A new method for obtaining the rock pore structure eigenvalue

• The graphical method is inflexible and causes inevitable computation errors.
• The results of trapezoidal method usually deviate from the true value.
• We proposed a new method for the calculation of the pore structure eigenvalues.
• The new method is more precise and can be widely used.

To obtain the pore structure eigenvalue, the following two methods are usually applied: the graphical method and the trapezoidal method. Both methods have intrinsic disadvantages. For the graphical method, the pore size distribution curve must satisfy the normal distribution and some of the data from the cumulative pore size distribution curve are selected and averaged; this makes the method inflexible and causes inevitable computation errors. For the trapezoidal method, the saturation range is restricted, which causes the obtained results to deviate from the true value. To overcome these disadvantages, we propose a new method that is based on the trapezoidal method. The software 1stOpt is applied to get the capillary pressure function by fitting with the measured data. By substituting the pore radius function derived by the capillary pressure function into the computed formula of the new method, we obtain the pore structure eigenvalues. In comparison to the conventional methods, the results obtained by the new method are closer to the true value because this method takes into account the entire saturation range for integrating. In addition, it can be applied in all kinds of pore size distributions.