准噶尔盆地莫索湾地区白垩系生物降解与成藏地球化学特征

Biodegradation and geochemical conditions for hydrocarbon accumulation of Cretaceous reservoir in Mosuowan area of Junggar Basin

通过分析准噶尔盆地莫索湾地区白垩系油藏原油25-降藿烷含量、烃类包裹体的均一温度及组分特征、地层埋藏史及热演化史,探讨了研究区生物降解分布、地点及时间,结合生物降解与未降解原油混合实验,揭示了不同期次油藏保存规模。结果表明:准噶尔盆地莫索湾地区白垩系普遍存在生物降解,纵向上生物降解受白垩系底部不整合面控制,导致垂向分布存在差异。油气存在2期成藏,早期成藏从早白垩世开始充注,并发生严重的本地生物降解,降解时间为早白垩世末—晚白垩世早期,受烃源岩排烃规模限制,第一期成藏油气规模小,对后期聚集的主成藏期油气破坏较小;第二期成藏为主成藏期,成藏时间对应下乌尔禾组大规模排烃期,即晚白垩世。

Content of 25-norhopane,homogenization temperature and composition of fluid inclusions,stratigraphic burial-thermal history and characteristic of rock fluorescence are analyzed.Distribution,location and time of biodegradation of Cretaceous reservoir in Mosuowan area of Junggar Basin were discussed.Combined with biodegradable and undegraded crude oil mixing experiment,the scale of sub-reservoir preservation in different periods was revealed.The results show that there is widespread biodegradation in Cretaceous reservoir in Mosuowan area of Junggar Basin,and vertical distribution of biodegradation is controlled by unconformity at the bottom of Cretaceous reservoir.There are two stages of oil accumulation in Cretaceous reservoir.Early accumulation began in Early Cretaceous,accompanied by severe local biodegradation.The degradation time was from the end of Early Cretaceous to the early of Late Cretaceous.However,due to limitation of the scale of hydrocarbon expulsion from source rocks,first stage of oil accumulation is small,resulting in a small impact of biodegradation on later oil accumulation.Second stage of accumulation is the main accumulation period,and accumulation time corresponds to large-scale hydrocarbon expulsion period of source rocks of the lower Wuerhe Formation,that is,during Late Cretaceous.