复杂地质特征中富有机质页岩脆性评价方法研究

Study on the Evaluation Method of Organic-Rich Shale Brittleness in Complex Geological Conditions

页岩脆性是页岩气勘探开发中"工程甜点"选区的重要评价指标。针对目前页岩脆性评价方法多样,加之我国复杂的各种地质条件与因素均对页岩脆性存在不同程度的影响,难以全面科学地表征页岩脆性等问题,本文通过对我国产气的主要页岩层系中现有的脆性评价方法的分析,结合页岩岩性岩相特征、埋深情况、有机质与石英含量、室内页岩的力学性质测试和镜下微观结构的观察等研究成果的调研,认为沉积环境和岩性岩相决定页岩脆性矿物种类;埋深环境决定岩石外部的围压和温度,进而影响岩石力学性质;有机质与石英含量两者的差异致使页岩脆性在纵向上产生变化;页岩层理结构和微观孔隙结构特征影响页岩破裂模式决定力学性质的各向异性。综合我国各种复杂地质特征,针对页岩内部与外部环境提出了一种简单的脆性理想评价模型,增强了复杂地质条件中页岩脆性评价的适用性。

Shale brittleness is an important evaluation index of engineering sweet spots in shale gas exploration and development.Due to various evaluation methods of shale brittleness and the complex geological conditions in China,and different degrees of influence on shale brittleness,it is difficult to scientifically characterize shale brittleness.This study on this issue is based on the analysis of the existing evaluation methods in the main shale series of domestic gas in China,combining with characteristics of shale lithofacies,burial depth,organic matter and quartz content,mechanical properties from laboratory tests and microscopic structure under microscope.The results show that the sedimentary environment and lithology facies determine shale brittle mineral types,the depth of the environment determines the confining pressure and temperature outside the rock and then affects the mechanical properties of rock.The differences of organic matter and quartz content can lead to longitudinal variations of shale brittleness.Shale bedding structure and microscopic pore structure characteristics can affect the overall shale rupture mode and determine its anisotropy of mechanical properties.Based on the complicated geological features in our country,a simple ideal evaluation model of brittleness is proposed for shale internal and external environments,which enhances the applicability of shale evaluation in complex geological conditions.