In carbonates,the petrophysical interpretation strongly reflects the porosity exponent(m)used in Archies Law for saturation calculation due to the variety of the pore types and the complexity of the pore geometry and topology.From extracting the pore network and calcualting pore geometry and topology,it is found that the key factors affecting porosity exponent are the ratio of pore cross-section area ratio to the pore-throat cross-sectional area ratio(PTAR)and Euler number representing the connectivity.With the increase of the PTAR and Euler number,both related to pore types,the porosity exponent increases.