Organic geochemical characterization of crude oils and source rocks from Concession 6, central Sirt Basin, Libya
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ORIGINAL PAPER
Organic geochemical characterization of crude oils and source rocks from Concession 6, central Sirt Basin, Libya Alsharef Albaghdady 1 & Richard Paul Philp 2 Received: 23 March 2020 / Accepted: 16 July 2020 # Saudi Society for Geosciences 2020
Abstract 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. Keywords Concession 6 . Sirt Basin . Libya . Crude oils . Source rocks . Geochemical parameters . Rock Eval . Stable isotopes . Biomarkers
Introduction The Sirt Basin is the sixth largest hydrocarbon producing province in the world, with oil and gas reserves estimated at 33 to 45 billion barrels of oil equivalent (BBOE; Macgregor and Moody 1998). It contains most of the hydrocarbon reserves and producing oilfields in Libya and approximately 29% of Africa’s total reserves (Chatellier and Slevin 1988), and, in the Sirt Basin, oil is more abundant than gas. The oils are in the range of 32 to 44 API gravity and sulfur content of 0.15 to 0.66% (Parsons et al. 1980). These oils are found in sandstone and limestone reservoirs ranging in age from Cambrian to Tertiary. Responsible Editor: Santanu Banerjee * Richard Paul Philp [email protected] 1
Department of Earth Science, The Libyan Academy, Tripoli, Libya
2
School of Geosciences, University of Oklahoma, Norman, OK 73019, USA
The Zaltan Platform is in the central Sirt Basin and stretches southward from the Gulf of Sirt (Fig. 1a). It contains several gas fields in the north and oil fields toward the south, reflecting deeper burial and higher maturity levels moving towards the north of the basin. In this study, selected crude oil and source rock
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