ABSTRACT
Based on the distributions and compositions of various biomarkers within different crude oils from the Huizhou Sag, it can be classified into coal-derived and lacustrine oils. The coal-derived oils from the HZ9-2-1 well are characterized by a higher Pr/Ph ratio (>4.5), abnormally abundant C24 tetracyclic terpane, a step-like decreasing pattern for C19-26 tricyclic terpanes, more abundant C29 norhopane, C31 homohopane, and lower neohopanes in C27-35 hopanes, absolutely predominant C29 rearranged and regular steranes in C27-29 steranes. These features are the main indicators to discriminate coal-derived oils from other oils. However, in lacustrine oils, their Pr/Ph ratios are relatively low (<3.0), the abundance of C24 tetracyclic terpane and C26 tricyclic terpanes are similar, the distribution of C19-26 tricyclic terpanes is normal and C21 component is the main peak, neohopanes rearranged hopanes are moderate, gammacerane index indicating paleosalinity is very low. It is noted that in this kind of crude oil, 2-methylhopanes and 4-methylsteranes indicating cyanobacteria and dinoflagellates input, respectively, are very abundant, and the variation of the relative abundance has a normal correlation, representing a specific ecosystem condition to be suitable for the growth of two kinds of microbes. They have an important role in oil-source correlation in this study.
