Abstract
The shallow biogenic gas system of the Pohang Basin (Miocene) in Korea is examined by analyzing organic matter (amount, type, and maturity) of bulk rocks and hydrocarbons (molecular and isotopic signatures) in the dissolved and void gases obtained from five wells. The high organic content (total organic carbon < 2.87 wt%, kerogen type II/III) and low thermal maturity (temperature of maximum hydrocarbon generation < 438 °C) of the organic matter indicate that gaseous hydrocarbon production is the result of bacterial metabolism. The dissolved and void gases contain CH4 as the main hydrocarbon component with small amounts of C2H6, and C3H8. The isotopic signatures of the dissolved gas (δ13CCH4 < −51.5‰, δDCH4 < −206‰) indicate a biogenic origin. On the other hand, the δ13CCH4 of the void gas exceeds that of the dissolved gas, increasing from the southern part (δ13CCH4 < −59.5‰) to the northern part (δ13CCH4 < −22.9‰) of the study area. The presence of 13C-rich CH4, C2H6, and C3H8 as well as the δ13CCH4 vs. δ13CC2H6 correlation of the dissolved and void gases indicate a mixed biogenic/ thermogenic origin. This study suggests that the biogenic gas was most likely generated in the early biogenic gas system and it has been mixed with thermogenic gas migrated from the deeper part.
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Acknowledgments
This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20172510102160), and the gas hydrate R&D project of Ministry of Trade, Industry and Energy, Korea (21-1143-2).
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Choi, J., Kang, NK., Hwang, I.G. et al. Geochemical characteristics and origins of hydrocarbon gases in the shallow gas field in the Pohang Basin, Korea. Geosci J 26, 349–365 (2022). https://doi.org/10.1007/s12303-021-0035-1
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DOI: https://doi.org/10.1007/s12303-021-0035-1