C

1

-C

7

light hydrocarbon of 150 canned cutting samples collected from a test well are analysed with capillary GC so as to study the regularity how light hydrocarbon composition varies with buried depth.Light hydrocarbon is mainly methane when rocks yielding it are buriedless than 2

650m;the ratio of(C

2

-C

4

)/(C

1

-C

4

)increases rapidly from less than 30% to 60% when buried depth is about 2

650m;but C

4

-C

7

turn to bethe primary components when buried more than 3

650m.It is obvious that with the increase of buried depth

the content of N-alkana and cycloalkane increases gradully while the iso-alkane decreases.Within the depth of 3

750m

cyclohexane/cyclopentane ratio increases with the increase of the depth

suggesting that cyclohexane is more stable than cy-clopentane in thermo dynamics.But the ratio shows obviously a decrease tendency with the increase of depth

when it is buried bellow 3

750m

this ap-pears to be related to the preferential aromatization of cyclohexane.In accordance with the mass-producing of wet gas

the methyl cyclopentane/cyclopentane and methylcyclohexane/cyclohexane ratios get the maximum values

similar variation is also observed in the dimethyl cyclopentane/cyclo-pentane ratio.The ratio of 1

1-dimethylcyclopentane to isomers of dimethylcyclopentaneis usually less than 0.1 and changes slowly when the buried depth is shal-lower

but increases rapidly to more than 0.3-0.4 when buried greater than 3

300m.It is believed that differential evolution and maturation are probably thegeneral characters in the evolution process of organic matter

and various ra-tio of light hydrocarbons mentioned above may be considered as indices ofmaturity.