Estimation of shale pore-size-distribution from N2 adsorption characteristics employing modified BJH algorithm

Accurate pore-size-distribution (PSD) is the key to comprehending porous media and shale rock characteristics. There are multiple methods for calculating the PSD of porous media. The Barrett–Joyner–Halenda (BJH) method is the most widely used and simplest calculation, and therefore, this study focus on the BJH algorithm to discuss the accurate shale PSD based on N2 adsorption characteristics. Despite conducting more than a hundred experiments there are certain phenomena for which the calculated pore volume is smaller than the actual pore volume. Therefore, we combined the Brunauer–Emmet–Teller (BET) multilayer adsorption theory and Halsey adsorption equation to analyze the capillary evaporation and desorption demarcation points in the desorption isotherm of each shale sample, and a modified PSD calculation model was established. In addition, we applied the modified BJH algorithm to a homogeneous silicon material with the pore radius known, for calculating the theoretical pore radius and subsequently the pore radii; this allowed determining the correctness of the modified algorithm. The calculation error was approximately 5% that indicated the accuracy of this algorithm. Therefore, this study could provide meaningful insights into the accurate PSD calculation and gas-in-place estimation in shale nanoporous media.