Abstract:

In petroleum exploration, diffusion coefficient measured with NMR techniques is often used to identify fluid types (e.g., oil, water, and gas) and to calculate the saturation degree of reservoir rocks. In the micro-pores, however, the apparent or effective diffusion coefficient must be lower than the free diffusion coefficient. In this paper, the relationship between pore size and apparent diffusion coefficient is simulated using the finite difference and random walk methods. The effects of restricted diffusion on the accuracy of the petrophysical parameter calculations were analyzed under the well-logging and laboratory
conditions. Lastly, the application conditions and advantages of the two simulation methods were discussed.

Key words: NMR, restricted diffusion, micropore, finite difference, random walk