Research Of Paleogene And Analysis Of Sedimentary Characteristics By Key Wells Of Bohai Bay Miaoxi Depression

Miaoxi Depression lines in the southest of Bohai depression, which is one of the widest and thickest depression in Bohai Bay, which is the centre of deposition and hydrocarbon generation in Bohai basin.We have developed several large oil-gas fileds,such as PL19-3 and PL25-6.Nowadays,the Miaoxi depression was developed too little.In order to analyse the changers of sedimentary facies accurately, and direct the exploration of oil-gas effectively, the sedimentary facies of Paleogene in Miaoxi Depression were rerecognized through the analyses of cores and loggings.In Miaoxi Depression, Paleogene can be divided into four 2nd-order sequences and seven 3rd-order sequences on a basis of the depositional characteristics. Paleogene is divided into Kongdian Formation, Shasi Formation,Shasan Formation, Shaer-Dongying Formation. Shaer-Dongying Formation can be divided into 4 members, named Sha1,2 and Dong2,3.The main sedimentary facies of Paleogene which can be divided into 3 sedimentary facies, is fan-delta, braided river-delta and lacustrine which can be divided into 8 subfacies,named as fan-deltaic plain,braided river- deltaic plain and delta front,shore-lake and abyss. The results show that sedimentary facies of Paleogene are mainly controlled by supply of deposits and change of lake surface.On the basis of research for depositional evolution in time and distribution in space, it suggests that the deposite-source of the Miaoxi depression is two paleo-fluvial which are paleo miaoxi river and paleo lvshun river. From Shahejie Formation to Dongying Formation, the lake surface was rising when the lake expanded. During Dong2 period, the lake surface was highest.