准噶尔盆地东部中二叠统芦草沟组烃源岩生烃潜力评价

Hydrocarbon-generating potential of the Middle Permian Lucaogou source rock in the eastern Junggar Basin

中二叠统芦草沟组是准噶尔盆地东部最重要的烃源岩层系,前期研究已证实其在吉木萨尔凹陷具备极好的生烃潜力,但在东部其他地区是否具备规模生烃潜力尚待深入研究。基于总有机碳和热解、有机岩石学、生烃模拟实验、盆地模拟、井—震联合解释等方法,系统比较了吉木萨尔凹陷和盆地东部其他地区芦草沟组烃源岩的生烃潜力,探讨了优质烃源岩的发育环境,刻画了规模有效烃源灶的分布。研究结果表明:准噶尔盆地东部芦草沟组烃源岩为一套以I—II型干酪根为主的倾油型烃源岩,总体为好—极好烃源岩。除继承性凸起区外,该区芦草沟组烃源岩在侏罗纪陆续进入生烃门限,在白垩纪普遍进入主生油窗,现今进入主生油窗的面积达1.1×10^(4) km^(2)。吉木萨尔凹陷与盆地东部其他地区芦草沟组烃源岩具有相似的生物标志物特征,表现为较低的姥植比和Pr/n-C_(17)、Tm/C_(30)藿烷、C_(19)/C_(21)三环萜烷和C_(24)四环萜烷/C_(26)三环萜烷值以及较高的β-胡萝卜烷丰度、伽马蜡烷丰度和Ts/Tm值,反映其沉积于还原性较强的咸水湖相环境,母质来源以藻类和细菌等低等生物为主。研究区芦草沟组烃源岩生油强度整体>3×10^(6) t/km^(2),在博格达山前、吉木萨尔凹陷、东道海子凹陷、五彩湾凹陷和沙帐断褶带发育多个生油强度>5×10^(6) t/km^(2)的生油中心,总面积约为12 500 km^(2),具备形成大中型油田的资源潜力。研究结果进一步夯实了准噶尔盆地东部地区油气资源基础,为寻找盆地油气勘探战略接替领域提供了有益的借鉴。

The Middle Permian Lucaogou Formation is the most significant source rock in the eastern Junggar Basin.Although previous studies have confirmed that it has excellent hydrocarbon-generating potential in the Jimsar Sag,its hydrocarbon-generating potential in the other areas of the eastern Junggar Basin remains problematic.Based on total organic carbon and pyrolysis,organic petrology,hydrocarbon simulation experiments,basin simulation,and combined well-seismic coupling interpretation,this study systematically compared the hydrocarbon-generating potential of the Lucaogou source rock in the Jimsar Sag with that in the other areas of the eastern Junggar Basin,discussed the sedimentary environment of the high-quality source rocks,and depicted the distribution of practical source kitchen.The Lucaogou source rocks in the eastern Junggar Basin are a set of oil-prone source rocks dominated by type I-II kerogens and are generally classified as good to excellent source rocks.Nowadays,the area of the Lucaogou source rocks that enter the main oil-generating window reached approximately 1.1×10^(4) km^(2).Except for the bulge area,the Lucaogou source rocks in the eastern Junggar Basin successively entered the hydrocarbon-generating threshold during the Jurassic and generally entered the main oil-generating window in the Cretaceous.The Lucaogou source rocks in the Jimsar Sag and the other parts of the eastern Junggar Basin shared similar biomarker fingerprints which are characterized by relatively low ratios of Pr/Ph,Pr/n-C_(17),Tm/C_(30)-hopane,C_(19)/C_(20)-tricyclic terpene,and C_(24)-tetracyclic terpene/C_(26)-tricyclic terpene and relatively highβ-carotene content,gammacerane index and Ts/Tm ratios.These characteristics reflected that they were deposited in a strongly reducing brackish lacustrine environment,with their parental sources dominated by lower organisms such as algae and bacteria.Generally,the Lucaogou source rocks in the eastern Junggar Basin had an oil-generating intensity of more than 3×10^(6) t/km^(2).Several oil-generating centers with an oil-generating intensity of more than 5×10^(6) t/km^(2) were developed in the front of the Bogda Mountain,Jimsar Sag,Dongdaohaizi Sag,Wucaiwan Sag,and Shazhang Fault Zone,covering a total area of approximately 12500 km^(2).These characteristics of the Lucaogou source rocks promised a favorable potential for the formation of large and medium oil fields.The results further consolidated the oil and gas resources in the eastern Junggar Basin and provided valuable references for exploring future oil and gas fields.