四川盆地具有丰富的致密砂岩气资源，目前对川西坳陷东部斜坡超深埋藏超致密砂岩储层孔隙演化的研究较为薄弱。利用岩心观察、铸体薄片鉴定、扫描电镜、碳氧同位素、包裹体均一温度等分析方法，结合埋藏史、热史，明确了川西坳陷东部斜坡须家河组二段（以下简称须二段）深埋藏超致密砂岩储层孔隙演化与油气充注耦合特征。须二段储层以岩屑砂岩、岩屑石英砂岩为主，填隙物主要为自生石英和碳酸盐，储集空间以粒内孔为主。各亚段储层致密化时期具有差异性，上亚段因泥岩岩屑等较高塑性物质，抗压实能力弱，在中晚侏罗世致密；此后在持续深埋和压溶石英双重破坏作用下，中、下亚段在晚侏罗世致密。白垩纪末，构造抬升形成的裂缝促进中、下亚段发生溶蚀，储层孔隙度提高至5%左右，渗透率提高更为显著。主要具有2期油气充注，上亚段耦合关系较差，致密化较早，不利于油气充注，不利于天然气富集；中、下亚段油气主充注期早于储层致密化时期，有利于天然气富集成藏。川西坳陷东部斜坡须二段具有古圈闭+通源断裂叠合型、古圈闭+内部烃源岩+晚期断裂叠合型、古圈闭+通源断裂+晚期断裂叠合型等3种“甜点”储层发育模式。研究内容为深埋藏超致密砂岩储层演化-油气充注耦合特征研究提供实例分析以及理论指导。

The Sichuan Basin has rich resources of tight sandstone gas. Currently, research on the pore evolution of ultra-deep, ultra-tight sandstone reservoirs in the eastern slope of the western Sichuan Depression is relatively scarce. Using core observation, cast thin section identification, scanning electron microscopy, carbon-oxygen isotope analysis, and homogenization temperature of fluid inclusion, combined with burial history and thermal history, the coupling characteristics of pore evolution and oil and gas charge in the ultra-deep, ultra-tight sandstone reservoirs in the second member of Xujiahe Formation (hereinafter referred to as Xu 2 member) on the eastern slope of the western Sichuan Depression were clarified. The Xu 2 member reservoir is mainly composed of lithic sandstone and lithic quartz sandstone, with authigenic quartz and carbonates as the primary cementing materials. The storage space is dominated by intragranular pores. The densification period of the reservoir varies among different submembers. The upper submember is less resistant to compaction due to the presence of higher plastic materials like mudstone clasts, and it became compacted during the Middle to Late Jurassic. Subsequently, under continuous deep burial and the dual destructive effects of pressure dissolution and quartz, the middle and lower submembers became compacted during the Late Jurassic. At the end of the Cretaceous, tectonic uplift led to the formation of fractures that promoted the dissolution of the middle and lower submembers, increasing the reservoir porosity to around 5%, with a more significant increase in permeability. There were two main periods of oil and gas charge. The upper submember had a poorer coupling relationship, with early densification that was unfavorable for oil and gas charge and natural gas accumulation. In contrast, the main oil and gas charge period for the middle and lower submembers occurred prior to the densification of the reservoir, which was favorable for natural gas accumulation and reservoir formation. The Xu 2 member on the eastern slope of the western Sichuan Depression exhibits three “sweet spot” reservoir development modes: ancient trap+source fracture superposition, ancient trap+internal source rock+late fracture superposition, and ancient trap+source fracture+late fracture superposition. The study provides examples and theoretical guidance for understanding the evolution-oil and gas charge coupling characteristics of deeply buried ultra-tight sandstone reservoirs.