Pore - Throat size distribution indices and their relationships with the petrophysical properties of conventional and unconventional clastic reservoirs

Mercury injection capillary pressure (MICP) curves provide significant information about the pore size distribution (PSD), which controls and defines the main petrophysical properties, namely porosity, and permeability. Due to the importance of the PSD, several indices and parameters were introduced to quantify this property. 140 MICP curves for conventional and unconventional clastic reservoirs, representing different geographic localities, geologic ages, and depositional environments, were used to study these parameters and indices, as well as their relationships with porosity and permeability. This study indicated that the most popular indices, namely Thomeer pore geometrical factor (Fg) and Brooks and Corey pore size distribution index (λ), have poor relationships with both porosity and permeability. On the other hand, displacement pressure and Swanson parameter, and pore-throat radius corresponding to the 25th percentile of mercury saturation give the best relationships with them. Therefore, permeability prediction equations based on Thomeer and Brooks and Corey indices were modified. Additionally, several new equations relating PSD parameters and indices to porosity and permeability were introduced.