Sedimentary Characteristics Of Prosopis Formation Of Lower Cretaceous In Baobab Block Bongor Basin Chad

Bongor Basin in Chad is a Mesozoic-Cenozoic intensively inversed rift basin under the influence of the Central African Shear Zone(CASZ), which has fracture structure, complexity structural evolution history and obvious inverse structural deformation. Bongor Basin is a half-graben with its uplifted footwall to the north. It is generally divided into three major structural unites from south to north: the southern uplift, the central depression, and the northern ramp. Bongor Basin experienced three evolutionary stages: rifting stage in early Cretaceous, strong uplift and inversion stage in late Cretaceous and finally basin-forming stage in Cenozoic. Its sedimentary fills are Early Cretaceous and Cenozoic with major hydrocarbon source and reservoir occurring in the Lower Cretaceous. Especially the exploration potential of Prosopis Formation reservoirs are the most prominent.Because of the difficulty of exploration of Bongor Basin and its complicated geographical situation, the work area is still in low degree of exploration and in short of enough drilling wells that reveal Lower Cretaceous strata, seismic data with good quality and the experimental analysis materials. These greatly restrict the prediction on distribution of favorable sedimentary facies, reservoir and the further hydrocarbon exploration.This research aims to carry on comprehensive study of sendimentary facies of Lower Cretaceous in Baobab area, guided by the theories of sedimentology and sequence stratigraphy. Studied distribution of sedimentary system and the types of sedimentary facies models and finally predicted distribution of favorable reservoir.This research is of crucial significance to thorough understanding of evolution of depositional system and distribution of favorable reservoir and further hydrocarbon exploration of Lower Cretaceous strata both in theory and practice.Then, the paper has studied the plane distribution of the sedimentary systems in each sequence of Cretaceous by analyzing single well and well-tie facies, seismic facies and seismic attributes. The results show that the sandstones of research area are derived mainly from two source areas lying to the northeast and southwest of the ancient land and fault. Baobab block mainly developed fan delta-lake sedimentarysystem, a model of fan delta-lake sedimentary facies is established. Baobab-N block is characterized by sublacustrine fan sediments, and found sedimentary model of sublacustrine fan sedimentary system.According to the study of sedimentary facies, diagenesis, and reservoir physical properties, this paper describes and classifies favorable reservoir of Prosopis Formation of Lower Cretaceous in details. It is considered that the fan delta front sandsones in Baobab block, and branch channel sandstones of middle-fan in Baobab-N block are favorable reservoir types of Lower Cretaceous in Baobab area.