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

doi:10.1007/s11707-022-1016-z

Front. Earth Sci.

2023, Vol. 17

Issue (1) : 109-120 https://doi.org/10.1007/s11707-022-1016-z

RESEARCH ARTICLE

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

Hui WANG^1,², Yanbin YAO^1,²(

), Zhentao LI³, Yanhui YANG⁴, Junjie YI⁵, Yongkai QIU^1,², Shengqiang ZHOU^1,²

¹. School of Energy Resource, China University of Geosciences, Beijing 100083, China
². Coal Reservoir Laboratory of National Engineering Research Center of CBM Development & Utilization, China University of Geosciences, Beijing 100083, China
³. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
⁴. PetroChina Huabei Oilfield Company, Renqiu 062552, China
⁵. Institute of Mineral Resources Research, Beijing 101300, China

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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.

Keywords coalbed methane gas diffusion CBM production coal deformation Qinshui Basin

Corresponding Author(s): Yanbin YAO

About author:

^* These authors contributed equally to this work.

Online First Date: 10 April 2023 Issue Date: 03 July 2023

Cite this article:

Hui WANG,Yanbin YAO,Zhentao LI, et al. Multi-stage gas diffusion and its implications for the productivity of coalbed methane in the southern Qinshui Basin, north China[J]. Front. Earth Sci., 2023, 17(1): 109-120.

URL:

https://academic.hep.com.cn/fesci/EN/10.1007/s11707-022-1016-z
https://academic.hep.com.cn/fesci/EN/Y2023/V17/I1/109

Fig.1 (a) Location of the SQB in Qinshui Basin and (b) Geological structures and exploration wells locations, and the background shows a burial depth of the No. 3 coal seam in the SQB.

Fig.2 Stratigraphic column in the SQB.

Tab.1 The primary properties of No. 3 coal seam in the SQB (well locations can be found in Fig.1)

