关键词: 塔里木盆地, 英南2气藏, 胶结物, 同位素分析, 气藏成藏机理

Abstract: The formation mechanism of strong carbonate-cement sand caprock of Yingnan-2 condensate gas reservoir in the eastern Tarim Basin was discussed.There are two luminescences of calcareous cement in tight sandstone exhibited under the cathodoluminescence microscope.The earlier phase calcite shows nacarat color,and the later phase calcite shows saffron.The earlier phase calcite was replaced by the later one.The carbon isotopic compositions of carbonate cement by using laser micro-pyrolysts show a strong negative isotopic excursion (δ¹³C value ranges from-7.17‰ to-9.06‰),which relates to microbe participating.The δ¹⁸O values ranged from-12.44‰ to-21.85‰ of carbonate cement show that the diagenesis of carbonates was formed by freshwater seepage.The carbonate cement was principally formed by oxidation of thermogenic migrating hydrocarbon.Bacterial oxidation of the migrating hydrocarbon within the lower Jurassic sands was probably by sulphate reduction and liberated carbon dioxide for subsequent carbonate precipitation.Therefore,the tight sandstone is the product of "hydrocarbon-related diagenetic zones"(HRDZs).The formation of HRDZs is a slowly biodegraded process of hydrocarbon.During formation of HRDZs,gas composition and δ13C values of gas reservoir in Yingnan-2 reservoir were fractionated.Yingnan-2 reservoir is a special condensate gas reservoir,in which source rock is under layer,and container rock lies on super stratum.The formation of gas reservoir is a process of earlier phase diffusion and later phase accumulation.Consequently,the formation process of Yingnan-2 gas reservoir is prominently related to the organic-inorganic interaction.

Key words: Tarim Basin, Yingnan-2 gas reservoir, cement, isotope analysis, gas reservoir formation mechanism