歧口凹陷中部古近系沙三一亚段水下扇沉积体系内部构成分析

歧口凹陷中部古近系沙三一亚段是重要的含油层段,其内部发育水下扇沉积体系。本文通过岩心、测井、地震资料及室内分析测试等手段,对研究区水下扇沉积体系进行了精细解剖。研究发现其内部可识别出扇面水道、非限制性朵叶体和开阔湖泊三种成因相组合,其中扇面水道由主干扇面水道和分支扇面水道两种成因相构成,非限制性朵叶体由近端朵叶体和远端朵叶体两种成因相构成。主干扇面水道切割近端朵叶体,将沉积物向盆地内部输送,在坡折带其所携带的沉积物可能在重力作用下发生再次分配,形成新的扇面水道和非限制性朵叶体;分支扇面水道多发育于远端朵叶体上部,被开阔湖泊泥岩所包围。在区域背景及生物相资料分析基础上,指出沙三一亚段歧口凹陷中部处于断陷盆地的裂陷幕,在构造坡折带或陡坡带,由于断层活动等因素影响,在半深湖-深湖背景下形成水下扇沉积体系。歧口凹陷沙三一亚段水下扇沉积体系的研究对于该区有利储集体预测具有重要指导意义。

Architecture of the Subaqueous Fan Depositional System in the First Sub-member of the Paleogenic Sha3 Member in the Middle of the Qikou Sag

The subaqueous fan depositional system developed in the first sub-member of the Paleogenic Sha3 member is an important oil-bearing reservoir in the center of the Qikou sag.Based on integrated well core,drilling,seismic,and lab analysis,three types of genetic facies associations were identified in the subaqueous fan depositional systems,i.e.,feeder channel,unconfined lobe,and lake deposit.The feeder channels were formed with two types of genetic facies,i.e.,main feeder channel,distributary feeder channel.The unconfined lobes compose of two types of genetic facies,i.e.,proximal lobes and distal lobes.The sediments were transported to the basin through the main feeder channels that cut the proximal lobes,and might have been distributed by the gravity in the slope-break zone and formed new feeder channels and unconfined lobes.Distributary feeder channels usually developed in the upper part of the distal lobes and surrounded by mudstone in the open lake.Analysis of the regional background and biological data show that the central part of the Qikou sag was in chasmic stage when it received the first sub-member of Paleogene Sha3 member sediments.The fault activity in the slope-break zone resulted in subaqueous fan depositional systems developed in the semi-deep lake.