川南龙马溪组页岩中黄铁矿微观特征及激发极化机制

Study of microscopic characteristics of pyrite and its induced polarization mechanism in shale reservoir of the Longmaxi Formation,southern Sichuan Basin,China

从微观角度探讨黄铁矿在页岩中的极化效应机制,为时-频电磁法应用于页岩气勘探提供理论基础。通过对川南龙马溪组页岩样品进行显微扫描电镜、有机地球化学测试和复电阻率测量,结果显示:黄铁矿微观形态为草莓状和晶形较好的立方体,它们的形态指示页岩的形成环境为富有机质的沉积水体,且H_2S含量较高;非氧化-还原环境利于黄铁矿产生完全极化的界面极化现象。黏土矿物和黄铁矿在页岩中的赋存关系密切,作为具有阳离子交换能力的黏土矿物并没有对页岩的极化产生积极贡献,相反在一定程度上减弱了黄铁矿的极化效应。页岩中黄铁矿的含量与页岩的极化率呈明显的正相关关系,黄铁矿和TOC具有储层空间上的对应关系。

Pyrite in the shale reservoir affects the electrical characteristics and its induced polarization effect is different from the conventional reservoir. From microscopic point of view, the polarization effect mechanism of pyrite in shale is studied in order to provide the theoretical basis for shale gas exploration by means of time frequency electromagnetic method. SEM and organic geochemical strawberry shaped and cubic shaped, indicating that the shale formation environment is organic rich sedimentary water with high H2S content. Non redox environment is favorable for fully polarized interface polarization of the pyrite. Though, clay minerals and pyrite are closely related to shale and clay minerals possess cation exchange ability, clay minerals did not make a positive contribution to shale polarization, instead, to a certain extent, weakened the polarization of pyrite effect. It shows that the content of pyrite in shale has a positive correlation with shale polarizability, and there is corresponding relation between pyrite and TOC in terms of reservoir space.