RECOGNITION OF CRUDE OIL TYPES IN THE JURASSIC RESERVOIRS OF CAINAN oil field, THE EAST JUNGGAR BASIN

Many oil fields including Cainan with reservoirs aged from the Carboniferous to the Jurassic have been found in the East Junggar Basin.Dark mudstones exist in different sags around Cainan oil field,and there hasn't been a conclusion about the oil origin of the Jurassic reservoirs in the area.According to the geochemical characters of stable carbon isotope and biomarkers,oils can be distinguished into five types.Oil of the Jurassic reservoirs in Cainan is conformity,and is characterized the δ¹³C value of -27.9‰ to -29.0‰ and the Pr/Ph ratio above 2.5,possibly is originated from mixed organic matters of sapropel and humus in lacustine source rocks of the Middle and the Lower Jurassic coal bearing sequence,instead of the mixture of hydrocarbons from different epochs and different facies of source rocks.