Multi-stage gas diffusion and its implications for the productivity of coalbed methane in the southern Qinshui Basin, north China

Abstract

The behavior of coalbed methane (CBM) diffusion considerably influences gas productivity. Based on the multi-porous diffusion model and on-site CBM desorption data of coal cores, the behavior of CBM diffusion and its implications on the gas productivity of No. 3 coal seam in the southern Qinshui Basin (SQB) were elaborately analyzed. Results indicate that CBM diffusion of No. 3 coal seam demonstrates noticeable three-stage characteristics, including the fast diffusion, transitional diffusion, and slow diffusion stages. During the gas diffusion process, the gas content and/or the degree of developed pores and fractures/cleats in coal seams can affect the desorption of CBM and the amount of diffused CBM by influencing the changes in gas pressure in pores, thus controlling the behavior of gas diffusion in different stages. Because gas content and the developed degree of pores and fractures/cleats are closely associated with the deformation degree of the coal seams, variably deformed coal seams exhibit unique characteristics of gas diffusion. The low-deformation degree of the coal seams have a relatively uniform distribution of gas production over the history of a well. By contrast, the moderate-deformation degree of the coal seams have a relatively high rate and amount of gas diffusion in the fast and transitional diffusion stages, producing most of the gas in the early-to-intermediate stages of the wells. Finally, the high-deformation degree of the coal seams has a high rate and amount in the fast diffusion stage, indicating that most of the production stage occurs during the early stage of the gas production history of a well. In summary, the behavior of gas diffusion can be used for predicting gas production potential.

Graphical abstract

Keywords

coalbed methane / gas diffusion / CBM production / coal deformation / Qinshui Basin

References

[1] Cai Y D, Liu D M, Yao Y B, Li J Q, Qiu Y K (2011). Geological controls on prediction of coalbed methane of No. 3 coal seam in southern Qinshui Basin, north China.Int J Coal Geol, 88(2–3): 101–112

[2] 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

[3] Cheng Y P, Pan Z J (2020). Reservoir properties of Chinese tectonic coal: a review.Fuel, 260: 116350

[4] 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

[5] Clarkson C R, Salmachi A (2017). Rate-transient analysis of an undersaturated CBM reservoir in Australia: accounting for effective permeability changes above and below desorption pressure.J Nat Gas Sci Eng, 40: 51–60

[6] Dong J, Cheng Y P, Pan Z J (2020). Comparison of transient and pseudo-steady diffusion of methane in coal and implications for coalbed methane control.J Petrol Sci Eng, 184: 106543

[7] Jia Q F, Liu D M, Cai Y D, Fang X L, Li L G (2021). Petrophysics characteristics of coalbed methane reservoir: a comprehensive review.Front Earth Sci, 15(2): 202–223

[8] Karacan C Ö, Ruiz F A, Cotè M, Phipps S (2011). Coal mine methane: a review of capture and utilization practices with benefits to mining safety and to greenhouse gas reduction.Int J Coal Geol, 86(2–3): 121–156

[9] Keshavarz A, Sakurovs R, Grigore M, Sayyafzadeh M (2017). Effect of maceral composition and coal rank on gas diffusion in Australian coals.Int J Coal Geol, 173: 65–75

[10] Li J Q, Lu S F, Zhang P F, Cai J C, Li W B, Wang S Y, Feng W J (2020). Estimation of gas-in-place content in coal and shale reservoirs: a process analysis method and its preliminary application.Fuel, 259: 116266

[11] 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

[12] Li Z T, Liu D M, Wang Y J, Si G Y, Cai Y D, Wang Y P (2021). Evaluation of multistage characteristics for coalbed methane desorption-diffusion and their geological controls: a case study of the northern Gujiao Block of Qinshui Basin, China.J Petrol Sci Eng, 204: 108704

[13] Liu D M, Yao Y B, Wang H (2022a). Structural compartmentalization and its relationships with gas accumulation and gas production in the Zhengzhuang Field, southern Qinshui Basin.Int J Coal Geol, 259: 104055

[14] Liu D M, Qiu F, Liu N, Cai Y D, Guo Y L, Zhao B, Qiu Y K (2022b). Pore structure characterization and its significance for gas adsorption in coals: a comprehensive review.Unconv Resour, 2: 139–157

[15] Liu D M, Yao Y B, Chang Y H (2022c). Measurement of adsorption phase densities with respect to different pressure: potential application for determination of free and adsorbed methane in coalbed methane reservoir.Chem Eng J, 446: 137103

[16] Liu T, Lin B Q, Fu X H, Gao Y B, Kong J, Zhao Y, Song H R (2020). Experimental study on gas diffusion dynamics in fractured coal: a better understanding of gas migration in in-situ coal seam.Energy, 195: 117005

[17] Lu S Q, Cheng Y P, Li W, Wang L (2015). Pore structure and its impact on CH₄ adsorption capability and diffusion characteristics of normal and deformed coals from Qinshui Basin.Int J Oil Gas Coal Technol, 10(1): 94–114

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

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

[20] Pan J N, Zhu H T, Hou Q L, Wang H C, Wang S (2015). Macromolecular and pore structures of Chinese tectonically deformed coal studied by atomic force microscopy.Fuel, 139: 94–101

[21] 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

[22] Staib G, Sakurovs R, Gray E M A (2015). Dispersive diffusion of gases in coals. Part I: model development.Fuel, 143: 612–619

[23] Tang X, Li Z Q, Ripepi N, Louk A K, Wang Z F, Song D Y (2015). Temperature-dependent diffusion process of methane through dry crushed coal.J Nat Gas Sci Eng, 22: 609–617

[24] Wang H, Yao Y B, Liu D M, Pan Z J, Yang Y H, Cai Y D (2016). Fault-sealing capability and its impact on coalbed methane distribution in the Zhengzhuang field, southern Qinshui Basin, north China.J Nat Gas Sci Eng, 28: 613–625

[25] Wang H, Yao Y B, Liu D M, Cai Y D, Zhou S Q (2022). Determination of the degree of coal deformation and its effects on gas production in the southern Qinshui Basin, north China.J Petrol Sci Eng, 216: 1107464

[26] 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

[27] 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

[28] Zhang J Y, Liu D M, Cai Y D, Yao Y B, Ge X (2018). Carbon isotopic characteristics of CH₄ and its significance to the gas performance of coal reservoirs in the Zhengzhuang area, Southern Qinshui Basin, north China.J Nat Gas Sci Eng, 58: 135–151

[29] Zhao J L, Tang D Z, Qin Y, Xu H, Liu Y L, Wu H Y (2018). Characteristics of methane (CH₄) diffusion in coal and its influencing factors in the Qinshui and Ordos Basins.Energy Fuel, 32: 1196–1205 

[30] Ziarani A S, Aguilera R, Clarkson C R (2011). Investigating the effect of sorption time on coalbed methane recovery through numerical simulation.Fuel, 90(7): 2428–2444

Acknowledgment

We acknowledge financial support from the National Natural Science Foundation of China (Grant Nos. 42125205, 41830427, and 42102227).

RIGHTS & PERMISSIONS

2023 Higher Education Press