PHAST Error 57 Well diameter too big

[mwleeds]

Hi,

I've just started using PHAST for a Master's thesis project. I'm using it to build a model to simulate a push-pull tracer test which I'll be undertaking on the campus (Birmingham) boreholes this summer. The aim is to test out the ion-exchange conventions at a field scale.

I get this error message when I run my model:

ERROR: 57  - INIT2 - Well-bore area is greater than cell area in the x-y plane; Well diameter too large

Done with transient flow and transport simulation.
ERROR: 57  - INIT2 - Well-bore area is greater than cell area in the x-y plane; Well diameter too large

ERROR exit.

The model runs with a well radius of 0.02m but fails at higher values. My node/cell spacing is 0.1m. It also runs with a radius of 0.05m (actual value) and a grid spacing of 0.2m. I've experimented with placing the well in a single cell (i.e. centered on a node) and centered within an element. I'm intending to model 1/4 of the radial flow, hence my well is towards one corner of my model with an active box that intersects the well axis. This seemed preferable to positioning the well at one corner of the model.

Does anyone have any thoughts on why well diameter seems to be restricted and dependent on cell size? Given the small scale of the modelling I think we'll need a very fine grid size (~0.025m) close to the well. If this is a known/documented restriction, suggestions of a workaround solution would be welcome :)

Thanks,

Mike

[dlparkhurst]

It does not make physical sense to have the cross sectional area of the well greater than the plane area of the grid cell. Wells are intended to be relatively small features in larger cells.

At least initially, you should probably use a coarser discretization to get your model working with plausible results. You can increase discretization later, but I doubt you will need it to be so fine.

[mwleeds]

Thanks for the reply. I'll proceed with a larger grid spacing for now as you suggest.