--> Organic Geochemical Characteristics and Factors Controlling the Organic Matter Accumulation in Silurian Black Shales From the Ovacik District, Central Taurus Region, Turkey: Implications for Source Rock and Gas Potential

AAPG ACE 2018

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Organic Geochemical Characteristics and Factors Controlling the Organic Matter Accumulation in Silurian Black Shales From the Ovacik District, Central Taurus Region, Turkey: Implications for Source Rock and Gas Potential

Zeynep Doner1, Mustafa Kumral1, Ismail H. Demirel2, Qinhong Hu3


1Department of Geological Engineering, Istanbul Technical University, Istanbul, Turkey.
2Department of Geological Engineering, Hacettepe University, Ankara, Turkey.
3Department of Earth and Environmental Sciences, University of Texas at Arlington, Arlington, TX, United States.


July 23 - 25, 2018 – AAPG ACE 2018,

Posted: July 23-25, 2018

Abstract

This work studies the organic geochemical properties of Silurian black shales of the Ovacik district in central Taurus Mountain Belt, southern Turkey. Throughout the Paleozoic, the Taurus Mountain Belt evolved as a continental shelf along the long and wide northern margin of Gondwana. Silurian black shales were deposited in dysoxic to anoxic environments according to many redox indicators such as V systematics (V/Sc, V/(V+Ni)) as well as ratios of Ni/Co, Th/U, Cu/Zn and Mo/Mn. However, the negative and/or weak relationship between TOC and productivity index (P/Ti) indicates that OM accumulation was not mainly controlled by primary productivity, but rather by dysoxic-anoxic bottom water environment.

A total of fifteen outcrop black shale samples were analyzed by Rock Eval Pyrolysis. The Total Organic Carbon (TOCpd) contents at the present time ranges from 0.32 to 1.57 wt. % with an average of 0.63 wt. %. Extremely high Tmax values (up to 608oC) and low Hydrogen Index (HI) values (1–9 mg HC/g TOC) indicate that these black shales are thermally over mature and seems to be a spent hydrocarbon source rock. The remaining hydrocarbon generative potential (S1+S2) of 0.02–0.22 mg HC/g rock also supports this assessment. When plotting the H/C versus O/C atomic ratios on the modified Van Krevelen diagram, the recent organic matter type is Type IV kerogen that can yield limited gas products. According to interpretive of shale gas potential parameters based on Jarvie’s equation reconstructed average original values of TOCo is 2.85 wt. %, HIo is 450 mg HC/g TOC, Ro 1.88 % and TRHI is 99.45 % indicating primarily dry gas window and good risk for gas. Though further researches are required, this study overall suggests a negative effect on the shale gas potential in the study area.

Keywords: Silurian black shale, Taurus Belt, Turkey, organic geochemistry, hydrocarbon potential, redox condition

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018