Theoretical And Experimental Investigation Of Thermodiffusion (Soret Effect) In A Porous Medium

Thermodiffusion (the Soret effect) is important for the study of compositional variation in hydrocarbon reservoirs. The development of research history, theoretical modeling and applications to multicomponent hydrocarbon mixtures is included in this work. The Firoozabadi model appears to be an appropriate model for thermodiffusion estimation for hydrocarbon mixtures, and it is derived based on the equation of entropy generation rate and four postulates in non-equilibrium thermodynamics. Two equations of state, the Peng-Robinson Equation of State (PR-EoS) and the volume translated Peng Robinson Equation of State (vt-PR-EoS), have been used to estimate the thermodynamic properties of mixtures. In this work, different cases are presented: first, a new thermodiffusion cell designed to perform high pressure measurements in a porous medium has been validated at atmospheric pressure. Two systems were investigated, (1) 1,2,3,4-tetrahydronaphtalene (THN) and n-dodecane (nC12), and (2) isobutylbenzene (IBB) and n-dodecane at 50% of mass fraction. Experimental results revealed an excellent agreement with benchmark values and a good agreement with theoretical data. Second, the thermal expansion and concentration expansion coefficients and the viscosity of mixtures are necessary properties for the determination of the thermodiffusion coefficient. The densities of binaries of nC12, IBB and THN for pressures from 0.1 to 20 MPa and a temperature centred on 25⁰ were measured. By an derivative method, the thermal expansion and concentration expansion coefficients were determined. Viscosities were directly measured using a high pressure high temperature viscometer. Finally, the thermosolutal convections of two ternary mixtures, methane (C1), n-butane (nC4) and n-dodecane (nC12) at a pressure of 35.0 MPa and nC12, THN and IBB at atmospheric pressure, in a porous medium, were investigated over a wide range of permeability. The effect of permeability in the homogeneous and heterogeneous porous media on fluid transport was studied with consideration of thermodiffusion and molecular diffusion. In the analysis of the homogeneous porous medium, it was found that, for permeability below 300 mD, the thermodiffusion for both mixtures was dominant; and above this level, buoyancy convection became the dominant mechanism. Also, the viscosity was found to influence the evaluation of the molecular and thermodiffusion coefficients. In the case of heterogeneous porous medium, the impact of permeability ratio on the composition of the mixture components, velocity in the porous medium and on the separation ratio was investigated. It was found that the heterogeneity of porous medium has a significant influence on the composition of the mixture components.