The Thrace Basin, NW Turkey, is one of the most important basins in Turkey in terms of hydrocarbon potential. Previous studies, starting in the 1930s, focused on tectonics, basin evolution, sedimentation and stratigraphy, depositional systems, and hydrocarbon potential. Eocene turbiditic sandstones and reefal limestones, and Oligocene deltaic sandstones are the major reservoir targets in the basin today. The focus of this research is the Upper Oligocene deltaic sandstones, namely the Danismen and Osmancik formations, which contain potential hydrocarbon reservoirs. The aims of research were to develop a better understanding of the geometric configuration of the Oligocene strata and to identify potential reservoirs within the study area. Accordingly, the geometric configurations of the strata were delineated using 3D seismic reflection data whereas petro-physical properties of the target formations were determined using wireline logs from three wells. A right-lateral strike slip or reverse fault system and associated NW-SE trending asymmetric fold extend across the study area. Both the fault system and the fold are truncated beneath the Miocene unconformity and are thus dated as late Oligocene to early Miocene in age. The Miocene unconformity forms a stratigraphic trap whereas the fault system and associated fold construct a NW-SE trending structural trap. Hydrocarbon-bearing, five main clean sandstone (shale volume less than %10) intervals were identified using wireline logs and evaluated as potential targets. Hydrocarbon concentrations increase through the fold structure. Thus, the fault system and the associated asymmetric fold were the main factors that affected the zonal distribution of hydrocarbons in the study area. / Master of Science / Thrace Basin, northwest part of Turkey, is one of the most important basins in Turkey in terms of oil and gas potential. Previous studies started in1930s and included studies on the geology of the basin. Major reservoir targets in the basin today are Eocene turbiditic sandstones and reefal limestones, and Oligocene deltaic sandstones. This study focuses on the Oligocene deltaic sandstones of the Danismen and Osmancik formations, which are significant in terms of the oil and gas potential in the basin. The main purpose of this thesis is to evaluate the geometric configurations of these two formations and to identify potential reservoirs within the study area. For this purpose, geometric representation of the study area was generated by mapping the formations with the help of 3D seismic data. Reservoir characteristics related to physical properties were determined by utilizing the data obtained from three wells within the study area. As a result, potential reservoir zones are discovered mainly in the Danismen Formation, which can further be incorporated with exploration activities in the basin.

This study investigates the depositional history of the Late Eocene sedimentary record in the northwest of the Thrace Basin in a sequence stratigraphic approach and estimates the contribution of regional tectonics, basin physiography and eustasy. Late Eocene sedimentary succession was analyzed in two third-order sequences based on two major data sets / seismic reflection and well data sets. Depositional Sequence-1, represented by progradational stacking patterns, comprises the coarse-grained Hamitabat turbidite system. The base of the Sequence-1 was defined as the base of channel fill deposits in the northern shelf setting and the base of slope fan deposits in the slope setting. This boundary separates Lower-Middle and Upper Eocene sediments. In the slope setting, the Hamitabat turbidite system was analyzed in three major depocenters / Western, Northwestern and Northeastern depocenters respectively. Hamitabat turbidite system was controlled by the interaction of regional tectonics, basin physiography and eustatic fluctuations in the Late Eocene. This study highlighted the role of the regional variables / tectonic influence and basin morphology on the submarine canyon formation. The facies distribution was controlled by the high subsidence rate of sea-floor dominantly instead of eustasy. Depositional Sequence-2, represented by mostly retrogradational stacking patterns, is a clastic-carbonate mixed system. Depositional Sequence-2 was subdivided into three higher-order sequences. The lower sequence boundaries were induced by the rapid relative sea-level rise. The upper boundary of the Depositional Sequence-2 was defined as the termination of clastic-carbonate mixed system and a candidate for the Eocene-Oligocene contact.

The Thrace Basin located in northwest Turkey displays attractive prospective traps for hydrocarbon and has received much attention from the petroleum industry. Despite the extensive exploration efforts, there are only few studies which address the fault kinematics and deformation mechanism of the region in connection with structural development. In this study, 3D raw seismic data set collected around Temrez High near Babaeski fault zone will be processed and interpreted along with the available borehole data to reveal the subsurface structure of the region that will contribute towards understanding the Neogene tectonic evolution of the central Thrace basin, origin of the transcurrent tectonics and possible role of the North Anatolian Fault Zone.

Thermal maturity modeling is widely used in basin modeling. Of the available models, Easy%Ro has gained acceptance. Thermal gradients (TG) at seventy wells in the Thrace Basin are calibrated against vitrinite reflectance (%Ro). A 90% confidence interval is used to assess the uncertainty. Best paleo-TG are obtained from the MSR curves. Comparison of the paleo-TG with the actual ones showed that thermal regime of the Thrace Basin did not dramatically change during geologic history. A correlation between geological and thermal properties of the basin is established. Thermal regime of the Thrace Basin is controlled by 1) basement edge affect / 2) crustal thickness variations ad basement heat flow / 3) lateral thermal conductivity variations within the stratigraphic column / 4) transient heat flow affect / and 5) influence of the tectonic features. Basement edge affect is traced at the steep northern margin. Central part of the basin demonstrates lower TG. THe Eocene Ceylan Formation with relatively lower thermal conductivity plays a thermal reducing role. Areas of high sediment influx are associated with low TG due to the transient effect of the immature sediments. Fault systems of the Thrace Basin do not possibly have influence on paleo-thermal gradients.

This study aims to analyze the leak-off tests carried out in the Thrace Basin of Turkey by Turkish Petroleum Corporation and find any relationship that may exist between leak-off test results and drilled formations as well as drilling parameters, such as mud weight, depth. The analysis of 77 leak-off tests indicated that there is no close correlation between the mud weight of test fluid and equivalent mud weight (fracture gradient) if the test is carried out within impermeable sections. On the other hand, the correlation between mud weight and equivalent mud weight increase while running the test within permeable-productive zones. It is also found that the leak-off test results are not dependent on the depth but the formation to be tested. The analyzed leak-off test results from Thrace Basin showed that the fracture gradient is not the limiting factor to set the casing of any section unless a gas show is observed during drilling operation which occurred only in 5 wells out of 78 wells analyzed.