Sedimentary Facies And Its Main Controlling Factors Of Tertiary In Lower Congo Basin

Lower Congo Basin is a salt-bearing basin developed in the passive continental margin since Oligocene.It has many exploration strata and many oil-bearing systems,it is one of the most concerned oil and gas exploration hotspots in the world.Guided by the theory of sequence stratigraphy and sedimentology,combining geology with geophysics techniques,and making full use of geological,seismic,drilling and logging data,this paper carries out the classification of sedimentary facies of the Tertiary in Congo,and makes clear the law of Sedimentary facies development,the influencing factors of sedimentary facies and the main controlling factors of sedimentary evolution.That has important guiding significance for further oil and gas exploration and development in the study area.Through core observation,based on the analysis of drilling,logging and seismic data,five types of sedimentary facies,such as by-pass turbidite channel,restricted turbidite channel,weak restricted turbidite channel,turbidite levees and deep-sea and semi-deep mud deposit,are developed in the study area,the drilling/logging,seismic characteristics and palaeogeomorphologic background of each sedimentary facies are defined.This paper points out that the by-pass turbidite channel channel in Block 15/06 is mainly developed in Pliocene,the restricted turbidite channel is most developed in Miocene,the weakly restricted turbidite channel is mainly developed in lower Miocene,and the turbidite levees is most developed in Oligocene.From Oligocene to Miocene,the study area is a relatively complete first-order sequence,characterized by a descent of the datum level,from bottom to top,turbidite levees,weakly restricted turbidite channels,restricted turbidite channels and by-pass turbidite transitional turbidite channels are developed,and within the second-order sequence,restricted and weakly restricted turbidite channels are developed,in the descending period,marine argillaceous deposits are dominant.On the basis of the above,the development model of turbidite in the background of multi-grade slope is established,and it is pointed out that the types of turbidite are influenced by the gradient of topography.The development model of turbidite in sequence framework and that of turbidite in multi-grade slope background are established,turbidite levees,weakly restricted turbidite channels,restricted turbidite channels and by-pass turbidite channel are developed in turn;gravity flow sedimentary types are greatly affected by topographic gradient,and the slope position is dominated by the development of Canyon Channels;The restricted watercourse began to develop,the slope became slower and the watercourse-natural dike system became weak and restricted,and the flat terrain developed levees.The multi-level undulation of seafloor topography causes the repetition of different gravity flow sedimentary sequences.