南海北部深水区白云凹陷渐新世晚期多物源充填特征

运用单井相、地震相、地震速度岩性分析等方法综合分析南海北部深水区白云凹陷渐新世晚期沉积体系特征。研究认为白云凹陷从渐新世晚期开始发生海进,海水可能由东部进入,由东向西发生海进。珠海层序内的主要沉积体系域都表现出一致的多物源充填特征,凹陷东北部(BY1-2附近)发育向南推进的大型S型前积,在凹陷南部发育由西向北东推进的大型S型前积,在凹陷北西部(BY1-1井及其以西地区)发育两个向南推进的中型帚状前积。根据地震速度提取并定量转换出的砂岩指数平面分布图,发现在凹陷东部、北部、西部角、西南方向和东南方向存在相对高含砂带。综合分析认为在低位体系域发育3大水系,即北部水系(河流—扇三角洲)、南部水系(扇三角洲)和东部水系(扇三角洲);高位体系域沉积期发育两大水系,即北部水系(河道—三角洲)和西部水系(三角洲—扇三角洲)。多物源充填特征表明整个渐新世晚期的沉积环境很可能为局限海环境。白云凹陷番禺低凸起南部缓坡带扇三角洲前缘和凹陷西部长轴方向三角洲体系有很重要的勘探价值。

Feature of Multi Sediment-source Filling during the Late Oligocene at Baiyun Depression in the Deep-water Region, the Northern South China Sea

This article firstly makes a comprehensive analysis about the features of depositional system during the Late Oligocene of Baiyun depression in the deep-water region of northern South China Sea,using single well facies,seismic facies and seismic velocity-lithology analysis.Study shows that transgression started developing during the Late Oligocene.Probably,the sea water entered from the east and overlaped towards the west.Main depositional system tracts of Zhuhai sequence displays the consistent feature of multi sediment-source filling.There is a large scale S-type progradational reflection configuration prograding to the south in northeast of the depression(around BY1-2).Another large scale S-type progradational reflection configuration prograding to the northeast exists in the south of the depression.In northwest of the depression(Well BY1-1 and the west area of it),there are two middle-sized brush-like progradational reflection configurations prograding to the south.According to the sandstone index distribution converted from seismic velocity-lithology analysis,there are several relative high sandy areas in the eastern part,northern boundary,west corner,southwest and southeast direction of the depression.There are three palaeodrainage patterns in LST: northern palaeodrainage pattern(fluvial-fan delta),southern palaeodrainage pattern(fan delta) and eastern palaeodrainage pattern(fan delta).There are two palaeodrainage patterns in HST: northern palaeodrainage pattern(fluvial channels-fan delta) and western palaeodrainage pattern(delta-fan delta facies).The feature of multi sediment-source filling shows that the depositional environment during the whole Late Oligocene likely was restricted sea circumstance.The fan delta front in the gentle slope of southern Panyu low uplift and delta regime in the long axis direction of southern Baiyun depression have great significance for exploration.