Source-sink characteristics of Weihe Graben and its controlling effect on deposition and reservoir characteristics
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摘要: 物源性质对于我国近海盆地古近系沉积与储层发育具有重要的控制作用,然而受限于取芯成本与地震资料多解性,相关认识缺少直观证据支撑。渭河地堑为新生代断陷盆地,区域地质研究揭示其南北物源体系差异显著,其构造背景、物源配置与近海盆地具有较强的类比性。本文基于渭河地堑野外露头与系统采样进行锆石U-Pb年代学、铸体薄片、背散射以及X衍射分析,对渭河地堑南北砂体物源体系、沉积及储层特征进行精细解剖。北部花城剖面碎屑锆石具有华北克拉通两个典型古老峰值以及对应加里东与海西运动的年轻峰值,层序底部砾岩砾石类型以碳酸盐岩、钙质碎屑岩以及变质岩为主,具备鲜明的渭北隆起物源特征;南部骊山周缘剖面碎屑锆石以加里东晚期与印支晚期峰值为主,砾石类型以花岗岩与变质岩为主,具备鲜明的南部秦岭物源区特征。渭北隆起碳酸盐岩物源区对应沉积体规模小且富泥,储层中泥质与钙质含量高。南部秦岭造山带对应沉积体展布规模大,多旋回富砂沉积,储层以砂砾岩、净砂岩为主,储层钙质含量低。不同类型物源体系为储层及后续成岩作用提供了物质基础与先决条件。渭河地堑野外露头系统分析可以为我国近海盆地相关研究提供借鉴。Abstract: Property of provenance plays an important role in controlling Paleogene deposition and reservoir development in China's offshore basins. However, due to the cost of coring and the interpretation ambiguity of seismic data, the relevant understanding lacks visual evidence support. Weihe Graben is a Cenozoic rifting basin. Regional geological studies reveal that there are significant differences in provenance system between north and south of Weihe Graben, and its tectonic setting and provenance system show strong analogy with the offshore basins. Based on outcrops and systematic sampling in Weihe Graben, zircon U-Pb dating, cast thin section, backscattering and X-ray diffraction analysis are carried out to analyze the source system, deposition and reservoir characteristics of the northern and southern sandbodies in Weihe graben. The detrital zircons in the northern Huacheng section have two typical peaks of ~2500 Ma and ~1800 Ma reflecting the influence of North China Craton, and two younger peaks correspond to Caledonian and Hercynian movement. The conglomerate gravel types at the bottom of the sequence are mainly carbonate rocks, calcarenous clastic rocks and metamorphic rocks, which have distinct characteristics of Paleozoic carbonate rocks and clastic rock of Weibei Uplift in the north. The late Caledonian and Late Indosinian peaks dominate the detrital zircons in the southern profiles, and the gravel types are dominated by granites and metamorphic rocks, with distinct provenance characteristics of the southern Qinling Mountains. Typical profile observations show that the difference in provenance leads to significant differences between sedimentary system and reservoir characteristics. The carbonate provenance area of Weibei Uplift corresponds to a small and mud-rich sedimentary body, and the bottom conglomerate directly changes to silty sand and mudstone, with high calcium content in the reservoir. The southern Qinling orogenic belt is characterized by large distribution of sedimentary bodies, multi-cycle sand-rich deposits, and low calcium content. Different types of provenance systems provide material basis and prerequisite for reservoir and subsequent diagenesis. The outcrop system analysis of Weihe graben can provide references for offshore basin research in China.
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Key words:
- Weihe Graben /
- Source-sink characteristics /
- sedimentary system /
- reservoir characteristics /
- Cenozoic
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