鄂尔多斯盆地西部盒8段-山1段砂岩次生孔隙特征与成因

针对鄂尔多斯盆地西部上古生界盒8段-山1段砂岩储层中长石缺乏的现象，在野外露头与岩芯观察基础上，通过薄片的微观观察与定量统计，并结合XRD射线衍射分析及岩心物性资料等，对研究区次生孔隙发育情况、成因以及影响因素进行了研究。研究发现本区主要发育溶蚀孔、高岭石晶间孔和破裂孔，其中溶蚀孔是本区最主要的孔隙类型。溶蚀孔主要是长石、岩屑等不稳定组分受煤系地层广覆式生烃排出的有机酸溶蚀造成。通过对本区广泛发育的高岭石特征进行剖析并结合长石溶蚀机理等发现有机酸结合晚古生代周缘火山活动造成的同沉积火山灰是造成研究区长石接近全部溶蚀的最根本原因。强水动力造成的中粗粒厚层砂岩，刚性岩屑，火山灰等为次生溶孔的发育提供了基础。压实作用、胶结作用是储层致密化的原因，溶蚀作用有效改善了储层质量。沉积作用与成岩作用共同控制了研究区次生孔隙的发育。

Characteristics and genetic mechanisms of secondary porosity in He 8th member and Shan 1st member in the west of Ordos Basin

Detrital feldspars are almost absent in sandstones from the late Paleozoic 8th member of lower Shihezi and the 1st member of Shanxi formations located in the West of Ordos Basin.Based on the field outcrop and core observation,thin section samples,X-ray diffraction data,and reservoir porosity and permeability data are collected for the study area.Dissolution pores are the main reservoir space,followed by kaolinite intercrystalline pores and fissures.Feldspars and lithic fragments dissolved by the organic acids expelled because of thermal maturation of humic-type kerogen are the origins of secondary porosity.According to the kaolinite characteristics and the dissolution mechanism of feldspars,Organic acids and the volcanic activities happened on the edge of Ordos Basin in the late Paleozoic are the main causes of feldspars absence in the study area.Thick medium-coarse sandstone supplied by high-energy channels,hard lithic fragments and volcanic ash are fundamental for the secondary dissolution porosity.Compaction and cementation are the main causes of reservoir quality reduction.Secondary dissolution enhanced reservoir quality.Sedimentary and diagenesis processes both control the secondary porosity development.