基于能量耗散的页岩脆性特征  

Shale brittleness estimation based on energy dissipation

作　　者：衡帅[1] 杨春和[1,2] 李芷[1] 王磊[1] 侯振坤[2] 

机构地区：[1]中国科学院武汉岩土力学研究所,岩土力学与工程国家重点实验室,湖北武汉430071 [2]重庆大学煤矿灾害动力学与控制国家重点实验室,重庆400044

出　　处：《中南大学学报（自然科学版）》2016年第2期577-585,共9页Journal of Central South University:Science and Technology

基　　金：国家自然科学基金资助项目(51104144);国家重点基础研究发展计划(“973”计划)项目(2010CB226701);中石化科技部项目(P11015)~~

摘　　要：针对脆性矿物含量作为页岩脆性评价标准时不能反映不同力学背景下脆性变化的局限性,基于单轴和三轴压缩时页岩的全过程应力-应变曲线,通过能量释放与耗散定义能综合反映岩石破坏前后力学特征的脆性指数和评价指标,并对不同围压下的脆性特征进行评价。研究结果表明:建议的脆性表征方法能同时反映岩石脆性破坏的难易程度和脆性的强弱,可深入分析脆性破坏的实质,评价不同力学背景下的脆性变化特征。页岩峰后稳定破坏所消耗的破裂能越小、剩余能越大,其破裂指数越大,脆性指数越小,脆性越强;反之,其破裂指数越小,脆性指数越大,脆性减弱而延性增强;建议的评价指标均从不同角度反映了页岩脆性特征,可用来对其进行脆性评价。一定围压范围内,随着围压的升高,页岩脆性减弱,破坏后岩块数不断减少,碎裂较不完全,其破坏机制依次为张拉破坏、张-剪破坏和剪切破坏,并呈现出脆性机制向延性机制转变的趋势。Given the brittleness criteria, which is defined by the brittle minerals contents, can not reflect the variation of brittleness at different mechanical conditions, brittleness estimation indices were proposed by the energy release and energy dissipation based on the complete stress- strain curves in uniaxial and triaxial compression tests. These proposed brittleness indices can comprehensively represent the mechanical properties of pre-peak and post-peak parts of shale. The brittleness at different confining pressure was evaluated using these brittleness indices. The results show that the proposed brittleness indices can simultaneously reflect the difficulty of brittle failure and the scale of brittleness. They can also be used to further analyses the failure mechanism of brittle rock and evaluate rock brittleness at different confining pressures. The shale brittleness is higher because the fracture index is larger and the brittleness index is smaller, when the post-peak rupture energy is smaller and the surplus energy is larger. But the brittleness is lower when the condition is opposed. These indices can be used to evaluate rock brittleness as they characterize the brittleness variation from different perspectives. With the increase of confining pressure within a certain range, the brittleness of shale decreases, and the incomplete failure can be easily observed as the number of broken rocks reduces gradually. It is indicated that the failure mechanism in turn is tensile failure, tensile-shear failure and shear failure. The failure mechanisms show the tendency that transforms from brittle at low confining pressure to ductile at high confining pressure. The results can provide technical reference for shale gas reservoir evaluation and for selection of high quality shale formations.

关 键 词：页岩 脆性 能量耗散 应力-应变曲线 评价 破坏形态 

分 类 号：TU443[建筑科学—岩土工程]