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

Abstract

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. C 35 + 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.