A Thermodynamic Model for Prediction of Solubility of Elemental Mercury in Natural Gas, Produced Water and Hydrate Inhibitors

Abstract

When it comes to mercury (Hg) there are strict regulation around health, safety and environment, and the level of Hg in discharge water. Further, Hg can potentially compromise the integrity of materials anywhere in the flow path of the produced fluid. Real-time onsite Hg monitoring presents health hazard from exposure to Hg and can also be economically prohibitive. Therefore, it is desirable to be able to reliably simulate Hg partitioning between the vapor, liquid hydrocarbon, and water phases. It is further of interest to evaluate potential Hg condensation when the produced fluid flows from the reservoir through flow lines and passes through process equipment. Commercial compositional reservoir, process and flow simulators employ models with different levels of complexity. It is desirable to be able to make consistent simulations across various simulation platforms using the same equation of state models and model parameters. In this work we present self-contained sets of parameters for use with the original formulations of the Peng-Robinson modification from 1978 and the Soave-Redlich-Kwong equations of state. We aim at using the lowest possible level of complexity of binary interaction parameters. We further give the acentric factors for the original Peng-Robinson equations of state from 1976 giving the same results as when using the Peng-Robinson modification from 1978. The model covers various hydrocarbon components and inorganic gases, H2O, and common hydrate inhibitors. The work is based upon and ties together the experimental and modelling work of others and supplemented with new model parameters where required. We further summarize the accuracy of the model and briefly touch upon how the model extrapolates beyond the limits of data used in this work.