Sulphur-containing Compounds in Sulphur-rich Crude Oils from Hypersaline Lake Sediments and Their Geochemical Implications

Three sulphur-rich commercial crude oils have been studied,which contain sulphur as high as up to4—12%.These samples were collected from Tertiary hypersaline lake sediments of the Jianghan Basin,Hubei Province at different depths,but above the oil generation threshold（2200m）.FPD—GC and GC-MSdata show that aromatic fractions of the crude oils are composed of different homologues of sulphur-containing compounds,including long-chain normal alkyl-thiophenes and-thiolanes,long-chainisoprenoid-thiophenes and-thiolanes,and benzothiophenes.It is worth noting that the distribution patternsof long-chain alkyl-thiophenes and-thiolanes from two shallow-seated crude oils are quite similar to thoseof normal alkanes showing marked even-odd predominance.It seems that the even-odd predominance ofsulphur-containing compounds decreases with increasing burial depth of the crude oils.The majorcomponent of aliphatic fraction is phytane,and similarly the major peaks of aromatic fractions also representC;isoprenoid thiophenes.Some preliminary conclusions have been drawn from the above discussion:（1）Abundant sulphur-containing compounds may be used as an indicator of low mature or immature crude oils produced fromhypersaline lake sediments;（2）Sulphur-containing compounds are considered to be early diageneticproducts of reactions between elemental sulphur or sulfides and alkanes or their precursors（phytols,fattyacids,alcohols,etc.）,or of bacterial activities,but not direc■ inputs of organisms.