四川盆地下寒武统烃灶动态演化分析

Dynamic evolution of the hydrocarbon kitchen in the Lower Cambrian,Sichuan Basin

四川盆地下古生界海相烃源岩具有早熟、过熟的特点,烃灶形式转换(即干酪根热解型烃灶演变为古油藏裂解型烃灶(简称油灶))及由此导致的接力供烃是高—过成熟下古生界层系高效成藏的关键。因此,烃灶动态演化分析及准确定位是勘探选区的基础工作。通过对四川盆地构造、沉积演化和热体制的分析,应用TSM盆地模拟系统,在烃源岩埋藏史、热演化史、生烃史分析基础上,刻画了下寒武统牛蹄塘组烃源岩干酪根型烃灶的空间展布,再结合地史时期的古构造、流体势、有效储层的分析,用成藏概率法对"古油灶"进行了定位,实现了对烃灶的动态连续追踪。结果表明,牛蹄塘组烃源岩生、排烃高峰为加里东和海西期,烃灶中心位于川西南资阳—宜宾—赤水、盆地东缘的秀山—利川和川东北盆缘一带;至晚印支期(T3)末,伴随烃源岩普遍达到过成熟,且由于前期大量的生排烃,干酪根烃灶的供烃能力逐渐衰竭,取而代之的是前期形成的古油藏(古油灶)的接力供烃。资阳—重庆—宜宾及盆地南缘、北缘和东北缘是古油灶分布概率最高的地区。

The Lower Paleozoic marine source rocks in the Sichuan Basin became mature during the early stage and are over mature now. The hydrocarbon kitchen changed from a kerogen pyrolysis type to an ancient oil reservoir cracking type, resulting in successive hydrocarbon supply, which controlled hydrocarbon accumulation in the Lower Paleozoic highly mature and over mature strata. As a result, the analysis and accurate identification of the dynamic evolution of hydrocarbon kitchen is fundamental for exploration. We studied the tectonic, sedimentary evolution and thermal systems in the Sichuan Basin, and described the distribution of the kerogen type hydrocarbon kitchen in the Lower Cambrian Niutitang Formation using a TSM basin modelling system, based on the burial, thermal evolution and hydrocarbon generation histories of source rocks. We also identified the location of the ancient oil kitchen and dynamically traced the hydrocarbon kitchen using an accumulation probability method, combined with the analyses of ancient structure, fluid potential and effective reservoir. The Niutitang source rocks generated and discharged hydrocarbon during the Caledonian and Hercynian periods, and the kitchen center was found in Ziyang, Yibin, and Chishui in the southwest, Xiushan and Lichuan in the east, and in the northeastern margin of the Sichuan Basin. At the end of Late Indosinian, most source rocks were over mature and had expelled a large amount of hydrocarbon. Ancient oil kitchens took the role of hydrocarbon supply instead of kerogen pyrolysis kitchens, and were found mainly in Ziyang, Chongqing, Yibin and the southern, northern, and northeastern margins of the basin.