Quantitative analysis of pore structure and permeability characteristics of sandstone using SEM and CT images

Permeability determines the exploration and development efficiency of the oil and gas field, while the pore structure directly affects the permeability of sandstones. Therefore, in the current study, the pore structure and permeability of sandstones were quantitatively analyzed from macro and micro perspectives. With SEM images at different magnifications, pore size distributions (PSD) were obtained, and results were compared with values from the mercury intrusion method. Based on fractal theory, relationships between fractal dimension, magnifications, and porosity were analyzed, they showed apparent regularity. According to the results of PSD, permeability was further studied, while predicted values were more extensive than experiment results. With multislice CT images, the pore structure was obtained from the three-dimensional (3D) reconstruction. The connectivity of pores was discussed. In addition, an improved permeability estimation method based on multiple binary images was proposed, the permeability of A1 and A2 are 1.97 fm(2) and 1.94 fm(2) respectively, which are close to the experimental result (1.48 fm(2) at the confining pressure of 1 MPa). Meanwhile, it can also eliminate the dispersion of the calculation based on the two-dimensional SEM image.