. School of Energy Resource, China University of Geosciences (Beijing), Beijing 100083, China . Coal Reservoir Laboratory of National Engineering Research Center of Coalbed Methane Development and Utilization, Beijing 100083, China . Beijing Key Laboratory of Unconventional Natural Gas Geological Evaluation and Development Engineering, Beijing 100083, China . China Petroleum Exploration and Development Research Institute, Langfang 065000, China
An improved evaluation method for estimating gas content during the inversion process of deep-burial coal was established based on the on-site natural desorption curves. The accuracy of the US Bureau of Mines (USBM), Polynomial fitting, Amoco, and the improved evaluation methods in the predicting of lost gas volume in deep seams in the Mabidong Block of the Qinshui Basin were then compared. Furthermore, the calculation errors of these different methods in simulating lost gas content based on coring time were compared. A newly established nonlinear equation was developed to estimate the minimum error value, by controlling the lost time within 16 min, the related errors can be reduced. The improved evaluation was shown to accurately and rapidly predict the gas content in deep seams. The results show that the deep coal bed methane accumulation is influenced by various factors, including geological structure, hydrodynamic conditions, roof lithology, and coalification. Reverse faults and weak groundwater runoff can hinder the escape of methane, and these factors should be considered in the future exploration and development of coalbed methane.
Online First Date: 23 July 2024Issue Date: 29 September 2024
Cite this article:
Haiqi LI,Shida CHEN,Dazhen TANG, et al. Gas content evaluation in deep coal seam with an improved method and its geological controls[J]. Front. Earth Sci.,
2024, 18(3): 623-636.
Fig.1 Geological background of the Qinshui Basin (modified from (Cai et al., 2014)). (a) Location of the basin. (b) Location of the Mabidong study area. (c) Composite stratigraphic columns in the Mabidong block.
Well Name
Number of samples collected
Number of gas content test samples
Industrial analysis and determination sample number
3#
15#
6
6
7
12
6-3-1, 6-15-1
16X
1
2
3
16X-3-1, 16X-15-1
27
6
4
10
27-3-1, 27-15-1
57
5
4
9
57-3-1, 57-15-1
58
7
4
11
58-3-1, 58-15-1
59
6
2
8
59-3-1, 59-15-1
66
5
5
10
66-3-1, 66-15-1
67
5
4
9
67-3-1, 67-15-1
69
4
3
7
69-3-1, 69-15-1
72
5
3
8
72-3-1, 72-15-1
2
7
3
10
2-3-1, 2-15-1
Tab.1 Sample collection and testing information table
Fig.2 Natural desorption device (AQSIQ , 2008): 1. thermostat power supply, 2. thermostatic device, 3. desorption tank, 4. tank cover, 5. air valve, 6. pressure gauge, 7. quick connector, 8. exhaust pipe, 9. conical bottle, 10. air valve, 11. drain pipe. 12. measuring cylinder, 13. meter bases and stands.
Fig.3 Lost gas estimation at different time zeros.
Calculation standard
Lost gas content/cm3
6-3-1
6-3-2
6-3-3
6-3-4
6-3-5
6-3-6
T1-1
860.68
694.53
720.39
339.57
491.6
1701.47
T1-2
1445.99
1296.25
4336.5
806.41
982.29
3256.28
T2-1
500.62
442.3
421.8
162.43
166.13
410.04
T2-2
831.19
762.06
2203.69
398.07
405.3
1034.87
Tab.2 Estimation of lost gas content under different calculation standards
Fig.4 Calculation of lost gas content by (a) polynomial fitting method, (b) Amoco method.
Fig.5 Gas content evaluation by the improved evaluation.
Fig.6 6-3-1 Sample isothermal adsorption test.
Fig.7 Relationship between desorption rate and the square root of desorption time for coal samples with different buried depths.
Fig.8 Extrapolation calculation of lost gas for simulating different lost time.
Fig.9 Lost gas error of different curve fitting methods.
Fig.10 Comparison of lost gas content calculated using different methods.
Fig.11 Total gas content by different estimation methods.
Fig.12 Correlation between Ro, max and gas content.
Fig.13 Effect of (a) moisture, (b) ash yield, (c) volatile matter, and (d) gross calorific to the gas content.
Fig.14 Relationship of (a) burial depth and (b) coal thickness with gas content.
Fig.15 Groundwater dynamic zoning map in the study area.
Fig.16 The control of lithology and tectonics on gas content in the study area. Relationship between roof and floor lithology and gas content: (a) 3#, (b) 15,. (c) Control of tectonics.
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