Organic geochemical study of Aleksinac oil shale

This paper summarizes the most important results and conclusions derived from organic geochemical investigations performed on the Miocene Aleksinac oil shale (Serbia) during the last 60 years. The Aleksinac oil shale is one of the richest and most studied European oil shale deposits. This paper is divided into four sections. The first section includes data from Rock-Eval pyrolysis, organic petrography, and biomarkers of outcrop samples, as well as samples taken from two layers (upper and lower), drilled from the well BD-4. The results consistently indicated that the Aleksinac oil shale contains immature, mostly algal-derived organic matter (kerogen types I and II), deposited in reducing brackish to freshwater environment. However, certain differences were observed between the upper and lower oil shale sequences in the well BD-4, which resulted in two times higher source potential index in the upper layer. The Aleksinac oil shale has been used as a model substance in numerous organic geochemical studies. The second section of the review paper describes how a standard procedure for determination of kerogen chemical structure (controlled gradual degradation of kerogen by an alkaline permanganate solution) is established, which was developed using the Aleksinac oil shale as a substrate. This oil shale was also used as a model substance to investigate the influences of native minerals on the thermal changes of bitumen and kerogen in sediments, and this process is described in the third section of the paper. In the final section, studies (performed on the Aleksinac oil shale) related to the influence of the pyrolysis type and variations of kerogen type on the yield and composition of liquid pyrolysis products are presented.