摘要
Kuqa depression bears not only plenty ofnatural gas, but also a large amount of condensate and smallquantity of crude oil. Based on the geochemical correlationbetween the Jurassic and Triassic terrestrial hydrocarbonsource rock, this paper confirms that the natural gas in Kuqadepression belongs to coal-type gas and the main gas sourcerock is attributed to the middle to lower Jurassic coal seriesformation, while the main oil source rock is the upper Tri-assic lacustrine mudstone. The authors indicated that Kuqadepression was slowly subsided in Mesozoic, but rapidlywent down in Late Tertiary, which made the Jurassic andTriassic source rock suddenly deep-buried and rapidlyevolved to high and over-mature phase since 5 Ma. TheTriassic source rock is postponed to the Early Miocene dur-ing 23-12 Ma when entering the oil-generating peak, whilethe Jurassic is suspended to the latest 5 Ma, especially since2.5 Ma to the dry gas-generating period, which is one of thecharacteristics of the source rock thermal evolution in Kuqadepression. This paper presents a two-stage trapping andlate gas trapping model in Kuqa depression whose charac-teristics are: The main oil and gas reservoirs have differentsources. The oil reservoir is formed early while the gas res-ervoir is formed lately. During the early stage, it, mainly asoil, takes long distance lateral migration, while in the laterstage, it, mainly as gas, takes the vertical migration and alsohas lateral migration. The trap formed in different time onthe south and north sides of the depression and evolved intoa distributional pattern with oil in the south part and gas inthe north, also oil on the outer ring and gas on the inner ring.This paper points out that the late trapping of the naturalgas in Kuqa depression is favorable for the preservation oflarge gas fields.
Kuqa depression bears not only plenty of natural gas, but also a large amount of condensate and small quantity of crude oil. Based on the geochemical correlation between the Jurassic and Triassic terrestrial hydrocarbon source rock, this paper confirms that the natural gas in Kuqa depression belongs to coal-type gas and the main gas source rock is attributed to the middle to lower Jurassic coal series formation, while the main oil source rock is the upper Triassic lacustrine mudstone. The authors indicated that Kuqa depression was slowly subsided in Mesozoic, but rapidly went down in Late Tertiary, which made the Jurassic and Triassic source rock suddenly deep-buried and rapidly evolved to high and over-mature phase since 5 Ma. The Triassic source rock is postponed to the Early Miocene during 23?12 Ma when entering the oil-generating peak, while the Jurassic is suspended to the latest 5 Ma, especially since 2.5 Ma to the dry gas-generating period, which is one of the characteristics of the source rock thermal evolution in Kuqa depression. This paper presents a two-stage trapping and late gas trapping model in Kuqa depression whose characteristics are: The main oil and gas reservoirs have different sources. The oil reservoir is formed early while the gas reservoir is formed lately. During the early stage, it, mainly as oil, takes long distance lateral migration, while in the later stage, it, mainly as gas, takes the vertical migration and also has lateral migration. The trap formed in different time on the south and north sides of the depression and evolved into a distributional pattern with oil in the south part and gas in the north, also oil on the outer ring and gas on the inner ring. This paper points out that the late trapping of the natural gas in Kuqa depression is favorable for the preservation of large gas fields.
