[petsc-users] Recommendations of possible preconditioner/ksp solver/snes solver for three phase flow reservoir simulator

[Smith, Barry F.]

  Chuks,

1)   Please run a successful case with -snes_view and send the output so we can see the exact solver options being used.

2)   Run a less successful case with -snes_monitor -ksp_monitor_true_residual -ksp_converged_reason -fieldsplit_ksp_monitor_true_residual -fieldsplit_ksp_converged reason so we can see how the linear solver (and the sub linear solves) are (not) converging.

 
    Barry


> On Dec 15, 2018, at 7:54 PM, Chukwudi Chukwudozie via petsc-users <petsc-users at mcs.anl.gov> wrote:
> 
> Hi,
> 
> I am developing a fully implicit control volume finite element black oil reservoir simulator using petscdmplex and snes. So far, for 2 phase flow problems (3 by 3 block for pressure, saturation and bottomhole pressure), my simulator runs fine for small time step sizes in the order of less than 5 days. However, increasing the time step size, it doesn't converge with -3 (-5 sometimes) diverge reason. Considering that this is a fully implicit but nonlinear problem, I expect unconditional stability for reasonable time step sizes.
> 
>  The background DM for the 3 block problem is a composite one with the first two being DMPLES's (bag->plexScalNode for pressure and saturation) and the last one, bag->WellRedun, a redundant DM for the wellbore pressures. See below.
> 
>     ierr = DMRedundantCreate(PETSC_COMM_WORLD,0,bag->numWells,&bag->WellRedun);CHKERRQ(ierr);
>     ierr = DMCompositeCreate(PETSC_COMM_WORLD,&bag->MultiPhasePacker);CHKERRQ(ierr);
>         ierr = DMCompositeAddDM(bag->MultiPhasePacker,bag->plexScalNode);CHKERRQ(ierr);
>         ierr = DMCompositeAddDM(bag->MultiPhasePacker,bag->plexScalNode);CHKERRQ(ierr);
>         ierr = DMCompositeAddDM(bag->MultiPhasePacker,bag->WellRedun);CHKERRQ(ierr); 
> 
> I have used nested matrices as shown below. In addition, I used the fieldsplit (composite multiplicative) preconditioner with FGRES and least square for newton solver. See below.
> 
> ierr = MatCreateNest(PETSC_COMM_WORLD,Msize,is,Msize,is,&bK[0],K);CHKERRQ(ierr);
> 
> 
>     ierr = SNESGetKSP(bag->snesP,&kspP);CHKERRQ(ierr);
>     ierr = KSPSetTolerances(kspP,1.e-8,1.e-8,PETSC_DEFAULT,PETSC_DEFAULT);CHKERRQ(ierr);
>     ierr = KSPSetType(kspP,KSPFGMRES);CHKERRQ(ierr);
>     ierr = KSPSetFromOptions(kspP);CHKERRQ(ierr);
>     ierr = KSPGetPC(kspP,&pcP);CHKERRQ(ierr);
>     ierr = PCSetType(pcP, PCFIELDSPLIT);CHKERRQ(ierr);
>     ierr = DMCompositeGetGlobalISs(bag->MultiPhasePacker,&is);CHKERRQ(ierr); 
>     for(i = 0; i < Msize; i++)  ierr = PCFieldSplitSetIS(pcP,NULL,is[i]);CHKERRQ(ierr);
>     ierr = PCFieldSplitSetType(pcP,PC_COMPOSITE_MULTIPLICATIVE);CHKERRQ(ierr);
> 
> Any ideas on possible precoditioner options/solver options/combinations to improve stability will be appreciated.
> 
> Chuks
>