Proceedings World Geothermal Congress 2005 Antalya, Turkey, 24-29 April 2005 1 Organic Geochemistry of Hydrothermal Petroleum in the Menderes-Gediz Graben System, Denizli-Saraykoy, Western Turkey: Preliminary Results Kadir Gürgey 1 , Bernd R.T. Simoneit 2 , Ismail H. Karamanderesi 3 and Baki Varol 4 1 Turkish Petroleum Corporation Research Center, 06520 Ankara, Turkey 2 Oregon State University, Corvallis, OR 97331,USA 3 Consultant EVKA-3 Mah., 126Sok. 1/6, 35050 Bornova-Izmir, Turkey 4 Geological Engineering Department, Ankara University, Ankara, Turkey gurgey@petrol.tpao.gov.tr Keywords: Denizli, Turkey, organic geochemistry, Büyük Menderes graben, hydrothermal petroleum ABSTRACT Western Turkey is situated in the geologic province of Aegean region. It is seismically one of the most active regions of the world and includes prospective areas for hydrocarbons, coal beds, and geothermal sources. The KB- 5 well, from which the petroleum sample was taken, has been located at the intersection of the geothermally active Menderes and Gediz grabens near the town of Saraykoy. During drilling, the petroleum erupted onto the surface with its associated thermal water (120 o C) from a depth of 120- 132 m (e.g., from Early to Middle Pliocene aged claystone and marl). Drilling was stopped at a depth of 253 m when it reached to reservoir limestones of the Sazak Formation. The purpose of this paper is twofold: (1) to understand the generation mechanism of the petroleum, either by geothermal-gradual or hydrothermal-rapid processes, and (2) to assess the nature of source from which it was derived. In order to achieve these purposes, the sample was analyzed by organic geochemistry using thin layer chromatographic separation followed by gas chromatography-mass spectrometry (GC-MS). The KB-5 petroleum is composed primarily of polar NSO compounds+asphaltenes (77%), aromatic hydrocarbons (19.22%), and minor saturated hydrocarbons (3.78%). This feature is similar to hydrothermal petroleum of Calcite Springs from Yellowstone National Park, Wyoming, U.S.A. TIC traces of the KB-5 sample shows n-alkanes ranging from n-C 20 to n-C 38 but depleted <n-C 20 and maximum at n- C 30 . An absence of acyclic isoprenoids (pristane, phytane) and considerably large UCM (unresolved complex mixture) point out that this oil has been subject to moderate degree of alteration possibly by hot geothermal waters.The parameters obtained from sterane and terpane biomarkers present in the oil (low C 29 NH/C 30 H ratio; presence of gammacerane, high C 35 /C 34 homohopane ratio; 18α(H)- oleanane, n-C 28 <n-C 27 <n-C 29 , C 28 <C 27 <C 29 steranes, %C 29 αααR>%C 27 αααR) suggest that the petroleum sample was generated from a Tertiary source rock with a clay-rich lithology, terrestrial-rich organic matter deposited in relatively saline and anoxic environmental conditions. Maturity sensitive biomarker parameters (Tm>Ts, C 29 20S/20S+20R=0.35, C 32 22S/22S+22R=0.57, low diasterane/regular sterane ratio) correspond to a maturity level of about 0.50-0.60 %Ro. This level of maturation could not be reached by such a young and shallow source rock and/or oil in the absence of “instantaneous” hydrothermal activity 1. INTRODUCTION Western Turkey is situated in the geologic province of Aegean region (Fig. 1a). It is seismically one of the most active regions of the world and includes prospective areas for hydrocarbons, coal beds, and geothermal sources. Although large amounts of geothermal resources have been already discovered (Şimşek and Yılmazer, 1977;Şimşek, 1985; Şimşek and Güleç, 1994; Şimşek, 2002), however, petroleum potential of the region appears to be limited regardless of the existing and promising structures. National oil company of the Turkey, TPAO, has drilled a few wells to explore any possible potential for commercial quantities of hydrocarbons in the area.One of the wells (Alaşehir-1; Fig.1) drilled in the Gediz Graben encountered petroleum at about 1991 m but it was in non-commercial quantities. The other well, (Nazilli-1; Figs.1b and 2) drilled again by TPAO was in the Büyük Menderes Graben where, no petroleum was encountered. Recently, the well drilled (KB- 5 well; Figs. 1b and 2) by a private geothermal water supply company, in the Büyük Menderes Graben, approx. 30 km away from the Nazilli-1 well (Fig.1) erupted with petroleum like material from 120-132 m interval with accompanying hydrothermal solution at 120 o C. Close association of hot geothermal fluids and petroleum in the KB-5 well made us to suspect that this petroleum might have been hydrothermaly generated. “The geothermal-gradual (conventional) petroleum is natural products of basin evaluation and are generated cotemporaneously with sediment compaction and heating. In contrast, petroleum generated in high temperature and with high-fluid flow regimes are defined here as hydrothermal in origin because the agent of thermal alteration and mass transfer, hot circulating water , is responsible fro petroleum generation and migration from the source rocks or unconsolidated sediments. Generation of hydrothermal oils and gases are relatively rapid, whereas geothermal oils are generated at a rate that is tied to basin subsidence” (Didyk and Simoneit, 1990). The purpose of this paper is twofold: (1) to understand the generation mechanism of the petroleum collected from the KB-5 well, either by geothermal-gradual or hydrothermal- rapid processes, and (2) to assess the nature of source from which it was derived. In order to achieve these purposes, petroleum like material from the KB-5 well, was compared to the petroleum from the nearby Alaşehir-2 well in the Gediz Graben. Both, the KB-5 and Alasehir-2 petroleum samples were analyzed by organic geochemistry using thin layer chromatographic separation followed by gas chromatography-mass spectrometry (GC-MS). The petroleum sample, which has been described to be