四川盆地南缘海相页岩发育，尤其是上奥陶统五峰组-下志留统龙马溪组下段是页岩气勘探开发的优质储层。为对其页岩岩相和沉积环境进行研究， 以四川盆地南缘Y5井龙马溪组页岩（L1段）为研究对象，基于页岩储层品质和压裂品质2个影响页岩气勘探开发的主要因素，提出了以有机碳含量和页岩矿物组成为基础的页岩岩相划分方案，利用X全岩衍射分析及有机碳含量测试资料，开展了页岩岩相划分，分析了不同岩相的属性；通过主量元素和微量元素分析，研究了不同岩相页岩的沉积环境；通过对不同岩相页岩的FE-SEM图像观察，利用Image J软件提取有机质孔和前人提出的有机质孔隙度计算方法，查明了不同岩相页岩有机质孔发育特征；最后总结了沉积环境对不同岩相页岩有机质丰度和有机质孔隙发育的控制作用。结果表明：L1段主要发育富有机质黏土质-硅质混合页岩（OR-M-1）和极富有机质钙质-硅质混合页岩（OER-M-3）；微量元素 V/Cr、Ni/Co 和 U/Th等指标表明龙马溪下段OR-M-1页岩形成于富氧-缺氧的海水中，而OER-M-3页岩形成于厌氧水体，Ba/Al、P/Ti和Cu+Zn+Ni等指标表明此2种岩相沉积环境古海洋生产力差异不大，样品中Al和Ti的百分含量表明OR-M-1页岩沉积期的陆源碎屑输入强度大于OER-M-3页岩；基于海平面变化和上升洋流造成的水体分层的古环境，导致OER-M-3页岩沉积期有机质形成条件好于OR-M-1页岩，OER-M-3页岩有机质孔隙体积占页岩总孔隙体积比更高，更有利于页岩气的吸附。

Marine shale is well developed in the southern margin of Sichuan Basin, especially the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi formation, which is a good reservoir for shale gas exploration and development.In order to study the shale facies and sedimentary environment, taking Longmaxi formation shale(member L1) of Well Y5 in the southern margin of Sichuan Basin as the research object, based on two main factors affecting shale gas exploration and development, shale lithofacies division scheme based on TOC content and shale mineral composition is proposed in this paper. By using X-ray diffraction analysis and TOC content test data, shale facies division is carried out, and the properties of shale with different lithofacies were analyzed; the sedimentary environments of different lithofacies shale were studied by the analysis of major and trace elements; the development characteristics of organic pores of different litho facies shale were found out by observing FE-SEM images of different lithofacies shale, extracting organic pores with Image J software and the calculation method of organic porosity proposed by predecessors; finally, the sedimentary environments for different lithofacies shale were summarized the control of the abundance of organic matter and the development of organic pores. The results show that the organic rich clayey siliceous mixed shale(OR-M-1) and organic rich calcareous siliceous mixed shale(OER-M-3) are mainly developed in the L1 member; the trace elements V/Cr, Ni / Co and U/Th indicate that the OR-M-1 shale in the lower Longmaxi member is formed in oxygen rich anoxic sea water, while the OER-M-3 shale is formed in anaerobic water, and the Ba/Al,P/Ti and Cu+Zn+Ni indicators indicate two lithofacies depositsare little difference in environmental paleomarine productivity. The percentages of Al and Ti in the samples indicate that the input strength of terrigenous clasts of OR-M-1 shale in sedimentary period is greater than that of OER-M-3 shale. Based on the Paleoenvironment of water body stratification caused by sea level change and upwelling current, the organic matter formation conditions of OER-M-3 shale in sedimentary period are better than that of OR-M-1 shale, and the ratio of organic matter pore volume of OER-M-3 shale to total pore volume of shale Higher, more conducive to shale gas adsorption.

0 引言

1 地质背景

2 试验方法与岩相划分方案

   2.1 元素地球化学分析试验

   2.2 岩相划分方案

3 结果和讨论

   3.1 岩相类型

   3.2 沉积环境

   3.3 岩相与沉积环境对页岩有机质孔发育的影响

4 结论