大港探区南部二叠系致密砂岩储层特征及成因

Characteristics and Genesis of Permian Tight Sandstone Reservoirs in Southern Dagang Exploration Area

【目的】大港探区南部二叠系致密砂岩获高产油气流,但其储层特征与成因机制尚不明确。【方法】综合利用岩心观察、薄片鉴定、阴极发光分析、扫描电镜观察、流体包裹体分析、碳氧同位素与氢氧同位素组成分析、电子探针及原位激光剥蚀等技术方法,结合埋藏演化史和油气充注史,对大港探区南部王官屯、乌马营地区二叠系深层砂岩储层进行研究。【结果】大港南区二叠系砂岩以高成分成熟度的石英砂岩、亚岩屑砂岩为特征,优质储层储集空间以次生粒间孔及高岭石晶间微孔为主。在构造运动的控制下,储层经历早期开放体系大气水淋滤溶蚀作用和晚期封闭体系烃源岩生酸溶蚀作用。优质储层的发育受多种因素控制,高成熟度的中粗砂岩是优质储层形成的物质基础,早期地层抬升剥蚀导致的大气淡水淋滤作用形成大量次生孔隙是优质储层发育的关键,早期烃类充注抑制胶结作用有利于次生孔隙的保存。【结论】地质历史时期为大气水淋滤注水区,而现今位于斜坡带—洼陷带的深埋储层,为下步有利勘探目标。该模式的建立对渤海湾盆地其他地区二叠系储层的钻前预测具有借鉴意义。

[Objective]Exploration of Permian sandstone in southern Dagang shows high-yield oil,but the reservoir characteristics and genetic mechanisms remain uncertain.[Methods]Core observations,thin-section identifications,cathodoluminescence analysis,scanning electron microscopy,fluid inclusion analysis,carbon and oxygen isotopic composition analysis,electron probe microanalysis,and in-situ laser ablation,coupled with the consideration of buri⁃al evolution history and hydrocarbon charging history,were used in this investigation into the deep-seated sandstone reservoirs in the Wangguantun and Wumaying regions of the southern Dagang exploration area[.Results and Discus⁃sions]It was found that the Permian sandstone in the southern Dagang region has a high compositional maturity,pre⁃dominantly characterized by quartz sandstone and sublithic sandstone.The storage spaces in high-quality reservoirs consist primarily of secondary intergranular pores and intercrystalline micropores in kaolinite.Influenced by tectonic movements,the reservoirs have undergone early open-system atmospheric-water leaching and dissolution,followed by late closed-system acid dissolution resulting from hydrocarbon source rock interactions.A range of factors influ⁃enced the development of high-quality reservoirs,with the high compositionally mature medium-to-coarse sandstones being the basic material.Early strata uplift and erosion,which led to significant secondary porosity from atmospheric fresh-water leaching,were critical factors.Early hydrocarbon charging inhibited by cementation processes favored the preservation of secondary porosity[.Conclusions]Reservoirs in the slope and depression zone that were formed in an area of atmospheric water leaching are appropriate exploration targets.This model is also relevant for pre-drilling pre⁃diction of Permian reservoirs in other regions of the Bohai Bay Basin.