塔里木北部轮台凸起凝析气藏成藏年代分析

GEOCHRONOLOGY OF CONDENSATE ACCUMULATION IN THE LUNTAI UPLIFT, NORTH TARIM BASIN

根据天然气成熟度对比法、油气水界面追溯法以及包裹体测温法等对轮台凸起凝析气藏的成藏年代做了较精细研究 ,认为该区凝析油气藏的形成主要有 2期 ,即康村期与库车期。其中康村期 (距今 1 7～ 5Ma)主要形成未熟—低熟气藏 ,库车期主要形成成熟凝析气藏。后者的主要注入时间为库车早_ 中期 (距今 5～ 3Ma) 。

Condensate reservoirs, as coal formed gases coming from the Jurrassic coal source rocks of the Kuqa depression, were main type of hydrocarbon accumulation in the Luntai Uplift, North Tarim Basin. The formation age of condensate reservoirs was analized comprehensivly by methods of reservoir geochemistry (gas source maturity correlation), oil or gas water contact retrospecting and fluid inclusion analysis. The former showed the natural gases composed of 2 kinds of maturity: immature and lower mature gas and mature gas, which was considered to be a result of different thermal evolution stages of the Jurrassic source rocks. According to the recovery of burial and thermal history of the source rocks, the both gases were believed to be filled during the Kangcun and early middle Kuqa periods of Neogene respectively. Two periods of gas filling events were also recorded in hydrocarbon inclusions of the gas reservoirs, which were different not only in their occurrences but in homogenized temperatures. Based on the model of burial and thermal history, the earlier generation of inclusions with lower homogenized temperature was thought to be formed in the Kangcun period ( 17～ 5 Ma ago), whereas the later one with higher homogenized temperature in the early middle Kuqa period (5～3 Ma ago). The oil or gas water contact retrospecting was also an important method for accumulation time determination, which revealed the earliest time of levelled oil or gas water contact being the time of hydrocarbon filling and accumulation. Analyses of evolutionary history of oil or gas water contact of the Yingmai 7 and Yaha condensate fields showed that both of them formed in the Kangcun and Kuqa periods. Therefore, two periods of petroleum accumulation could be distinguished, i.e. the Kangcun period ( 17～5 Ma ago) and early middle Kuqa period (5～3 Ma ago), which were earlier than the filling time of higher mature and over mature gases discovered widespread in the Kuqa forland thrust belts such as the Kela 2 and Yinan 2 gas fields. The Kangcun period was formation time of lower mature and immature gas reservoirs, the early middle Kuqa period being formation time of mature gas reservoirs, and also the major period for formation of condensate reservoirs in the Luntai Uplift.