鄂尔多斯盆地南部晚三叠世异重流沉积机制

Hyperpycnal flow deposits generated from high-density flooding river diving into the bottom of low-density water has become the frontier research field of geology abroad in recent years. Deep-water sandbodies, organic matters accumulation and lithologic hydrocarbon reservoir relating to hyperpycnal flow have attracted wide attention of petroleum geologists. Although deep lacustrine basin is more conducive to forming hyperpycnal flow than ocean basin, depositional mechanisms of hyperpycnal flow and hyperpycnite in Mesozoic lake has been rarely reported both at home and abroad. Discovery of hyperpycnal flow deposits (in the seventh section of Yanchang formation) in the southern part of the late Triassic deep lacustrine Ordos basin create the objective conditions for the probing of depositional mechanism of hyperpycnal flow, genesis and distribution rule of deep-water sandstone reservoirs in continental lacustrine basin. Applicants may pay attention: ① to analysis sedimentary characteristics of hyperpycnal flow deposition and controlling factors of the development of sandbodies, ② to probe for hyperpycnal flow depositional mechanism in lacustrine environment, ③ to establish identification symbols and sedimentary model of lacustrine hyperpycnite,and ④ to study on physical properties of sandstone reservoir deposited in hyperpycnal flow, based on measurement of drill cores and outcrops with large scale proportion, serially sampling and sample analysis, combining with investigation on modern sediments. As a special turbidite current deposition, hyperpycnal flow deposition not only has the value of scientific theoretical research, but also has important practical significances for sandbody prediction and exploration on oil and gas reservoir in deep-water basin.

由高密度洪水河流潜入低密度水体底部形成的异重流（hyperpycnal flow）沉积已成为近年来国外地质学研究的前沿领域，与异重流相关的深水储集砂体、有机质富集及岩性油气藏吸引了国外石油地质学家的广泛关注。虽然深水湖盆比海洋盆地更有利于形成异重流，但国内外关于异重流沉积机制及中生代湖相异重流沉积的研究鲜有报道。鄂尔多斯盆地南部晚三叠世深水湖盆异重流沉积（延长组长7油层组）的发现，为探索陆相湖盆异重流沉积机制、深水储集砂体的成因与储层分布规律创造了客观条件。 本项目将通过大比例尺岩心-露头测量、系统采样和样品分析，结合现代沉积考察，分析湖相异重流沉积特征与砂体发育控制因素，探索湖相异重流沉积机制，建立湖相异重流沉积识别标志与沉积模式，研究异重流沉积砂体的物性特征。异重岩作为一种特殊类型的浊流沉积，不仅具有重要的地质学理论研究价值，而且对于深水储集砂体预测和油气勘探具有重要的现实意义。

异重流（hyperpycnal flow）沉积已成为近年来国外地质学研究的前沿领域，与异重流相关的深水储集砂体、有机质富集及岩性油气藏吸引了国外石油地质学家的广泛关注。虽然深水湖盆比海洋盆地更有利于形成异重流，但国内外关于异重流沉积机制及中生代湖相异重流沉积的研究鲜有报道。鄂尔多斯盆地南部晚三叠世深水湖盆异重流沉积（延长组长7油层组）的发现，为探索陆相湖盆异重流沉积机制、深水储集砂体的成因与储层分布规律创造了客观条件。.本项目以鄂尔多斯盆地南部延长组长7油层组钻井岩心和盆地南部的5条野外剖面和钻井岩心为重点，重点开展了以下研究：i.宏观沉积特征的观测与分析，研究单层厚度以及层内粒序变化、沉积构造、界面特征与沉积环境分析、粒序层组合特征分析；ii. 沉积物组构、沉积背景与储集性能分析，研究砂岩组结构与储集性能分析、泥质岩组分分析、沉积背景分析；iii. 异重岩沉积序列、识别标志与砂体分布规律与控制因素分析；iv. 异重流沉积物搬运-沉积机制研究，建立湖相异重流沉积模式。.异重流是一种由洪水期河口直接注入、因密度大于汇水盆地水体密度而沿水体底部分层流动的持续型浊流。盆地水体密度小、近物源、地形高差大、中-小河流发育、构造活动强烈的陆相淡水湖泊更利于异重流的产生，但陆相湖盆异重流沉积并未引起足够的重视。.由异重流形成的沉积岩被称作异重岩（hyperpycnite），以发育由洪水增强-减弱所产生的逆粒序-正粒序组合、层内微侵蚀面、富含陆源有机质区别于其它浊积岩。结合中生代湖相异重岩研究实例，建立了“沟道-舌状体-朵状体”异重流沉积模式。认为深入研究异重流沉积，不仅有益于完善重力流沉积理论、分析沉积环境，而且有利于指导深水非常规油气勘探，具有重要的科学价值和现实意义。