TOC and Rock-Eval Pyrolysis of Middle Miocene Coal Seams in the Orhaneli Coalfield (NW Türkiye)

Bircan C., Oskay R. G., Karayiğit A. İ., Türkmen İ.

3rd International Conference on Engineering and Applied Natural Sciences, Konya, Turkey, 14 - 17 January 2023, pp.204

  • Publication Type: Conference Paper / Summary Text
  • City: Konya
  • Country: Turkey
  • Page Numbers: pp.204
  • Hacettepe University Affiliated: Yes


The Orhaneli Basin is one of the northernmost graben basins in western Türkiye, and hosts two mineable coal seams within the Middle Miocene fluvio-lacustrine deposits. The upper seam (5–6 m) is thicker than the lower seam (0.5-2 m) and mostly composed of matrix and xylite-rich coals, while xylitic coals with dirt bands are more common in the lower seam. This study focuses on the TOC and Rock-Eval pyrolysis of both seams in the Gümüşpınar sector of the Orhaneli coalfield. The TOC contents of the studied samples vary between 20.6-57.6% (avg. 44.1%). TOC contents of the samples from the upper seam are slightly higher than samples from the lower seam due to their lower ash yield contents. The S1, S2, S3 peaks of the samples from both seams range from 0.9–3.0 (avg. 1.6), 18.6–60.3 (avg. 40.8) mg/HC g TOC, and 14.7–34.2 (avg. 26.1) mg/HC g CO2, respectively. The Tmax (410-424, avg. 418°C) and HI (67-113, avg. 91 mg/HC g TOC) values are significantly low in both seams; in contrast, the OI values (51–74, avg. 61 mg/HC g CO2) are higher. Such values are not surprising since xylitic coals are common in both seams. Considering the possible presence of oxygenated functional groups and carbonate minerals in the samples, their breakdown could cause suppression on S2 peak measurements and elevations on S3 measurements due to the release of additional COx gasses during pyrolysis. As a result, evaluating the hydrocarbon generation potential of xylitic coals using Rock-Eval pyrolysis should be performed with caution.