柴北缘西段鄂博梁构造带储层碳酸盐胶结物成因及其油气地质意义——来自碳、氧同位素的约束

Origin of Carbonate Cements in Reservoir Rocks and Its Petroleum Geologic Significance: Eboliang structure belt,northern margin of Qaidam Basin

碳酸盐胶结物是古流体活动的产物,蕴含着成岩环境、成岩流体演化等方面的有益地质信息。综合运用岩石学、矿物学和地球化学方法,对柴北缘西段鄂博梁构造带侏罗系、古近系、新近系储层中普遍存在的碳酸盐胶结物的成因机制进行了研究。结果表明,研究区碳酸盐胶结物以方解石和含铁方解石为主。鄂博梁I号构造主要见方解石,其碳、氧同位素分布范围较大:-13.47‰<δ13CPDB<2.54‰,-15.93‰<δ18OPDB<-4.74‰,成因多种多样,与有机质脱羧、同生—准同生、甲烷生成等作用有关;鄂博梁III号—鸭湖构造则主要见含铁方解石,其碳、氧同位素分布集中:-4.24‰<δ13CPDB<-1.99‰,-11.17‰<δ18OPDB<-9.41‰,为沉积压实水沉淀而成。碳酸盐胶结物的成因揭示了鄂博梁构造带无机—有机流体的活动信息,从而为该地区油气成藏研究提供了重要依据。

Carbonate cement is the product from activity of palaeo fluids,containing much profitable geological information on diagenetic environment and diagenetic fluid evolution. In this paper,integrating methods of petrology,mineralogy and geochemistry,the origin mechanism of carbonate cements are investigated in Eboliang structure belt,northern margin of Qaidam Basin. The result shows that the major carbonate cements are calcite and Fe-bearing calcite in the study area. The calcite cements are mainly discovered in Eboliang structure I,their carbon and oxygen isotope values have wide range（-13. 47‰〈δ13CPDB〈2. 54‰,-15. 93‰〈δ18OPDB〈-4. 74‰） and varied origin,such as organic matter decarboxylation,syngenetic or parasyngenetic,bacterial methanogenesis. However,The Fe-bearing calcite cements are maily discovered in Eboliang structure III and Yahu structure,the distribution of carbon and oxygen isotope values concentrates at-4. 24‰〈δ13CPDB〈-1. 99‰,-11. 17‰〈δ18OPDB〈-9. 41‰, precipitated from sedimentary compacted water. The carbonate cements origin reveals the information on interaction between inorganic and organic fluid activity in Eboliang structure belt,which provides the important evidence for the hydrocarbon accumulation study in this area.