Structural Features Analysis Of Key Areas In Lower Congo Basin

The Lower Congo Basin is located at mid-south part of West African coast and belongs to the passive continental margin basin.It has become one of the key exploration targets of the West African continent in recent years and has good prospect for exploration.Combined with previous research results and based on project data and three-dimensional seismic data in the area,this paper analyzes the fault and salt structure features of the Lower Congo Basin by carrying out fine interpretation of seismic data and drawing basic maps,calculating fracture activity parameters,and using 2DMove software to restore the history of tectonic evolution,which provides more theoretical support and scientific basis for further oil and gas exploration.The Lower Congo Basin has successively experienced four evolutionary stages:anterior rift—intracontinental rift—intercontinental rift and drift.The stratum is divided into subsalt sequence,salt rock sequence and upper salt sequence by taking the Aptian stage salt rock as the boundary.Due to the poor quality of seismic data in the subsalt sequence in the key research area of the Lower Congo Basin,this paper only focuses on studying the structural characteristics of the salt and above sequence.Through structural-stratigraphic comprehensive interpretation and drawings making of the main faults in the combined area of 23 seismic sections,as well as the analysis of fault elements,it shows that the key research areas have higher fault levels,mainly NW or NNW trend.By calculating the fracture growth index,activity rate and fault drop index,it's known that the regional faults mainly happened in miocene,especially in middle miocene.By summarizing structural styles of the salt sequence and upper salt sequence within the seismic section and combining the division results of the structural belts carried out by our predecessors,the structural belts in the key research area are divided and the plane change characteristics of the structural styles were found out.The key research area of the Lower Congo Basin has the characteristics of “belt divided in east-west direction,block divided in north-south direction”.From west to east direction,the basin is divided into extruded area,transition area and extensionarea respectively.Salt wall,salt tent and other structures are developed in the extruded area,while salt diapirs are developed in the extension area,and small salt rafts and salt pillows are developed in the transition area.The faults in extension and transition areas are dominated by normal faults,while the faults in extruded area are constituted of thrust faults and small-scale normal faults.Through analysis of the balance profile by using salt-related structures technique,it is known that the salt rock activities concentrated in Miocene,and there was a small-scale movement before Upper Cretaceous.The salt rock in the key research area is closely related to the formation and development of the faults.The paper summarized salt structure and the formation and development model,both of them jointly control the sedimentation.By comparing and analyzing the seismic sections of the 1706 and 1806 work areas,combining with data such as fault activity,the faults in the extension area of the 1806 work area have little effect on the sedimentary thickness of the strata,the faults belt in the transition area concentrated in Miocene(Early Miocene and mid-Miocene)plays a certain role in controlling sedimentation.