Well	β₁	D₁/(h⁻¹)	V₁/(m³·t^–1)	β₂	D₂/(h⁻¹)	V₂/(m³·t^–1)	β₃	D₃/(h⁻¹)	V₃/(m³·t^–1)
ZS-1	0.57	1.06 × 10⁻²	10.4	0.31	1.52 × 10⁻³	5.7	0.12	4.70 × 10⁻⁴	2.2
ZS-2	0.57	1.45 × 10⁻²	12.8	0.33	1.73 × 10⁻³	7.4	0.10	5.35 × 10⁻⁴	2.2
ZS-3	0.35	1.32 × 10⁻²	6.8	0.37	1.83 × 10⁻³	7.2	0.28	8.50 × 10⁻⁴	5.4
ZS-4	0.39	8.85 × 10⁻³	9.4	0.35	1.45 × 10⁻³	8.5	0.27	7.33 × 10⁻⁴	6.5
ZS-5	0.33	7.96 × 10⁻³	6.9	0.38	1.85 × 10⁻³	7.9	0.29	7.20 × 10⁻⁴	6.0
ZS-6	0.36	5.68 × 10⁻³	7.5	0.38	1.46 × 10⁻³	7.9	0.26	4.35 × 10⁻⁴	5.4
ZS-7	0.37	5.85 × 10⁻³	7.8	0.35	1.62 × 10⁻³	7.4	0.28	6.28 × 10⁻⁴	5.9
ZS-8	0.41	9.30 × 10⁻³	8.2	0.42	1.30 × 10⁻³	8.4	0.17	5.50 × 10⁻⁴	3.4
ZS-9	0.38	4.15 × 10⁻³	3.1	0.34	1.85 × 10⁻³	2.8	0.28	6.60 × 10⁻⁴	2.3
ZS-10	0.32	4.83 × 10⁻³	5.5	0.42	2.05 × 10⁻³	7.3	0.26	7.10 × 10⁻⁴	4.5
ZS-11	0.56	1.58 × 10⁻²	11.4	0.33	6.91 × 10⁻⁴	6.7	0.11	2.10 × 10⁻⁴	2.2
ZS-12	0.44	4.03 × 10⁻³	10.7	0.31	2.40 × 10⁻³	7.5	0.25	6.10 × 10⁻⁴	6.1
ZS-13	0.42	5.76 × 10⁻³	10.5	0.38	1.98 × 10⁻³	9.5	0.20	6.58 × 10⁻⁴	5.0
ZS-14	0.33	4.53 × 10⁻³	6.3	0.39	2.15 × 10⁻³	7.4	0.28	7.08 × 10⁻⁴	5.3
ZS-15	0.47	5.53 × 10⁻³	11.2	0.29	1.82 × 10⁻³	6.9	0.24	5.73 × 10⁻⁴	5.7
ZS-16	0.35	3.46 × 10⁻³	6.6	0.38	1.85 × 10⁻³	7.2	0.27	4.22 × 10⁻⁴	5.1
ZS-17	0.38	1.95 × 10⁻³	10.3	0.39	1.60 × 10⁻³	10.6	0.23	5.10 × 10⁻⁴	6.2
ZS-18	0.46	8.21 × 10⁻³	12.8	0.37	2.30 × 10⁻³	10.3	0.17	4.40 × 10⁻⁴	4.7
ZS-19	0.33	6.50 × 10⁻³	7.0	0.37	2.00 × 10⁻³	7.9	0.30	8.20 × 10⁻⁴	6.4
MS-2	0.72	5.72 × 10⁻³	10.2	0.15	4.59 × 10⁻⁴	2.1	0.13	2.20 × 10⁻⁴	1.8
MS-3	0.56	3.35 × 10⁻³	11.5	0.27	6.20 × 10⁻⁴	5.5	0.17	3.70 × 10⁻⁴	3.5
AS-1	0.66	5.48 × 10⁻³	5.9	0.20	4.23 × 10⁻⁴	1.8	0.14	1.35 × 10⁻⁴	1.3
AS-2	0.60	3.88 × 10⁻³	5.9	0.24	1.80 × 10⁻³	2.4	0.16	6.00 × 10⁻⁴	1.6
AS-3	0.41	1.28 × 10⁻³	9.4	0.31	2.05 × 10⁻³	7.1	0.28	7.80 × 10⁻⁴	6.4
AS-4	0.71	5.30 × 10⁻³	8.5	0.19	5.13 × 10⁻⁴	2.3	0.10	2.00 × 10⁻⁴	1.2
AS-5	0.48	1.05 × 10⁻³	7.2	0.34	7.07 × 10⁻⁴	5.1	0.18	5.10 × 10⁻⁴	2.7
AS-6	0.73	5.01 × 10⁻³	7.3	0.18	6.63 × 10⁻⁴	1.8	0.09	1.60 × 10⁻⁴	0.9
AS-7	0.70	5.56 × 10⁻³	6.9	0.19	6.23 × 10⁻⁴	1.9	0.11	1.70 × 10⁻⁴	1.1
AS-8	0.57	2.21 × 10⁻³	10.5	0.25	1.35 × 10⁻³	4.6	0.18	5.18 × 10⁻⁴	3.3
AS-9	0.68	5.19 × 10⁻³	0.6	0.18	6.50 × 10⁻⁴	0.2	0.14	1.40 × 10⁻⁴	0.1
AS-10	0.72	5.38 × 10⁻³	6.8	0.15	6.15 × 10⁻⁴	1.4	0.13	1.36 × 10⁻⁴	1.2

Tab.2 CBM diffusion parameters of 31 coal cores from No. 3 coal seam of the SQB based on the multi-porous diffusion model

Fig.3 Fitting results of the on-site CBM desorption data of representative wells in the SQB. The behavior of CBM diffusion can be well represented by the multi-porous diffusion model (Eqs. (1) to (4)) and demonstrates obvious three-stage characteristics.

Fig.4 The regional distribution of WCSI (avg.) of the No. 3 coal seam in the SQB with some wells added the proportion of fast, transitional and slow diffusion stages. The background of this figure is referenced from the previous studies by Wang et al. (2022), in which the deformation degree of the coal seams can be divided into low (WCSI (avg.) < 40), moderate (40 < WCSI (avg.) < 60) and high (WCSI (avg.) > 60) by a parameter of WCSI (avg.).

Fig.5 Contour map of the fast diffusion coefficient (a), the transitional diffusion coefficient (b) and the slow diffusion coefficient (c) of No. 3 coal seam in the SQB.

Fig.6 The relationship between the proportion of fast diffusion stage and gas content (a), fast diffusion coefficient and gas content (b), the proportion of transitional diffusion stage and gas content (c), transitional diffusion coefficient and gas content (d), the proportion of slow diffusion stage and gas content (e) and slow diffusion coefficient and gas content (f), L,M and H respent low to high defor mation degree coal seams, respectively.

Fig.7 The CBM production trend of five representative wells in the SQB. The location of these wells can be seen in Fig. 1.

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