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PSIs the Largest Petroleum Trap of the World in NW Turkey: Korudag Anticlinorium in the South Thrace Basin?*
Samil Sen and Selin Yillar
Search and Discovery Article #70058 (2008)
Posted December 9, 2008
*Adapted from poster presentation at AAPG Annual Convention, San Antonio, TX, April 20-23, 2008.
Geology Department, Istanbul Univeristy, Istanbul, Turkey ([email protected])
The oil and gas-bearing Thrace Basin (NW Turkey) contains Upper Cretaceous to present sediments, reaching a maximum thickness of over 9000 m (Figures 1, 2, and 3). The Korudag Anticlinorium in the SW Thrace Basin was defined in the Korudag region; however, its extensions are not studied as yet. Our studies, based on geological, structural geological and seismic interpretation (Figures 4, 5, 6, and 7), suggest that the anticlinorium is approximately 300 km long and 40 km wide and extends between the Aegean Sea in the west and the area of the Sea of Marmara to the east. The Korudağ Anticlinorium has asymmetrical geometry represented by several folds along the south flank and one fold on the north flank. The anticlinorium was formed by effects of the Neotethyan subduction-accretion complex during late Early Miocene time. In addition, it was deformed to its present day structure by the Oldest Splay of the North Anatolian Fault and the Northern Branch of the North Anatolian Fault.
Presently the Ghawar Anticline located in Saudi Arabia, which is 280 km long and 30 km wide, is considered to be the largest petroleum trap in the world. The Ghawar Anticline is also a unified asymmetrical structure, which is steeper on the western flank and becomes more complex at depth where it comprises several en echelon horst blocks. It also comprises reverse faults and a minor component of right-lateral strike-slip. Therefore, the dimensions of the Korudag Anticlinorium are larger than that of Ghawar Anticline.
According to organic geochemical, oil and gas to source rock correlation and basin modeling studies (e.g., Figure 8), three levels of the basin sediments have oil and gas generation potential, and oil and gas have been generated. The basin also has many potential reservoirs. Although gas and oil are being produced from the Korudağ Anticlinorium and its sub-parallel anticlines, it has not yet been tested and explored comprehensively.
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Formation of the Korudag Anticlinorium The Korudag Anticlinorium formed during the Early Miocene, as folded pre-Lower Miocene sediments are seen to be unconformably overlain by unfolded Middle Miocene sediments. The tectonic stresses controlling the formation of the Korudag Anticlinorium were created by the closure of the Neotethys Ocean during late Early Miocene. However, the present Korudag Anticlinorium was shaped by the Oldest Splay of the NAF (late Middle Miocene) and effects of the NAF-N (not earlier than 200 Ka).Petroleum Geology of the Korudag Anticlinorium The source rocks in the south Trace Basin are represented by a) the Karaagac or Hamitabat Formation, b) the Gazikoy or Ceylan Formation, c) the Mezardere Formation. The reservoir rocks in the south Thrace Basin are represented by a) the Karaagac Formation, b) the Ficitepe Formation, c) the Sogucak Formation, d) the Gazikoy Formation, e) the Kesan Formation, f) the Osmancik Formation, and g) the Danisment Formation. Production of the North Marmara, Degirmenkoy, Cayirdere, Seymen, Karacali, Yulafli, Tekirdag, Sevindik and Vakiflar fields should be associated with the Korudag Anticlinorium and its sub-parallel anticlines. Therefore, exploration should be tried in extensions of the Anticlinorium, such as offshore Tekirdag, including targeting the Hamitabat Formation with deeper wells. Despite the 19 unsuccessful exploration wells, potential reservoirs of the Sogucak, Ficitepe and Karaagac formations in the Korudag Anticlinorium should be tested in the SW Thrace and NW Aegean Sea. Presently, the Ghawar Anticline located in Saudi Arabia, which is 280 km long and 30 km wide and harbors 60 billion barrels of oil and much gas, is considered to be the largest unified petroleum trap in the world (Xian, et al., 2003; Afifi, 2005; Durham, 2005; Saner et al., 2005; Dasgupta, 2005). However, Korudag Anticlinorium, at nearly 300 km long and 40 km wide, is larger than the Ghawar Anticline. Although giant structures are not always giant petroleum traps, such as the Destin Dome in the Gulf of Mexico, the Korudag Anticlinorium has not been tested and explored extensively. This work was supported by the Research Fund of Istanbul University (Project number 1773/21122001) and the Turkish Petroleum Corporation (TPAO). We thank I. Erdal Kerey (Beykent University), Sener Usumezsoy and Esref Yalcinkaya (Istanbul University), Salih Saner (Schlumberger Oilfield Services, Saudi Arabia), Gilbert Kelling (Keele University), Aynur Buyukutku (Ankara University), Mete Gurel, Zihni Aksoy, Hasan Emiroglu and Attila Ozatar (Turkish Petroleum Company) and Selami Incedalci (Petroleum Affairs of Turkey) for helpful and constructive comments. We also would like to thank Gretchen M. Gillis, Gary L. Prost, Patrick M. Shannon, Ronald A. Nelson, and Laird B. Thompson for their helpful comments and suggestions that greatly improved our manuscript. A.M. 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