Petroleum Generation History Of Sirte Basin Source Rocks,Libya

This thesis aims to describes and to evaluate the source rocks in the largest and richest sedimentary basin in Africa and Libya with approximate area around 600,000 km²,in the main basin troughs which includes?Dur Al Abd-Zallah trough,Hagfa trough,Ajdabiya trough,Kotla trough,Dur Attlha trough,Maragh trough and Eastern Sirte Basin troughs?from where the Sirte basin hydrocarbons generated,expelled and migrated.This work basically based on different types of data mainly geochemical data such as Rock-Eval,TOC data,stratigraphic data,structural data,cultural data,maturity data which includes mainly Vitrinite reflectance data and pyrolysis Tmax data,all these data are collected using 58 well located in the basin troughs and penetrated the target source rocks for this study?Mid Nubian,Etel,Rachmat,Sirte shale,Kalash,and Hagfa shale?.The only way to evaluate these source rocks for their organic facies characteristics type and distribution in the basin and also to evaluate these source rock intervals in their maturity levels to establish the generation history of the Cretaceous and late Paleocene source intervals is to divide the whole basin into 7 main troughs,for each individual trough the organic facies geochemical characteristics their distribution and their maturity assessments are cried out based on well to well geochemical correlation using master geochemical sections,geological cross-section and 1D & 2D maturity maps using pyrolysis Tmax data,measured vitrinite reflectance data and modeled maturity using models approaches based on 1D burial history models?LLNL and Arco models?,also kerogen transformation modeling work has been on these source rock intervals using 1D well control data and 2D modeling using Trinity software.Organic facies results indicate in this study that Oil bulk property data from more than 20 oil and gas fields indicates D/E organic facies are significant oil and gas contributors similar as B in Sirte Basin.In the western Sirte Basin in Zallah-Dur Al Abd,Hagfa,Kotla and Dur Attalha troughs,F organic facies has identified for Etel,Kalash and Hagfa having %TOC_avg < 0.6,whereas the good quality D/E and B organic facies present in Rachmat and Sirte shale both have %TOC_avg >1.1.Results from the deepest trough?Ajdabiya?,Etel?Gas prone in Wadayet trough?,Kalash and Hagfa constitute F organic facies,Rachmat and Sirt shale both have D/E to B organo-facies with %TOC_avg >1.2,thus indicating the best organic facies quality in Ajdabiya trough.In Maragh trough,results show that Etel F organic facies and D/E,C to B organic facies related to Middle Nubian,Rachmat and Sirte shale all have %TOC_avg > 0.66.Towards the eastern Sirte Basin,in troughs?Hameimat,Faregh,and Sarir?results show that the Middle Nubian,Etel,Rachmat and Sirte shales are strongly dominated by D/E,C and B(%TOC_avg > 0.75)organic facies.Source rock maturity show results from 3 selected wells located in Zallah and Dur Al Abd trough show Etel in over-mature level with %Ro?1.38?,Rachmat with %Ro?1.02?in late-mature stage and Sirte shale in mid-mature level with %Ro?0.72?,Kalash and Hagfa both in this trough shows early to mid-mature level %Ro?0.4-0.7?.Towards Kotla and Dur Attalha troughs by using 4 selected wells,analysis show Etel in late-mature stage %Ro?1.31?,Rachmat shows mid-mature to late-mature %Ro?0.91?and mid-mature Sirte shale with %Ro?0.67?.Kalash and Hagfa both are in early to mid-mature level.In Ajdabiya trough?the deepest in Sirte basin?,results from 5 selected wells show that Etel in range of mature level with %Ro?1.81?,Rachmat shows over-mature level with %Ro?1.77?and Sirte shale in mid-mature level having %Ro?1.21?.Analysis of 9 selected wells from eastern part of the basin where the maximum hydrocarbon expulsion occurred mainly in Maragh,Faregh,Sarir,Hameimat troughs,indicate that Mid Nubian shale have late to over-mature %Ro level?1.25?,Etel have mature to late-mature %Ro?1.16?and Rachmat and Sirte shale show mid-mature levels with %Ro?0.6-0.95?.The transformation ratio and the expulsion efficiency of the Sirte basin source rocks slight variation for the source rock in different troughs due to the variation of the thermal gradient and maturity levels.The expelled amount of the hydrocarbons have been estimated throughout the basin main troughs from where these source rocks deposited and the results shows that huge amount of petroleum have been generated,expelled,and migrated since the early-late Paleocene,early Miocene,and middle Oligocene time.