Evaluation of the hydrocarbon potential, mineral matrix effect and gas-oil ratio potential of oil shale from the Kabalar formation, GÖynÜk, Turkey

Abstract

The present study focuses on the evaluation of the hydrocarbon potential, retention effect of mineral matrix and the gas-oil ratio potential (GORP) of oil shale from the Kabalar Formation in the Göynük area, Turkey, to assess the quality of its organic matter. The results of Rock-Eval pyrolysis generally suggest relatively high organic carbon content (TOC) for Kabalar oil shale, ranging from 1 to 13.23 wt%. These values are consistent with data on source rocks that may have a good to excellent source rock potential. The kerogen in Kabalar oil shale was characterized based on Hydrogen Index (HI) value, S2/S3 ratio, and organic petrographic studies. The results indicate that most of the studied samples are characterized as containing oil prone (type I and II kerogen) organic matter. The low spore color index (SCI) and high S2/S3 ratio with a commonly low Tmax (< 440 °C) demonstrate that most of the oil shale samples are in the immature to early mature stages of thermal maturity. After calculating the transformation ratio (TR), the oil shale samples were divided into mature (TR = 0.2) and immature (TR = 0) subdivisions in order to take the maturity effects on organic carbon content (TOC) and hydrocarbons retention into account and also select the appropriate GORP overlay. After correcting the mineral matrix effect in the immature subdivision, the mean HI value of the Kabalar Formation increased by about 268 and reached 855 mg HC/g TOC. Due to the relatively higher thermal maturity values, the mineral matrix effect is minimized in the mature subdivision. Based on GORP factor, the TOC(live) of Kabalar oil shale is composed only of oil prone material, which is in good agreement with the results inferred from organic petrographic and pyrolysis studies.