Yuan Tao, Wei Yuanlong, Chen Shiwan, Liu Wei, Zhao Lingyun, Zhang Xiong
College of Resources and Environment Engineering, Guizhou University, Guiyang 550025, China.
Key Laboratory of Unconventional Natural Gas Evaluation and Development in Complex Tectonic Areas, Ministry of Natural Resources, Guiyang 550081, China.
ACS Omega. 2022 Jul 29;7(31):27185-27195. doi: 10.1021/acsomega.2c01757. eCollection 2022 Aug 9.
The deformation and damage characteristics of coal are the important foundation that affects the fracturing potential of coal reservoirs and the development plan of coalbed methane (CBM). To reveal the influence regulation of primary fractures and the bedding angle of coal on its failure and provide theoretical basis for CBM development, raw coal samples of no 16 coal seam in Wenjiaba Coal Mine, Zhijin County, Bijie City with different bedding angles were selected as the research object, and uniaxial compression tests were carried out on them, and CT scanning and crack reconstruction before and after sample failure were carried out. The results show that (1) the compressive strength, elastic modulus, and Poisson's ratio of coal show a strong bedding angle effect, and the changing trend of each index is basically the same. The coal samples with bedding angles of 0 and 90° are the highest, while the coal samples with bedding angles of 30° are the lowest, and the overall distribution is an approximate "U" with the increase in bedding angle. With the increase in bedding angle of 0-90°, the failure modes of coal samples are tension-shear combined failure, shear-slip failure, and splitting tension failure in turn. (2) The observation of raw coal and CT scanning show that the primary cracks in coal samples are well developed, especially in the lower part of 0° samples, the cracks in 30° samples, 60° samples, and 90° samples are evenly distributed and develop at a certain angle with the weak bedding surface, and microcracks parallel to and nearly perpendicular to the weak bedding surface are developed in 45° samples. At the same time, banded minerals in coal and rock samples are also well developed. (3) The characteristics of crack propagation and evolution in coal samples with different bedding dip angles are significantly different. The bedding dip angles and primary cracks of coal seam have a great influence on crack propagation. With different bedding angles, the propagation modes are different. The crack propagation mainly includes two ways: forming a certain angle with bedding and extending along the bedding plane. (4) The fracture characteristic parameters of coal in the primary state and after failure have the same law with the bedding dip angle, showing a trend of high at both ends and low in the middle, which is an irregular "U"-shaped distribution and has a similar law with mechanical characteristic parameters.
煤体的变形破坏特征是影响煤储层压裂潜力及煤层气开发方案的重要依据。为揭示原生裂隙和煤体层面夹角对其破坏的影响规律，为煤层气开发提供理论依据，选取毕节市织金县文家坝煤矿16号煤层不同层面夹角的原煤样为研究对象，对其进行单轴压缩试验，并在试样破坏前后进行CT扫描及裂纹重构。结果表明：(1)煤体的抗压强度、弹性模量和泊松比呈现较强的层面夹角效应，各指标变化趋势基本一致。层面夹角为0°和90°的煤样各指标最高，层面夹角为30°的煤样各指标最低，整体分布随层面夹角增大呈近似“U”形。随层面夹角由0°增大到90°，煤样破坏模式依次为拉剪复合破坏、剪切滑移破坏和劈裂拉伸破坏。(2)原煤观察及CT扫描表明，煤样原生裂隙发育良好，尤其是0°试样下部、30°试样、60°试样和90°试样的裂隙分布均匀，且与软弱层面呈一定角度发育，45°试样中发育有平行和近垂直软弱层面的微裂隙。同时，煤岩样中条带状矿物也发育良好。(3)不同层面倾角煤样裂纹扩展演化特征差异显著。煤层层面倾角和原生裂隙对裂纹扩展影响较大，不同层面夹角下裂纹扩展方式不同。裂纹扩展主要有与层面成一定角度扩展和沿层面延伸两种方式。(4)煤体原生状态及破坏后的断裂特征参数随层面倾角变化规律相同，呈两端高、中间低的不规则“U”形分布，与力学特征参数规律相似。
