The role of gravity and temperature on hydrogen-containing mixtures in the subsurface

A model for thermal and gravity-induced compositional grading of hydrogen-containing gas mixtures using a cubic equation of state is presented. The theoretical background of compositional gradient modeling is reviewed, and the implementation of a thermal gradient model is used to predict the compositional variation of a hydrogennatural gas mixture for both depleted gas reservoir and salt cavern applications. We show that near-uniform gas composition versus depth is expected during the storage of hydrogen mixed with natural gas over 100 m of vertical relief. Further study into the calculation and significance of the ideal portion of the component molar enthalpy is needed to increase confidence in model implementation and application.