基于多元力学实验的深层页岩气储层脆性影响因素分析与定量评价

在地下高温高压条件下，川南深层海相页岩塑性显著增加，现有单一脆性评价方法难以准确表征其可压裂性，严重制约了该区“甜点”优选和工程改造。以川南深层五峰组—龙马溪组页岩为研究对象，通过三轴高温高压、断裂韧性及X射线衍射实验，开展了多种类型的页岩岩石力学性质评价及其影响因素分析，量化了不同载荷条件下岩石破裂的形态特征，并以此为标准，进行了脆性影响因素分析及综合量化评价研究。研究认为川南深层海相页岩具有高弹性模量、较低的I型断裂韧度特征，其脆性性质主要受控于矿物组分、温压条件及页理发育程度，并通过裂纹分形维数量化了岩石破裂的形态特征，且在高石英矿物含量（>50%）、低围压（<20 MPa）、中低温（<60 ℃）及页理化程度较高条件下，实验结束后的样品试件分形维数较高，破裂裂纹以复杂劈裂与剪切复合裂缝为主，相应的脆性较高。通过归一化的岩石力学参数和应力—应变曲线的脆性指数与分形维数之间的相关性分析，利用层次分析法建立了能够表征深层海相页岩脆性的综合评价指标。该评价指标能够很好地表征深层海相页岩脆性特征，且评价认为龙一段3¹小层脆性指数较高，为后期页岩气开发的主力目的层。

Quantitative evaluation and influencing factors analysis of the brittleness of deep shale reservoir based on multiple rock mechanics experiments

Due to the significant increase in plasticity of deep marine shale reservoir in southern Sichuan Basin under high temperature and high pressure conditions， recently， single brittleness evaluation method is difficult to accurately characterize its fracability， which severely restricts the selection of sweet spots and engineering transformation in the area. As a case from deep marine shale reservoir of the Wufeng-Longmaxi formations in the southern Sichuan Basin， through triaxial high-temperature and high-pressure experiments， fracture toughness and X-ray diffraction experiments， the mechanical properties and influencing factors of shale reservoir are studied， and the rock fracture morphology under different loading conditions is quantified. According to the morphological characteristics of shale， the analysis of brittleness influencing factors and comprehensive quantitative evaluation have been carried out. It is believed that deep marine shale reservoir in southern Sichuan Basin is characterized by the high elastic modulus and low type I fracture toughness. The brittleness is mainly controlled by the mineral composition， temperature and pressure conditions and the degree of bedding development， and the morphological characteristics of rock fracture are quantified by the fractal dimension of cracks， and in the case of high quartz mineral content （>50%）， low confining pressure （<20 MPa）， medium and low temperature （<60 ℃） and high physical and chemical degree， the fractal dimension of the sample after the experiment is high， and the fracture cracks are mainly complex shear cracks， and the corresponding brittleness degree is high. Through the correlation analysis between the normalized rock mechanical parameters and the brittleness index of the stress-strain curve and the fractal dimension， a comprehensive evaluation index is established using the analytic hierarchy process. This evaluation index can better characterize brittleness of deep marine shale. It is shown that the 3¹ sublayer of the first Member of Longmaxi Formation has a high brittleness index， which is the main target layer for later shale gas development.