1. School of Energy Resources, 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
Petrophysics of coals directly affects the development of coalbed methane (CBM). Based on the analysis of the representative academic works at home and abroad, the recent progress on petrophysics characteristics was reviewed from the aspects of the scale-span pore-fracture structure, permeability, reservoir heterogeneity, and its controlling factors. The results showed that the characterization of pore-fracture has gone through three stages: qualitative and semiquantitative evaluation of pore-fracture by various techniques, quantitatively refined characterization of pore-fracture by integrating multiple methods including nuclear magnetic resonance analysis, liquid nitrogen, and mercury intrusion, and advanced quantitative characterization methods of pore-fracture by high-precision experimental instruments (focused-ion beam-scanning electron microscopy, small-angle neutron scattering and computed tomography scanner) and testing methods (m-CT scanning and X-ray diffraction). The effects of acoustic field can promote the diffusion of CBM and generally increase the permeability of coal reservoirs by more than 10%. For the controlling factors of reservoir petrophysics, tectonic stress is the most crucial factor in determining permeability, while the heterogeneity of CBM reservoirs increases with the enhancement of the tectonic deformation and stress field. The study on lithology heterogeneity of deep and high-dip coal measures, the spatial storage-seepage characteristics with deep CBM reservoirs, and the optimizing production between coal measures should be the leading research directions.
The permeability of different partition blocks varies greatly, and some horizontal drainage wells exist
Tunlun
No. 3
P1 (Shanxi Formation)
2.0–3.0
400–900
0.02–0.10
>1100 (Tun well 2)
The permeability is generally low
Enhon
No. 9, 16, and 23
P2 (Xuanwei Formation)
1.2–1.5
500–1500
0.04–6.10
500 (Well EH-5)
High porosity and permeability
Jixian–Hancheng
No. 5 and 8
C—P (Shanxi Formation, Taiyuan Formation)
1.1–2.1
350–1500
0.01–43
852 (Jishi well 3); >2500 (Jishi well 1)
The permeability of the two layers of coal is very different, and some CBM wells allow the two layers of coal to be discharged together
Zaoyuan
No. 3
P1 (Shanxi Formation)
0.5–0.8
550–750
0.5–1.8
706 (Well FZ-007)
The fracture has strong conductivity, and the permeability is very high
Baode
No. 8 and 9
C—P (Shanxi Formation, Taiyuan Formation)
0.8–1.4
400–800
0.01–3.73
1482 (Well 3V)
The coal reservoir has a high water content, and the permeability difference is enormous.
Binchang
No. 4
J2 (Yanan Formation)
0.5–0.7
400–650
3.06–5.73
12964 (Well DFSC-02)
High permeability and porosity
Tiefa
No. 4–2, 9, 12, and 15–2
J3—K1 (Fuxin Formation)
0.5–0.6
300–950
0.10–1.60
5750 (Well DT3)
High gas content and permeability
Tab.1
Fig.14
Fig.15
Fig.16
Coalfield (Basin)
Mercury injection test data
Pore size distribution
Porosity /%
Displacement pressure/MPa
The average diameter of pore throat /mm
Incoming mercury saturation/%
The efficiency of mercury withdrawal /%
Macropores /%
Mesopores /%
Small pores /%
Micropores /%
Northern Qinshui
3.50
7.01
0.06
23.1
65.6
6.5
6
67.0
20.5
Central Qinshui
3.78
6.83
0.05
19.4
61.0
7.4
6.1
69.3
17.2
Southern Qinshui
4.23
7.67
0.12
24.6
65.6
8
7.9
26.4
57.7
Datong
4.24
11.37
0.04
22.0
82.7
4.3
2.6
32.4
60.7
Pingdingshan
6.75
7.93
0.08
43.4
73.0
9.1
10.3
54.7
25.9
Anhe
8.38
3.71
0.18
27.5
43.7
11.4
12.2
71.4
5
Jiaozuo
10.30
3.98
1.26
36.9
39.5
20.7
11
37.7
30.6
Yongxia
2.80
7.08
0.04
17.3
65.7
6
5.7
49.1
39.2
Xinggong
10.38
3.92
0.23
31.8
55.8
13.8
11.1
59.8
15.3
Huainan
4.61
0.07
12.27
37.1
33.1
18.8
6.5
57.9
16.8
Huaibei
3.94
0.15
11.14
55.2
37.8
27.6
15.4
37.7
19.3
Tab.2
Fig.17
Grinding rod time/min
Macerals
Density level/(g·cm−3)
<1.35
1.35–1.40
>1.40
5
Vitrinite
73.26%
34.57%
49.77%
Inertinite
26.74%
65.43%
50.23%
10
Vitrinite
75.83%
31.84%
44.62%
Inertinite
24.17%
68.16%
55.38%
15
Vitrinite
74.49%
32.80%
45.11%
Inertinite
29.51%
67.20%
54.89%
20
Vitrinite
70.78%
34.70%
45.99%
inertinite
34.22%
65.30%
54.01%
30
Vitrinite
66.53%
39.77%
46.45%
Inertinite
33.47%
60.23%
53.55%
Tab.3
Fig.18
Fig.19
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