鄂尔多斯盆地延长组火山碎屑沉积物特征及其石油地质意义

Characteristics and its Petroleum Geological Significance of Voicanoic Detritai Sediments in Yanchang Formation, Ordos Basin

延长组是鄂尔多斯盆地重要含油层系，岩性由湖相及三角洲相砂泥岩韵律层组成，其中含有大量的火山碎屑物质既可作为判断分析沉积物源和区域地层划分对比标志，也对油气生储特征有重要影响。本文从火山物质沉积地质背景入手，通过组分分析和沉积成岩特征研究，探讨了火山沉积物与烃源岩演化之间的关系，以及成岩变化对低渗储层特征的影响。认为延长组火山物质以中酸性安山岩、流纹质熔结凝灰岩和玻屑凝灰岩为主，形成于盆地构造强烈回返期，源自盆地东部吕梁山方向，以悬浮漂移和河流挟砂带入两种方式进入湖盆，赋存状态有火山岩碎屑颗粒、火山灰填隙物、沉凝灰岩薄层以及蚀变浊沸石和绿泥石粘土矿物等方式，主要分布在长8、长7和长6油组。火山物质以及蚀变浊沸石易溶有利于储层次生孔隙形成，蚀变绿泥石矿物又保护了原生粒间孔隙，又是引起储层非均质性的重要因素，烃源岩之上大范围沉积的火山物质加速了烃源岩演化，有利于油气成藏。

The relationship between volcanic deposit and hydrocarbon source rock evolution, and the influence of diagenetic variation to low-permeability reservoir characteristics, is discussed in the paper, proceeding from the geologic background of volcanic deposition, through the component analysis and sedimentary diagenetic characteristic research. The volcanic matter of Yanchang Formation is considered to be mainly the neutral-acidic andesite, rhyo-ignimbrite, and vitroclastic tuff. It is formed at intensely returning stage of the basin tectonics, with the source from the eastern basin＇s Luliang mountain direction. The materials enter the lake basin in two ways of the suspended drifting and carrying sands by rivers into. The presented states are volcanic rock detrital particles, volcanic ash pore-filling matters, tuffite thin layers as well as altered laumontite, chlorite clay minerals and so on, being mainly distributed in Chang8, Chang7 and Chang6 oil reservoir sets. The volcanic matters and altered lanmontite are easily dissolved. This is advantageous to the forming of secondary porosity in reservoirs. Altered chlorite minerals have protected the primary intergranular pores, and also are major factors that cause the reservoir anisotropic. The volcanic matters deposited widespreadly on the hydrocarbon source rock accelerate the evolution of hydrocarbon source rock, and is advantageous to forming of oil/gas reservoirs.