Fluid Modeling of Underground Hydrogen Storage in a Depleted Natural Gas Field

Abstract

AbstractUnderground Hydrogen Storage (UHS) allows the storage of energy that is generated by fluctuating renewable energy sources such as solar and wind. Depleted hydrocarbon fields can be used to store hydrogen. The remaining hydrocarbon gas can be used as cushion gas. To engineer the UHS process, accurate phase, volumetric and transport behavior ("PVT") of hydrogen-hydrocarbon mixtures is required. In this paper, we develop an EOS and viscosity model to describe the operating envelope of a UHS operation in Austria.Constant Composition Expansion (CCE) experiments were performed using a customized visual HPHT PVT set-up minimizing volume and density errors to ensure high accuracy of the measurements involving hydrogen. Viscosity experiments were performed using a capillary rheometer. Both experimental setups show a total measurement uncertainty of less than 2%. Experiments were performed for various hydrogen- hydrocarbon mixtures to cover the full range of the depleted gas field which is considered. The composition of hydrocarbon-hydrogen mixtures was confirmed using gas chromatography. The results were used to develop an EOS for the hydrogen-hydrocarbon system and to "tune" reduced density corresponding state models to match measured viscosity data.The measured PVT and viscosity data of hydrogen-hydrocarbon mixtures measured in this study deviate somewhat from the default fluid models used in most commercial simulators. In this paper, a fluid model was developed using the Peng-Robinson EOS with volume shifts, and a reduced density corresponding state LBC viscosity model [1]. The fluid model was matched to (1) hydrogen-hydrocarbon gas laboratory measurements presented in this paper, (2) measured hydrogen-methane binary data (density and viscosity) taken from the literature, and (3) REFPROP (NIST) [2] calculated density and viscosity data for the hydrogen-hydrocarbon gas, hydrogen-methane binary system, and pure components. The required alteration (tuning) of the parameters in the fluid model development is discussed.The impact of hydrogen content on gas mixture viscosity is studied based on a large number of literature studies for the hydrogen-methane binary system, and the hydrogen-hydrocarbon gas system presented in this paper for relevant operating conditions. Some literature data for hydrogen-methane systems show an anomalous, near-constant gas viscosity behavior at constant pressure and temperature with increasing hydrogen content, until a critical hydrogen content is reached (>50 mole%). Similar behavior is also seen in the hydrogen-hydrocarbon gas mixture presented in this paper.