Fractal theory-based permeability model of fracture networks in coals

被引：0
|
作者：
Xia B. [1 ,2 ]
Liao C. [1 ,2 ]
Luo Y. [1 ,2 ]
Ji K. [1 ,2 ]
机构：
[1] State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing
[2] National & Local Joint Engineering Laboratory of Gas Drainage in Complex Coal Seam, Chongqing University, Chongqing
来源：
Meitiandizhi Yu Kantan/Coal Geology and Exploration | 2023年 / 51卷 / 08期
关键词：
coalbed methane; fractal dimension; permeability; tortuosity; true triaxial stress;
D O I：
10.12363/issn.1001-1986.23.01.0006
中图分类号：
学科分类号：
摘要：
Fractures in coal reservoirs, which act as the major seepage pathways for coalbed methane (CBM), determine the permeability and CBM productivity of coal reservoirs. Research on the relationships between fracture structures and reservoir permeability is of great theoretical and practical significance for the accurate prediction of CBM productivity. Based on the classical cubic law-based permeability model, as well as the fractal theory, fracture network structures, and effective stress, this study built a permeability model containing complex bending fractures, which was then combined with the S & D (Shi-Durucan) model to build the permeability model of fractured coals under the action of true triaxial stresses. Then, gas seepage experiments under true triaxial stresses were conducted, followed by the comparison of the results of the final permeability model with the experimental results and the fitting data of the S & D model. As shown by the comparison results, the results of the permeability model agreed well with the experimental results and thus can reflect the trend of the influence of stress on permeability under the loading of triaxial stresses. The comparison results alsoindicatethatthepermeabilitymodelbuiltinthisstudycanreflecttheanisotropyofcoalpermeabilitymoreeffectivelythanthe S & D model. Using this permeability model, this study quantitatively analyzed the effects of fracture structures of coals on coal permeability. The results indicate that the coal permeability exhibited positive power-law relationships with porosity ϕ(0.05-0.41), fractal dimension Df (2.37-2.81), maximum fracture length lmax (3.5-8.0 cm), and proportionality coefficient β (0.010-0.065) and negative power-law relationships with tortuosity fractal dimension DTf (2.005-2.275) and fracture dip angle θ (10°-80°). The results of this study will play an important role in accurately predicting the permeability of coal reservoirs and revealing the flow mechanisms of CBM in coal reservoirs. © 2021 Tunnel Construction. All rights reserved.
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页码：107 / 115
页数：8
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