Organic Geochemical Characteristics of Core Samples from Central Primorsk-Emba Province, Precaspian Basin, Kazakhstan

Tolganay S. Jarassova, Mehmet Altunsoy

2021

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DOI 10.2118/207044-ms
Data confidence 70 medium
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Abstract

Abstract The Primorsk-Emba province is one of the main oil and gas region of the Precaspian basin. The resources of the Primorsk-Emba oil and gas region range from 5 to 12 billion tons of oil and from 2 to 6 trillion m³ of natural gas. This study primarily concentrates on investigating the organic geochemistry and petroleum geology characteristics of sedimentary units that generated oil in the central Primorsk-Emba province. 20 core samples taken from the Jurassic units in the western part of the study area are characterized by organic matter amount, hydrocarbon production potential, type of organic matter, maturity of organic matter. According to the Rock-Eval results Jurassic aged rocks generally have a petroleum potential ranging from weak to excellent, the organic matter is between Type II (oil prone), Type II-III (gas-oil prone) and Type III (gas prone), and the degree of maturation is immature-mature stage. Oil extracts were characterized by geochemical methods including Gas Chromatography (GC) and Gas Chromatography–Mass Spectrometry (GC–MS). n-alkanes and isoprenoids were evaluated by High-Resolution Gas Chromatography (GC-HR), aromatic hydrocarbons were evaluated by Low Thermal Mass Gas Chromatography (GC-LTM), terpanes (hopanes), steranes / diasteranes and aromatic hydrocarbons were evaluated by Gas Chromatography-Mass Spectrometry (GC-MS). The GC and GC-MS data obtained, it has been determined whether the paleoenvironment characteristics of the study area, hydrocarbon potential, type of kerogen, maturity level of organic matter and whether it is affected by biodegradation. Distribution of n-alkanes in the GC showed that no biodegradation was observed in analyzed samples, source rock deposited in a marine environment under reducing conditions and an organic matter that occurred were generated by marine carbonates. Based on maturity parameters, studied oils are mature and located on the oil generation window. According to biomarker age parameters C28 / C29 and norcholestane (NCR)/nordiacholestane (NDR) samples are generally Mesozoic (Triassic-Jurassic- Cretaceous) origin, nevertheless there are also levels corresponding to the Paleozoic (Permian) late stages.