About the regular and radial mesh

Hi everyone,

I was using TOUGHREACT V1.2  ECO2N to run a simple injection simulation，and When I set up multiple injection points(such as 5 points and each is spaced 20m apart, that is, one or two meshes apart inside my model），i found that：

（1）when I use the regular mesh， Even when using a very small injection rate（such as 1e-3 kg/s), he reports an error, which can be mitigated a bit by spacing out the injection points a bit or delete some inj points to alleviate the non-convergence, but often counts a few days or less than a year before reporting the error；

（2）when I use radial mesh，everything seems to work just fine，I can set the injection rate up to  few hundred! （Although sometimes it doesn't stop even after a few years.）

So I'd like to ask why these two grids cause this difference? Hopefully someone can give me a rationale！