FRACTAL CHARACTERISTICS OF LOW-PERMEABILITY SANDSTONE RESERVOIRS

The sandstone micro-structure is one of the most important parameters for quantitative evaluation of groundwater/oil/gas resources and prediction of flow rates of water/oil/gas. In this study, we applied seven low-permeability sandstone samples obtained from North China to study the structures of pore and solid phase based on digital core technology and the fractal theory. In this work, rock images were collected by scanning electron microscopy (SEM), and then image software (image pro plus) was applied to convert the SEM images into binary images and calculated the perimeter and area of pores and particles. Using the fractal medium criterion, we analyzed the fractal characteristics of pore and solid phases, and then we extended the criterion from the pore phase to both pore and solid phases. This paper explores the relationship among the pore and solid phase fractal characteristics, porosity, pore size, particle size and fractal dimensions for pores and particles. The results were compared with the experimental data and showed that the solid phase satisfies the fractal distribution, while the pore phase dissatisfies the fractal distribution. It was also found that the minimum and maximum pore and particle sizes, magnification times have a significant effect on the results. In addition, by introducing the diameter and mean hydraulic radius into Ergun-Wu equation, the permeabilities of the samples were calculated.