Effect of pore framework and radius of pore throats on permeability estimation

• Measuring r35 from capillary pressure curves of different sand and lime samples.
• Determining the pore throat cutoff and micro-porosity graphically.
• Enhancing the permeability prediction from porosity using the NMR logging tool.
• Discriminating the studied samples based on permeability to test Coates equation.
• Constructing pore throat radii with the porosity model for permeability prediction.

The purpose of this study is to understand and develop a model pore geometry, petrophysical parameters of (porosity, pore throat radius and permeability), and reservoir performance characteristics. Number of both sandstone and limestone samples extracted from different oil fields in Egypt and Arabian Gulf were conducted for petrophysical study. This study used the pore throat size distribution derived from capillary pressure by mercury injection (MICP) to determine the pore throat parameter for all the studied samples, r35 and the amount of micro-porosity in the studied samples. The pore throat and micro-porosity cut-off were determined graphically from the two curves of cumulative flow capacity and storage capacity.The idea that micro-porosity will hold a great part of irreducible water volume was verified by comparing the micro-porosity, with water saturation data determined from Dean and Stark technique which showed a good match between the two calculated values. It was used also to calibrate the T2-cutoff to enhance the permeability prediction from porosity using the NMR logging tool.The all studied samples were discriminated based on permeability cutoff 10 md. For the measured permeability values higher than 10 md, the regression coefficient increased form when the permeability was plotted with macro-porosity instead of total porosity or with calculated permeability using Coates et al., equation model. For the calculated permeability values less than 10 md, there was very weak correlation between either the macro or total porosity with measured one.In our work, we have introduced a radius of pore throat at mercury saturation of 35% (r35) together with the pore space configuration parameters to enhance the permeability prediction. The r35 was assumed to present different pore throat parameters.The present study showed that, pore throat size, (r35) improves permeability estimation. The combination of pore space configuration and pore throat parameters in the new model has enhanced the relationship between porosity and permeability.Finally, the validity of the new model represented by porosity and (r35) was tested using 123 rock samples (sandstone and limestone). The estimated permeability using the new model was plotted against the measured permeability and revealing high coefficient of correlation.