基于氮吸附的致密砂岩储层纳米级孔隙分布表征

Characterization of Nanoscale Pore Distribution in Tight Sandstone Reservoir Based on Nitrogen Adsorption

为研究致密砂岩储层纳米级孔隙分布特征,采用扫描电镜观察和低温氮吸附实验,对鄂尔多斯盆地华庆油田延长组长63储层致密砂岩样品进行测试分析,并统计了样品的比表面积和孔体积分布特征,开展了纳米级孔隙结构特征对比分析。研究表明:扫描电镜和低温氮吸附实验两者结果具有相对一致性;吸附等温线均属于IUPAC分类的Ⅳ型等温线,迟滞回线主要是H1、H2及H3型,孔隙形态主要是圆柱状、墨水瓶状及狭缝状;孔径分布曲线呈现出小单峰、双峰式以及多小峰3种模式;致密储层纳米级孔隙多以中孔为主,决定了纳米级总孔的发育程度。致密砂岩纳米孔隙的精细表征为储层分类及明确渗流特征提供了重要依据。

In order to study the nanoscale pore distribution patterns of tight sandstone reservoir,scanning electron microscope observation and low-temperature and low-temperature nitrogen adsorption were adopted to test the Chang63 reservoir sandstone samples of Yanchang Formation in Huaqing Oilfield of Ordos Basin. A statistic of specific surface area and pore volume distributions were gained to perform a comparative analysis for the nanoscale pore structure. Research indicates that there is a relatively consistency between the scanning electron microscope and low-temperature nitrogen adsorption tests. The adsorption isotherms are all classified as the Category-IV isotherm proposed by IUPAC. Hysteresis loops are mainly classified as Category-H1,Category-H2 and Category-H3. The pore morphology includes cylinder,ink-bottle and slit categories. The pore size distribution shows three patterns,including small singlet,doublet and multiple small peaks. The nanoscale pore in tight reservoir is dominated by mesoporous,which determines the development level of total nanoscale pores. Fine characterization of tight sandstone nanoscale pores provides a significant reference for reservoir classification and seepage mechanism investigation.