Factors influencing methane diffusion behaviors in micro-nano coal pores: a comprehensive study

Abstract

Gas diffusion in the coal matrix plays a significant role in forecasting the production performance of coalbed methane (CBM) wells. To better understand methane diffusion behavior, a systematic study was performed on various rank coals with vitrinite reflectance (R_o,m) ranging from 0.46% to 2.79%. Multiple experiments, including coal petrographic analysis, field emission scanning electron microscopy (FESEM), low-temperature N₂ adsorption/desorption, and mercury intrusion porosimetry (MIP), were conducted to quantitatively characterize the multiscale micro-nano pore system in different rank coals, which showed that the pore structure of coals exhibited a multimodal pore size and volume distribution. Isothermal adsorption-diffusion experiments using the volumetric method were also performed to understand the methane diffusion characteristics in the micro-nano pores of the coal reservoir. The applicability of the multiporous diffusion model is verified, and methane diffusion in the multi-scale pores of coal reservoirs exhibits the characteristics of early fast diffusion, transitional diffusion in the medium term, and slow diffusion in the later period. In addition, the factors affecting methane diffusion in coals were systematically analyzed, and gray relational analysis (GRA) was employed to analyze and identify the importance of these factors on methane diffusion. The results show the impact ranking of factors, in order from the most important to the least: particle size > moisture > surface area > pore volume > pressure > coal rank > temperature in all of three diffusion stages. These findings are helpful for forecasting production performance and enhancing the production efficiency of CBM.

Graphical abstract

Keywords

coalbed methane reservoir / micro-characteristic / diffusion coefficient / grey relational analysis

References

[1] Bai L H, Liu B, Du Y J, Wang B Y, Tian S S, Wang L, Xue Z Q (2021). Distribution characteristics and oil mobility thresholds in lacustrine shale reservoir: insights from N₂ adsorption experiments on samples prior to and following hydrocarbon extraction. Petrol Sci, 19(2): 486–497

[2] Busch A, Gensterblum Y, Krooss B M, Littke R (2004). Methane and carbon dioxide adsorption-diffusion experiments on coal: upscaling and modeling.Int J Coal Geol, 60(2–4): 151–168

[3] Cai Y D, Li Q, Liu D M, Zhou Y F, Lv D (2018). Insights into matrix compressibility of coals by mercury intrusion porosimetry and N₂ adsorption.Int J Coal Geol, 200: 199–212

[4] Cai Y D, Pan Z J, Liu D M, Zheng G Q, Tang S H, Connell L D, Yao Y B, Zhou Y F (2014). Effects of pressure and temperature on gas diffusion and flow for primary and enhanced coalbed methane recovery.Energy Explor Exploit, 32(4): 601–619

[5] Charrière D, Pokryszka Z, Behra P (2010). Effect of pressure and temperature on diffusion of CO₂ and CH₄ into coal from the Lorraine Basin (France).Int J Coal Geol, 81(4): 373–380

[6] Chen S B, Li X Y, Chen S, Wang Y, Gong Z, Zhang Y K (2021). A new application of atomic force microscopy in the characterization of pore structure and pore contribution in shale gas reservoirs.J Nat Gas Sci Eng, 88: 103802

[7] Clarkson C R, Bustin R M (1999). The effect of pore structure and gas pressure upon the transport properties of coal: a laboratory and modeling study. 2. Adsorption rate modeling.Fuel, 78(11): 1345–1362

[8] Crank J (1956). The Mathematics of Diffusion. Oxford: The Clarendon Press

[9] Crosdale P J, Beamish B B, Valix M (1998). Coalbed methane sorption related to coal composition.Int J Coal Geol, 35(1–4): 147–158

[10] Desbois G, Urai J L, Kukla P A, Konstanty J, Baerle C (2011). High-resolution 3D fabric and porosity model in a tight gas sandstone reservoir: a new approach to investigate microstructures from mm- to nm-scale combining argon beam cross-sectioning and SEM imaging.J Petrol Sci Eng, 78(2): 243–257

[11] Fang X L, Cai Y D, Liu D M, Zhou Y F (2018). A mercury intrusion porosimetry method for methane diffusivity and permeability evaluation in coals: a Comparative analysis.Appl Sci (Basel), 8(6): 860

