库车油气系统油气成藏期与成藏史

Accumulation Timing and History of Kuche Petroleum System, Tarim Basin

根据圈闭形成时间法、生烃史法、油藏地球化学方法、包裹体测温法、露点压力法、油气水界面追溯法等多种方法对库车油气系统油气成藏期综合分析认为 ,该油气系统具有多期成藏、多阶连续的成藏特点。其主要成藏期有 3期 :即晚第三纪康村早中期 (17～ 10Ma)、康村晚期—库车早中期 (10～ 3Ma)、库车晚期—第四纪西域期 (3～ 1Ma)。前 2期为轮台凸起油气藏形成的主要时期 ,形成三叠系湖相油藏以及侏罗系中低成熟煤成凝析油气藏。库车晚期—西域期是库车坳陷气藏的主要形成时期 ,主要形成高—过成熟气藏以及少量次生油藏 ,最近发现的克拉 2大气田以及克拉 3、大北 1、依南 2、吐孜 1等气藏均属该时期成藏。

The Kuche petroleum system is a forland type one riched in oil and particularly natural gas generated from the Triassic and Jurassic source rocks including coal source. Many natural gas and condensate fields as well as some oil fields have been discovered, of which the natural gas and condensate are thought to have been generated mainly from coal source of Jurassic and the normal oil from the Triassic mudstone source. Study of these fields' accumulation timing and filling history is significant to exploration in Kuche and therefore the major concern of this paper. Based on synthetic analyses of trap timing, reservoir geochemistry (gas maturity correlation), hydrocarbon fluid inclusions, dew-point pressure and oil/gas-water contact evolution, 3 periods of the formation and filling history of oil and natural gas reservoirs in the Kuche petroleum system are discerned, i.e. early-middle Kangcun period (17～10 Ma), late Kangcun to early-middle Kuche period (10～3 Ma) and late Kuche to Xiyu period (3～1 Ma). The late Kuche to Xiyu period is the major one for formation of natural gas fields of high maturity to over-maturity in Kuche forland thrust belts, in which the discovered gas fields of Kela 2, Kela 3, Dabei 1, Yinan 2 and Tuzi 1 were formed. The late Kangcun to early-middle Kuche period is a critical moment for accumulation of oil and condensate of low to intermediate maturity. And the early-middle Kuche period is a minor one for formation of low-maturity oil and gas reservoirs sourced from coal-type organic matter. Oil and gas fields of early-middle Kangcun and late Kangcun to early-middle Kuche periods were distributed mainly in the Luntai uplift, whereas gas fields of late Kuche to Xiyu period totally in the Kuche forland thrust belts. The early formed oil and condensate accumulations in the forland thrust belts, if there is, have possibly been adjusted and even destroyed by the later strong orogeny and/or the intrusion of natural gas of high maturity and over maturity. The remanined oil accumulations in the thrust belts were mostly secondary reformed during the late Kuche to Xiyu period.