基于岩石破坏全过程能量演化的脆性评价指数

发布时间：2018-10-18 10:57

【摘要】：目前用于评价页岩可压性的脆性指数大都孤立地考虑峰值前后的力学特性,并不能反映岩石整个破坏过程的脆性特征。基于岩石的全应力应变曲线,分析岩石材料由塑性变形转化为脆性断裂过程中各种应变能的演化规律,认为峰前耗散能和峰后断裂能水平是决定岩石是否发生脆性断裂的本质因素。结合这2种能量建立能反映岩石破坏前后力学特征的脆性评价指数,对不同岩石材料在不同围压下的脆性特征以及页岩脆性的各向异性进行评价。研究结果表明:建立的脆性评价指数能同时反映岩石脆性破坏的难易程度和脆性的强弱,可评价不同力学条件下的脆性变化特征。不同岩石材料峰前耗散能以及峰后断裂能随着围压增大而增大,脆性程度不断降低,但降低趋势有所不同,红砂岩和页岩分别在低围压时和高围压时出现了脆塑性的转化,而花岗岩在围压不断增大的整个过程中都保持着较强的脆性。另外页岩脆性具有明显的各向异性,不同层理方向的页岩所表现出的脆性程度差异显著,随着层理倾角b的增大,页岩脆性表现出稳减增的变化趋势,β=0°时页岩的脆性程度要强于β=90°时,β=60°时页岩脆性最弱且表现出很强的塑性特征。实验结果很好地验证了提出的脆性指数的可靠性,研究成果为岩石脆性的定量评价提供了一条新思路。
[Abstract]:At present, most of the brittle indices used to evaluate shale compressibility consider the mechanical properties before and after the peak value in isolation, and can not reflect the brittleness characteristics of the whole rock failure process. Based on the full stress strain curve of rock, the evolution law of various strain energy during the transformation of rock material from plastic deformation to brittle fracture is analyzed. It is considered that pre-peak dissipation energy and post-peak fracture energy level are essential factors to determine whether brittle fracture occurs in rock. Combined with these two kinds of energy, the brittleness evaluation index which can reflect the mechanical characteristics of rock before and after failure is established, and the brittleness characteristics of different rock materials under different confining pressures and the anisotropy of shale brittleness are evaluated. The results show that the index of brittleness evaluation can reflect the degree of brittleness failure and the strength of brittleness at the same time, and can be used to evaluate the characteristics of brittleness variation under different mechanical conditions. The pre-peak dissipation energy and post-peak fracture energy of different rock materials increase with the increase of confining pressure, and the brittleness decreases continuously, but the decreasing trend is different. At low confining pressure and high confining pressure, the brittle ductility of red sandstone and shale are transformed respectively. The granite maintains strong brittleness during the whole process of increasing confining pressure. In addition, shale brittleness has obvious anisotropy, and the brittleness degree of shale with different bedding direction is obviously different, with the increase of bedding dip angle b, The brittleness of shale shows a tendency of steady decreasing and increasing. The brittleness of shale at 尾 = 0 掳is stronger than that at 尾 = 90 掳, and the brittleness of shale at 尾 = 60 掳is the weakest and shows a strong plastic characteristic. The experimental results verify the reliability of the proposed brittleness index and provide a new idea for the quantitative evaluation of rock brittleness.
【作者单位】：东北石油大学石油工程学院;
【基金】：国家科技重大专项项目(2016ZX05046004 004) 东北石油大学研究生创新科研项目(YJSCX2017 009NEPU)~~
【分类号】：TU45

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