Abstract: The fluid diffusion coefficient in core can be deduced from the mass diffusion equation, but some mass concentration as a key basic parameter of fluid should be obtained in core lab.The calculation of fluid diffusion coefficient is restricted for little volume of the fluid by conventional core test, so one-dimensional mathematical model of mass transfer diffusion is developed, and method of combining numerical simulation with experimental result is put forward.With this method, just one-time measurement of the average mass concentration of high volume of fluid is conducted, followed by tuning and match, the diffusion coefficient is offered.The modeling result shows that the proper diffusion coefficient is influenced by mass concentration, type, flowing velocity of fluid and rock permeability, etc.But the limit-range change of a solution diffusion coefficient has little effect on the distribution of fluid mass concentration.For this reason, the diffusion coefficient is normally assumed to be a constant.

Key words: diffusion, diffusion coefficient, mathematical model, method