1. Department of Unconventionals, Research Institute of Petroleum Exploration and Development, PetroChina, Langfang 065007, China 2. Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process (Ministry of Education), China University of Mining and Technology, Xuzhou 221008, China 3. School of Resource and Geosciences, China University of Mining and Technology, Xuzhou 221116, China
Flowability of gas and water through low-permeability coal plays crucial roles in coalbed methane (CBM) recovery from coal reservoirs. To better understand this phenomenon, experiments examining the displacement of water by gas under different displacement pressures were systematically carried out based on nuclear magnetic resonance (NMR) technology using low-permeability coal samples of medium-high coal rank from Yunnan and Guizhou, China. The results reveal that both the residual water content (Wr) and residual water saturation (Sr) of coal gradually decrease as the displacement pressure (P) decreases. When P is 0–2 MPa, the decline rates of Wr and Sr are fastest, beyond which they slow down gradually. Coal samples with higher permeability exhibit higher water flowability and larger decreases in Wr and Sr. Compared with medium-rank coal, high-rank coal shows weaker fluidity and a higher proportion of irreducible water. The relationship between P and the cumulative displaced water content (Wc) can be described by a Langmuir-like equation, Wc = WLP/(PL + P), showing an increase in Wc in coal with an increase in P. In the low-pressure stage from 0 to 2 MPa, Wc increases most rapidly, while in the high-pressure stage (P>2 MPa), Wc tends to be stable. The minimum pore diameter (d') at which water can be displaced under different displacement pressures was also calibrated. The d' value decreases as P increases in a power relationship; i.e., d' the coal gradually decreases with the gradual increase in P. Furthermore, the d' values of most of the coal samples are close to 20 nm under a P of 10 MPa.
. [J]. Frontiers of Earth Science, 2020, 14(4): 673-683.
Minfang YANG, Zhaobiao YANG, Bin SUN, Zhengguang ZHANG, Honglin LIU, Junlong ZHAO. A study on the flowability of gas displacing water in low-permeability coal reservoir based on NMR technology. Front. Earth Sci., 2020, 14(4): 673-683.
Remaining water in different displacement pressure/g
0.5 MPa
1 MPa
2 MPa
4 MPa
6 MPa
8 MPa
10 MPa
YL1
5.077
2.517
3.27
0.023
0.447
0.433
0.358
0.341
0.331
0.329
0.324
0.320
YCK
5.150
2.514
4.96
0.402
0.736
0.328
0.287
0.225
0.246
0.234
0.241
0.249
YL2
5.064
2.528
6.15
0.081
0.686
0.486
0.424
0.312
0.263
0.252
0.219
0.198
DHS
5.012
2.527
5.57
0.011
1.196
1.014
0.968
0.933
0.933
0.924
0.896
0.842
LJ
5.014
2.482
5.43
0.045
0.986
0.826
0.81
0.77
0.769
0.753
0.715
0.714
Tab.2
Sample No.
Ro,max/%
Left Peak value/ms
Average Pore diameter value/nm
Transfer formula
ρ2
YL1
0.86
0.244
30
d = 122.95T2
20.49
YCK
0.93
0.198
19
d = 95.96T2
15.99
YL2
0.98
0.198
34
d = 171.72T2
28.62
DHS
2.14
0.425
16
d = 37.65T2
6.27
LJ
2.38
1.047
14
d = 13.37T2
2.23
Tab.3
Fig.2
Fig.3
Fig.4
Fig.5
Fig.6
Fig.7
Coal number
fHe/%
K/mD
WL/g
PL/MPa
Equation
YL1
3.27
0.023
0.15
1.64
Wc = 0.15P/(P+ 1.64)
YCK
4.96
0.402
0.49
0.02
Wc = 0.49P/(P+ 0.02)
YL2
6.15
0.081
0.51
0.69
Wc = 0.51P/(P+ 0.69)
DHS
5.57
0.011
0.34
0.61
Wc = 0.34P/(P+ 0.61)
LJ
5.43
0.045
0.28
0.55
Wc = 0.28P/(P+ 0.55)
Tab.4
Fig.8
Fig.9
Sample No.