[12] Groen J C, Peffer L A A, Pérez-Ramírez J (2003). Pore size determination in modified micro- and mesoporous materials. Pitfalls and limitations in gas adsorption data analysis.Microporous Mesoporous Mater, 60(1–3): 1–17

[13] Guo H J, Yuan L, Cheng Y P, Wang K, Xu C, Zhou A, Zang J, Liu J J (2018). Effect of moisture on the desorption and unsteady-state diffusion properties of gas in low-rank coal.J Nat Gas Sci Eng, 57: 45–51

[14] Bytee K (2004). Coalbed-methane reservoir simulation: an evolving science.J Pet Technol, 56(4): 61–63

[15] Hu H X, Li X C, Fang Z M, Wei N, Li Q S (2010). Small-molecule gas sorption and diffusion in coal: molecular simulation.Energy, 35(7): 2939–2944

[16] Jia T, Liu C, Wei G, Yan J, Zhang Q, Niu L, Liu X, Zhang M, Ju Y, Zhang Y (2021). Micro-nanostructure of coal and adsorption-diffusion characteristics of methane.J Nanosci Nanotechnol, 21(1): 422–430

[17] Karacan C Ö, Okandan E (2001). Adsorption and gas transport in coal microstructure: investigation and evaluation by quantitative X-ray CT imaging.Fuel, 80(4): 509–520

[18] Li Z T, Liu D M, Cai Y D, Shi Y L (2016). Investigation of methane diffusion in low-rank coals by a multiporous diffusion model.J Nat Gas Sci Eng, 33: 97–107

[19] Liu J, Qin Y P, Zhang S, He C (2019a). Numerical solution for borehole methane flow in coal seam based on a new dual-porosity model.J Nat Gas Sci Eng, 68: 102916

[20] Liu P, Qin Y P, Liu S M, Hao Y J (2018b). Non-linear gas desorption and transport behavior in coal matrix: experiments and numerical modeling.Fuel, 214: 1–13

[21] Liu S F, Forrest J, Yang Y J (2012). A brief introduction to grey systems theory.Grey Syst, 2(2): 89–104

[22] Liu X F, Song D Z, He X Q, Nie B S, Wang L K (2019b). Insight into the macromolecular structural differences between hard coal and deformed soft coal.Fuel, 245: 188–197

[23] Liu Z S, Liu D M, Cai Y D, Pan Z J (2018a). The impacts of flow velocity on permeability and porosity of coals by core flooding and nuclear magnetic resonance: implications for coalbed methane production.J Petrol Sci Eng, 171: 938–950

[24] Lu X, Armstrong R T, Mostaghimi P (2020). Analysis of gas diffusivity in coal using micro-computed tomography.Fuel, 261: 116384

[25] Medveď I, Černý R (2011).Surface diffusion in porous media: a critical review. Microporous Mesoporous Mater. 142: 405–422

[26] Meng Y, Li Z P (2016). Experimental study on diffusion property of methane gas in coal and its influencing factors.Fuel, 185: 219–228

[27] Moore T A (2012). Coalbed methane: a review.Int J Coal Geol, 101(1): 36–81

[28] Pan Z J, Connell L D, Camilleri M, Connelly L (2010). Effects of matrix moisture on gas diffusion and flow in coal.Fuel, 89(11): 3207–3217

[29] Pillalamarry M, Harpalani S, Liu S M (2011). Gas diffusion behavior of coal and its impact on production from coalbed methane reservoirs.Int J Coal Geol, 86(4): 342–348

[30] Quan F K, Wei C T, Zhang J J, Feng S L, Hao S Q, Lu G W, Hu Y B (2020). Study on desorption and diffusion dynamics of coal reservoir through step-by-step depressurization simulation——an experimental simulation study based on LF-NMR technology.J Nat Gas Sci Eng, 75: 103149

[31] Rigby S P (2005). Predicting surface diffusivities of molecules from equilibrium adsorption isotherms.Colloids Surf A Physicochem Eng Asp, 262(1–3): 139–149

[32] Ruckenstein E, Vaidyanathan A S, Youngquist G R (1971). Sorption by solids with bidisperse pore structures.Chem Eng Sci, 26(9): 1305–1318

[33] Salmachi A, Bonyadi M R, Sayyafzadeh M, Haghighi M (2014). Identification of potential locations for well placement in developed coalbed methane reservoirs.Int J Coal Geol, 131: 250–262

