断陷湖盆灰质砾岩体储层特征及其油气成藏主控因素分析:以渤海湾盆地歧口凹陷埕海断阶区为例OA

[Objective]The faulted basins in eastern China represent significant crude oil production bases.After decades of intensive exploration and development,enhancing the scale and efficiency of conventional oil and gas resource exploitation has become increasingly challenging.Consequently,deep,unconventional,and complex lithological reservoirs have emerged as key exploration targets.[Methods]Based on integrated geological,drilling,and geophysical data from Chenghai fault step zone in Qikou Sag of Bohai Bay Basin,this study systematically analyzed the sedimentary and reservoir characteristics of limestone conglomerate bodies.The main controlling factors of oil and gas accumulation were also investigated to summarize their geological patterns.[Results]The results indicated that during the Early Paleogene sedimentary stage,the Chenghai fault step zone developed fan-delta facies limestone conglomerate bodies,sourced from the Ordovician of Chengning uplift.Three main lithofacies were identified:Limestone conglomerate facies,sandstone facies,and mudstone facies.Reservoir types were classified into four categories:Limestone conglomerate,sandstone-bearing limestone conglomerate,limestone conglomerate-bearing sandstone,and sandstone.The reservoir spaces were dominated by intergranular dissolution pores and fractures.The distribution of limestone conglomerate bodies within the fan delta was controlled by paleo-channels,with thicker reservoirs occurring within these channelized zones.Sandwiched between three sets of effective source rocks(the lower unit of the First,the Second,and Third members of Shahejie Formation),oil and gas migration was facilitated by step faults,unconformities,and reservoir layers,resulting in an overall oil-bearing characteristics of limestone conglomerate bodies.Furthermore,the distribution of high-quality reservoirs was governed by dominant sedimentary microfacies and lithofacies,with fine-grained sandstone facies in subaqueous distributary channels at the fan-delta front exhibiting enrichment and high-yield production.[Conclusion]The study provides a reference for the exploration of limestone conglomerate bodies.