d' in different Displacement pressure/nm
Fitting formula
0.5 MPa
1 MPa
2 MPa
4 MPa
6 MPa
8 MPa
10 MPa
YL1
8296
1680
1300
1300
1680
1200
1100
d' = 2971P-0.48(R2 = 0.60)
YCK
327
76
31
25
23
20
20
d' = 100.9P-0.84(R2 = 0.85)
YL2
4000
1900
773
413
254
84
83
d' = 1868P-1.29(R2 = 0.97)
DHS
_
3854
1180
389
48
41
35
d' = 4672P-2.21(R2 = 0.96)
LJ
42.52
32
29
27
25
25
25
d' = 34.46P-0.16(R2 = 0.90)
Tab.5
1
O Aguirre, J Glorioso, J Morales, J Mengual (2007). Porosity with nuclear magnetic resonance in naturally fractured clastics reservoirs in the Devonian of the Bolivian Sub-Andean
2
M Ahmed, B Y Gomaa Zhang, Q Qu, N Scott, J H Chen (2014). Using NMR technology to study the flow of fracture fluids inside shale formations
3
J Arnold, C Clauser, R Pechnig, S Anferova, V Anferov, B Blümich (2006). Porosity and permeability from mobile NMR core-scanning. Petrophysics, 47: 306–314
4
G C Borgia, V Bortolotti, P Fantazzini (1999). Magnetic resonance relaxation-tomography to assess fractures induced in vugular carbonate cores. In: SPE Annual Technical Conference and Exhibition
5
G R Coates, L Xiao, M G Primmer (2000). NMR Logging Principles and Applications. Houston: Gulf Publishing Company
6
G Fu, Y Zhang, D Zou (1997). The measurement and analysis of the balanced contact angle between coal and pure water. Coal Convers, 20(4): 60–62 (in Chinese)
7
A Jatukaran, J Zhong, A Abedini, A Sherbatian, Y Zhao, Z Jin, F Mostowfi, D Sinton (2019). Natural gas vaporization in a nanoscale throat connected model of shale: multi-scale, multi-component and multi-phase. Lab Chip, 19(2): 272–280 https://doi.org/10.1039/C8LC01053F
pmid: 30565619
8
R L Kleinberg (1996). Utility of NMR T2 distributions, connection with capillary pressure, clay effect, and determination of the surface relaxivity parameter ρ2. Magn Reson Imaging, 14(7–8): 761–767 https://doi.org/10.1016/S0730-725X(96)00161-0
pmid: PMID:8970079
9
J R Levine (1996) Model study of the influence of matrix shrinkage on absolute permeability of coal bed reservoirs. In: Gayer R, Harris I, eds., Coalbed Methane and Coal Geology: Geological Society Special Publication, 109: 197–212
10
Y Li, C Zhang, D Tang, Q Gan, X Niu, K Wang, R Shen (2017). Coal pore size distributions controlled by the coalification process: an experimental study of coals from the Junggar, Ordos, and Qinshui Basins in China. Fuel, 206: 352–363 https://doi.org/10.1016/j.fuel.2017.06.028
11
Y Li, Z Wang, Z Pan, X Niu, Y Yu, S Meng (2019). Pore structure and its fractal dimensions of transitional shale: a cross section from east margin of the Ordos Basin, China. Fuel, 241: 417–431 https://doi.org/10.1016/j.fuel.2018.12.066
12
Y Li, Y Wang, J Wang, Z Pan (2020a). Variation in permeability during CO2–CH4 displacement in coal seams: part 1 – experimental insights. Fuel, 263: 116666 https://doi.org/10.1016/j.fuel.2019.116666
13
Y Li, J Yang, Z Pan, W Tong (2020b). Nanoscale pore structure and mechanical property analysis of coal: an insight combining AFM and SEM images. Fuel, 260: 116352 https://doi.org/10.1016/j.fuel.2019.116352
14
Y Qin, T A Moore, J Shen, Z Yang, Y Shen, G Wang (2018). Resources and geology of coalbed methane in China: a review. Int Geol Rev, 60(5–6): 777–812 https://doi.org/10.1080/00206814.2017.1408034
15
J Mitchell, L F Gladden, T C Chandrasekera, E J Fordham (2014). Low-field permanent magnets for industrial process and quality control. Prog Nucl Magn Reson Spectrosc, 76: 1–60 https://doi.org/10.1016/j.pnmrs.2013.09.001
pmid: 24360243
J Shen, J Zhao, Y Qin, Y Shen, G Wang (2018). Water imbibition and drainage of high rank coals in Qinshui Basin, China. Fuel, 211: 48–59 https://doi.org/10.1016/j.fuel.2017.09.039
18
Strategy Research Center of Oil and Gas Resources Department of the Ministry of Land and Resources (2006). Assessment of Coalbed. Beijing: China Land Press (in Chinese)
19
Y Q Song, S Ryu, P N Sen (2000). Determining multiple length scales in rocks. Nature, 406(6792): 178–181
20
X Sun, Y Yao, D Liu, Y Zhou (2018). Investigations of CO2-water wettability of coal: NMR relaxation method. Int J Coal Geol, 188: 38–50 https://doi.org/10.1016/j.coal.2018.01.015
