上扬子地区新元古界含油气系统与油气勘探潜力

Hydrocarbon systems and exploration potentials of Neoproterozoic in the Upper Yangtze Region

近年来,四川盆地震旦系天然气勘探获得重大发现,揭示上扬子克拉通盆地新元古界具备寻找原生型大气田的条件。然而,受勘探程度和认识程度的制约,对该领域油气资源潜力与分布的认识尚不清楚。国外的研究成果表明,新元古界含油气系统受气候条件、构造古地理环境控制,温室气候期冰川融化可导致海平面上升,有利于富有机质沉积物堆积,是新元古界重要油气源岩沉积的主要时期;早期裂谷—晚期克拉通坳陷的构造带利于形成油气富集区。上扬子克拉通在中—新元古代经历了可全球对比的重要地质事件,南华纪以板内拉张活动为主、震旦纪为克拉通坳陷沉积,形成了两套各具特点的含油气系统:震旦系含油气系统(也可称为后冰川期含油气系统)和南华系含油气系统(也可称为间冰川期含油气系统)。前者发育多套烃源岩和大面积分布的储集层,源—储配置条件好,是一个已被证实的含油气系统,也是近期该区天然气勘探的重点领域;后者受裂陷(谷)盆地分布控制,发育优质烃源岩,是潜在的油气勘探领域。川中地区发育南华系裂谷,应加强地质评价研究,优选风险勘探目标。

In the past few years,important discoveries have been made in the Sinian strata in the Sichuan Basin,which indicates that there are conditions for finding primary type large gas fields in the Neoproterozoic strata of craton basins in the Upper Yangtze Region.However,restricted by exploration extent and identification degree,the understanding is not clear yet about the oil and gas potential and distribution in this domain.Foreign studies show that Neoproterozoic hydrocarbon systems were controlled by climate conditions and tectonic paleogeographic environments.During the greenhouse climate periods,glaciers were melted,which led to sea level rising,and was favorable for the accumulation of organic-rich sediments.They were the major deposition periods for Neoproterozoic source rocks.Structural belts between the early rifts and the late craton depressions were favorable for forming hydrocarbon enrichment areas.In this paper,we found that the craton basins in the Upper Yangtze Region underwent important tectonic events that were globally correlatable across the Mesoproterozoic-Neoproterozoic boundary; during the Nanhua Period,the major tectonic events were intraplate extensional movements; and during the Sinian Period,they were craton depression deposits,forming two suites of hydrocarbon systems with distinct characteristics：the Sinian hydrocarbon system （also called post glacial stage hydrocarbon system） and the Nanhua hydrocarbon system （also called inter glacial stage hydrocarbon system）.The former proven hydrocarbon system has developed several source rocks,widely distributed reservoirs and good source-reservoir assemblage condition,so it is an important domain for recent exploration.Controlled by the distribution of rifted （valley） basins,the latter hydrocarbon system has well-developed high quality source rocks so it is another potential target in gas exploration there.The Nanhua system rifts were so developed in central Sichuan Basin that geological evaluation should be enhanced in this study area to optimize exploration targets while potential risks are mitigated.