富长石粗碎屑砂岩孔隙演化定量分析——以渤海湾盆地辽东凸起北段沙河街组二段为例

Quantitative analysis on pore evolution in feldspar-rich coarse clastic sandstone: A case study of Es^2 in the north part of Liaodong uplift

孔隙演化与油气充注的耦合关系是油气成藏的重要影响因素,储层孔隙度演化定量分析的准确性是关键。通过富长石粗碎屑砂岩储层的显微组构、自生矿物、成岩序列及热演化史分析,确定孔隙度演化定量计算参数,建立储层孔隙演化模式。研究表明,渤海湾盆地辽东凸起北段沙河街组二段砂岩储层中长石的水岩反应过程及产物,是影响孔隙度的关键因素,储层的分选系数、胶结物质量分数、残余原生粒间孔面孔率、总面孔率和溶蚀孔面孔率分析是影响定量计算准确度的重要参数;计算结果表明,压实作用对储层破坏最强,孔隙度平均减小了15%,压实作用主体减孔时间为距今38~23.3 Ma,胶结作用次之,孔隙度平均减小了10.4%,胶结作用几乎贯穿整个成岩时期,溶蚀作用平均增加了9.8%孔隙度,溶蚀作用持续时间为距今19~2 Ma;伴随着油气的充注,储层物性逐渐变好,油气充注结束,储层物性变差。

The coupling relationship between pore evolution and hydrocarbon charging plays an important role in hydro-carbon accumulation.However,an accurate quantitative analysis of the pore evolution is difficult.A porosity evolution model was therefore constructed with quantitative calculation parameters determined through analyses of microfabric,authigenic minerals,diagenetic sequences and thermal evolution of feldspar-rich coarse clastic sandstone reservoirs in the second member of the Shahejie Formation(Es^2) in the north part of Liaodong uplift.The results show that the water-rock reaction of feldspar together with its products has a dominant effect on the reservoir porosity.While analyses of parameters including reservoir sorting coefficient,cement mass fraction,plane porosity of residual primary intergranular pores,total plane porosity,and plane porosity of dissolved pores,are important to the accuracy of quantitative calculation.The research indicates that compaction caused the strongest damage to the reservoirs from 38 to 23.3 Ma,resulting in a porosity decrease of 15%.Cementation,which lasted almost the whole diagentic period,followed up to cut back the porosity by another 10.4% on average.However,erosion from 19 to 2 Ma served to increase the porosity by 9.8%.The physical properties of the reservoirs were gradually improving with hydrocarbon-charging and deteriorating as hydrocarbon charging ended.