Determining Diffusivity, Solubility and Swelling for Gaseous Solvent-Heavy Oil Systems

ABSTRACT

The values of the diffusion coefficient, swelling, and solubility are frequently required for designing processes which involve contact of various gases with liquids. Solubility determines the capacity of a liquid phase to dissolve gas, diffusivity controls the rate and extent of mass transfer, and swelling is the amount of volume change due to gas dissolution. Accurate estimation of these parameters by reliable and practical techniques is of continuing interest. In this study, 1D magnetic resonance imaging (MRI) is coupled with a numerical model to evaluate the diffusivity of gaseous solvents in heavy oil with a moving boundary condition. Diffusion tests are conducted for various solvents (dimethyl ether, propane, ethane, and carbon dioxide) under constant pressure and temperature inside a closed pressure volume temperature (PVT) cell. Spatial and temporal signal amplitudes are acquired during the diffusion tests which are further analyzed to obtain the concentration profiles and calculate the concentration-dependent diffusion coefficients using the measured correlation between the signal amplitude and solvent content. Oil swelling is found by tracking the gas–liquid interface and solubility is calculated by PVT analysis. Finally, the diffusivity results are compared with the pressure decay method considering both equilibrium and quasi-equilibrium boundary conditions.

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