Sedimentary Characteristics And Reservoir Comprehensive Evaluation Of PI Formation In Baobab N Block,Bongor Basin,Chad

The Bongor basin of Chad,which belongs to the strong-reversed rift basin,has a strong tectonic movement.The reservoir is reformed by uplifting and then burial,and the diagenesis is complex.The study area is the Baobab N area in Bongor Basin.The current exploration area has a low degree of-exploration,very few core wells,the core sedimentary phenomenon is virablewith multi-resolution.The sedimentary facies research on this area is controversial.On the basis of making full use of the data of core,logging and seismic,this paper carefully interprets the sedimentary facies in the study area,gains a clear idea of the profile,plane and space distribution pattern of the sand body,and finally completes the comprehensive evaluation of the reservoir.1.Using high-resolution sequence stratigraphy,the long-term,medium-term,and short-term cycles of the PI formation in the Baobab N block in the Bongor Basin of Chad were divided.The study shows that the study area develops a complete three-level sequence,which can be divided into two long-term cycles and five mid-term cycles.Five of the mid-cycles are divided into MSC1-MSC5 from bottom to top.Multiple short-term cycles.MSC3-MSC5 can be divided into a long-term cycle of water withdrawal,while MSC1-MSC2 can be divided into a long-term cycle of water intake.2.Through the good correspondence between lithology and logging curves,a lithologic classification and classification template for the study area was established.The lithology of the study area was divided into sandstone,conglomerate,siltstone and mudstone,corresponding to four different log curves.Lithology identification standard was obtained through establising intersection map.3.Core data and aspects of lithologic features and sedimentary structures in the study area were systematically analyzed and summarized,so that the types of lithofacies and their types of lithofacies were finally classified.In this paper,12 types of lithofacies such as Gm,St,Sm,and Mm can be identified,and 5 types of conglomerate phases,5 types of sandstone phases,and 2 types of mudstone facies can be subdivided.On this basis,4 types of lithofacies can be distinguished.4.Based on the fine observation of the cores and log phase analysis,it is believed that a fan-delta-lake sedimentary system develops in the PI group of Baobab N oil field.The study area develops both delta front and sandy debris flow.The development of sand clastic flow deposition is due to the slumping effect.It mainly develops at the front edge of the front of the fan delta.The sand body has good connectivity and is mostly stacked,which is a good reservoir.The sedimentary environment of the lake is mainly between the semi-deep and the lake-deep lake,which mainly develops lacustrine mudstone.5.Using the data of reservoir properties,heterogeneity,and mercury intrusion parameters,five-layer pore-permeation distribution floor plans and heterogeneity distribution floor plans were drawed.And according to the reservoir classification criteria for the reservoirs in the study area,the performance of the layer is evaluated comprehensively.It is considered that the underwater distributary channel and the mouth bar sand body of the PI4 group in the study area are well-classified as type I reservoirs,and submarine distributary channels and the mouth bar sand bodies of the PI2,PI1 and PI5 are classified as type II –good reservoirs,PI3 group mainly deposited mudstone and a small amount of mat sand,poor pore permeability,strong heterogeneity,which is classified as the type III-poor reservoir.