Effects of gas sorption-induced swelling/shrinkage on the cleat compressibility of coal under different bedding directions

Peng, Shoujian; Fang, Zhiming; Shen, Jian; Xu, Jiang; Wang, Geoff

doi:10.1038/s41598-017-14678-1

Cited by 19 publications

(13 citation statements)

References 27 publications

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“…Most of the coal permeability models include several key parameters to describe the physical and mechanical properties of the coal, including typically Poisson's ratio (ν), modulus of elasticity (E), porosity (ϕ), swelling and strain coefficients (ε L and β), and cleat compressibility (C f ). Commonly, the cleat compressibility is found by regression of the model to measured permeability data (k) , Peng, et al 2017, Zheng, et al 2012. A more useful approach would be to determine cleat compressibility independently since a primary objective in many cases is to predict permeability, rather than use it as a measured value to extract coal properties.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Anisotropic coal permeability estimation by determining cleat compressibility using mercury intrusion porosimetry and stress–strain measurements

Raza

Rufford

et al. 2019

International Journal of Coal Geology

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This paper presents a novel method to calculate the anisotropic and stress-dependent coal permeability by determining cleat compressibility using the Mercury Intrusion Porosimetry (MIP) and stress-strain measurements. Cleat compressibility is often assumed isotropic and constant in the literature and is usually obtained by numerical fitting to a matchstick permeability model e.g. the model by Seidle, et al. (1992) despite the gross simplification of this representation of the coal pore network. This paper provides a method to calculate anisotropic cleat compressibility using only MIP and stress-strain measurements which are easy to conduct, and without permeability information, which is harder to come by, requiring laboratory experiments on the core or through fitting field data. We report the measured stress-strain behaviour of a coal sample, with hydrodynamic loading/unloading over the range 0.5-4.0 MPa, and the permeability in face cleat (k F ) and butt cleat (k B ) directions using the Triaxial Stress Permeameter (TSR). The stress-strain measurement is used to calculate the anisotropic modulus of elasticity (E F , E B, and E V ) in face cleat, butt cleat and bedding plane directions, and cleat compressibility in the face cleat (C fF ) and butt cleat (C fB ) directions using the fractal dimension analysis with MIP measurement. Finally, the cleat compressibilities are used to calculate the anisotropic coal permeability by Seidle, et al. (1992) permeability model and compared with the measured permeability of the coal sample.

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Section: Accepted Manuscriptmentioning

confidence: 99%

Anisotropic coal permeability estimation by determining cleat compressibility using mercury intrusion porosimetry and stress–strain measurements

Raza

Rufford

et al. 2019

International Journal of Coal Geology

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“…Injection of pure CO 2 into coal seams usually has a negative effect—coal swelling‐induced permeability decreasing, due to the greater adsorption affinity of CO 2 to coal than of CH 4 . Related studies show that CO 2 injections will cause a reduction in coal permeability by nearly two orders of magnitude, especially near the injection well .…”

Section: Introductionmentioning

confidence: 99%

“…25 Injection of pure CO 2 into coal seams usually has a negative effect-coal swelling-induced permeability decreasing, due to the greater adsorption affinity of CO 2 to coal than of CH 4 . 5,[25][26][27] Related studies show that CO 2 injections will cause a reduction in coal permeability by nearly two orders of magnitude, especially near the injection well. 9,12,15 Even if the CO 2 -ECBM is completed, the decreased coal permeability cannot rebound to initial values, thus results in the deterioration of well injectivity.Another gas injected into coal seams is N 2 , which has a different mechanism of ECBM recovery than CO 2 .…”

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confidence: 99%

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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“…This interacts quite strongly with the coal and may increase the cleat compressibility by softening the coal material. Peng, et al (2017) showed in a study with coals from the Qinshui Basin that cleat compressibility factors determined from CO2 core flooding experiments were much higher than cleat compressibility factors determined from CH4 core flooding experiments, as shown in Table 4-4.…”

