【作者】 叶先灯；

【导师】 夏斌； 姜在兴；

【作者基本信息】 中国科学院研究生院（广州地球化学研究所） ， 构造地质学， 2006， 博士

【摘要】 Melut盆地属于拉张裂陷中的弱反转被动裂谷盆地，具有裂谷盆地典型的构造特征。综合运用各类资料，在研究层位白垩系—古近系共识别出从SB1到SB8的8个层序界面，建立了全盆地的白垩系—古近系层序地层格架。与Melut盆地在白垩纪和古近纪经历的三个裂陷阶段和一个坳陷阶段相对应，划分为4个长期基准面旋回，分别是K1段、K2段、Samma-Lau组和Jimidi-Agor组。通过钻／测井相、地震相和少量岩心分析，并结合重矿物、粒度分析等资料，在Melut盆地识别出了辫状三角洲体系、扇三角洲体系、河道-冲积平原体系、滑塌浊积扇和湖相等5种沉积体系类型。沉积特征和充填演化过程表现为：盆地地形高差相对不大，宏观沉积相带分异性不明显；两次强裂陷阶段形成了厚层烃源岩和大套稳定泥岩盖层；盆地构造格局相对稳定，物源方向具有继承性，岩石成分单一；盆地内的构造调节带控制了大型砂体的展布。Melut盆地从早白垩世到古近纪强烈的伸展断陷活动，为盆地广泛形成断陷型深湖盆和优越的成烃环境，为富油气凹陷的形成提供了先决条件。盆地内多个凹陷就属于这类湖盆，如北部凹陷、东部凹陷、中部凹陷、西部凹陷和南部凹陷。勘探实践表明，每个裂陷期形成一套烃源层，控制着一定地质时期的富油气区从盆地演化史、沉积层序特征及地球化学分析来看，Melut盆地应以白垩系烃源岩为主。根据Melut盆地的构造发育、沉积演化、石油地质特征，建立了油气跨时代聚集的模式。紧紧围绕Melut盆地白垩系生油、古近系储油这一明显不同于Muglad和Doba等盆地的特点，提出了一系列新观点，包括：“晚期增温”导致盆地热演化时间迟滞，控制了晚期排烃和晚期成藏，油气跨越巨厚储层段进行长距离垂向和侧向运移，并在盆地横向构造调节带上优势聚集等，丰富了裂谷盆地的石油地质学，达到了国际领先水平。明确了北部凹陷是一个富油气系统，通过对地层、构造、成藏组合等条件分析和成藏组合研究，在Melut盆地北部共划分了10个有利的成藏带，这些成藏带一般以背斜圈闭为主，Yabus和Samma组砂体发育，单储系数高。为进一步新增储量奠定了坚实的基础，为进一步勘探提供了新的接替区。更多还原

【Abstract】 Melut basin is a weakly-inversed passive rift basin within extension tectonic background and demonstrates typical tectonic features of intra-cratonic rift basin. Comprehensively applying many kinds of data, this paper established the stratigraphical framework from Cretaceous to Paleogene formations in the basin after divided eight sequence boundaries from SB1 to SB8 in Cretaceous -Paleogene ages. The paper also set up four long-term base-level cycles, including Early Cretaceous, Late Cretaceous, period from Samma Fm to Lau Fm and period from Jimidi Fm to Agor Fm, which correspond with the three rifting stages and one depressing stage during Cretaceous -Paleogene ages in the basin.Five sedimentary systems were identified based on drilling data, log facies, seismic facies and results of core analysis, together with results of heavy mineral and grain-size analysis. These systems include braided river delta, fan delta, river-alluvial plain, collapse turbidite fan and lacustrine facies. Sedimentary features of the basin and its filling evolution history are resulted from low intra-basin relief, indistinct differentiation of macro-facies, thick source rocks and cap rocks, relatively stable tectonic architecture and successive provenance with simple ingredient composition; consequently, distribution of major sand bodies in the basin was controlled by the structural accommodation zones.The intense rifting activities from Early Cretaceous to Paleogene had resulted in a quite favorable framework for development of deep lacustrine lakes and source-rich depressions. Both are fundamental elements for hydrocarbon-rich depressions. North depression is a depression of such kind in the basin. Exploration practices demonstrate that one set of source rock deposited in a given depression during a rifting stage controls its hydrocarbon distribution. The predominant source rock in the basin is Cretaceous shales based on tectonic evolution history, characters of stratigraphical sequences and geochemistry analysis.Era-spanning pattern of hydrocarbon enrichment was established based on tectonic development and sedimentary evolution of the basin and its Petroleum geologic properties . The pattern is distinguishable from that in Muglad and Doba basin. Several new viewpoints have been put forward based on the distinct features of hydrocarbon enrichment in the basin, where hydrocarbon was sourced by Cretaceous lacustrine shales and accumulated in Paleogene reservoir. These viewpoints include that "late geothermal increment" led to delay of thermal evolution and controlled late hydrocarbon migration and enrichment subsequently, and hydrocarbon was trapped predominately in the structural accommodation zones after migrating through a series of strata with giant thickness vertically and long distance horizontally. These new viewpoints have broadened the knowledge of petroleum geology of rift basin and reached international advanced level.The north depression has been recognized as an oil-rich petroleum system according to results of stratigraphical, structural studis and accumulation assemblage analysis. Ten favorable plays have been identified in the basin. These plays are rich of sand bodies in Yabus and Samma formations with high reserves per unit volume and possess anticlines as the main structure style. These conclusions have laid a sound foundation for the new discoveries and put forward subsequent prospective areas for the future exploration campaigns.更多还原