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多旋回叠合盆地为油气勘探的热点地区,其储层致密且多为隐蔽性的岩性油气藏,尤其成岩作用与孔隙演化较为复杂,备受地质学家关注。本次研究依据陕北地区探井取心物性分析、薄片鉴定、扫描电镜、阴极发光及铸体薄片等资料,系统分析研究区延长组长8油层组储层特征、成岩作用、孔隙定量演化。结果表明区内长8油层组砂岩为分选中-好、次棱角状为主的细粒长石砂岩或细粒岩屑长石砂岩,孔隙度平均值为8.5%。渗透率平均值为0.42×10-3μm2,为特低孔-超低渗储层,长8储层原始孔隙度平均值为38.03%,压实后的孔隙度平均为21.58%,胶结作用下砂岩孔隙度平均接近6.89%,后期溶蚀作用增加孔隙度在2.04%~6.56%,平均孔隙度接近10.77%,孔隙演化的定量计算与岩心的物性分析结果较为一致,同时本区长8储层致密时期主要发生在早期的压实和胶结作用,而后期的溶蚀作用极大的改善了储层的物性。
Multi-cycle superimposed basin is a hotspot area for oil and gas exploration. Its reservoir is dense and mostly concealed lithologic reservoirs. In particular, diagenesis and pore evolution are more complicated and have attracted more attention from geologists. This study systematically analyzed the reservoir characteristics, diagenesis and quantitative evolution of pores in Chang 8 oil layer of Yanchang Formation in the study area based on the data of coring heartbeat, sheet identification, SEM, cathodoluminescence and cast sheet in northern Shaanxi. The results show that the Chang 8 reservoir sandstone is fine-grained feldspathic sandstone or fine-grained feldspathic sandstone with medium-fine and sub-angular shapes, and the average porosity is 8.5%. The average permeability is 0.42 × 10-3μm2, which is the ultra-low porosity and ultra-low permeability reservoir. The average porosity of the Chang 8 reservoir is 38.03%, and the average porosity after compaction is 21.58%. The sandstone The average porosity is close to 6.89%, the late dissolution increases the porosity from 2.04% to 6.56%, and the average porosity is close to 10.77%. The quantitative calculation of pore evolution is in good agreement with the physical property analysis of cores. At the same time, Mainly occurred in the early compaction and cementation, and later erosion greatly improved reservoir physical properties.