Section: Equation 4-9mentioning

confidence: 87%

“…Most of the coal permeability models include several key parameters to describe the physical and mechanical properties of the coal, including typically Poisson's ratio (ν), modulus of elasticity (E), porosity (ϕ), swelling and strain coefficients (εL and β), and cleat compressibility (Cf). Commonly, the cleat compressibility is found by regression of the model to measured permeability data (k) (Zheng, et al 2012, Peng, et al 2017. A more useful approach would be to determine cleat compressibility independently since a primary objective in many cases is to predict permeability, rather than use it as a measured value to extract coal properties.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of anisotropic permeability in coal seam gas reservoirs

Raza¹

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In this work, the effect of stresses and the reservoir boundary conditions on the permeability anisotropy, mechanical properties and swelling/shrinkage of the coals will be examined.Permeability is the fundamental parameter to understanding and modelling the fluid flow in the porous coal, and thus crucial to estimating the commercial gas and water production from coal seam gas (CSG) reservoir. Although permeability is a primary parameter to determine the reservoir production, the fundamental research behind the permeability change during pressure drawdown is not extensively examined in context with reservoir stresses and boundaries which can directly affect the reservoir production estimates. This project provides a mean to understand permeability change in CSG reservoir by conducting experiments and modelling studies to relate coal permeability, mechanical properties and sorption behaviour to different reservoir stresses and boundary conditions.The first objective of this project was to manage the design, construct, and demonstrate a state of the art triaxial stress permeameter (TSP) to measure anisotropic-permeability and stress-strain on coal sample simultaneously. The TSP was designed to measure anisotropic permeability by rotating a 40 mm cubic coal sample in orthogonal direction so that permeability can be measured in directions that align with face cleats, butt cleats, and bedding-plane of the coal. TSP is used in a series of experiments on coal sample UQ-B1 from the Surat Basin to determine in the modulus of elasticity (E) and cleat compressibility (Cf) of the coal sample UQ-B1 (Chapter 4), measure permeability using helium and methane gases (Chapter 5), and the effect of using either constant-stress (free swelling) or constant-volume boundary conditions on the observed relationship between net stresses and permeability changes (Chapter 5).Chapter 4 reports experiments in the TSP to determine the modulus of elasticity (E) and cleat compressibility (Cf) of coal sample UQ-B1 at effective stresses of 0.5 -4.0 MPa. These experiments confirm that these coal properties are anisotropic and stress-dependent. The experimental data also shows that cleats become 'softer' as stress is reduced on the sample which can result in the permeability rise by increasing the cleat width. The calculated modulus of elasticity of the bulk coal was E1 = 4.35 GPa, E2 = 4.90 GPa and E3 = 7.06 GPa perpendicular to face cleat, butt cleat, and bedding-plane directions, respectively. The cleat compressibilities (Cf) calculated from the relationship of pore size to pore compressibility were Cf1=0.1102-0.0333MPa -1 perpendicular to the face cleats and Cf2=0.0588-0.0251MPa -1 perpendicular to butt cleats at effective stresses of σeff = 0.5 -4.0 MPa.

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Effects of gas sorption-induced swelling/shrinkage on the cleat compressibility of coal under different bedding directions

Cited by 19 publications

References 27 publications

Anisotropic coal permeability estimation by determining cleat compressibility using mercury intrusion porosimetry and stress–strain measurements

Anisotropic coal permeability estimation by determining cleat compressibility using mercury intrusion porosimetry and stress–strain measurements

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

Dynamics of anisotropic permeability in coal seam gas reservoirs

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Effects of gas sorption-induced swelling/shrinkage on the cleat compressibility of coal under different bedding directions

Cited by 19 publications

References 27 publications

Anisotropic coal permeability estimation by determining cleat compressibility using mercury intrusion porosimetry and stress–strain measurements

Anisotropic coal permeability estimation by determining cleat compressibility using mercury intrusion porosimetry and stress–strain measurements

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

Dynamics of anisotropic permeability in coal seam gas reservoirs

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