摘要：

通过录井、测井、地震、野外剖面与岩心资料的深入剖析, 探讨中上扬子地区下志留统页岩段的沉积相与总有机碳的关系, 预测页岩气有利勘探区。中上扬子地区下志留统龙马溪组为一套20～268 m厚的黑色页岩夹灰绿色泥质粉砂岩沉积, 在等时框架内自下而上可识别出2个三级层序即SQ1与SQ2, 它们分布稳定、可对比性好。下部层序(SQ1) 的海侵体系域(TST)发育一套有利于页岩气形成的富有机质页岩, 此时期呈现出“北面向次深海敞开、东西南三面受古陆围限、陆棚广布”的沉积格局, 深水陆棚相广泛发育, 面积为255000 km², 平均厚度35 m。受海平面下降的影响, 从下部层序至上部层序水体变浅, 岩相从深水陆棚相黑色页岩向中—浅水陆棚相沙纹层理粉砂质页岩转变。岩相的发育受海平面升降、古陆、海底地形、物源供给等因素的影响, 岩相类型有碳质或硅质或钙质页岩、纹层状页岩、生物扰动粉砂质页岩、沙纹层理的粉砂质页岩、块状砂岩或介壳灰岩薄夹层5类。研究表明, 沉积相对富有机质页岩的形成具有内在的控制作用, 高TOC含量页岩发育于深水陆棚相、中陆棚相和潟湖相中。目前, 已有多口井在龙马溪组页岩获得工业气流, 揭示了该区良好的页岩气勘探前景；综合分析认为涪陵—赤水—仁怀、威远—长宁、鄂西—渝东为中上扬子地区下志留统页岩气勘探的主要方向和有利目标区。

关键词: 页岩气, 海侵体系域, 深水陆棚, 岩相, 下志留统, 中上扬子地区

Abstract:

Based on detail analysis of data of well logging, seismic records, outcrops and cores, the relationship between shale-member sedimentary facies and total organic carbons(TOC) of the Lower Silurian in Middle-Upper Yangtze area was discussed, and the favourable exploration directions were predicted. The Lower Silurian Longmaxi Formation consists of black shales interbedded with greenish-gray mudy siltstones, with the thickness of 20～268 m, in Middle-Upper Yangtze area, and two third-order stratigraphy sequences of SQ1 and SQ2, which distributed|stably could be|easily correlated, were distinguished from bottom to top within synchronous|stratigraphic framework. The transgressive systems tract(TST)of lower sequence SQ1 developed a set of organic-rich shale which is favorable for shale gas. During the depositional period of TST, the sedimentary pattern can be described as “abyss-area was open towards north, old lands were located in the east, south and west, deep shelf distributed extensively”, with the deep shelf area of 255 000 km², and the average thickness of 35 m. Affected by the fall of sea-level, the shallowing of water took place, and lithofacies changed from black shales of deep shelf to laminated silty shales of middle and shallow shelf facies from the lower sequence to the upper sequence. The development of lithofacies was controlled by eustacy of sea-level, old lands, sea-bottom topography and sediment supply, and five lithofacies types including carbonaceous or siliceous or calcareous shales, laminated shales, biologic-stirred silty shales, laminated silty shales and interbeds of massive sandstones or shell limestones were developed. It was proved that the forming of organic-rich shales were intrinsically controlled by sedimentary facies, with deep shelf, middle shelf and lagoon generating high|content of TOC. So far, there were several wells of industry gas flow from the Longmaxi Formation, which had revealed well exploration prospect, for the Middle-Upper Yangtze area. It is synthetically concluded that zones of Fuling-Shishui-Renhuai, Weiyuan-Changning and western Hubei Province-eastern Sichuan Province are the main exploration directions and favorable targets of shale gas in the Lower Silurian of Middle-Upper Yangtze area.

Key words: shale gas, transgressive systems tract, deep shelf, lithofacies, Lower Silurian, Middle-Upper Yangtze area

中图分类号: 

• P618.130.2