砂—泥岩协同成岩作用及成岩物质迁移机理研究

Fluid-rock reactions are easily occurred at the sandstone-mudstone contacts during the progressive burial history. Pore water and diagenetic materials were transferred from the mudstones to adjacent sandstones, but little people paid attention on the regime of mass transfer between adjacent sandstone and mudstone. Turbidite sandstones and interbedded mudstone are well developed in the 3rd Member of Shahejie Formation in Dongpu Sag, which provided good conditions for us to discuss the diagenetic alterations and mass transfer between adjacent sandstone and mudstone. This study takes adjacent sandstone and mudstone as a whole diagenetic system, the diagenetic trends near sandstone/mudstone contacts were studied using multiple petrologic and geochemical analysis methods. The synergistic diagenetic alterations between adjacent sandstone and mudstone were discussed on the basis of the investigation of the paragenetic sequence, the time of fluid flow, and ion migration types. Meanwhile, the influence of the fluid released from adjacent mudstone on sandstone diagenesis was investigated. In terms of two types of transport models: advection and diffusion, the controlling factors and regimes of mass transfer between adjacent sandstone and mudstone were investigated. This study can not only deepen the basic geological theory of diagenetic system, but also provides a reasonable forecast of the distribution law of secondary porosity, and guide the prediction of reservoir quality in sandstones and interbedded mudstones . In a word, this study has important theoretical and practical significance.

砂—泥岩界面是水—岩相互作用的活跃带，发生过流体和成岩物质的交换过程，但对微观尺度下成岩物质的迁移方式和机理前人研究较少。本项目选择东濮凹陷北部沙三段中广泛发育的砂泥岩互层为研究对象，将砂岩与邻近泥岩作为一个完整的成岩系统，综合应用多种岩矿分析测试和精细地球化学手段，分析砂—泥岩界面与砂岩内部成岩作用的差异；通过对比分析砂岩与邻近泥岩在成岩演化序列、成岩流体活动时间和成岩物质迁移类型三个方面的耦合关系，开展砂—泥岩协同成岩作用研究，探讨泥岩成岩流体性质和组成对砂岩成岩演化的影响；针对扩散和对流两种运移方式，阐明深埋过程中砂泥岩间成岩物质迁移机理及控制因素，建立砂—泥岩协同成岩演化模式。项目研究对于完善砂泥成岩系统基础理论和指导砂泥互层的砂体储层预测有着重要的理论意义和实际意义。

为了研究微观尺度下成岩物质的迁移方式和机理，本项目选择东濮凹陷北部沙三段中广泛发育的砂泥岩互层为研究对象，将砂岩与邻近泥岩作为一个完整的成岩系统，综合应用多种岩矿分析测试和精细地球化学手段，分析了砂—泥岩界面与砂岩内部成岩作用的差异，开展了砂—泥岩协同成岩作用研究，探讨泥岩成岩流体性质和组成对砂岩成岩演化的影响，阐明了深埋过程中砂泥岩间成岩物质迁移机理，建立了砂—泥岩协同成岩演化模式。研究认为，沙三段储层以长石质石英砂岩、长石岩屑质石英砂岩为主，碳酸盐胶结发育，表现为中-高成分成熟度特征。储层整体低孔低渗，局部发育相对高孔渗储层，孔渗相关性好，以孔隙性储层为主。高能、厚层砂体利于优质储层的发育，但砂体内孔隙度分布及成岩非均质性强。频繁砂泥互层中泥岩成岩流体演化对砂岩碳酸盐胶结作用有重要的影响，碳酸盐岩胶结物含量与距砂泥岩界面距离有关。泥岩流体影响的范围主要在距离砂泥岩界面2m范围内，在厚层砂岩顶、底容易形成碳酸盐致密胶结层。泥岩与砂岩C-O同位素分析结果表明，东濮凹陷沙三段储层砂岩中的碳酸盐胶结物主要来自湖湘碳酸盐岩和泥岩中富含碳酸盐岩颗粒的溶解，而有机质脱羧溶蚀作用不明显。 在压实流和扩散作用共同影响下，泥岩中伊蒙混层矿物进一步向伊利石转化释放出的Na+、Ca2+、Mg2+、Fe3+和Si4+等离子进入孔隙水后随压实流体进入砂岩储层，这些流体进入砂岩之后没有或具有较弱的溶解能力，但具有较强的沉淀作用能力，可为砂岩成岩作用提供物质来源，因此，碳酸盐岩胶结物优先沉积在砂、泥岩的接触带上，形成“钙壳”的特征。砂泥成岩系统的成岩演化受砂泥组合样式、不同的构造埋藏史以及烃类充注与否、是否发育超压等影响。根据成岩作用主控因素不同，建立了研究区4种砂—泥岩协同成岩演化模式：有机酸溶蚀、烃类充注孔隙保存型，异常高压孔隙保存型，早期溶蚀增孔、后期胶结减孔型和早期胶结致密型。项目研究对于完善砂泥成岩系统基础理论和指导砂泥互层的砂体储层预测有着重要的理论意义和实际意义。