Development of a State-of-the-Art Thermodynamic Model for Mixtures Containing Water, Carbon Dioxide, Salts and Hydrocarbons in Bulk and in Confinement
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Accurate models for the prediction of thermodynamic properties of complex chemical systems are of outmost importance for the oil & gas industry. Research in academia and industry for the last several decades has resulted in different models with variable range of accuracy. Today, challenges refer to model development for highly polar mixtures and mixtures with strong electrostatic interactions. The aim of this project is to develop state-of-the-art molecular modelling techniques to describe and predict the thermodynamic properties and phase behavior of multicomponent systems that include water and carbon dioxide in the presence of salts and light oil components. This will be achieved under the umbrella of the state-of-the-art statistical associating fluid theory for potentials of variable range (SAFT-VR). The plan in the first instance is to combine the two SAFT-VR approaches to model the multicomponent mixture using the more realistic Mie potentials to predict the phase behavior (bubble points, dew points, salting out) and thermodynamic properties of the mixtures. An understanding of the effect of the presence of concentrated brines on the phase behavior of carbon dioxide and light oil components is of topical interest. In the first part of the work, we will consider strong, fully dissociated electrolytes, and will further extend the current capability of the method by incorporating a reactive SAFT model that can account for so-called speciation; i.e., the formation of new species as the charged and uncharged species react, to form example carbonates from the combination of CO2, H2O and Na+ under different conditions of concentration, pH, and thermodynamic conditions of temperature and pressure. A second novel aspect of the proposed work will bring together the accurate representation of the free energy of the liquid phase provided by the SAFT-VR Mie equation of state with a 2-dimensional model that will be used to represent a solid substrate, providing a way to study adsorption. We plan to develop models for the fluids of interest at different scales, from atomistic and united atom models to coarse-grain models that are more amenable to simulation. These latter ones will be used for comparison with the theory when needed, to calculate transport properties, to assess the robustness of the coarse grained potentials and to assess the effect of confinement on the phase behavior of the fluids. Both research groups in this project have long experience in the development of SAFT-based models for water + dioxide mixtures with and without strong electrolytes and molecular simulation force-fields and computational approaches for the same fluid mixtures. One of the co-PIs has been involved in the development of thermodynamics models for confined fluids. The two groups have on-going collaboration with Qatar Petroleum and Qatar Shell. The new model will be eventually applied for process simulation purposes by these industrial partners.