Predictability of Equation of State (EoS)-based Gas Hydrate Models for Single and Binary Gas Mixtures

Abstract

The better models are necessary to design and understand the phase behavior of produced trapped natural gas from natural gas hydrates from subsea environments. Most of the models available in an open literature are primarily applicable at relatively low pressure condition thus making their use very limited for gas hydrate reservoir modeling. In order to produce methane from these gas hydrates, it is important to understand the phase behavior through suitable models which can be applied at in-situ reservoir conditions of high pressure and low temperature. These models can be used for better reservoir modeling of natural gas hydrate reservoir. In the present study the well-known Chen and Guo hydrate model has been used along with the set of several equations of state models (EoS). This model uses the published Lennard-Jones potential parameters obtained by fitting the L-J functions for typical gas species assuming the adsorption to be carried out in small cavities 5¹². The code (in Matlab®) is developed based on the three famous equations of state Peng-Robinson (P-R), Patel-Teja (P-T), and Soave-Redlich-Kwong (SRK). We optimized the computed phase diagrams based on three EoS with experimental phase diagram data from literature and determined the model parameters for the model with less percentage average deviation. The present papers discusses about the modeling of pure CH₄, C₂H₆, CO₂ and H₂S and then discuss the work extended to model the phase behavior of binary gas mixture hydrates like CH₄-C₂H₆, CH₄-CO₂ and CH₄-H₂S. Model predictions are validated against the experimental data from the literature, and observed to be in well agreement for high pressure range, suggesting their applicability for gas hydrate reservoir modeling.

Keywords: Binary Gas Mixture Hydrates, Equations of State, Fugacity, Hydrate Model, Natural Gas Hydrates