Program Considerations

Program Options

The uses and capabilities of FEHM are summarized below with reference to the macro input structure discussed in Input Data

FEHM Capabilities and Associated Macro Command Statements

• Mass, energy balances in porous media
  • Variable rock properties (rock)
  • Variable permeability (perm, fper)
  • Variable thermal conductivity (cond, vcon)
  • Variable fracture properties, dual porosity, dual porosity/dual permeability (dual, dpdp,, gdpm)
• Multiple components available
  • Air-water isothermal mixture available (airwater, bous, head), fully coupled to heat and mass transfer (ngas, vapl, adif)
  • Up to 10 solutes with chemical reactions between each (trac, rxn)
  • Multiple species particle tracking (ptrk, mptr, sptr)
  • Different relative permeability and capillary pressure models (rlp, exrl)
• Equation of state flexibility inherent in code (eos)
• Pseudo-stress and storativity models available
  • Linear porosity deformation (ppor)
  • Gangi stress model (ppor)
• Numerics
  • Finite element with multiple element capabilities (elem)
  • Short form input methods available (coor, elem, fdm)
  • Flexible properties assignment (zone, zonn)
  • Flexible solution methods
    • Upwinding, implicit solution available (ctrl)
    • Iteration control adaptive strategy (iter)
  • Finite volume geometry (finv, isot)
• Flexible time step and stability control (time)
• Time-dependent fixed value and flux boundary conditions (flow, boun, hflx)

Initialization

The coefficient arrays for the polynomial representations of the density (crl, crv), enthalpy (cel, cev), and viscosity (cvl, cvv) functions are initialized to the values enumerated in Appendix of the “Models and Methods Summary” of the FEHM Application (Zyvoloski et al. 1999), while values for the saturation pressure and temperature function coefficients are found in Appendix of that document. All other global array and scalar variables, with the exception of the variables listed in the table below, are initialized to zero if integer or real, character variables are initialized to a single blank character, and logical variables are initialized as false.

Initial (Default) Values

Restart Procedures

FEHM writes a restart file for each run. The restart output file name may be given in the input control file or as terminal input, or if unspecified will default to fehmn.fin (see Control File or Terminal I/O Input). The file is used on a subsequent run by providing the name of the generated file (via control file or terminal) for the restart input file name. It is recommended that the restart input file name be modified to avoid confusion with the restart output file. For example, by changing the suffix to .ini, the default restart output file, fehmn.fin would be renamed fehmn.ini, and that file name placed in the control file or given as terminal input. Values from the restart file will overwrite any variable initialization prescribed in the input file. The initial time of simulation will also be taken from the restart file unless specified in the macro time input.

Error Processing

Due to the nonlinearity of the underlying partial differential equations, it is possible to produce an underflow or overflow condition through an unphysical choice of input parameters. More likely the code will fail to converge or will produce results which are out of bounds for the thermodynamic functions. The code will attempt to decrease the time step until convergence occurs. If the time step drops below a prescribed minimum the code will stop, writing a restart file. The user is encouraged to look at the input check file which contains information regarding maximum and minimum values of key variables in the code. All error and warning messages will be output to an output error file or the main output file.

The table below provides additional information on errors that will cause FEHM to terminate.

Error Conditions Which Result in Program Termination