论文详情
页岩脆性是评价页岩气资源潜力的重要指标, 岩石电学属性可为电磁法勘探提供理论支撑, 现有研究较少关注页岩脆性与岩石电学属性的关系。为明确不同脆性页岩电性特征, 选取川东上二叠统吴家坪组页岩样品, 综合运用扫描电镜、TOC测试、X衍射全岩分析、孔隙度及复电阻率测试等实验, 探究页岩脆性与电性特征, 在导电与极化影响因素分析的基础上, 进一步探讨不同脆性页岩电性特征差异的内因。结果表明: 低脆性页岩具有高黏土含量、低孔隙度特征; 而高脆性页岩呈现高石英含量、高孔隙度特征, 其石英类型以生物成因为主, 生物成因石英对页岩脆性具有较大贡献。电阻率受页岩中黄铁矿含量及有机质孔隙影响, 极化率主要受黄铁矿含量影响。在强压实作用下, 低脆性页岩中孔隙被破坏, 孔隙中离子移动受阻, 黄铁矿含量低, 进而表现出高阻、低极化特征; 而高脆性页岩中高含量有机碳为有机质孔发育提供充足物质基础, 生物石英骨架为孔隙保存提供有利条件, 促进孔隙中导电离子移动, 且黄铁矿含量高, 从而呈现低阻、高极化特征。采用电性参数回归模型可较好地评价页岩的脆性特征。研究结果可为页岩储层脆性评价提供电学依据。
Shale brittleness is an important parameter in shale gas resources assessment, and electrical properties of rocks are the basis of electromagnetic exploration.However, the relationship between shale brittleness and electrical properties is ambiguous.To answer this question, we investigate shale samples acquired from the Upper Permian Wujiaping Formation in the eastern Sichuan Basin, based on experimental results of scanning electron microscopy, TOC testing, X-ray diffraction-based bulk-rock analysis, porosity testing, and complex resistivity testing.In addition to the controls on conductivity and polarization, we also discuss internal factors affecting shale electrical discrepancies with different degrees of brittleness.The results indicate that low brittle shales have high clay content and low porosity, while high brittle shales exhibit high quartz content and high porosity.Quartzs, which are mainly biogenic quartzs, make a significant contribution to shale brittleness.Resistivity is influenced by pyrite content and organic matter-hosted porosity, while polarizability is mainly related to pyrite content.Strong compaction leads to a porosity reduction in low brittle shales and consequent hindered ion movement in pores.Pyrite content is low.Thus, shales exhibit high resistivity and low polarizability.For high brittle shales, high TOC content facilitates the development of organic matter-hosted pores, which could be well preserved in the biogenic quartz frame for conducting ion movement.Pyrite content is high, and shales exhibit low resistivity and high polarizability.The regression models based on electrical parameters could be used to evaluate shale brittleness.The research provides an electrical method for shale brittleness evaluation.