Characteristics And Distribution Of Source Rocks Of The Papuan Basin

The Papuan Basin is located between northern Australia and Papua New Guinea.The main part of the basin is located in Papua New Guinea.It is generally distributed in the northwest-southeast direction,including land and marine areas.It is a Mesozoic-Cenozoic basin developed on the basement of Paleozoic.After experiencing long-term complex tectonic evolution,the basin has deposited thick sediments in the Mesozoic and Cenozoic,which is rich in oil and gas resources and has good exploration potential.Studying the characteristics of source rocks in the basin is of great significance to the exploration and development of the Papuan Basin and the evaluation of its resource potential.Based of previous studies on source rocks in the Papua Basin,this paper systematically analyses the organic geochemical characteristics of the main source rocks under the guidance of structural geology,petroleum geology and geochemistry,combined with the structural evolution and sedimentary facies distribution of the basin.Through the drilling,logging,geochemical and other data to identify and calculate the source rock thickness,the geochemical characteristics and distribution characteristics of the source rocks of each layer are analyzed.According to the effective source rock evaluation standard,the hydrocarbon generation potential of source rocks is evaluated and the favorable hydrocarbon generation areas are determined.The source rocks are mainly developed during the Mesozoic with extensional basin and compression collision period and the Cenozoic with subduction compression and foreland collision.Jurassic argillaceous source rocks are mainly developed in delta facies,which is the main source layer.The Lower Cretaceous develops littoral and neritic argillaceous source rock,Miocene develops littoral and neritic argillaceous source rock,and Pliocene develops littoral and neritic argillaceous source rock,which are the secondary source layers.The organic matter abundance,type and maturity of the source rocks are evaluated by the geochemical data of main layers,the Jurassic source rocks have high organic matter abundance and the source rocks are mainly deposited in the delta environment with good organic matter types,mainly II₂-III,and the maturity of organic matter is high,the thermal evolution degree reaches the stage of low maturity to maturity,partially enters the stage of high maturity,and the Jurassic source rocks are comprehensively evaluated as good to very good source rocks.The Lower Cretaceous source rocks have high abundance of organic matter,and develops littoral and neritic argillaceous source rock,the main organic matter types are type III,and the thermal evolution degree reaches the stage of low maturity to maturity,the Lower Cretaceous source rocks are comprehensively evaluated as good to good source rocks.Miocene source rocks have the lowest abundance of organic matter,organic matter type is mainly type III,thermal evolution degree is immature to low maturity stage,comprehensively evaluated as poor to medium source rocks.Pliocene source rocks have slightly low abundance of organic matter,organic matter type is mainly type III,thermal evolution degree is immature to low maturity stage,comprehensively evaluated as medium to good source rocks.Therefore,the hydrocarbon generation potential of Mesozoic source rocks is better than that of Neogene.The Jurassic and Lower Cretaceous source rocks are mainly distributed in the western part of the basin,while the Miocene and Pliocene source rocks are mainly distributed in the central and eastern parts of the basin.The source rocks with Ro greater than 0.5%are effective source rocks.According to the evaluation standards of dividing hydrocarbon potential area,they are classified into three grades,which are class I,class II and class III hydrocarbon generating potential areas.Effective hydrocarbon generating areas of Jurassic are distributed in the western part of the basin with a north-south direction.Effective hydrocarbon generating areas of class I are distributed in the predelta-neritic area of Wabuda sag,they coincide roughly with the high-value areas of source rock thickness,and hydrocarbon potential areas of class II and class III are circular around the hydrocarbon potential areas of class I.And the immature area is distributed in the southwestern part of the basin.The Lower Cretaceous effective hydrocarbon generation area is mainly distributed in the northwestern part of the basin,showing a northwest-southeast direction.Class I effective hydrocarbon generating areas are relatively small and mainly distributed in the southern part of the middle section of the Papuan fold belt and the northern part of the Wabuda sag.Class I and class II effective hydrocarbon generating areas are located in the south of the high-value area of source rock thickness.The immature areas are distributed in the southwestern part of the basin,along the north-south direction.The Miocene hydrocarbon generation areas are mainly distributed in the central and eastern part of the basin along the northwest-southwest direction,class I effective hydrocarbon generating areas distribute in the basinal face area,and in the eastern part of the high value area of source rocks.Class II and class III effective hydrocarbon generating areas distribute on the east and west sides of Class I effective hydrocarbon generating areas.The immature areas are widely distributed,mainly in the western and southern parts of the basin.The Pliocene effective hydrocarbon generating area is mainly distributed in the middle of the basin,along the north-south direction,the class I effective hydrocarbon generating areas coincide with the high-value areas of the source rock thickness,and distribute in the neritic-bathyal area.Class II and III effective hydrocarbon generating areas distribute in the south and north of the Class I effective hydrocarbon generating areas.The immature areas are widely distributed,mainly in the southwest and northeast parts of the basin.On the whole,Mesozoic effective hydrocarbon generation area is wider,while the Neogene hydrocarbon generation potential area is smaller.