Modeling Adsorption in Shale

Abstract

The existing conventional methods to characterize reservoir storage properties face challenges in shale formations due to their fine grained texture, low porosity, and low permeability. An integrated analysis of standard core measurements, such as adsorption-desorption isotherms and mercury intrusion capillary pressure, helps us to better understand these formations by determining the pore size that controls the stored volume and flow conductance at a larger scale.

We propose a new model to distinguish and characterize the pore-body and pore-throat size distributions for the connected pore space of shale formations. We simultaneously analyze different sorption mechanisms such as multilayer adsorption and capillary condensation for nitrogen adsorption-desorption isotherms to determine the pore-body size. By accounting for the coupled processes, we predict the amount of gas adsorbed in the studied core samples. The model provides an explanation for the gas storage behavior at the core scale that can be extended to assess the formation. We also analyze mercury intrusion data not to validate the pore-body size obtained from nitrogen adsorption but to determine the pore-throat size. The integrated analysis of these measurements enables us to fully characterize the pore space of a shale formation.