Model Comparison for High-pressure Adsorption in Shale and its Influence on Phase Equilibria

Shale formations are of great importance in the last decades since they are large potential sources of oil and natural gas. The shale reservoirs are characterized for its low permeable and low porosity nature, due to these characteristics, adsorption plays a major role in the storage and phase equilibria of the hydrocarbons within the rock. The aim of this work is to provide a comparison and analysis of different models for pure and multicomponent adsorption at high pressure in shale found in recent literature. Additionally, an insight of the phase equilibria calculations under a capillary pressure difference coupled with the adsorption film thickness is given. The models used for pure component are: Langmuir, the modified Toth-Langmuir, and the Potential Theory of Multicomponent Adsorption using Dubinin-Radushkevich potential (MPTA-DRA). The three models show similar deviations close to 10%. For the multicomponent adsorption comparison, Multicomponent Langmuir (ML), Ideal Adsorbed Solution Theory (IAST) and MPTA were evaluated. MPTA shows the lowest deviation with 17.9%. In connection to the phase equilibria, the influence of the adsorption film on the phase envelope was studied. The adsorption film thickness modifies the effective capillary radius enhancing the capillary pressure of the system. These combined effects modify the saturation pressure in the whole temperature range except in the critical point. Having its biggest influence on the bubble point branch, away from the critical point.