Energy-Based Brittleness Index and Acoustic Emission Characteristics of Anisotropic Coal Under Triaxial Stress Condition
Energy-Based Brittleness Index and Acoustic Emission Characteristics of Anisotropic Coal Under Triaxial Stress Condition
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DOI：
10.1007/s00603-018-1535-9
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发表时间：
2018-07
影响因子：
6.2
通讯作者：
Jun Zhang;Chi Ai;Yuwei Li;Ming-guang Che;Rui Gao;Jia Zeng
中科院分区：
文献类型：
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作者：
Jun Zhang;Chi Ai;Yuwei Li;Ming-guang Che;Rui Gao;Jia Zeng
评价煤层水力压裂形成裂隙网络的能力对煤层气储集层的开发具有重要意义。从煤体破坏能量演化的角度出发，建立了一种新的煤脆性评价指标。利用声发射监测系统对煤进行了单轴和三轴压缩试验，分析了新指标的适用性以及围压和割理方位对煤脆性的影响。峰前耗散能和峰后耗散能是决定煤脆性的基本因素。新指标可以表征外应力和割理取向对煤脆性的影响，也可以综合反映煤在峰前和峰后阶段的力学性质。相应的声发射能量曲线可分为快速断裂型、稳定断裂型和塑性断裂型。对于快速断裂类型，当达到屈服应力和峰值强度时，声发射能量积累率出现突变，表现为高脆性。塑性断裂类型表现为低脆性，累积的声发射能量曲线呈先凹后凸的光滑曲线。本文研究的煤脆性指数可为优选煤层气储集层和优化压裂方案提供新的方法。
Evaluating the ability of coal seams to form fracture networks by hydraulic fracturing is important for the development of coalbed methane (CBM) reservoirs. In this paper, a new index for evaluating coal brittleness was established from the perspective of energy evolution during coal failure. Uniaxial and triaxial compression tests of coal monitored by an acoustic emission (AE) system were carried out and the applicability of the new index and the influence of the confining pressure and cleat orientation on the coal brittleness were analyzed. The pre-peak and post-peak dissipated energies were the essential factors in determining the coal brittleness. The new index can characterize the influence of the external stress and cleat orientation on coal brittleness, and can also comprehensively reflect the mechanical properties of the coal during the pre-peak and post-peak stages. The corresponding AE energy curves can be divided intoRapid Fracture Type, Stable Fracture TypeandPlastic Fracture Type. For theRapid Fracture Type, the accumulation rate of AE energy showed sudden changes when reaching the yield stress and peak strength, which represented high brittleness. ThePlastic Fracture Typerepresented low brittleness, and the accumulated AE energy curves were smooth—first concave and then convex. The brittleness index of coal studied in this paper can provide a new method for selecting the optimal CBM reservoir and optimizing the fracturing scheme.