H and C isotope trends and anomalies in hot and mature oils from the Pannonian Basin

Abstract Crude oil samples from uncommonly hot (>170°C) reservoirs of the SE-Pannonian Basin were studied for stable carbon and hydrogen isotope compositions of their different fractions. From two fields, 15 samples of different depths and temperatures were chosen for this study. The aim was to study the impact of extreme reservoir conditions on the isotope ratios of the different fractions and to find the ratios that show correlation with increasing depth and temperature. We have shown that the behaviour of isotopes in these very hot oils differs from those from lower temperatures. The combined application of carbon and hydrogen isotope techniques is useful and may provide approximate information on reservoir conditions