Geochemical Characteristics and Genesis of Reservoir Bitumen of Feixianguan Formation in Well Puguan 2,  Northeast of Sichuan

Key words: 
• reservoir bitumen /
• geochemical /
• genesis /
• Feixianguan Formation /
• Well Puguang 2 /
• northeast of Sichuan Basin /
•  /

Abstract: Based on the information about reservoir bitumen, such as occurrences, types, group composition, the characteristic of saturated hydrocarbon' gas chromatogram and biomarkers, as well as the reservoir bitumen reflectivity, this paper thoroughly analyze the geochemical characteristic of reservoir bitumen from Feixianguan Formation in Well Puguang 2 and its possible cause of formation. It is concluded that the reservoir bitumen which is classified to thermal pyrobitumen is the residue formed after ancient reservoir cracked. nalkane in reservoir bitumen distribute integrally with the carbon number range from C14 to C30, without obvious trace of biodegradation. Pr/Ph、Pr/nC17 and Ph/nC18 are all smaller than 1.0, OEP varies from 1.25 to 1.43 and CPI varies from 0.98 to 1.19, without odd even predominance of normal alkanes. Among regular silane series, C27 plays a dominant role with the appearance of "V" shape of the distribution of C27C29. Isomerization of sterane in initial stage, the ratio is obviously below average value. It is believed that "S" configuration crack faster than "R" configuration is the reason. The content of pregnane and litres of progesterone silane steroid in Fei1 Formation and Fei2 Formation is apparently higher than the counterpart of Fei3 Formation as the result of the difference of environment of sedimentation or source rock. Among terpene series, pentacyclic triterpenoids dominate, tricyclic ones develope well, especially ,C23 is the base peak, the content of gammacerane is relatively high. All of these characteristics mentioned above demonstrate that reservoir bitumen in Puguang2 Well mainly derived from lower level hydrobiont, thermal evolution stayed at middlehigher stage. Parent materials formed in marine sedimentary environment with high salinity. The high content of C25norhopane is associated with high thermal evolutional stage rather than biodegradation.