东海西湖凹陷保俶斜坡带平湖组“古地貌-古水系-古坡折”特征及其对沉积体系的控制

Distribution of sedimentary system multi⁃controlled by palaeo⁃geomorphology,water system and break during the deposition of Pinghu Formation,Baochu slope belt,Xihu Sag,East China Sea Shelf Basin

西湖凹陷是我国东海陆架盆地油气勘探的主战场,同时也具有巨大的勘探潜力。已有很多研究认为西湖凹陷始新统平湖组是潮坪沉积为主的海—陆过渡体系,其物源主要来自西部和北部凸起区。然而关于砂体从物源区到汇聚区的“源—渠—汇”过程目前研究较为缺乏,并且对“源—渠—汇”体系发育的制约因素探讨不够深入。该文以西湖凹陷保俶斜坡带平湖组为主要研究对象,利用钻井、地震等资料开展高精度古地貌恢复,并在古地貌基础上对古水系、古坡折进行定性与定量分析。研究表明,古地貌控制了沉积汇聚区的位置,古水系约束了输砂通道的分布,古坡折控制了沉积相带的空间配置;“古地貌—古水系—古坡折”3个因素联合约束了砂体从物源区通过河流输运在汇聚区沉积的全过程,进而控制着整个保俶斜坡带沉积体系的展布。

The Xihu Sag has huge exploration potential and is the main target for oil and gas exploration in the East China Sea Shelf Basin.At present,it has been known that the Xihu Sag has a transitional facies with sedimentary system mainly composed of tidal flat deposits,and the provenance of which is dominated by western and northern uplift area.However,the transport process of sands from source area to deposit area,namely“source-channel-sink”system,has not been well studied.In this study,we take the Pinghu Formation of Baochu slope belt in the Xihu Sag as research object,and use borehole and seismic data to preform high⁃precision restoration of palaeo⁃geomorphology.Moreover,on the basis of palaeo⁃geomorphology restoration,we make qualitative and quantitative analyses of palaeo⁃water⁃system and palaeo⁃break.Results show that the location of sink zone is controlled by palaeo⁃geomorphology,the distribution of sand transporting channel is controlled by palaeo⁃water⁃system,and the development of sedimentary facies is controlled by palaeo⁃break.Through comprehensive analysis,we suppose that the combination of“palaeo⁃geomorphology,palaeo⁃water⁃system and palaeo⁃break”restricts the process of sand body deposition from prove⁃nance to convergence area through river transportation,and controls the distribution of the sedimentary system of Baochu slope belt.