Development,Distribution And Hydrocarbon Generation Characteristics Of Oligocene Coal Measure Source Rocks In Qiongdongnan Basin

This article is based on the basic fact that the Qiongdongnan Basin is rich in oil and gas resources and mainly derived from Oligocene coal-series source rocks.It adopts basic theories such as geophysics,coal geology,petrology,sedimentology,and sequence stratigraphy.Geochemical,logging,paleontological and other basic data,fully absorbing the latest research results of previous people,carried out the coal-based source rock deposition system,sequence stratigraphy,development and distribution,hydrocarbon generation evolution and other related contents in the Oligocene of Qiongdongnan Basin Because the coal-measure source rocks are mainly developed in the Yacheng Formation and the Ling 3 Member,this article will focus on the Yacheng Formation and the Ling 3 Member to analyze the development,distribution and hydrocarbon generation characteristics of the coal-measure source rocks.Gained innovative understanding in the following aspects:In the Oligocene Yacheng formation of Qiongdongnan Basin,the marine land transitional facies is the main sedimentary facies,while in the Lingshui formation,the shore shallow marine facies is the main sedimentary facies,mainly including braided river delta facies,fan delta facies,alluvial fan facies,shallow sea facies,barrier coast facies and barrier free coast facies.The Oligocene can be divided into two second-order sequences and six third-order sequences through the identification and tracking of sequence boundaries.According to the coal seam identification technology of well logging and seismic,the coal seam identification technology is used to identify the areas with low exploration degree.Combined with the factors such as paleoclimate,paleoenvironment,paleostructure,base level rise and fall that control the development of coal scams,it is predicted that the coal seams of Oligocene are mainly distributed in the basin margin,the periphery of northern depression belt,the South and north margin of central depression belt,and mainly develop Delta,fan delta and tidal flat Coal sedimentary environment:the distribution and development of terrigenous marine mudstones are controlled by many factors.In this paper,it is discussed that the distribution of terrigenous marine mudstones has a good correlation with the terrain gradient.Based on this,it is predicted that the Oligocene terrigenous marine mudstones are mainly distributed in the basin margin,the bulge and the depression margin,and the littoral shallow sea sedimentary system is developed.The thermal simulation experiment of hydrocarbon generation shows that the source rock of Oligocene coal series still has great hydrocarbon generation potential at present.According to the basin simulation technology and vitrinite reflectance parameters,the thermal evolution burial history of Qiongdongnan basin is reconstructed,showing that the Oligocene stratum has experienced multiple structural ups and downs,and each subsidence is a ripening effect on the source rock.Combined with the thermal evolution characteristics,it can be seen that the thermal evolution The evolution from bulge depression margin depression center is a rising process,and the depression center is in the over mature stage,mainly gas generation.Based on the comprehensive analysis of the distribution and development characteristics,thermal evolution characteristics and hydrocarbon generation thermal simulation characteristics of the source rocks of the coal measures,three hydrocarbon generation zones are predicted in the Oligocene,which are respectively the hydrocarbon generation zone in the northern margin of the central fault depression,the hydrocarbon generation zone in the Southern margin of the central fault depression and the potential hydrocarbon generation zone in the northern margin of the northern fault depression.