超深层致密砂岩储层致密初始期的厘定--以中东鲁卜哈里盆地为例

摘要

鲁卜哈里盆地奥陶系S组为一套典型的超深致密化砂岩储层，石英次生加大为主的硅质胶结作用是导致本区储层致密的最主要因素。利用阴极发光、包裹体测温、自生伊利石矿物同位素测年，结合构造沉降史、埋藏史和热演化史，以首批油气充注的尾声即焦沥青在孔隙中的充填映射储层致密初始期的时间下限；以首次石英次生加大集中发育导致孔隙急剧缩减映射其时间上限，估算奥陶系储层致密初始期约在晚三叠世—早侏罗世，并计算出储层致密化速率约30．6 m／Ma。此外，储层致密化后油藏继续热演化，部分原油热裂解生成天然气可在圈闭内部重新调整聚集形成凝析气藏，部分裂解天然气朝上倾方向继续逃逸或通过颗粒间微孔隙透析成为弥散状油气分布体。%The Ordovician S Formation in the Rub’ Al Khali Basin in the Middle East is a typical ultra⁃deep tight sandstone reservoir. Siliceous cementation dominated by the secondary overgrowth of quartz is the main cause for reservoir porosity reduction in the study area. The period of the pyrobitumen charge is taken as the beginning of reservoir tightening, while the secondary overgrowth of quartz, which sharply reduced porosity, is taken as the end of reservoir tightening. We combined mineral cathodoluminescence, fluid inclusion temperature, authigenic illite isotopic dating with tectonic subsidence, burial and thermal evolution history analyses, and concluded that the Ordovician reservoirs were cemented from the Late Triassic to Early Jurassic with a tightening rate of 30.6 m/Ma. The reservoir continued thermal evolution after tightening. Oil partially cracked to gas, some of which condensed in traps, and some of which escaped upwards or migrated through micro⁃pores to become diffused mix⁃tures of oil and gas.