莺歌海盆地砂质块体搬运沉积及其天然气聚集

通过莺歌海盆地XF13区三维地震、钻井资料分析,新识别出上中新统黄流组一段砂质块体搬运沉积体系,进而研究其沉积模式及优质天然气聚集机制。钻井岩心以砂质碎屑流沉积为主,发育块状层理、平行层理、突变接触面、泥岩撕裂和变形层等重力流沉积构造;地震资料上其与围岩差异显著,呈"削截"接触关系。砂质块体搬运沉积由多期构成,每期经历"早期侵蚀-充填迁移"和"晚期废弃"2个沉积阶段,相应发育近物源砂质碎屑流、块状厚层砂岩朵叶体和远物源泥质浊流、席状砂的沉积构型。构建了外陆架、海侵-高位体系域砂质块体搬运沉积新模式。以XF13大气田为例,从砂质块体搬运沉积、构造-岩性圈闭的形成到输导体系和天然气成藏过程分析,探讨了优质天然气聚集机制,认为莺歌海盆地中深部具备形成"优质储集体、高烃类气"天然气聚集的地质条件。 

Sandy mass transport deposit model and its natural gas accumulation in the Yinggehai Basin

The sandy mass transport deposit of the first member of the Huangliu Formation in the Upper Miocene was newly recognized using 3D seismic data and drilling data collected from the XF13 area of the Yinggehai Basin. The depositional model and natural gas accumulation mechanism have been investigated. Cores recorded sedimentary characteristics of sandy mass transport deposit very well, developing massive stratifications and parallel stratifications, abrupt contact surfaces, mudstone avulsions, and deformation layers. The sandy mass transport deposit had distinct seismic reflection features compared with those of surrounding rocks. They consisted of multiple periods of sedimentation, and each period experienced early erosion, filling, migration and a late abandonment stage. They developed a double-layer sedimentary architecture, which consisted of massive thick compound lobe sandbody and sheety sandbody, respectively. Each period of sandy mass transport deposit developed sandy debris flow massive thick sandstones with slide-slump movement near provenance, and muddy turbidity current deposits laterally far from the source. A new model with a transgressive-highstand systems tract and outer continent environment was proposed. A case study was made in the XF13 gas field. Through the integrated analyses of sandy mass transport deposit, structural-lithological trap formation, fault/fissure migration pathway and natural gas pooling process, natural gas accumulation mechanism were considered. The central and deep sections of the basin have favorable geologic conditions for gas enrichment and preservation.