Hydrocarbon Potential of Middle Jurassic Sediments (Stefanets Mb. of Etropole Fm.) from the Western Part of Balkan Orogenic System, Bulgaria

Sediments of Stefanets Mb. (Etropole Fm.), consisting mainly of shale and siltstones, are investigated by Rock-Eval pyrolysis. The samples from the Middle Jurassic section (Bajocian in age), outcropping within the western part of the Balkan orogenic system in Bulgaria, were analyzed to study their hydrocarbon generative potential. The obtained TOC contents are in the range of 0.69–1.97 wt.%. Inorganic carbon (TIC) and total sulphur (TS) contents are low and coincide with previously published data. The values of S1 and S2 are between 0.01 and 0.10 (mg HC/g rock) because of the high thermal maturity level, as indicated by Tmax values of 566-610 °C. The rocks are in the postmature stage and consequently the HI values are very low (< 10 mg HC/g TOC). The fair to good quantity, low quality, as well as the high level of thermal maturity of the organic matter, assume minor remaining gas-prone generation potential of Stefanets Mb.