珠江口盆地深水区珠海组陆架边缘三角洲特征及其意义

陆架边缘三角洲发育于大陆架边缘、由物源越过陆架坡折并在陆坡沉积而形成, 分布广、储层发育, 其富油气性已经全球多个地区的勘探实践所证实。基于最新钻井与地震资料综合分析, 首次系统揭示了珠江口盆地深水区珠海组大型陆架边缘三角洲的分布与结构充填, 分析了其发育的主控因素与油气勘探意义。研究表明, 珠海组陆架边缘三角洲剖面上呈S形、斜交或叠瓦状前积结构, 钻井揭示为厚层水下分流河道、河口坝、席状砂与前三角洲泥互层沉积, 平面上北东向展布于白云凹陷至鹤山凹陷一带。白云凹陷段三角洲规模相对较小, 以斜交前积为主;白云南洼东段呈S形前积结构, 顶积层为厚层水下分流河道与河口坝砂岩, 前端深水水道与深水扇发育;南部隆起段以斜交、叠瓦状前积为主, 规模较小;鹤山凹陷段以S形前积结构为主, 发育大型下切谷与深水扇。晚渐新世构造活动相对平静, 深水区形成了稳定的陆架坡折带, 古珠江携带的充沛物源与珠海组时期相对海平面下降促使了陆架边缘三角洲的发育。珠海组陆架边缘三角洲的泥质沉积是一套中等-好的烃源岩, 同时其发育也为海相泥岩带来了丰富的陆源有机质;陆架边缘三角洲的河口坝、水下分流河道、席状砂分布广、纵向厚度大, 是深水区重要的储层类型, 其前端发育的深水扇体是有利勘探目标。

The Shelf-margin Delta Feature and Its Significance in Zhuhai Formation of Deep-water Area,Pearl River Mouth Basin

A shelf-margin delta is built up on shelf-margin, where sediments pass across the shelf break and settle down to form the delta. Oil richness of shelf-margin delta has been confirmed by exploration in the world for its wide distribution and well-developed reservoirs. Based on analysis of seismic and drilling data, distribution and architecture of large shelf-margin delta in Zhuhai Formation in deep-water area have been systematically studied for the first time, as well as the main control factors and exploration significance. With “S”, oblique and imbricated progradation configuration in profile, interbedding of underwater distributary channel, mouth bar, sand sheet and prodelta clay on wells, the large shelf-margin delta striking NE is located in Baiyun and Heshan sag. In Baiyun sag, this delta is relatively small with mainly oblique progradation configuration. The delta in South Baiyun depression developed deepwater channel and fans with “S” progradation configuration. The segment in southern uplift show oblique and imbricated progradation configuration. In Heshan sag, the delta developed incised valley and fans with “S” progradation configuration. Shelf break developed firmly in deepwater area for quiescence of tectonic movement in Late Oligocene. Shelf-margin delta developed because of the abundant sediment from Paleo-Pearl River and falling of relative sea-level. The delta takes abundant terrestrial organic matter to marine mudstone and, moreover, mudstone in the delta is fair-good source rock. With wide distribution and big thickness, underwater distributary channel, mouth bar and sand sheet in shelf-margin delta are significant reservoir in deepwater area and the deepwater fans before delta are profitable target.