Investigating the effects of pore types on the pore geometry, topology and electrical resistivity in fractured and vuggy samples using pore-scale models

The interpretation of electrical resistivity for assessing the saturation in rocks with complicated pore structures and various pore types requires the intrinsic parameters quantifying pore structures incorporated in modified resistivity models. Therefore, the objectives are to investigate pore types effect on the pore morphology and electrical resistivity and to determine the key pore morphological parameters for each pore type. The maximal ball method was applied to extract the pore networks of the reconstructed pore-scale models using a process-based method, and the pore morphology was characterized using a pore-network analysis and a random walk simulation. The resistivity was simulated using a finite element method. The key parameters determined by the Morris screening method for the fractured, isolated and connected vuggy models were the Euler number, the cross-sectional pore-to-throat area ratio (PTAR) and the pore radius, respectively. The qualitative relationships between the Euler number, the PTAR and the porosity exponent for the fractured and vuggy models were determined and validated using three Coquinas carbonates. This investigation will help to elucidate the variations of the porosity exponent and to further derive a new electrical resistivity model that correlates the pore morphology to the resistivity in fractured and vuggy carbonate reservoirs.