Geochemical significances of 8,14-secohopanes in marine crude oils from the Tazhong area in the Tarim Basin,NW China

摘要

8,14-secohopanes in the marine oils from the Tazhong area in the Tarim Basin are detected by gas chromatography-mass spectrometry(GC-MS)and gas chromatography-mass spectrometry-mass spectrometry(GC-MS-MS),and their distributions and compositions are compared in order to study their potential significances in oil-source correlation.C35+extended hopane series and three series of extended 8,14-secohopanes can be detected in two kinds of end-member oils in the Tazhong area in the Tarim Basin,and they are different in distribution,suggesting that they may have some special geochemical significance.The presence of 8,14-secohopanes in two kinds of end-member oils in the Tarim Basin suggests that these biomarkers are primary,and not related to biodegradation.The relative abundance of 8,14-secohopanes in the type-A oil is much less than that in the type-B oil,and the 8,14-secohopanes content in end-member oils is much less than that in the corresponding mixed oils.Based on the relative contents of 8,14-secohopanes and the compositions of common steranes and triterpanes,it is very effective to distinguish different crude oils from the Tazhong area.The great difference in the relative abundance of 8,14-secohopanes between the type-A oil and type-B oil suggests that their formation may require some specific geological-geochemical conditions.