Geochemical Characteristics Study Of Source Rocks And Crude Oils In The Muglad Basin,Sudan

Muglad Basin is located in the southern Sudan,which is a component of West and Central Africa Rift System?WCARS?.It is a typical Mesozoic-Cenozoic rift lake basin.We systematically analyzed the geochemical parameters of 282 source rock samples which distribute among the sections of AG1,AG2,AG3 in Abu Gabra Formation and17 oil samples from the Muglad Basin.The results show that source rocks from AG1section of Abu Gabra Formation are characterized by relatively lower organic matter,mainly type?-II₂ kerogen,which are lower mature-mature source rocks.But source rocks from sections of AG2 and AG3 are characterized by relatively higher organic matter,mainly type I-II₁ kerogen,which are mature source rocks.Biomarkers in source rock extracts were further analyzed by various analysis methods.Source rock samples from AG1 section show that the distribution of n-alkane have unimodal and bimodal pattern,and C₂₇-C₂₉ regular steranes have L-type distribution with C₂₇ sterane dominant and inverted"L"type distribution dominated by C₂₉ sterane,which indicates different organic matter input,one part of organic matter input is mainly lower aquatic organisms and another is mainly from higher plants,all of which were mixed-source.But source rocks from sections of AG2 and AG3 show with similar geochemical characteristics,such as the distribution of n-alkane being unimodal,and C₂₇-C₂₉ regular steranes have L-type distribution with C₂₇ sterane dominant,indicating that the main input of organic matter is low-grade aquatic organisms.Based on the characteristics of Pr/Ph ratios,tricyclic terpane,and Ga/C₃₀H,source rocks from sections of AG1,AG2,and AG3integrally belong to a lacustrine sedimentary environment with weak oxidation and weak reduction.In addition,crude oils of the three concaves from Muglad Basin show with similar geochemical characteristics,such as the distribution of n-alkane having mainly unimoda,the distribution of C₁₉-C₂₄ tricyclic terpane with C₂₁ sterane dominant,the distribution of C₂₇-C₂₉ regular sterane showing a"V"distribution.Source rocks from sections of AG2 and AG3 in Abu Gabra Formation contribute more to crude oil,while AG1 sections has less contribution to crude oil on the basis of the geochemical characteristics of crude oils and source rocks from sections of AG1,AG2,AG3 in Abu Gabra Formation.