Geologia Croatica, Vol. 79 No. 3, 2026.
Original scientific paper
Organic geochemical assessment of the origin and maturityof crude oils from the Drava Basin, Croatia
Slavica Marinović
; INA – Industrija nafte d.d., Exploration & Production, E&P Laboratory, Zagreb, Croatia
*
Goran Mikša
; INA – Industrija nafte d.d., Exploration & Production, E&P Laboratory, Zagreb, Croatia
Mirna Biondić
; INA – Industrija nafte d.d., Exploration & Production, E&P Laboratory, Zagreb, Croatia
Darko Španić
; retired
Ksenija Stojanović
; University of Belgrade, Faculty of Chemistry, Belgrade, Serbia
* Corresponding author.
Supplements: GC_79_3_Marinovic+et+al.+(2026)+suppl.pdf
Abstract
Six crude oils (Jagnjedovac, Lepavina, Čepelovac, Letičani, Šandrovac and Pavljani) from the western part of the Drava Basin, in the Croatian part of the Pannonian Basin, were investigated to define origin, depositional environment and thermal maturity. The oil fields are surrounded by the largest gas and gas-condensate fields (Molve, Kalinovac and Stari Gradac), located in the northwestern part of the Drava Basin. The complex structural, lithological, and stratigraphic features of this area resulted in the specific physical characteristics of the hydrocarbon fluids. The study utilized bulk parameters, gas chromatography (GC) of the gasoline fractions and gas chromatography-mass spectrometry (GC-MS) of biomarkers and phenanthrene derivatives of oils and representative samples of gas condensates from the surrounding fields. Although crude oils from the western part of the Drava Basin have different bulk properties (e.g., API gravity, sulphur content, pour point), according to the biomarker “fingerprints”, all the analysed oils have a common origin and were generated from siliciclastic source rocks containing a mixture of marine and terrestrial organic matter (OM). Precursor OM was deposited in a deltaic suboxic-oxic environment. Particular differences in the distributions of n-alkanes and bulk parameters are attributed to the post-generative alteration (initial stage of biodegradation and evaporative fractionation). Maturity parameters derived from biomarkers and methylphenanthrenes (MP), in combination with the similarity of the gasoline fractions and the MP distributions of oils and surrounding condensates, indicated that five oils represent a mixture of low immature oil and condensate. One sample, Pavljani (geographically the most distant from the gas-condensate fields), is an oil of low maturity generated from source rocks at a vitrinite reflectance of 0.60–0.70 %.
Keywords
geochemical characteristics; crude oil; Drava Basin; origin; maturation; biomarkers
Hrčak ID:
352784
URI
Publication date:
7.10.2026.
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