Study On Sedimentary Evolution Of Coal-bearing System And Sedimentary Model Of Source Rock Development In The Central And Northern Part Of Qiongdongnan Basin

Qiongdongnan basin is an important oil-bearing basin in the north margin of the south China sea and one of the large offshore oil-rich basins in China.Based on the data of core,well logging,earthquake,paleontology and elements,this paper further studied the sedimentary environment and sedimentary facies evolution of coal-bearing systems in the north,south and lingshui depressions in the central and northern part of qiongdongnan basin,comprehensively evaluated the source rocks,and established the development and deposition model of source rocks in the research area.Firstly,the sequences of Eocene and Oligocene in the study area are divided by lithology and seismic data.Based on the data of core,well logging,earthquake and paleontology,the factors affecting the source rocks of coal measures are analyzed from the aspects of sedimentary environment and evolution law of sedimentary facies belt.Finally,based on the study of the characteristics and distribution of source rocks,the development and deposition patterns of source rocks in the study area are established and the favorable exploration areas are predicted.The main understandings are as follows:(1)The Eocene in the study area is divided into an ultra-long periodic cycle sequence SSC1,which contains two long periodic cycle sequences,namely LSC1 and LSC2.The yasheng formation in the early Oligocene was divided into an ultra-long periodic cycle sequence SSC2,which contained three long periodic cycle sequences,namely LSC3,LSC4 and LSC5.The lingshui formation in late Oligocene is divided into 1 super-long periodic cycle sequence SSC3,which contains 3 long periodic cycle sequences,namely LSC6,LSC7 and LSC8.(2)The evolution of sedimentary environment and facies zone controls the distribution of source rocks and the preservation conditions of organic matter,and the supply and preservation conditions of organic matter dominate the quality of source rocks in coal measures.From Eocene to yacheng formation to lingshui formation,the study area underwent a transition from delta-lacustrine sedimentary system to delta-littoral shallow Marine system and then to shallow-bathyal.Cliff,cliff south and north of lingshui sag are benefit to the deposition conditions of the hydrocarbon source rock development and preservation conditions,including in north and south cliff cliff cave terrestrial higher plant input is large,the best preservation condition,hydrocarbon source rock of the most widely development,water depth,lingshui sag terrestrial higher plant input is limited,poor coal measures hydrocarbon source rock development.(3)There are two sets of source rocks in the Oligocene period in the study area,the yacheng formation is the source rock of Marine and continental transitional facies,and the lingshui formation is mainly the source rock of terrestrial and Marine facies.