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Allochthonous Blocks and Thrust Tectonics Effects to Petroleum Exploration in the Ulus Basin, Western Black Sea of Turkey

Abstract

The Black Sea of Turkey is currently an area of increased interest for the petroleum industry. The Ulus Basin and the Central Black Sea Basin of Black Sea are similar basins with the Midland and Delaware Basin of West Texas because their central areas are represented by uplifts of the carbonate platforms, respectively. Altough detailed hydrocarbon exploration assessments of the Central Black Sea Basin are present, any detailed investigation related with the Ulus Basin, which extends from Zonguldak in the west to Kastamonu in the east, nearly 250 km long and 150 km wide is not present. Mudstone-marl and turbiditic shales of the Lower Cretaceous Ulus Formation in the Western Black Sea Basin of Turkey have poor to fair source rock potential with maturity levels of early mature and middle mature because TOC content ranges from 0.34 to 1.18 % and T-max values have been measured between 438 and 457 °C. HI values are also low (between 20 and 259). The data suggest that the formation produces limited oil and wet gas-condensate. Turbiditic conglomerates and sandstones of the Ulus Formations and platform carbonates of the Inalti Formations are potential reservoir rocks. Main seals are represented by mudstones/shales of the Lower Cretaceous Ulus Formation and micritic limestone of the Kapanbogazi Formation. Stratigraphic trap possibilities associated with the turbiditic channel conglomerate and sandstones are present. Many extensional faults, rollover structures, anticlines and thrusts are potential structural traps. Although three onshore exploration wells were drilled in the basin, no oil and gas was found. The causes of the unsuccessful conventional exploration are allochthonous blocks and thickening of sediments by thrust tectonics. Limestones and magmatic rocks that crops out around west of Yenice, north of the Karabuk-Safranbolu-Eflani-Pinarbasi are allochthonous blocks. The sediments consist of both mega blocks inside shale/mudstone and of blocks inside a mudstone-sandstone matrix. The Ulus Basin has intense trusth tectonics. The tectonics can clearly be seen both seismic-cross section scale and outcrop-scale