Division of high-resolution stratigraphy in sedimentary sequence theory and prediction of lithological traps: a case study of the Neogene in Enping Sag, Pearl River Mouth Basin
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摘要:
南海北部珠江口盆地恩平凹陷大面积三维地震资料揭示了新近系类型丰富的砂体，在古珠江三角洲演化及相带迁移的控制下形成了较好的岩性圈闭发育条件。近年来，凹陷内发现的多个构造-岩性圈闭均与河道砂体相关。但在已有的层序地层划分方案中，河道砂体的成因、分类和展布特征与体系域的耦合关系差，砂体发育规律不明，制约了岩性圈闭的勘探效果。基于沉积层序理论，利用大范围井震资料，系统厘定了恩平凹陷珠江组一段—韩江组六段的高精度层序地层框架，并在此基础上开展了精细的三维地震沉积学解剖。分析结果显示，目的层发育的大型辫状河道、小型曲流河道和中型曲流河道，分别与低位、海侵和高位等特定体系域具有密切的耦合发育关系，进而建立了层序格架对河道砂体的有效预测模式，系统指明了凹陷不同区域、不同体系域内岩性圈闭的发育潜力及有利区。本文相关认识对其他海相三角洲盆地岩性圈闭勘探具有启示作用。
Abstract:Abundant sand-rich deposits in Neogene sequence were identified by a large area of 3D seismic data in the Enping Sag of Pearl River Mouth Basin, in the northern South China Sea (SCS). The mechanism of formation of the lithological traps in the Neogene reservoirs was studied by examining the variation of facies belts in the ancient Pearl River Delta system. Previous studies have shown that many structural-lithological traps in the Shenzhen Branch of the Enping Sag are closely associated with fluvial deposits. However, few studies provide systematic understanding on the origin, classification, and distribution of the fluvial deposits, which impeded the exploration progress in the studied area. A high-precision sequence stratigraphic framework of the first member of the Zhujiang Formation to the sixth member of the Hanjiang Formation was depicted and established systematically through 3D seismic interpretation and sedimentary and seismological analysis. Results show that large braided channel, small curved channel, and medium curved channel developed in the Enping Sag are closely correlated to lowstand, transgression, and highstand systems, respectively. The model of fluvial system was built in combination of stratigraphic variation and channel morphology. This model demonstrates the potentiality and distribution of various types of fluvial deposits in the Enping Sag. This study could effectively guide the exploration of lithological traps in the Enping Sag and other offshore basins in the future.
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Key words:
- Enping Sag /
- sedimentary sequence /
- channel classification /
- lithological trap
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表 1 恩平凹陷新近系河道分类
Table 1. The fluvial channel classification of the Neocene strata in the Enping Sag
体系域 含砂率/% 河道类型 砂体厚度/m 沉积构造 水动力 河道规模 岩性圈闭潜力 HST 35～60 曲流河道 5～10 平行层理 中—强 中—大 好 TST 30～50 弯曲河道 3～8 波状层理平行层理 弱—中 中—小 好 LST 85～100 辫状河道 8～20 交错层理平行层理 强 大 差 
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