摘要： 为探讨古老深层致密砂岩储集层孔隙的形成与保存机制,综合运用岩心、薄片、扫描电镜、X衍射及流体包裹体等多种分析测试手段,系统分析了鄂尔多斯盆地中东部长城系深层砂岩储集层的沉积环境、岩石学、储集空间等特征,进而阐明孔隙形成与保存机制。研究发现长城系主要发育潮道沉积环境的石英砂岩和岩屑石英砂岩,具有中等结构成熟度和高成分成熟度特征,储集空间以剩余粒间孔和岩屑粒内溶孔为主,平均孔隙度为6.6%;长城系砂岩压实作用普遍较强,胶结作用主要以石英和伊利石胶结为主,溶蚀作用以岩屑颗粒的酸性溶蚀最为发育,其次为石英的碱性溶蚀。研究表明: 强水动力条件下形成的长城系潮道砂岩粒度粗、分选较好、杂基含量少且成分成熟度高,是其原生孔隙发育的主要原因; 早期大气淡水的淋滤溶蚀、中期有机酸的溶蚀以及晚期的硅质碱性溶蚀为长城系次生孔隙的形成提供有利条件。长城系砂岩储集层刚性石英颗粒含量较高,粒度较粗和分选较好,早期黏土包膜抑制石英次生加大边的形成,早期长时间浅埋、后期快速深埋的埋藏过程等因素有利于孔隙的保存。

关键词: 古老深层, 致密砂岩, 孔隙形成与保存, 长城系, 鄂尔多斯盆地

Abstract: To investigate the pore formation and preservation mechanisms of ancient deep tight sandstone reservoirs,a combination of core,thin section,scanning electron microscopy,X-ray diffraction and fluid inclusion analysis techniques was used to systematically analyze the sedimentary environment,petrology,reservoir space,porosity and diagenesis of the deep sandstone reservoirs of the Changcheng System in the central and eastern Ordos Basin. On this basis,the mechanisms of pore formation and preservation was clarified. The results show that the Changcheng System mainly develops quartz sandstone and lithic quartz sandstone in tidal channel sedimentary environment,with medium textural maturity and high compositional maturity. The reservoir space is dominated by residual intergranular pores and intragranular dissolution pores of rock fragments,with an average porosity of 6.6%. The compaction of the Changcheng System sandstone is generally strong,and it is mainly composed of quartz and illite cementation. The acidic dissolution of rock fragment is the most developed,followed by alkaline dissolution of quartz. The results indicate that the coarse grain size,good sorting and low matrix content are the main reasons for the primary pore development in the Changcheng System tidal channel sandstones,which formed under strong hydrodynamic conditions. The Changcheng System sandstone reservoirs have experienced leaching dissolution of meteoric fresh water during the early stage,organic acids dissolution during the middle stage and alkaline dissolution of quartz during the late stage,which provides favorable conditions to the formation of secondary pores. The pore preservation of the Changcheng System sandstone reservoirs is mainly attributed to the rich in rigid compressive quartz grains,coarse grain size and good sorting,the quartz cementation inhibited by early authigenic clay coating and the burial process of early long-term shallow burial and rapid deep burial in the later stage.

Key words: ancient deep strata, tight sandstone, formation and preservation of pores, Changcheng System, Ordos Basin

中图分类号: 

• TE122.2+1