[34] Sander R, Connell L D, Camilleri M, Pan Z J (2020). CH₄, CO₂, N₂ diffusion in Bowen Basin (Australia) coal: relationship between sorption kinetics of coal core and crushed coal particles.J Nat Gas Sci Eng, 81: 103468

[35] Si L L, Zhang H T, Wei J P, Li B, Han H K (2021). Modeling and experiment for effective diffusion coefficient of gas in water-saturated coal.Fuel, 284: 118887

[36] Smith D M, Williams F L (1984). Diffusional effects in the recovery of methane from coalbeds.Soc Pet Eng J, 24(5): 529–535

[37] Staib G, Sakurovs R, Gray E A (2013). A pressure and concentration dependence of CO₂ diffusion in two Australian bituminous coals. Int J Coal Geol, 116–117: 106–116

[38] Tosun N (2006). Determination of optimum parameters for multi-performance characteristics in drilling by using grey relational analysis.Int J Adv Manuf Technol, 28(5–6): 450–455

[39] Wang X L, Zhang D M, Su E L, Jiang Z G, Wang C Y, Chu Y P, Ye C (2020). Pore structure and diffusion characteristics of intact and tectonic coals: implications for selection of CO₂ geological sequestration site.J Nat Gas Sci Eng, 81: 103388

[40] Warren J E, Root P J (1963). The behavior of naturally fractured reservoirs.Soc Pet Eng J, 3: 245–255

[41] Xu H, Tang D Z, Zhao J L, Li S, Tao S (2015). A new laboratory method for accurate measurement of the methane diffusion coefficient and its influencing factors in the coal matrix.Fuel, 158: 239–247

[42] Xu S P, Hu E F, Li X C, Xu Y (2021). Quantitative analysis of pore structure and its impact on methane adsorption capacity of coal.Nat Resour Res, 30(1): 605–620

[43] Yang R, Ma T R, Xu H, Liu W Q, Hu Y, Sang S (2019). A model of fully coupled two-phase flow and coal deformation under dynamic diffusion for coalbed methane extraction.J Nat Gas Sci Eng, 72: 103010

[44] Yao Y B, Liu D M, Tang D Z, Tang S H, Huang W H (2008). Fractal characterization of adsorption-pores of coals from north China: an investigation on CH₄ adsorption capacity of coals.Int J Coal Geol, 73(1): 27–42

[45] Zeng F H, Peng F, Guo J C, Wang D Y, Zhang S R, Zhang P, Zhang B (2019). Gas transport study in the confined microfractures of coal reservoirs.J Nat Gas Sci Eng, 68: 102920

[46] Zhang H L, Wang J, Zhang H Y (2016). Investigation of the main factors during shale-gas production using grey relational analysis.Open Petrol Eng J, 9(1): 207–215

[47] Zhang H (2001). Genetical type of proes in coal reservoir and its research significance.J China Coal Soc, 26: 40–44

[48] Zhang K Z, Cheng Y P, Wang L, Dong J, Hao C M, Jiang J Y (2020). Pore morphology characterization and its effect on methane desorption in water-containing coal: an exploratory study on the mechanism of gas migration in water-injected coal seam.J Nat Gas Sci Eng, 75: 103152

[49] Zhang S H, Tang S H, Tang D Z, Pan Z J, Yang F (2010). The characteristics of coal reservoir pores and coal facies in Liulin District, Hedong Coal Field of China.Int J Coal Geol, 81(2): 117–127

[50] Zhao J L, Xu H, Tang D Z, Mathews J P, Li S, Tao S (2016). A comparative evaluation of coal specific surface area by CO₂ and N₂ adsorption and its influence on CH₄ adsorption capacity at different pore sizes.Fuel, 183: 420–431

[51] Zhao Y X, Liu T, Danesh N N, Sun Y F, Liu S M, Wang Y (2020). Quantification of pore modification in coals due to pulverization using synchrotron small angle X-ray scattering.J Nat Gas Sci Eng, 84: 103669

[52] Zheng S J, Yao Y B, Liu D M, Cai Y D, Liu Y (2018). Characterizations of full-scale pore size distribution, porosity and permeability of coals: a novel methodology by nuclear magnetic resonance and fractal analysis theory.Int J Coal Geol, 196: 148–158

RIGHTS & PERMISSIONS

Higher Education Press