GC and GC-MS analysis was performed on compounds possibly containing information on maturity in four light oil samples selected in Hetianhe gas field.Maturity indexes including heptane index

isoheptane index

methyldiamantane index

MPI

methyldibenzothiophene(MDBTs)and Ts/(Ts+Tm) indicate that the light oil in Hetianhe gas field is at high maturation stage(gas condensate).In contrast

methylnaphthalene

C

29

sterane 20S/(20S+20R) and C

29

sterane ββ/(αα+ββ) suggest that the source rocks have not entered peak oil generation stage.Indexes such as light hydrocarbon show that high maturity of the light oil is consistent with its physical properties.The anomalies of naphthalenes may be the result of weak biodegradation

while the low sterane indexes may be the result of overturning at the end of evolutionary balance.Comprehensive analyses of the maturity indexes reveal that the light oil is at the end of maturation-high maturation stage.Furthermore

comparison with the typical local source rocks indicates that both the light oil and natural gas are generated by the Cambrian source rocks

a conclusion supported by oil-source correlation based on sterane and terpane.