence: 99%

Experimental and Numerical Simulation of Desorption and Diffusion Process of the Adsorbed Gas in Coal Rock under Isothermal Conditions

Zhang

Li²,

Wang

et al. 2021

Geofluids

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Investigation of desorption of diffusion migration of native adsorbed gas in coal under the action of temperature has always been one of the important directions of coal mine safety research. Five coal samples from the Sichuan Furong mining area are studied under the different isothermal conditions (35°C, 30°C, 24.5°C, 36.2°C, and 40°C) by means of laboratory tests; the desorption, diffusion, and migration processes of adsorbed gas were studied; the escaped gas volume in the process of diffusion, the escaped gas pressure, and the change of the concentration of the gas component content are summarized; and the emitted gas volume curve will be eventually found to be constant under the isothermal process. In addition, the escaped gas concentration showed a trend of increasing first and then decreasing. Based on the CT scan slice of coal samples, a network model of coal fracture based on the Tyson polygon contraction method is established in this paper, and LS-DYNA software is used to analyze the transient diffusion behavior of methane under three isothermal conditions (24.5°C, 30°C, and 42°C), and the experimental results are verified.

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Section: The Influence Of Temperature On the Gas Diffusion Processmentioning

confidence: 99%

Experimental and Numerical Simulation of Desorption and Diffusion Process of the Adsorbed Gas in Coal Rock under Isothermal Conditions

Zhang

Li²,

Wang

et al. 2021

Geofluids

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“…The gas flow in unconventional reservoirs is a complex process including gas desorption, gas diffusion, and the mass transport and stress transfer between matrix and fracture systems . Meanwhile, the evolution of intrinsic permeability is determined by the strongly coupled response incorporating these factors. , In our recent work, effective strain-based permeability models for both matrix and fracture systems have been proposed − with the interactions between the two systems fully considered. The impacts of the crossflow between different gas-containing units on the intrinsic permeability have been rarely studied.…”

Section: Introductionmentioning

confidence: 99%

Influence of Well Types on Optimizing the Co-production of Gas from Coal and Tight Formations

et al. 2022

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Co-production of gas from both coalbeds and tight formations is considered a viable means to improve well productivity. Most previous studies focused on the geology and resource estimates for gas production viability with little attention to the effectiveness of gas co-production with regard to well types. To make up for this weakness, a two-phase flow and reservoir deformation coupled model is proposed together with an anisotropic permeability model. The coupled model is first verified using gas and water production data from a vertical well from the Linxing block in the Ordos Basin, China. Then a reservoir model is built, including one coal seam and one tight gas formation separated by a low-permeability stratum with four simulation scenarios designed. Based on the results, the impacts of the crossflow between different reservoirs are addressed and the mechanisms of the gas co-production rate profile types observed in the Linxing block are analyzed. It is also found that high water-saturated adjacent reservoirs would keep the water relative permeability of the gas-rich reservoir at a high level, impeding the gas flow. The use of a horizontal well is strongly recommended when most gases are stored in a specific thin reservoir and the life of the well is short; however, a vertical well is favored when two or more gas-rich and high permeability reservoirs co-exist and the well life is relatively long. For the application of vertical wells, the hydraulic fractures should extend in the horizontal planes and interact with the pre-existing natural fracture. For horizontal wells, the hydraulic fracture should extend in the host reservoir and penetrate into the adjacent strata. This work can shed new light on the co-exploitation of coal measure methane.

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“…Low-permeability reservoirs such as shale − and coal , play an increasingly significant role in the energy market. Hydraulic fracturing is required to enhance or maintain the permeability of tight reservoirs. − Hydraulic fractures created by shear stress , and the pre-existing natural fractures reactivated in shear mode result in a new fracture network. − The changes in both the relative position of fractures and fracture aperture lead to a variation in reservoir permeability, which dominates the hydromechanical behavior of the host fractured rock. , Therefore, the permeability evolution under shear conditions has a significant impact on the hydraulic properties of low-permeability reservoirs.…”

Section: Introductionmentioning

confidence: 99%

Analysis of the Upper and Lower Boundaries of Permeability Evolution during Shale Rock Shear Deformation

Sun

Chen

Zhu³

et al. 2022

Energy Fuels

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Understanding the evolution of permeability during rock shear displacement plays an important role in many geosciences and geo-engineering, such as shale gas exploitation. In previous studies, permeability data were obtained under different experimental conditions with varied in situ stress environments, fracture apertures, or loading stresses. However, the mechanisms controlling the permeability evolution during the shear process have not been well explained. In this study, two special conditions, fractures with constant stiffness (CS) and constant volume (CV), are proposed to define the upper and lower boundaries of permeability evolution. An inverted "L-shaped" model containing a matrix and fracture was established to investigate the permeability evolution and internal morphological changes in the fractures. The impacts of the initial fracture aperture and normal stress in the shear process are discussed together with the apparent fracture aperture, effective flow area, and pore throat radius. Under the CS condition, the self-supporting effect produced by the contact between the upper and lower fracture surfaces plays a dominant role in changing the permeability, and three stages of permeability evolution with shear displacement are observed: rapid increase, slow increase, and decrease. Under CV conditions, the submergence effect of the fracture closed the effective flow channels, thereby reducing the permeability in three stages: rapid decrease, slow decrease, and recovery. The model results show that both a smaller initial fracture aperture or a greater normal stress lead to a greater variation in the permeability and the roughness of fracture surface determines the permeability evolution range. The new model was applied to generate a series of shale permeability evolution boundaries under different limit conditions. These boundaries are consistent with experimental observations reported in other literatures. This work provides new insights into the permeability evolution of rock strata under shear action.

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Time-dependent coal permeability: Impact of gas transport from coal cleats to matrices

Cited by 37 publications

References 59 publications

Experimental and Numerical Simulation of Desorption and Diffusion Process of the Adsorbed Gas in Coal Rock under Isothermal Conditions

Experimental and Numerical Simulation of Desorption and Diffusion Process of the Adsorbed Gas in Coal Rock under Isothermal Conditions

Influence of Well Types on Optimizing the Co-production of Gas from Coal and Tight Formations

Analysis of the Upper and Lower Boundaries of Permeability Evolution during Shale Rock Shear Deformation

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