歧口凹陷沙一下亚段重力流沉积特征及储层精细描述

Sedimentary characteristics of gravity flow and fine description of reservoir in the lower submember of Shahejie Formation in Qikou Sag,Bohai Bay,China

探讨渤海湾盆地歧口凹陷沙一下亚段受葛沽物源控制的重力流沉积体系的平面特征、沉积机制以及沉积模式,探讨其优质储层的控制因素。以“构造-层序-沉积-储层”一体化研究为思路,通过对研究区岩心、测录井、三维地震、测试分析等资料的综合分析,葛沽物源控制的重力流沉积体系主要沿中央隆起带运移,在隆起带及隆起带两侧沉积,自北向南多级断坡输送、长距离搬运、沿路沉积,整体为隆起-断裂沟槽-凹陷组合沉积模式。平面上主要发育内扇、中扇、外扇3种沉积亚相,包括主水道、分支水道、水道侧缘、越岸席状砂、浊积席状砂、深湖泥6类沉积微相,成因机制上识别出泥质碎屑流、砂质碎屑流、过渡型液化流、似涌浪浊流(高密度-低密度悬移)4种重力流类型。储层物性研究表明,重力流沉积体储层致密,主要为超低渗-低渗,孔隙的峰值在特低孔范围,中央隆起带的构造活动有效改善了储层物性,相比之下最优质的储层分布在重力流主水道微相。葛沽物源控制并形成兼具牵引流性质和重力流性质的水道型重力流,沉积微相是其有利区带的主控因素,未来油气勘探方向应以中央隆起带的重力流主水道沉积体为主。

In this paper,the plane characteristics,depositional mechanism and depositional model of the gravity flow depositional system controlled by Gegu provenance in the first sub-member of Shahejie Formation in Qikou Sag of Bohai Bay Basin are studied,and the controlling factors of the high quality reservoir in the study area are discussed.Through the application of“structure-sequence-sedimentation-reservoir”to the analysis of drilling core,logging,3D seismic and laboratory data,it is considered that the gravity flow depositional system controlled by Gegu provenance mainly migrated along the central uplift zone,deposited in the uplift zone and on both sides of the uplift zone,and the long distance migration of the gravity flow was transported from north to south along multi-stage faulted slope and deposited along the entire path.The whole depositional system is a combination of uplift-fault trough-depression.On the plane,there are mainly three kinds of sedimentary subfacies:inner fan,middle fan and outer fan;six kinds of sedimentary microfacies:main channel,branch channel,channel side edge,over shore sheet sand,turbidite sheet sand and deep lake mud.Four types of gravity flow are recognized in terms of genetic mechanism:muddy debris flow,sandy debris flow,transitional liquefaction flow and surge-like turbidity current(high density to low density suspension).Reservoir physical property study shows that the gravity flow sedimentary body is characterized by tight reservoir with ultra-low permeability and the peak of porosity is in the ultra-low porosity range.The structural activity of the central uplift zone effectively improves the reservoir physical property.In contrast,the best quality reservoirs are distributed in the main channel microfacies of the gravity flow.It is realized that the Gegu provenance controls and forms a watercourse type gravity flow with both tractive and gravity flow properties.Sedimentary microfacies are the main controlling factor of its favorable zone.In the future,gravity flow main channel sedimentary body in the central uplift zone should be the main target of oil and gas exploration.