A Study On The Relationship Between Structural Features And Hydrocarbon Accumulation In Campos Basin,Brazil

This Paper,primarily based on the interpretation to seismic section,data statistics,map compilation and summary of predecessors' search data,investigates the effects of structural characteristics of basin,tectonic characteristics,evolutionary history of basin and intra-basin hydrocarbon accumulation of the Campos Basin on one side of South Atlantic in South America,and explores the control and influence of basin evolution on petroleum geological conditions in the basin,realizing the following understandings on the achievements:There are two sets of fault systems in the basin,and a set of extremely thick salt bed of Aptian is developed in the central.The faults in the lower part were formed in the rift period and mainly normal faults,and such faults controlled the uplift and depression patterns of the basin and had the basin presented the structural sandwiching two depressions with a unit of uplift.The fault system in the upper portion was influenced by Aptian Salt Deposit,showing shovel and plough structural styles.As the interlayer separating two sets of fault systems,Aptian Salt Deposit delivered influence and control effects on the formation of fault systems in the basin.The developmental evolution of the Campos Basin is divided into four stages: The basin cracked under the tensile action of the South Atlantic in the rift stage,forming a series of normal faults and graben-horst structure,and showing two uplifts and two depressions.Meanwhile,a set of basalts developed in the basin under the influence of volcanic activity.The intra-basin tectonic activity weakened and the basin changed from the fault depression to depression in the stage of inter-continental rift.Then,a set of carbonate rocks dominated with shell limestone was formed in the higher site of the basin,being a set of great reservoir.A restrictive environment was formed in the basin and the Aptian Salt Deposit was developed because of the impacts of Rio Grande Ocean Ridge and Werwis Volcanic Ridge.An important sea-level rise and decrease occurred in early stage of drift,the basin changed from a limited environment to an open environment,and a set of marine carbonate rocks developed in the upper part of Aptian Salt Deposit.Due to the tectonic uplift,the rocks contacted with the underlying strata in an unconformity plane.In the late stage of drift,the crust started to drift on a large scale,and it inclined and sank intensely in the eastern part of the basin,forming a large-scale slope inclined to the east.The main source rocks in the Campos Basin are the black calcareous shale of the Lagerfeld Formation formed in the rifting period.The main reservoir is a set of carbonate rocks dominated with the shell limestone under the salt,and the caprock is mainly the extremely thick salt deposit of in Aptian period.The great matching of source rocks,reservoirs and caprocks in the space and time is an important control and influence factor of hydrocarbon accumulation in the Campos Basin.The fault system in the rift period controlled the uplift and depression patterns of the basin,and the depression formed under the control of the fault was the position of main source rock development location in the basin.The salt tectonic activity regulated the two sets of fault systems under salt and above salt.