鄂尔多斯盆地三叠系延长组伊利石包膜成因及其地质意义

通过系统分析延长组伊利石包膜的成因及其地质意义，开展了薄片分析、扫描电镜观测及能谱分析，对伊利石包膜的产状、成分、分布及其与绿泥石包膜的关系进行了研究。研究结果表明：①鄂尔多斯盆地三叠系延长组伊利石包膜与自生蒙脱石包膜具有相似的特征，是自生蒙脱石包膜伊利石化的产物；②研究区自生蒙脱石和绿泥石包膜均是火山物质溶蚀的产物，其相对含量受火山物质的组份控制，且二者均以颗粒表面为基底同时垂直生长；蒙脱石包膜发生伊利石化时，常伴随着钾长石的溶蚀；③弯曲片状伊利石晶体直径和晶间孔均远大于竹叶状绿泥石，但厚度薄，导致显微镜下黏土包膜内层为绿泥石、外层为伊利石，而扫描电镜下仅易见伊利石；伊利石包膜虽然降低了储层渗透率，但有利于砂岩孔隙的保存和亲水性的保留，对油气的开采具有重要意义。该研究成果对鄂尔多斯盆地三叠系延长组优质储层预测及开发均具有借鉴意义。

Genesis and geological implication of illite coatings of Triassic Yanchang Formation in Ordos Basin

Based on the anaysis of genesis and geological implication of illite coatings of Yanchang Formation,the occurrence,chemical composition,distribution characteristics of the illite coatings and its relationship with chlorite coatings were studied by thin section analysis,SEM observation and EDX.The results show that:(1)The illite coatings of Triassic Yanchang Formation in Ordos Basin that are of the same occurrence of authigenic smectite coatings,were formed by the mesogenetic replacement of authigenic smectite coatings.(2)The authigenic smectite and chlorite coatings grew vertically on detrital grain surfaces at the same time owing to the dissolution of volcanic materials whose composition controlled the type of coatings.The illitization of smectite coatings were often ac‐companied by the dissolution of K-feldspar.(3)The curved flake illite is much larger and thinner than chlorite,and the intercrystalline matrix porosity of illite coatings is much higher than that of chlorite coatings,resulting in that only chlorite and illite can be observed in the inner layer and outer layer of illite coatings in thin sections respectively,while only illite can be easily seen under the scanning electron microscope.Although illite coating reduces reservoir permeability,it is conducive to the preservation of pores and water wettability of sandstone,which is of great significance for oil and gas production.The research results have reference significance for the prediction and development of high-quality reservoirs of Triassic Yanchang Formation in Ordos Basin.