S Tao, S Chen, Z Pan (2019a). Current status, challenges, and policy suggestions for coalbed methane industry development in China: a review. Energy Sci Eng, 7(4): 1059–1075 https://doi.org/10.1002/ese3.358
23
S Tao, S Chen, D Tang, X Zhao, H Xu, S Li (2018). Material composition, pore structure and adsorption capacity of low-rank coals around the first coalification jump: a case of eastern Junggar Basin, China. Fuel, 211: 804–815 https://doi.org/10.1016/j.fuel.2017.09.087
24
S Tao, Z Pan, S Chen, S Tang (2019b). Coal seam porosity and fracture heterogeneity of marcolithotypes in the Fanzhuang Block, southern Qinshui Basin, China. J Nat Gas Sci Eng, 66: 148–158 https://doi.org/10.1016/j.jngse.2019.03.030
25
S Tao, Z Pan, S Tang, S Chen (2019c). Current status and geological conditions for the applicability of CBM drilling technologies in China: a review. Int J Coal Geol, 202: 95–108 https://doi.org/10.1016/j.coal.2018.11.020
26
Y Wu, P Tahmasebi, C Lin, M Zahid, C Dong, A Golab, L Ren (2019). A comprehensive study on geometric, topological and fractal characterizations of pore systems in low-permeability reservoirs based on SEM, MICP, NMR, and X-ray CT experiments. Mar Pet Geol, 103: 12–28 https://doi.org/10.1016/j.marpetgeo.2019.02.003
27
J Yang, L Ma, H Liu, Y Wei, B Keomounlath, Q Dai (2019). Thermodynamics and kinetics analysis of Ca-looping for CO2 capture: application of carbide slag. Fuel, 242: 1–11 https://doi.org/10.1016/j.fuel.2019.01.018
28
Z Yang, Y Li, Y Qin, H Sun, P Zhang, Z Zhang, C Wu, C Li, C Chen (2019a). Development unit division and favorable area evaluation for joint mining coalbed methane. Pet Explor Dev, 46(3): 583–593 https://doi.org/10.1016/S1876-3804(19)60038-8
29
Z Yang, Y Qin, C Wu, Z Qin, G Li, C Li (2019b). Geochemical response of produced water in the CBM well group with multiple coal seams and its geological significance—a case study of Songhe well group in western Guizhou. Int J Coal Geol, 207: 39–51 https://doi.org/10.1016/j.coal.2019.03.017
30
Z Yang, Y Qin, T Yi, J Tang, Z Zhang, C Wu (2019c). Analysis of multi-coalbed CBM development methods in western Guizhou, China. Geosci J, 23(2): 315–325 https://doi.org/10.1007/s12303-018-0037-9
31
Z Yang, Y Qin, Z Qin, T Yi, C Li, Z Zhang (2020). Characteristics of dissolved inorganic carbon in produced water from coalbed methane wells and its geological significance. Pet Explor Dev, 47(5): 1–9
32
Z Yang, Z Zhang, Y Qin, C Wu, T Yi, Y Li, J Tang, J Chen (2018). Optimization methods of production layer combination for coalbed methane development in multi-coal seams. Pet Explor Dev, 45(2): 312–320 https://doi.org/10.1016/S1876-3804(18)30034-X
33
Y Yao, D Liu (2012). Comparison of low-field NMR and mercury intrusion porosimetry in characterizing pore size distributions of coals. Fuel, 95(5): 152–158 https://doi.org/10.1016/j.fuel.2011.12.039
34
Y Yao, D Liu, Y Che, D Tang, S Tang, W Huang (2010). Petrophysical characterization of coals by low-field nuclear magnetic resonance (NMR). Fuel, 89(7): 1371–1380 https://doi.org/10.1016/j.fuel.2009.11.005
35
Y Yao, D Liu, S Xie (2014). Quantitative characterization of methane adsorption on coal using a low-field NMR relaxation method. Int J Coal Geol, 131: 32–40 https://doi.org/10.1016/j.coal.2014.06.001
36
Z Zhang, Y Qin, T Yi, Z You, Z Yang (2020). Pore structure characteristics of coal and their geological controlling factors in eastern Yunnan and western Guizhou, China. ACS Omega, 5(31): 19565–19578 https://doi.org/10.1021/acsomega.0c02041
pmid: 32803051
37
Z Zhang, Y Qin, Z Yang, J Jin, C Wu (2019). Fluid energy characteristics and development potential of coalbed methane reservoirs with different synclines in Guizhou, China. J Nat Gas Sci Eng, 71: 102981 https://doi.org/10.1016/j.jngse.2019.102981
38
S Zheng, Y Yao, D Liu, Y Cai, Y Liu (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 https://doi.org/10.1016/j.coal.2018.07.008
39
J Zhong, A Abedini, L Xu, Y Xu, Z Qi, F Mostowfi, D Sinton (2018). Nanomodel visualization of fluid injections in tight formations. Nanoscale, 10(46): 21994–22002 https://doi.org/10.1039/C8NR06937A
pmid: 30452051
40
H Zhu, X Xu, L An, C Guo, J Xiao (2016). An experimental on occurrence and mobility of pore water in tight gas reservoirs. Acta Petrol Sin, 37(2): 230–236
