Research on the Properties and Origin of the Crude Oil from the Transition Zone of Southern Xingshugang District in Daqing Oil Field,Northeastern China

The crude oil of the southern Xingshugang district in Daqing oil field is of lower density, lower viscidity,lower colloid,high wax and lower freezing point,and belongs to the typical light oil type. It also has higher saturated hydrocarbon content,overall hydrocarbon content and higher saturated to aromatic hydrocarbon tatio,which indicates the input of original algae. The carbon number distribution of normal alkanes shows a range from C_ 15 to C_ 39 with a peak at nC_ 22 or n C_ 23 . Moreover,the whole oil and its family group show a feature of light carbon isotopes. The crude oil is very rich in steranes and contains a few 4-methyl steranes. The C_ 27 and C_ 29 sterane compound concentrations and the C_ 28 sterane compound concentrations are low,and the distribution of C_ 27 ,C_ 28 and C_ 29 steranes is “L shaped. The pentacyclic triterpanes in the crude oil are also plentiful. They are mainly hopanes,novel hopanes and gammaceranes. The oil-source rock correlation indicates that the crude oil has the similar carbon isotope compositions,and the similar steranes,terpanes distribution with the mudstone of the Lower Qingshankou Formation in Sanzhao sag,which suggests that the crude oil in the study area was derived from the Lower Qingshankou Formation in Sanzhao sag.