Why do big and small cells show problems in reservoir simulation?

[DAH7542]

Hey everybody, I would like to understand the mathematical (numerical) and technical reasons that explain the problem when fluid flows from big to small cells when working with reservoir simulation, it's common to hear that this situation causes convergence problems but I would like to know the very basic reasons and explanations... thanks in advanced.....

[vinomarky]

Not familiar with this exact issue, but I do know that when you get into high pore-volume throughput conditions (ie small cells) in a given timestep we often get problems. Fully implicit simulation methods are meant to be unconditionally stable, but in reality significantly exceeding mobile pore volume flux per cell in a given timestep will often cause problems.

I think the problem you have heard of is less related to big cell connecting small cell, and more related to small cell with high flux

[DAH7542]

Thank vinomarky, could you please elaborate (numerical explanation) a little bit more on this "small cell with high flux " problem? thanks....

[06pg22]

refer chapter of grid size selection in SPE Monograph: Reservoir Sinulation, By Mattax, Dalton