Unconventional Gas Potential of Black Shales from Silurian Findikli Formation in northwestern Anatolia, Türkiye: Characterization of Geochemistry

As conventional hydrocarbon resources become depleted and theoretical innovations in hydrocarbon exploration advance, unconventional resources have gained substantial attention from researchers and explorers in recent decades. In the global energy consumption structure, unconventional shale gas progressively assumes a crucial role in the overall energy landscape. This research is motivated by the high probability of deriving gas accumulations encountered in drilling on the northwestern Anatolia (Akcakoca area) offshore from Paleozoic-aged rocks. Studied black shales from the Silurian Findikli Formation in the Sakarya region of northwestern Anatolia are one of the alternative unconventional resources.

Working with outcrop samples, this work evaluates the unconventional gas potential by performing geochemical characterization of these black shale samples. Studied samples were analyzed by Rock-Eval Pyrolysis. The present-day total organic carbon (TOC_pd) contents range from 0.54 to 1.57 wt.%. High Tmax (up to 504^oC) and low Hydrogen Index (HI) values (4-38 mg HC/g TOC) indicate that these shales are thermally over-mature and seem to be a spent hydrocarbon source rock. The remaining hydrocarbon generative potential (S1+S2) of 0.06–0.49 mg HC/g rock also supports this assessment. The recent organic matter type is Type IV kerogen which can yield limited gas products plotting on the H/C versus O/C atomic ratios on the modified Van Krevelen diagram. According to the interpretive of shale gas potential parameters based on Jarvie’s equation reconstructed these black shales originally may have good to very good source rock potential, with the calculated average original values of TOC_o being 1.72 wt.% and HI_o is 448 mg HC/g TOC. It can be concluded that the characteristics of studied shales seem to be nearly compatible with those of Utica shales in terms of the hydrocarbon generative potential. The studied black shales have lost 95% of their original hydrocarbon potentials, and seem to be a spent hydrocarbon source rock, indicating good risk for gas. However, the source rock may be very deep and deformed from the past to the present day, considering the paleogeographical location and geological evolution of the study area. Further research is required.

Keywords: Unconventional Gas Potential, Source Rock, Geochemical Characteristics, Silurian Black Shales, Northwestern Anatolia (Türkiye)