GEOCHEMICAL CHARACTERISTICS AND THERMAL MATURITY OF OILS FROM THE THRACE BASIN (WESTERN TURKEY) AND WESTERN TURKMENISTAN

Crude oils in the Thrace Basin (western Turkey) and western Turkmenistan are believed to have been generated by a common Oligocene siliciclastic source rock. This widespread source rock extends over the urea between western Turkey and the eastern South Caspian Basin. Oils from three Eocene reservoirs in the Thrace Basin and from four Pliocene reservoirs onshore western Turkmenistan were analyzed to investigate and compare their source-rock characteristics. In order to understands controls on the timing of hydrocarbon generation and source-rock maturation in both basins, the results (^quantitative, basin modelling were compared with those of geochemical analyses. The results indicate that all the oil samples exhibit similar geochemical characteristics, such as IP13-IP20 acyclic isoprenoid, terpane, regular sterane, methylsterane, and dinosteraneprofiles. The low tricyclic/pentacyclic lerpane ratios, low C(29)norhopane/C(30) lwpane ratios and low diasterane / regular sterane ratios, and the presence of f8(x (H) oleanane and gammacerane further support a common source or source fades. Based on these observations, it is concluded that shallow-marine elastics of Oligocene age constitute source rocks in both hasins. The oils are of tow maturity (Req (%) < 0.60). as indicated hy their low ethylcholestane 20S/20S+20R, 17a(H), 21(beta)(H)-bishomohopane22S/22S+22R, and high 17(beta)(H), 21 a (H) moretane/17(beta)(H), 21 a (H) hopane ratios. However, oils from west Turkmenistan appear to be more mature than those from the Thrace Basin. This is consistent with their earlier generation, which resulted from the higher sedimentation rate and higher healing rate. Present-day reservoir depths and temperatures appear to play only a minor role in determining the oilsʹ maturities.