泥页岩单轴抗压破裂特征及UCS影响因素

正确认识泥页岩单轴抗压破裂特征及UCS影响因素对探究泥页岩破裂机制、钻完井设计、压裂评价、微裂缝预测、测井解释及地震响应等方面均具有重要参考价值。本文在对国内外近些年有关泥页岩单轴抗压及UCS研究系统调研及近期研究成果全面分析基础上，对泥页岩破裂特征及UCS影响因素进行了综合分析。研究结果表明，泥页岩单轴加载曲线的非弹性段变形机制受微裂缝的滑动、新微裂缝的产生、扩展及孔隙坍塌的综合影响。泥页岩单轴抗压破裂呈张性或张剪性，张性破裂易发生于刚度较高、固结程度较强的部位；而剪性破裂易发生于刚度较低、固结程度较弱的部位。S型破裂准则可以较为准确的描述泥页岩从单轴到三轴发生破裂时所对应的强度变化。从地质学角度，对影响泥页岩UCS的因素进行了归纳，分别为矿物组成、层理面角度、分选性、微组构、有机质含量及分布、孔隙度、水分、微裂缝8方面因素，详细分析了不同影响因素的影响机制。在这些影响因素中，微裂缝由于分布特征复杂，其对泥页岩单轴抗压破裂及UCS的影响机制研究尚不深入。因此建议未来应加强泥页岩微裂缝参数的定量化研究，从微观尺度研究微裂缝对泥页岩单轴抗压破裂的具体影响机制，该研究可以为页岩油气勘探、开发提供科学指导。

Shale uniaxial compressive failure property and the affecting factors of UCS

Correct understanding of the uniaxial compressive strength of shale failure characteristics and its UCS influencing factors has an important reference value in detecting shale failure mechanism, drilling and well completion, fracturing evaluation, micro crack prediction, logging interpretation and seismic response. In this paper, based on the systematic study and comprehensive analysis of the recent research results of shale uniaxial compressive characteristics and the UCS study, reviewed the shale uniaxial failure characteristics and its UCS affecting factors. The results show that, the shale inelastic deformation mechanism in uniaxial loading curve is affected by the sliding of micro cracks, the production and extension of micro cracks, and the pore collapse. The shale uniaxial compression characteristics present tensile or tensile shear fracture. The tensile fracture is easy to occur in location that has high rigidity and degree of consolidation. The shear fracture is easy to occur in location that has low rigidity and degree of consolidation. The S shape failure criterion can accurately describe the shale compressive failure strength variation from uniaxial to three axis failure. From the point of view of geology, making an induction and summary of shale UCS affecting factors, they are composition, bedding plane angle, sorting, micro fabric, organic matter content and its distribution, porosity, moisture content, and microcracks. The affecting mechanism of these factors are analyzed in detail. Among these factors, due to the complex distribution characteristics of micro cracks, the mechanism of micro cracks on shale UCS is not well understood. So, it is recommended that quantitative research of shale micro crack parameters and study of the influence mechanism of micro cracks on shale uniaxial compressional failure from the microscope scale should be strengthened in the future. This study can provide a scientific guidance for shale oil and gas exploration and development.