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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
DOI: 10.1306/06272321195
The analysis of the micro-occurrence state of irreducible
water
in anthracite fracture network based on digital core
water
in anthracite fracture network based on digital coreLei Han,1 Jian Shen,2 Jing Qu,3 Changjiang Ji,4 and Huijie Cheng5
1Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou, China; School of Resources and Geosciences, China University of Mining and Technology, Xuzhou, China; State Key Laboratory of Coal and CBM Co-Mining, Jincheng, Jincheng, China; [email protected]
2Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou, China; School of Resources and Geosciences, China University of Mining and Technology, Xuzhou, China; [email protected]
3Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou, China; School of Resources and Geosciences, China University of Mining and Technology, Xuzhou, China; [email protected]
4State Key Laboratory of Coal and CBM Co-Mining, Jincheng, Jincheng, China; [email protected]
5Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou, China; School of Resources and Geosciences, China University of Mining and Technology, Xuzhou, China; [email protected]
Abstract
The micro-occurrence state and the mobility of irreducible
water
in coal is important in achieving high coalbed methane (CBM) production. Displacement system and computed tomography experiments were conducted using high-rank coals collected from the Qinshui Basin of China. The registered wet and dry computed tomography images were subtracted to provide differential images, within which the contrast between the different features is high. The results show that the volume distribution of irreducible
water
in coal fractures follows the power law. With the displacement pressure increasing from 0 to 1 MPa, the irreducible
water
saturation in semibright coal changed from 93.10% to 20.08% and that in semidull coal changed from 73.62% to 9.35%. Based on the
water
volume and shape factor, the single irreducible
water
cluster (pore-scale droplets) was classified into four shapes: network shape, patchy shape, corner shape, and isolated shape. The network-shaped irreducible
water
cluster has a large volume, has a complex structure, and occupies several fractures. The patchy-shaped irreducible
water
is distributed mainly in the narrow-apertured or dead-end fractures. The corner-shaped irreducible
water
is small, and the structure of corner-shaped irreducible
water
is simpler. The isolated-shaped irreducible
water
is made up of small and fragmented droplets that can not block the fractures even stacking together. In the present study, the network-shaped irreducible
water
volume proportion in both samples changes from 94.27% to 71.17% for semibright coal and from 87.93% to 49.78% for semidull coal. Therefore, the network-shaped irreducible
water
plays a dominant role at different displacement pressures. Larger irreducible
water
is easily transformed into smaller irreducible
water
with increased displacement pressure. The corner- and isolated-shaped irreducible waters are higher in number than the network- and patchy-shaped irreducible waters. Compared to semidull coal, the better fracture connectivity in semibright coal causes a larger reduction of the network-shaped irreducible
water
volume with increased displacement pressure. Although we tested only two samples, the test shows that the mobilization of irreducible
water
for different shape types also varies with different lithotypes. The significant reduction of network-shaped irreducible
water
improves the CBM relative permeability in coal. This study develops the understanding of the irreducible
water
micro-occurrence state, which can be studied further and include capillary pressure distribution, irreducible
water
mobilization, and CBM production promotion.
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