川中地区震旦系灯影组-寒武系龙王庙组储层焦沥青赋存特征与成因机制

Occurrence characteristics and genesis mechanism of pyrobitumen in Sinian Dengying to Cambrian Longwangmiao reservoirs in central Sichuan Basin

川中地区震旦系灯影组—下寒武统龙王庙组储层内存在明显的热液活动痕迹,焦沥青也表现出热液蚀变的特征,然而很少有研究去探讨热液活动与天然气成藏演化的关系,导致现今对灯影组油气成藏演化史的认识还存在明显不足。然而,热液对灯影组油气成藏的影响不可忽略,要正确认识灯影组天然气的成藏演化过程并识别勘探有利区,还需要对热液裂解气聚集成藏方面进行更深入的研究。基于对焦沥青的充填特征、光学纹理及结构特征的详细研究,结合热液矿物捕获的流体包裹体地球化学的研究方法,探讨了灯影组—龙王庙组储层内焦沥青的成因,分析了热液活动与原油裂解之间的关系。川中地区灯影组—龙王庙组焦沥青形成于热液活动期间,具有与中间相相同的光学各向异性特征。焦沥青可以划分为4种类型:细粒镶嵌型、中粒镶嵌型、粗粒镶嵌型及流线型,其形成温度过300℃,远超地层最大埋深温度,显示出热液成因的特征。热液活动发生于晚二叠世,与峨眉山地幔柱活动相关,热液流体温度超过300℃,导致了灯影组—龙王庙组储层内的原油裂解。研究发现热液活动将灯影组—龙王庙组古油藏内原油裂解的时间提前到了晚二叠世,打破了灯影组—龙王庙组现有的成藏模式,有助于对天然气成藏演化过程的重新认识和聚集有利区的识别。

Reservoirs in the Sinian Dengying(DY)to Lower Cambrian Longwangmiao(LWM)formations in the central Sichuan Basin exhibit evident hydrothermal activities with pyrobitumen showing signs of alterations caused by hydrothermal fluids.However,few studies have explored the relationship between hydrothermal fluid activity and the evolution of natural gas accumulation,resulting in a significant lack of understanding of oil and gas accu⁃mulation history in the DY Formation.The impact of hydrothermal fluids on oil and gas accumulation in the DY Formation is substantial,and a correct understanding of the natural gas accumulation process and the identification of favorable exploration areas in the DY Formation require further research into hydrothermal cracking gas accumulation.By examining the filling features,optical textures,and structural characteristics of pyrobitumen and conducting geochemical studies on fluid inclusions trapped by hydrothermal minerals,this study explored the genesis of pyrobitumen in the DY to LWM formations.The relationship between hydrothermal fluid activity and oil cracking was also analyzed.The the pyrobitumen in the DY to LWM formations in the central Sichuan Basin were formed during hydrothermal fluid activity,exhibiting the same optical anisotropy characteristics as the mesophase pyrobitumen.Pyrobitumen can be divided into four types:fine⁃grained mosaic,medium⁃grained mosaic,coarse⁃grained mosaic,and streamline types.Its formation temperature exceeded 300℃,far surpassing the maximum burial temperature of the strata,indicating its hydrothermal fluid⁃driven genesis.The hydrothermal fluid activity occurred during the Late Permian and was related to the Emeishan mantle plume.The temperature of the hydro⁃thermal fluids exceeded 300℃,leading to crude oil cracking in reservoirs of the DY to LWM formations.This study found that hydrothermal fluid activity advanced the cracking time of crude oil in the paleo reservoirs of the DY to LWM formations to the Late Permian,disrupting the existing accumulation model and helping us reunderstand the evolution process of gas reservoirs and identify favorable accumulation areas.