滇东威信地区龙潭组煤系致密砂岩储层孔隙分形特征

Pore fractal characteristics of the tight sandstone reservoir of the Longtan Formation in Weixin area,eastern Yunnan

针对滇东威信地区龙潭组煤系致密砂岩气勘探开发程度较低的现状,利用铸体薄片和扫描电镜观察,分析致密砂岩孔隙显微特征;利用高压压汞实验和分形原理,分析致密砂岩储层的分形特征.结果表明,研究区龙潭组致密砂岩孔隙主要以次生孔隙为主,原生孔隙不甚发育,其中纳米孔隙占优势地位.计算得到的压汞分形维数范围为2.728~2.966,平均值为2.886,表明岩石内部孔隙结构复杂,联通性差,且岩石内部非均质性较强.计算的扫描电镜分形维数范围为1.352~1.559,平均值为1.466.对两分形维数进行回归分析,二者相关性显著.

In view of the low exploration and development level of tight sandstone gas in the Longtan Formation coal measures in Weixin area of eastern Yunnan,casting thin sections and scanning electron microscopy were used to analyze the microscopic characteristics of tight sandstone pores.The fractal characteristics of tight sandstone reservoirs were analyzed through a high-pressure mercury injection experiment and fractal principle.The results showed that the pores in the tight sandstone of the formation in the study area were mainly secondary pores,and primary pores were not very developed,and nanopores were dominant.The calculated fractal dimension of mercury injection ranged from 2.728 to 2.966,with an average value of 2.886,indicating that the pore structure inside the rock was complex,the connectivity poor,and the heterogeneity inside the rock strong.The calculated fractal dimension of scanning electron microscope ranged from 1.352 to 1.559 with an average of 1.466.The regression analysis of the above two fractal dimensions showed that the correlation between them was very obvious.