济阳坳陷馆陶组辫状三角洲—浅水湖泊沉积体系

对于济阳坳陷馆陶组下段沉积相的认识一直停留在河流相的基础之上 ,并且一直认为缺乏良好的盖层 ,这些认识明显束缚了对馆陶组下段的油气勘探 .本文从古地貌、古生物、沉积构造等 6个方面的研究出发 ,发现济阳坳陷北部地区馆陶组下段存在以浅水湖泊为背景的辫状三角洲沉积体系 .辫状三角洲由辫状平原、前缘和前辫状三角洲组成 .水下分流河道为前缘骨架砂体 ,河口坝和远砂坝不甚发育 ,前辫状三角洲发育普遍较薄 .该沉积体系总体表现为多物源、近物源的多个辫状三角洲在横向的叠置 ,形成湖泊陆源碎屑丰富 ,滨浅湖相带窄的沉积格局 .湖相泥岩在横向和侧向上形成遮挡 ,与油源断层配合 ,可以在一定范围内形成具有一定规模的隐蔽油气藏

Braded river delta-shallow lacustrine depositional system of Guantao Formation in Jiyang Depression

Being lack of systematical research, for a long time, it has been held that the lower member of Guantao Formation in Jiyang Depression is fluvial facies and it lacks good cap rocks, which evidently fetters the exploration of it. Through the recent exploration practice and the research of it, it is found that there exists a braided river delta depositional system on the basis of shallow lacustrine deposit in the lower member of Guantao Formation in the northern region of Jiyang Depression. The authors provide the evidences for the existence of this depositional system from six aspects such as palaeo-geomorphology, paleontology, and sedimentary structure etc. The depositional system is characterized by shallow water with a great coverage of braided river delta front sand bodies. The braided river delta is composed of braided delta plain, braided delta front and braided prodelta. The character shows that the sand from subaqueous distributary channel composes its main body; and the river mouth bars and infralittoral bars are less developed and pro-delta facies belts are thin. Cooperating with oil-source faults, lacustrine shale stone can serve as lateral and horizontal barrier beds, which can enclose oil and gas. As a result, subtle traps are formed on a large scale in a certain area. The discovery of the braided river delta depositional system obviously breaks through the traditional understanding of lower member of Guantao Formation in Jiyang Depression, which will bring great impact on the shallow formation exploration in this area. Great efforts should be made in such work as the readjustment of exploration projects, the reevaluation of petroleum resources and the rearrangement of well pattern. These efforts will turn those old fields into new ones.