The Sirt Basin contains most of Libya's producing oil fields and is in northern Libya, south of the Gulf of Sirt in the Mediterranean Sea. The main aims of this study were to characterize the type of organic matter and depositional conditions of the source rocks and thermal maturity of the crude oils in this region using a variety of geochemical techniques including gas chromatography (GC), gas chromatography/mass spectrometry (GCMS), stable carbon and hydrogen isotopes, total organic carbon (TOC), and Rock Eval analysis. Twelve crude oil samples from Cambrian-Ordovician Gargaf, Upper Paleocene Zaltan, and Middle Eocene Gialo reservoirs and seventy-nine source rock samples representing Sirt Shale samples from nine wells were collected from the Zaltan Platform and surrounding troughs in the central Sirt Basin. Organic geochemical parameters indicate that these oils were sourced from marine organic matter deposited under oxic to suboxic conditions. The oils were divided into three groups based on their whole oil carbon and hydrogen isotopic composition and thermal maturity as manifested by several saturate and aromatic hydrocarbon maturity parameters. Based on the geochemical data, it is proposed that there are at least two sources for the crude oils in the Zaltan Platform area of the central Sirt Basin. The study also indicates that the Sirt Shale source rocks from Maradah Trough are dominated by marine organic matter and have reached the main phase of oil generation.

The Murzuq Basin, in Southwestern Libya, is one of Libyan’s most productive petroleum basins, with reserves estimated at 23 billion barrels recoverable of hydrocarbon equivalent within giant oil fields. Four crude oil samples collected from A1-NC186, E1-NC101, E2-NC101, H10-NC115 wells from Murzuq Basin, Libya, were suggested for bulk analysis and physical proprieties, alkane distribution and isoprenoids and the hopane, tricyclic terpane and sterane distributions of the oils, to confirm the presence of non-marine organic matter sources and/or any evidence of its existence. The oils show no significant variation in the ratios of the carbon, hydrogen, nitrogen and sulfur content (CHNS) composition. All samples recorded high to very high API° gravity, ranges 33.8 to 40.3; the sulfur values ranged from 0.31 to 0.45%, the wax ratio in crude oils is showing a great variety, E1-NC101and E2-NC101 oils show higher wax content, ranging from 6.1 to 6.7%. Pristine to Phytane ratios (Pr/Ph) range from 1.61 to 2.22 and the Pr/n-C17, Ph/n-C18, n-C17/n-C27 and CPI values determined as indicators of the depositional environment of the crude oils. The data of search confirmed that the crude oils were derived from marine, mixed and terrestrial sediments.

This present paper includes a detailed evaluation of specific biomarkers together with stable carbon isotope (δ13C) by gas chromatography-mass spectrometry (GC–MS) and Gas Chromatograph–Isotope Ratio Mass Spectrometry (GC–IR–MS). Eight crude oil samples were collected from the A, B, H (east) and H (west) Fields, located in the Murzuq Basin, Libya. Stable Carbon isotope data (δ13C) together with biomarker ratios data of individual hydrocarbons, n-alkanes, isoprenoids, terpenes, hopanes, steranes and aromatic have been determined in crude oils to delineate their bacterial degradation, source facies, organic matter precursors, depositional conditions and a variation of maturation. Based on source-specific parameters including n-C19 alkane, % C27S, %C28S, %C29S, %C23TT, %C30αβ, %rC28, DBT/P, CPI, Pr/Ph, Ts/Tm, dh 30/h 30, 1 MN, 2 MN,         26-27 DMN, 15 DMN, 236 TMN, 146-135 TMN, 125 TMN, 136 TMN ratios and δ13C‰ of saturates and aromatics fractions. Such oils showed non-biodegradation, n-C19 peak proved oils generated from a Lower Palaeozoic source rocks as emphasizedvian-C19 peak, the dominance of C29steranes over C27 and C28 with light Carbon isotope ratio (δ13C‰) values. The abundances of isosterane C29, C27, C28.Tricyclohexaprenol and bacteriohopane polyols and aminopolyols, recommended as mixture bioprecursors of tricyclic terpenes and hopanes, furthermore regular sterane ratio gives values characteristic of Lower Palaeozoic marine source rocks and holding green algae and most likely a quantity of contribution from acritarchs. Carbon preference indices (CPIs)>0.9 pointed to an anoxic deposition, dibenzothiophene to phenanthrene (DBT/Prange 0.49 - 0.58) recommend a siliciclastic source rather than carbonate and/or evaporate saline deposition. The ratios of CPIs, pristane/n-C17 and phytane/n-C18, n-alkanes (C16 to C22) against (C23 to C33), Ts/Tm, C30diahopane/C30hopane, methylnaphthalene, dimethyl naphthalene and trimethyl naphthalene indicated that the oils analysed are mature except the B Field oil being slightly less mature than the A, H (east) and  H (west) Fields oils.

No abstract

Labuan is an island, located offshore west of Sabah, East Malaysia. The rocks on Labuan Island are divided into three main units; Temburong, Setap Shale and Belait formations. The relationship between these units is still unclear. An organic geochemical study was performed on ten samples from these main rock units. The main aim of this study was to determine the thermal maturity of these sediments and to differentiate between the formations based on organic geochemical parameters. The study suggests the thermal maturity is early mature to mid mature for oil generation, the Belait Formation being least mature and Temburong the most mature. Based on organic geochemical parameters and supported by vitrinite reflectance data, the Layang Layangan Unit I should be grouped within the Belait Formation. Abstrak: Labuan adalah sebuah pulau yang terletak di luar pesisir pantai di bahagian barat negeri Sabah, Malaysia Timur. Batuan di Pulau Labuan dibahagikan kepada tiga unit utama: Formasi Temburong, Syal Setap dan Formasi Belait. Hubungan di antara unit-unit ini masih kurang jelas. Suatu kajian geokimia organik dilakukan ke atas sepuluh sampel dari unit-unit utama batuan ini. Tujuan utama kajian ini ialah untuk menentukan tahap kematangan term a sedimen-sedimen ini dan untuk membezakan di antara formasi-formasi ini berdasarkan parameter-parameter geokimia organik. Kajian ini mencadangkan kematangan terma adalah diperingkat awal ke pertengahan bagi penjanaan minyak di mana Formasi Belait yang paling kurang matang dan Temburong yang paling matang. Berdasarkan parameterparameter geokimia organik dan disokong oleh data dari pantulan vitrinit, Unit I Layang Layangan sepatutnya diletakkan di dalam Formasi Belait.