华南中上扬子早志留世古地理与生储盖层分布

Early Silurian paleogeography and source-reservoir-cap rocks of the Middle-Upper Yangtze region in South China

依据"构造控盆、盆地控相、相控油气基本地质条件"思路,重建华南中上扬子地区早志留世鲁丹期、埃隆期和特列奇期岩相古地理格局,并从盆地沉积演化的角度总结生储盖层发育条件与时空分布规律。赫南特期末期冰川消融后全球的快速海进和构造挤压造成的地壳挠曲,导致中上扬子地区在鲁丹期形成以深水陆棚为主的古地理格局,发育的多个坳陷区成为有利烃源岩的沉积中心。埃隆期处于构造挤压的间歇期,由于相对海平面下降等因素,形成特殊的混积型碳酸盐缓坡,以礁滩相为主的碳酸盐岩储集层主要分布在沿岸的潮下高能带。特列奇期构造运动加剧,盆地整体抬升。东部作为构造挤压的前锋带,形成滨岸/潮坪/三角洲组成的复合性海岸环境,有利于储集砂体的发育,其中以小河坝组的临滨砂坝和三角洲前缘席状砂最具储集潜力,而广泛分布的韩家店组潮坪—陆棚相泥页岩可作为下伏含油气层系的良好封盖层。

The lithofacies paleogeography for the three successive ages （Rhuddanian, Aeronian and Telychian） in the Middle-Upper Yangtze region of South China in the Early Silurian （Llandoverian Epoch） is reconstructed according to the concept that structures control a basin, a basin controls facies, which, in turn, control the basic geology of oil and gas. The time-space distribution and sedimentology of ir-cap rocks are summarized. In the Rhuddanian age, the study area inherited and developed a semi-confinement stagnant basin resulting from tectonic compression started on Late Ordovician. The widely-covered organic-rich muddy shales occurred on deep-water shelves in a global-scale transgression after the Hirnantian glaciation and subsequent relatively slow regression. The sagged areas, formed mainly by tectonic tilting and plugging effect of rigid continental nucleus, are sedimentary centers of favorable source rocks. At the intermittent stage of tectonic compression during the Aeronian age, a mix-sedimented ＂carbonate ramp＂ formed by global sea-level drop, warm-humid climate and slight elastic sources. The reef-bank type carbonate reservoir rocks within Shiniulan Formation occurred in subtidal high-energy environments within inner ramp. In the subsequent Telychian stage, tectonic compression intensified, resulting in regression and overall uplifting of the basin, terminated the development of carbonate depositional environments. The eastern region was then dominated by shoreface and tide-dominated deltas where sand barrier type reservoir rocks in the Xiaoheba Formation occurred. The widespread muddy sediments of the Hanjiadian Formation could be cap rocks for the underlying potential oil-bearing layers.