Assessment of quality and geological evolution of possible source rocks from the Srbobran local depression: Organic-geochemical approach

Abstract

Possible petroleum source rocks of the Lower, Middle and Upper Miocene from the Srbobran local depression (Pannonian Basin, Serbia) were investigated in detail. The objective was to define oil potential of these samples and to determine the origin, depositional environment and the maturity of the organic matter (OM) on the basis of organic-geochemical investigations. Group organic-geochemical parameters and results of Rock-Eval pyrolysis indicate that all samples, except one, have petroleum generation potential. The OM is of mixed algal-terrestrial origin and consists predominantly of Type II kerogen. Contribution of algal biomass was greater in OM of Pannonian samples that resulted in higher oil generation potential. The OM of the majority of the samples was deposited in fresh water to brackish environment, under slightly toxic conditions. The OM maturity in most of the samples corresponds to the early catagenetic stage. The oil generation in the Srbobran local depression begins at present day relative depths of 2000-2200 m. The oil window, as in other local depressions in the Serbian part of Pannonian Basin, is relatively narrow and shifted to lower vitrinite reflectance values, due to the rapid sedimentation and heating rates, especially during Upper Miocene.

U radu su prikazani rezultati detaljnih ispitivanja uzoraka mogućih naftno-matičnih stena donjeg, srednjeg i gornjeg miocena iz bušotina sa naftnih polja 'Turija' i 'Turija sever', lokalne depresije Srbobran (južna Bačka). Cilj eksperimentalnog rada je bio da se na osnovu organsko-geohemijskih ispitivanja utvrdi naftni potencijal ovih uzoraka i odredi poreklo, sredina taloženja i stepen zrelosti organske supstance. Grupni organsko-geohemijski parametri i rezultati Rock-Eval analize pokazuju da svi ispitivani uzorci, osim jednog, imaju potencijal za generisanje nafte. Organska supstanca je mešovitog algalno-terestričnog porekla, pretežno predstavljena kerogenom tipa II. Većim udelom biomase algalnog porekla i većim naftnim potencijalom karakterišu se uzorci panona. Organska supstanca većine uzoraka taložena je u blago oksičnim uslovima, u slatkovodnoj ili brakičnoj sredini. Zrelost organske supstance ispitivanih uzoraka uglavnom odgovara početnoj fazi katageneze. Relativna dubina početka generisanja nafte u lokalnoj depresiji Srbobran se danas nalazi na oko 2000- 2200 m. Naftni prozor je, kao i u ostalim lokalnim depresijama našeg dela Panonskog basena, relativno uzan i pomeren ka nižim vrednostima refleksije vitrinita - zbog brze sedimentacije i zagrevanja, posebno tokom gornjeg miocena.