A Study of recovery mechanisms in a nitrogen diffusion experiment

To understand the peculiar recovery phenomenon in a core nitrogen diffusion experiment, anumerical study has been carried out to investigate various governing forces and their interactions. The mathematical model used to simulate the experiment combines the analytical solution in the fracture (open space) and numerical solutions in the core. The analytical solution of the composition distribution in the fracture includes both molecular diffusion and bulk velocity of the gas stream. The numerical solution in the core includes molecular diffusion, capillary pressure, gravity, and Darcy flow. The fully implicit compositional formulation used in the numerical model is necessary because of the large capillarity and composition effects, and the small pressure gradients in the system.