Geochemical Characteristics and Origin Classification of Crude Oil in Wangjiagang Area in Dongying Sag

The correlation of geochemical characteristics of saturated hydrocarbon and aromatic hydrocarbon compounds among crude oil,oil-bearing sandstone and source rock extractive matters in the studied area is conducted.The result shows that the crude oil can be divided into four types of origins.The first type of crude oil is characterized by low density,low sulfur,high wax content,gas chromatography of saturated hydrocarbon showing single peak,m(Pr)/m(Ph) ratio ranging from 0.51 to 0.72,relative content of sterane of C29C27C28 showing reverse L shape and high maturity,reflecting the origin of higher plants,which originates from Ek2 source rock;the second type by high density,high sulfur,low wax content,single peak shape,m(Pr)/m(Ph) ratio less than 1.0,sterane content of C27C29C28 showing asymmetrical V shape,high gammacerane content and high maturity,reflecting the origin of lower aquatic organism,which originates from Es4 source rock;the third type shows dual-peak shape,sterane content of C29C27C28 also showing reverse L shape,reflecting the mixed origin of lower aquatic organism and higher terrigenous plants,which originates from Ek2 and Es4;the fourth type by biodegradation and lack of n-alkane,being an origin-mixed crude oil of Es4.The fourth types of crude oils in this area assume regular distribution spatially.