It is one of the new advances in reservoir geochemistry to study leakage of fault with geochemical techniques.According to the distribution of n-alkane and the characteristics of biomarkers

there exist 5 types of crude in Kokyar oil reservoir

including original-state oil

residual oil from fractionation through migration

condensate and light oils from evaporation and retrograde condensation

residual crude from gas washing

and crude with wax crystallization.The second type of crude is mainly distributed on the top of the structure

indicating that leakage occurred along small faults and the top of the structure

leading to the obvious difference between ancient and present OWC.Moreover

molecular geochemical analysis of the crude verifies that crude on the top of the structure have relatively higher maturity and higher contents of heavy components and those uneasily to be migrated.