The Diagenetic Impact on Reservoir-guality Evolution of Fluvial-deltaic Sandstones
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摘要: 延长油区上三叠统长 2地层河流相—三角洲相砂岩储层的物性明显受埋藏—成岩作用事件的影响。埋藏压实作用是导致砂岩孔隙丧失的主要原因,造成的平均孔隙度丧失为 17.8%。其中黑云母的早期成岩蚀变是造成原生孔隙丧失的一个重要原因。胶结作用造成的平均孔隙度丧失为 7.1%。其中碳酸盐胶结物和次生石英加大是造成砂岩物性降低的主要胶结物。碎屑颗粒周围绿泥石薄膜的存在阻止了一部分石英次生加大及碳酸盐胶结物的沉淀,使一部分原生粒间孔隙得以保存。晚期成岩阶段有机质分解形成的酸性流体及表生成岩作用阶段的大气降水是形成次生孔隙的主要原因,从而使长 2砂岩的物性得到改善Abstract: The reservoir guaiity of the Upper Triassic Chang 2 fiuviai-deitaic sandstones of the Yanchang Oii Fieid in Ordos basin is strongiy infiuenced by the buriai history and facies-reiated diagenetic events. The mechanicai compaction in the eariy diagenetic phase, which resuited in 17.8% porosity ioss, is the main factor causing the ioss of porosity for the sandstones. The diagenetic aiteration of biotite during eariy diagenetic phase accounts for a part of primary porosity ioss in the sandstones. The porosity ioss caused by cementation is 7.1%. In the cements, carbonate and guartz overgrowths are the main cements that reduced the reservoir guaiity of the sandstones. Thin chiorite fiim around detritai guartz grains prevented part of guartz overgrowth and carbonate cement precipitation, which resuited in a part of primary pore preservation and hence caused a better reservoir guaiity. The acidic iiguid reiated to decomposition of organic mater during hydrocarbon enrichment in the iate diagenesis, and meteoric-waters during epidiagenesis, have resuited in dissoiution of detritai feidspars and carbonate cements, and in the formation of kaoiinite, contributing a better retention of reservoir guaiity for the sandstones.
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