Abstract

An improved analytical solution has been developed for the pressure decay experiment, which models both equilibrium and non-equilibrium boundary conditions for the diffusion of solvent gases in bitumen. This solution describes a description of the role of film resistance at the surface. The model allows direct use of experimental pressure in parameter estimations, and accounts for the relation between gas cap pressure decline and concentration at the interface.

Results of this model lead to improved interpretations of pressure decay tests and more reliable estimation of the diffusion parameters. Through this technique, three mass transfer parameters could be measured with the same experiment. Proper modeling and accurate estimation of interface resistance allows for better understanding of the physics and better estimation of D. The study reveals that closer to the onset of deasphaltene, liquid shows more resistance to diffusion. This effect does not exist far before or right after deasphaltene onset point.