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Source Rock Potential of The Middle Triassic - Lower Jurassic Cudi Group Units, Southeast Anatolia, Turkey

Abstract

Southeast Anatolia is the main oil producing region of Turkey. The area is located along the northern margin of the Arabian plate. The region contains rock units ranging in age from Paleozoic to Mesozoic. The Triassic to Lower Jurassic Cudi Group, which is composed mainly of intercalated shales, is thought to be the source of the solid bitumens in SE Turkey. The main area of this study, the Cudi Group represented by the Bakük, Girmeli, Çamurlu, Telhasan, Dinçer, Kozluca and Yolaçan Formations in the eastern part of Turkey. The Group consists of dolomite, limestone with minor evaporite, shale and chert and It is around 1450 m thick in the study area. Sediments have an average of 0.15 % total organic carbon (TOC). Commonly, TOC is higher in carbonate - rich facies than is evaporitic deposits. Where a significant amount of sulfate exists in the sediment (in the Bakük, Telhasan, and Kozluca Formations), the organic content is generally very low, presumably because the conditions associated with the intrasedimentary growth of calcium sulfate from interstitial brines involved oxidation of the organic materials. The S1 (average 0.25 mgHC/grock), S2 (0.40 mgHC/grock), HI (average 235 mgHC/gTOC), OI (average 231 mgCO2/gTOC) and Tmax (average 422oC) values from the Rock - Eval pyrolysis indicate that the dominant organic matter consists of types II and III kerogen, which have gas generative potential. Optical investigations in transmitted and fluorescent light reveal that the organic matter contain mainly amorphous organic matter (70–90 %) of marine origin and a small amount of humic - terrigenous organic matter (10–30 %) of ligneous origin generally hydrogen depleted. PI values of 0.1 and 0.4 mark the entrance and exit from the oil window in the absence of hydrocarbon migration either out of or into the sample under examination. Little or no control exists, howewer, to estimate the extent to which hydrocarbons have moved out of these samples. This value difference may indicate the presence somewhat of different litologic units in the formations. Tmax values are generally less than 435oC, confirming that the sediments are immature with respect to hydrocarbon generation. Organic geochemical determinations indicate that, considering the amount, type and level of maturation of Cudi Group units, these formations shouldn't serve as oil source rock. Within the study area, howewer, the hydrocarbon production may be poor oil and gas.