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莺歌海盆地中央带上中新统黄流组一段近年新发现一套浅海重力流沉积体系,夹持于海南古隆起和越南昆嵩古隆起之间,探讨其物源供给对掌握砂体展布规律以及“源-汇复合体系”的研究具有重要意义.结合东方气田新钻井资料和岩石测试资料,如砂岩碎屑组分、重矿物组合特征及元素地球化学特征对研究区黄流组物源进行了分析,结果表明:(1)西部昆嵩隆起物源是本区浅海重力流沉积体系的主要物源区,浅海重力流砂岩长石、岩屑含量较高,结构成熟度高,泥质含量低(平均3.8%),以岩屑石英细-极细砂岩为主;源自东部物源浅海砂坝砂岩的长石、岩屑含量较低,成分成熟度高,但泥质含量高(平均18.6%),以岩屑石英粉砂岩-石英粉砂岩为主;(2)源于西部物源的浅海重力流砂岩锆石、电气石含量低,磁铁矿、石榴石含量高,源于东部物源的浅海砂坝锆石、电气石、白钛矿含量高,磁铁矿、石榴石含量低.此外,区域古水流方向主要为南东-东西向,反映其可能受到西部越南水系的影响;(3)岩心样品相似的稀土元素配分模式表明浅海重力流砂岩具有一致的物质来源,稀土元素含量及比值、Th-Sc及Co/Th-La/Sc图解均显示中性-长英质源岩特征,La-Th-Sc三角图、Th-Sc-Zr/10三角图以及主量元素判别图解均显示样品落在主动大陆边缘或大陆岛弧区域,说明浅海重力流砂岩源区为挤压构造背景,与昆嵩隆起相符合;(4)中央底辟带西侧的浅海重力流砂体规模大,物性好,含气丰富,为下一步向西部勘探的主力砂体,而中央底辟带东侧的浅海砂坝储层规模较小,储层质量较差.
In the middle of the Yinggehai Basin, a shallow sea gravity flow sedimentary system was newly discovered in the first section of the Miocento-Huangliu Formation in the central part of Miocene. It was sandwiched between the paleohigh sea uplift in Hainan Province and the ancient uplift in Kun Song Song in Vietnam, Cloth law and “source - sink compound ” research is of great significance.Combined with the new drilling data and rock test data of Dongfang gas field, such as sandstone detrital components, heavy mineral assemblages and elemental geochemical characteristics of the Yellow River The results show that: (1) The Kunquon uplift source in the west is the main source area for the shallow-sea gravity flow sedimentary system in this area. The shallow-sea gravity flow sandstone with high feldspar content and high structural maturity , With low shale content (3.8% on average), mainly composed of lithic quartz fine-ultrafine sandstone; feldspars derived from sandstone of eastern source shallow sea sand bar have low content of rock fragments and high maturity of composition, (18.6% on average), mainly lithic quartz siltstone-quartz siltstone. (2) The shallow sea gravity flow sandstone originating from western provenance is characterized by low content of tourmaline, high content of magnetite and garnet The shallow sea sandbars originating from the eastern provenance have high zirconium, tourmaline and white titanium contents , Magnetite and garnet are low.In addition, the direction of the paleocurrent in the area is mainly south-east-east-west, which may be affected by the western Vietnam water system. (3) The similar pattern of rare earth elements in core samples indicates that the shallow sea gravity flow sandstone With consistent material sources, REE contents and ratios, the Th-Sc and Co / Th-La / Sc plots show the characteristics of Neutral-Chang source rocks, La-Th- 10 triangle diagram and the master elemental discriminant diagram all show that the sample falls on the active continental margin or the continental island arc region, indicating that the sand source region of the shallow sea gravity flow is an extrusion tectonic setting consistent with the Kunseong uplift. (4) The central diapir belt The shallow-sea gravity flow sand body on the west side is large in scale with good physical properties and rich gas content, which is the main sand body to be explored to the west in the next step. The shallow sea sand dam with the east side of the central diapason has smaller reservoirs and poorer reservoir quality .