Geochemical Evaluation of the Silurian, Devonian, and Carboniferous Source Rocks at the Erawin Field, Murzuq Basin, SW Libya

Abstract

Eighty-five rock samples corresponding to the Palaeozoic formations were taken from two wells in the NC 200 Block of the Murzuq Basin. The study aimed to find out geochemical characteristics of Silurian Bir Tlacsin/Tanezzuft Formations, the Devonian Awaynat Wanin/BDS II Formations, and the Carboniferous Marar/Lower Marar Formations. Rock-Eval analysis, Total organic carbon (TOC) parameters and specific Gas Chromatography-Mass Spectrometry (GC-MS) biomarkers were applied to determine the potential hydrocarbon generation. Per se, Rocks are good sources and hold fair content of organic matter, crossing in the range of good accumulation, in which the very good source rocks have an organic carbon richness (TOC) reached of 3.7 wt%. The studied rocks are ranged from immature to late mature organic matter (OM) with total organic carbon richness (TOC) range between 0.4 – 3.7 wt%.  Rock-Eval parameters S1, S2, S3, Tmax, S2/S3, OI, PI and HI of the source rock samples have values ranged from 0.02 – 0.3, 0.22 – 6, 0.36 – 4, 423 – 443, 24= 350, 0 – 0.27 and 42 – 384 respectively. The range of hydrogen index (HI) related to oxygen index (OI) displays that all kerogen types from Type II to Type III are exist and increase with depth. The Tmax parameter is wide-ranging among studied formations, indicating different levels of organic matter maturity, from immature oil window and to late mature for the Devonian-Carboniferous and Silurian source rocks, associated with more depth. Molecular composition analysis of n-alkanes and other biomarkers supported the findings of Rock-Eval pyrolysis data, revealing varied hydrocarbon signatures across the formations. The Carbon isotope analysis (δ13C) suggested multiple sources contributing to the generated oil, including Type I to Type III kerogens.