渤海湾埕岛东部古近系层序地层及沉积特征研究

Sequence stratigraphy and sedimentary characteristics of Paleogene hydrocarbon reservoirs in eastern Chengdao offshore oilfield of Bohai Gulf

由于埕岛东部古近系油藏主要受岩性控制,油藏隐蔽性强,而层序地层学是确定隐蔽油气藏有利勘探区的一种最好方法,因此在该区开展层序地层学研究非常关键。目前该区带勘探程度低,沉积相带、砂体面貌认识不明,为加强该区块勘探开发,在国内外学者研究的基础上,根据基准面旋回级次的划分,在渤海湾埕岛油田东部古近系较大规模的地层旋回中,识别出构造基准面旋回和长期基准面旋回,将主力层系古近系东营组长期旋回又进一步划分为4个中期基准面旋回,建立了古近系东营组高分辨率层序地层格架。通过研究得出,东营组内部不同的层序(中期旋回)及同一层序的不同部分,在研究区的分布具有不同的特征,其总体的分布均遵循沉积物的体积分配原理。东营组旋回在不同时期沉积体系有所不同,在基准面上升期主要发育较深水湖—浊积扇沉积体系,基准面下降早期发育扇三角洲体系,中期以辫状河三角洲体系为主,晚期则以低弯度河流—冲积平原相体系覆盖全区。以上研究对分析该区油气分布规律及控制因素、指导该区的油气勘探部署有积极意义。

Paleogene ore accumulations in eastern Chengdao Oilfield are controlled by lithology and concealed at depth, and hence sequence stratigraphy seems to be the best means in search for beneficial exploration areas of concealed oil accumulations. Therefore, it is crucial to carry out the research on sequence stratigraphy in this area. In view of the low exploration extent and unclear sedimentary facies belt and sandstone characteristics of this area and with the purpose of accelerating the exploration work in this area, the authors carried out a study of sequence stratigraphy and sedimentary characteristics on the basis of previous research work both at home and abroad. First, tectonic base-level cycles and long-term base-level cycles were identified according to grade division of base- level cycles based on high precision sequence stratigraphy. Then the Paleogene Dongying Formation was further divided into four mid -term base -level cycles. High resolution sequence stratigraphic framework of Dongying formation was established. It can be seen that different sequences or different parts of the same sequence of Dongying Formation have different distribution characteristics, with the general distribution pattern following the principle of volume distribution of sediments. The sedimentary system of the Dongying Formation circles had different characteristics in different periods： deep lakes and turbidite fans were mainly developed during the rising of the base level, the fan-delta system was developed at the early base level descending stage, the braided river delta system was mainly developed at the middle stage, and the low-tortuous river and alluvial plain system covered the whole area at the late stage. The results obtained by the authors are of active significance in analyzing the oil-gas distribution and controlling factors and guiding oil-gas exploration arrangement in this area.