• Error reversing flow in multilayer wells


    I am trying to run a model with seasonal geothermal storage and therefore need to change the flow direction in my existing wells at certain times.
    However, when changing flow I get the standard error:

    PCG has diagonal element <=0.

    I know this is usually a discretization error or too big contrasts in material properties in neighboring layers/elements.
    I have tried to refine the model both vertically and horizontally and changed the reservoir parameters to be homogenenous, but none of these solutions helped.
    Also played around with the time-step length, but that didn't seem to have any influence either.
    Worth noting that I use a few days of zero flow rate before I reverse to pumping/injection respectively.

    Could the dip in my reservoir layers have an effect here?

    I have done similar simulations before on simple box models and had no issues.

    Any ideas would be much appreciated!