页岩脆性的室内评价方法及改进

INDOOR EVALUATION METHOD FOR SHALE BRITTLENESS AND IMPROVEMENT

页岩气储层脆性对页岩的脆性进行测试、评价具有重要的意义。鉴于此,通过文献调研和室内测试,总结脆性测试的20种基本方法,包括基于强度、硬度和坚固性的评价方法,并重点讨论基于全应力-应变特征的页岩脆性测试原理和试验方法。针对页岩脆性破裂机制结合断裂特征定义脆性,认为页岩的脆性是材料的综合特性,受自身非均质性和外在测试环境共同影响;峰后与峰前应力-应变特征均是表征脆性的关键,模拟地下环境的全应力-应变测试能够提高脆性评价的准确度;试样破坏前抵抗非弹性变形的能力和破坏后承载力丧失速度的快慢是脆性强弱的主要力学表现。为提高脆性评价的准确性,对已有的力学测试方法提出改进方案。开展室内真三轴岩石力学实验,对我国南方黑色页岩的脆性特征进行评价。

Brittleness of gas shale reservoir is of vital significance to testing and evaluating the brittleness of shale. In view of this, through literature investigation and lab tests, 20 kinds of basic methods for testing brittleness, including methods based on strength, hardness and ruggedness are summarized, focusing on discussing testing theory and lab method for shale brittleness based on complete stress-strain characteristics. Considering brittleness fracture mechanism and fracture feature, brittleness of shale is defined as a synthetic characteristic of material, affected by its heterogeneity and external testing environment. To identify brittleness of shale, complete stress-strain curve consisted of pre-peak and post-peak parts should both be considered. To improve the accuracy of brittleness evaluation, complete stress-strain testing in underground environment should be simulated. Capacity for resisting inelastic deformation before rupture and losing rate of bearing capacity after rupture are the main mechanical performance of brittleness. To improve the evaluation accuracy, existing mechanical testing schemes are also modified. Meanwhile, brittleness characteristics of black shale from South China is tested through true triaxial rock mechanics tests and then evaluated using improved methods.