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High-sulfur,heavy petroleum is widely occurring in the Tertiary lacustrine Jiyang sub-basin, Bohai Bay Basin.They are differentiated into two families based on the bulk properties and biomarker compositions.Family 1 is characterized by high resins(40%-71%)and sulfur(2%-4%),and low wax (l%-6%),with n-alkanes removed by biodegradation,whereas family 2 is characterized by extremely abundant sulfur(3%-10%),and high asphaltenes(7%-31%)and wax(2%-19%),with no evidence of microbial attack.The oils of family 1 are distributed in the reservoir,lower than 1500 m throughout the sub-basin.Biomarker assemblages,such as low pristane/phytane ratios(<1 Pr/Ph)and a high abundance of carotane,gammacerane,and dinosterane,suggest that they are derived from the calcareous mudstones and shales among the stratified,saline Es_4~u unit,in addition to the in situ biodegradation-concentrated sulfur content.However,the oils of family 2 are identified only in the western Zhanhua and eastern Chezhen depressions,with a depth deeper than 1700 m.Physical properties,together with biomarker ratios,including even-numbered n-alkanes,<1 Pr/Ph,trace diasteranes,higher C35 homohopanes,and abundant dibenzothiophene series,with>1 dibenzothiophene/phenanthrene,indicate an origin from carbonate source rocks.The X-ray diffraction analysis showed that the carbonate source rock is limited in the Es_4~u unit of the Bonan sag,which is different from most other source rocks in the same horizon.It is suggested that the high-sulfur,heavy oils are generated at the early stage of the oil window.Bacterial sulfate reduction might be responsible for the occurrence of sulfur species in the high-sulfur,heavy oils,while heavy biodegradation will enhance sulfur concentrations.
High-sulfur, heavy petroleum is widely occurring in the Tertiary lacustrine Jiyang sub-basin, Bohai Bay Basin. They are differentiated into two families based on the bulk properties and biomarker compositions. Family 1 is characterized by high resins (40% -71% ) and sulfur (2% -4%), and low wax (l% -6%), with n-alkanes removed by biodegradation, while family 2 is characterized by extremely abundant sulfur (3% -10%), and high asphaltenes (7% -31%) and wax (2% -19%), with no evidence of microbial attack. The oils of family 1 are distributed in the reservoir, lower than 1500 m throughout the sub-basin. Biomarker assemblages, such as low pristane / phytane ratios (<1 Pr / Ph) and a high abundance of carotane, gammacerane, and dinosterane, suggest that they are derived from the calcareous mudstones and shales among the stratified, saline Es_4 ~ u unit, in addition to the in situ biodegradation-concentrated sulfur content. Yet, the oils of family 2 are identified only in the western Zhanhua and eastern Chezhen depressions, wit ha depth deeper than 1700 m.Physical properties, together with biomarker ratios, including even-numbered n-alkanes, <1 Pr / Ph, trace diasteranes, higher C35 homohopanes, and abundant dibenzothiophene series with> 1 dibenzothiophene / phenanthrene, origin from carbonate source rocks.The X-ray diffraction analysis showed that the carbonate source rock is limited in the Es_4 ~ u unit of the Bonan sag, which is different from most other source rocks in the same horizon. It is suggested that the high -sulfur, heavy oils are generated at the early stage of the oil window. Bacterial sulfate reduction might be responsible for the occurrence of sulfur species in the high-sulfur, heavy oils, while heavy biodegradation will enhance sulfur concentrations.