Deformation Characteristics And Formation Mechanisms Of Salt Structures In Lower Congo Basin

The Lower Congo Basin is located on the coast of West Africa,which is also one of hot regions of oil and gas exploration because of its rich oil and gas resources.Under the background of passive continental margin,different types of salt structures induced by the Aptian thick salt rock have been developed in the Lower Congo Basin,and the salt structures have key influences on hydrocarbon accumulation.Based on seismic interpretation,cross section restoration and physical modeling,this paper mainly addresses the deformation characteristics,evolution processes and controlling factors of salt structures.Finally,the formation model of salt structures in the basin is established.The results show that the Lower Congo Basin is typically characterized by obvious structural deformation zones,including the posterior margin extensional zone,the middle transitional zone and frontal compressional structural belt.Salt rolling,salt rafting and shovel faults are mainly developed in the posterior margin extensional zone;salt diapirs in different forms are mainly developed in the middle transitional zone;halon,thrust faults and thick salt rocks are mainly developed in the frontal compressional structural belt.The evolution of the salt structures mainly experienced three stages: the initial active stage from the Albian to the late Cretaceous,the intense active stage from the late Oligocene to the end of Pliocene,and the weak active stage from the end of Pliocene to the present.Gravity sliding and overlying differential loading are the main factors leading to the plastic flow deformation of the salt structures in the Lower Congo Basin.Meanwhile,deformation of the salt structures are also controlled by the tilt degree of the basement,the thickness of the salt layer,the shape of the basement and the deposition rate.The salt structures of the Lower Congo Basin are mainly developed under the geological background of steep basement slope,thick initial salt layer and slow deposition rate.