Based on oil physical features

group compositions

biomarker compounds and biodegradation

the crude oil in the Daerqi oilfield is classified into five types.Type I oil is a low viscosity and density

light oil. Its group composition is predominately the saturated hydrocarbon

with a low contents of nonhydrocarbon and asphaltic components. This type of oil is unbiodegraded

with a high sterane isomerization index and maturity. Type Ⅱ oil is immature and extremely viscous

with a relatively high density. Its group composition is dominated by nonhydrocarbon and asphaltic components

with a low content of saturated hydrocarbon. This type of oil is unbiodegraded

with a low sterane isomerization index. Type Ⅲ oil is a mixed product of type I oil and type Ⅱ oil. Type Ⅳ oil is a common viscous oil

with a relatively high viscosity and density

which is formed by biodegradation of type I oil. Type V oil could be caused by biodegradation of type Ⅲ oil. Its density and viscosity are similar to that of type Ⅳ oil

but sterane isomerization index is relatively low. Excluding the type Ⅱ oil (immature and extremely viscous oil) from the shallow immature source rock of the Duhongmu Formation

all the oil of other four types are mainly derived from the higher mature

deep-seated source rocks of the Tenggeer Formation and/or A'ershan Formation.