The permeability properties of bedded coal and rock: Review and new insights

• Published in: Energy science & engineering Vol. 10; no. 4; pp. 1544 - 1565
• Main Authors: Song, Zhixiang, Zhang, Junwen, Zhang, Lichao, Dong, Xukai, Niu, Weimin, Zhang, Yang
• Format: Journal Article
• Language: English
• Published: London John Wiley & Sons, Inc 01-04-2022; Wiley
• Subjects: "five guarantees" coring technology; 3-D printers; Anisotropy; bedding effect; Coal; Coal mining; Control stability; Coring; energy‐permeability evolution model; Evolution; Gases; initial high in situ stress reduction; Lithology; Mechanical properties; Mines; Mining engineering; Oil and gas industry; Permeability; phase‐field coupling; Radioactive wastes; Rocks; structural evolution theory; Underground mining; Underground storage; Waste storage; China
• ISSN: 2050-0505; 2050-0505
• DOI: 10.1002/ese3.1092

It is beneficial to understand deeply the permeability properties of coal and rock for the stability control of mining engineering, underground engineering, oil and gas engineering, nuclear waste storage engineering, and so on. Therefore, new insights for the permeability properties of bedded coal and rock are summarized and proposed. (1) "Five guarantees" coring technology is worth for vigorous promotion and application. (2) The internal spatial fabric has the significant effect on the mechanical behavior evolution law of (bedded) coal and rock, but the effect is not dominant. (3) The permeability‐energy evolution models of (bedded) coal and rock should be constructed considering the idea of initial high in situ stress reduction, which is helpful for the energy visualization characterization of (bedded) coal and rock. Meanwhile, it can be combined with the structural evolution theory for in‐depth characterization and disclosure. (4) Researches on the permeability properties of (bedded) coal and rock under multi‐field or multi‐phase or phase‐field coupling conditions should be strengthened based on considering the initial damage produced and the distribution characteristics of in situ stress under the coring environment. (5) More accurate and scientific permeability evolution models of (bedded) coal and rock should be vigorously constructed based on the above insights.
Stress–strain curves and permeability evolution curves under various conditions: (A) conventional triaxial loading; (B) "three‐stage" triaxial loading and unloading; (C) Diagram of stress distribution of roadway excavation.Note: σx shifts to σx’ due to the unloading confining pressure in stage II. And H is buried depth; σx, σy, and σz are high initial in situ stress in the X, Y, and Z direction, respectively; σx’ is the minimum principal stress after unloading; σz’ is the maximum principal stress in stage Ⅲ; σ1, σ3, and k are the axial load, confining pressure, and permeability. σ1cf, kmin1, and kmax1 are the axial peak strength, minimum permeability, and maximum permeability under conventional triaxial loading condition, respectively, (MPa), (mD), and (mD). σ1cf’, kmin2, and kmax2 are the axial peak strength, minimum permeability, and maximum permeability under “three‐stage” triaxial loading and unloading condition, respectively, (MPa), (mD), and (mD). Stage Ⅰ: Initial high in situ stress state reduction stage; Stage Ⅱ: Constant axial pressure‐unloading confining pressure stage; Stage Ⅲ: Axial loading stage. ①: Compaction stage; ②: Linear elastic deformation stage; ③: Stable crack development stage; ④: Unstable crack development stage; ⑤: Post‐peak strain softening stage; Ⅲ‐①: Second compaction stage; Ⅲ‐②: Linear elastic deformation stage; Ⅲ‐③: Stable crack development stage; Ⅲ‐④: Unstable crack development stage; Ⅲ‐⑤: Post‐peak strain softening stage.