莺歌海盆地深部油气储层物源识别：陵水组-梅山组碎屑锆石U-Pb年龄和Hf-O同位素制约

Yinggehai Basin, a large Cenozoic strike-slip and extensional basin, is located on the northern margin of the South China Sea continental shelf. It’s very difficult to identify the sediment provenance of this basin as it has several source regions hindering the prediction and exploration of the high quality reservoirs. However, investigating the provenance of high quality reservoirs is significant for deep-sea oil and gas exploration. In this study, multiple methods will be employed including investigation of the heavy minerals, whole-rock geochemistry, LA-ICPMS U–Pb ages and Hf–O isotopes of detrital zircon from the Oligoene Lingshui to Miocene Meishan formation sedimentary rocks in different gas fields of Yinggehai Basin. Combined with the study of regional geological evolution, we will build the signatures of the potential source regions, and determine the provenance and establish the characteristic spectrums of the deep-sea oil and gas reservoirs via the heavy minerals, geochemistry and age of detrital zircons. These results will serve as a foundation to help us evaluate the contribution and transportation route of the surrounding source areas, build the dynamic evolution model, understand the distribution and direction of the promising reservoirs, and provide useful guide for deep-sea oil and gas exploration in Yinggehai Basin.

莺歌海盆地是一个位于南海北部大陆边缘的大型走滑-伸展型盆地。其新生代沉积物源复杂多样，辨识难度非常大，给深海优质储层的寻找和预测带来很大困难。深海优质油气储层物源研究历来是深海油气研究的关键问题和重要课题。本次研究将通过盆地不同油气构造区陵水组-梅山组重砂矿物、碎屑沉积岩地球化学以及关键层位碎屑锆石LA-ICPMS U-Pb年代学和Hf-O同位素测试分析，并结合源区地质演化的系统性综合分析和研究，建立莺歌海盆地源区的识别标志，确定莺歌海盆地不同油气构造区深部储层物质来源，并建立深部油气储层的重砂矿物、地球化学和碎屑锆石年龄频谱特征图，从而认识莺歌海盆地周边物源体系对盆地的贡献及其来源路径，提出有关新生代莺歌海盆地形成动力学演化模型，了解深海有利油气储层的分布范围和方向，为深海油气勘探提供科学依据。

莺歌海盆地处于太平洋、印度-澳大利亚和欧亚三大板块的交汇部位，显示良好的油气勘探前景。但其物源识别尚停留在以推测为主的模糊认识阶段，严重制约了油气评价和勘探。该项研究在前人工作的基础之上，利用碎屑锆石U-Pb年代学、Lu-Hf同位素以及全岩地球化学和Sr-Nd-Pb同位素等研究方法，建立了莺歌海盆地潜在物源区的锆石年龄频谱和识别标志，有效地识别了莺歌海盆地自30 Ma以来，陵水组、三亚组、梅山组、黄流组、莺歌海组和乐东组的物源分布特征，探讨了各源区晚中新世以来物源在空间和时间对盆地的影响，揭示了古红河水系流域范围并非保持稳定不变，其主要源头可能在多个地质历史时期被渐进式袭夺。通过现代河流沉积物来约束各物源区的大地构造演化历史。同时，利用微量元素和同位素地球化学特征有效揭示了优质油气储层的分布，为油气勘探做出了重要贡献。