鄂尔多斯盆地陇东地区长7段致密砂岩微孔隙特征

The study of Chang 7 tight sandstone micro pore characteristics in Longdong area,Ordos Basin

致密油是当今非常规油气领域的研究热点。鄂尔多斯盆地长7段已发现致密油储量丰富,是中国最主要的致密油区之一。前人研究表明,纳米级孔喉对于非常规油气储层具有重要意义。采用氮气吸附、镜下观察、孔渗分析、X-射线衍射分析及粒度分析等实验手段研究长7段致密砂岩微孔隙特征,计算微孔分布、孔隙结构参数、微孔在总孔隙中的比例,并讨论了微孔隙类型以及矿物成分、粒度、分选对微孔发育的影响。研究表明,长7致密砂岩微孔隙结构复杂,微孔主要由"墨水瓶"型孔和平行壁狭缝型毛细孔组成,主要以黏土晶间孔及层间缝、云母层间片状孔、溶蚀微孔及杂基粒间微孔的形式存在。微孔体积分布在(2.40~13.04)×10^(-3)cm^3/g之间,约占总孔隙体积的1/4左右,微孔分布可分为2类:双峰型和单峰型。此外,对微孔体积与矿物成分、粒度及分选进行相关性分析,发现微孔体积与黏土矿物含量呈正相关关系,与碳酸盐矿物含量呈负相关关系;而微孔体积与石英+长石含量、中值粒径、标准偏差没有明显的相关性。因此,可认为长7段致密砂岩的黏土和碳酸盐矿物对其微孔的发育有一定的影响。

Tight oil has become a research focus in global unconventional petroleum nowadays.Chang 7 section in Ordos Basin is one of the most typical tight oil producing unit in China because of its geological reserves totaling upwards of 0.9 billion tons.Previous studies have shown nanoscale pore-throat plays an important role in unconventional reservoirs.In this study,nitrogen adsorption,microscopic observation,porosity-permeability analysis,X-ray diffraction analysis and grain-size analysis are applied to investigate micropore characteristic of Chang 7 tight sandstone.Pore size distributon,pore structure parameters,micro pore proportion in the total porosity are also calculated,and micro pore type is exhibited.Beside this,effect of mineral composition,granularity and sorting on the micro pore development is discussed.The results show that micro pore structure of Chang 7 tight sandstone is complex and exhibits with the shape of ink bottle type and slit-shaped pores.It is mainly compose of clay intergranular pore,seam between the layers,mica flake hole between the layers,dissolution micro pores and micro pores in matrix.Micro pore volume ranges from 2.40 to 13.04×10^-3cm^3/g,making up about a quarter of the total pore volume.Micro pore size distributon can be divided into bimodal type and unimodal type.In addition to this,correlation analysis between micro pore volume,mineral composition,granularity and standard deviation indicates that micro pore volume is positively correlated with clay mineral content while negatively related with carbonate mineral content.There is no obvious correlation between micropore volume and quartz and feldspar content,the median particle size,orstandard deviation.Therefore,it can be believed that clay and carbonate minerals content has certain influence on the development of micro pore in Chang 7tight sandstone.