A Study On The Structural Features And The Evolutionary History Of The Santos Basin

Santos Basin is a typical passive continental margin basin developed in the Brazilian side of the South Atlantic Ocean.It is an area where deepwater oil and gas exploration has made great breakthrough in the world in recent years,and the tectonic deformation is quite complicated.This paper takes the structural characteristics of Santos Basin as the research object,and analyzes the structural characteristics,structural evolution stages and the influence of tectonic action on oil and gas formation conditions of Santos Basin through seismic section interpretation and structural evolution section drawing.The following understandings are obtained:The evolution and development of the Santos Basin can be divided into four stages.The first is the rifting stage,formed under the extension of the South Atlantic Ocean cracking.In this stage,due to the effect of strong tensile tension,a large number of normal faults developed,and formed the structure of the horst and graben.In the second depression stage,the tectonic activity of the basin weakened,the basin changed from fault depression to depression,and a set of carbonate rocks mainly composed of laminated limestone was formed in the high part of the uplift in the basin.The third stage is the intercontinental rift stage,in which the basin is blocked by the volcanic ridge,and the water exchange is not smooth,forming a confined Marine sedimentary environment,and evaporative salt rocks are widely developed.The fourth is the drift stage.In the early stage,due to the rise of sea level,the basin changed from a confined Marine environment to an open ocean environment,and Marine carbonate rocks and Marine shale developed.The fault system developed in Santos Basin can be divided into two sets.The first set of fault system developed in the rift layer system and formed in the rift stage.Most of the faults are normal faults and are the main basin-controlling faults,which affect the uplift and sag distribution of the basin and make the basin present a structural pattern of three depressions and two uplifts.The second fault system is developed in the drift strata and is mainly controlled by the activity of the Appadian salt beds.Most of the faults are shovel type and accompanied by compression faults.The two fault systems are separated by a middle set of super-thick Aptian salt beds.The development of salt rock has a great influence on the overall tectonic pattern of the basin.The salt structural patterns in the basin are complex and varied.A series of salt structural patterns can be seen from the seismic profiles,such as salt pillow,salt window,salt welding,salt ridge and salt base split.The salt rock shows zonation in the lateral direction.The main source rocks in the Santos Basin are the Guaratiba lacustrine shales formed during the pre-salt rift,the Aptic,and the Suprasal Semino-Mastrian Marine calcareous shales.The main reservoir is the subsalt laminated limestone carbonate rock,and the main cap rock is the super-thick salt bed deposited in the Aptian stage.The main source rock is in the depression formed under the control of normal faults developed in the rift stage.The main reservoir is developed in the high part of the structure.Salt bed is not only a good cap bed,but also plays a regulating role in two sets of fault systems,namely pre-salt and pre-salt,and has a great influence on hydrocarbon accumulation.