Mass computation and conservation

The total fluid mass of species within a volume is (1) It must be checked that MOOSE calculates this correctly, using the PorousFlowFluidMass postprocessor, in order that mass-balances be correct, and also because this quantity is used in a number of other tests.

Single-phase, single-component fluid

A 1D model with , and with three elements of size 1 is created with the following properties:

Table 1: Parameter values in the single-phase, single-component test

ParameterValue
Constant fluid bulk modulusPa
Fluid density at zero pressurekg.m
Van Genuchten 0.5
Van Genuchten Pa
Porosity0.1

The porepressure is set at .

# checking that the mass postprocessor correctly calculates the mass
# 1phase, 1component, constant porosity
[Mesh]
  type = GeneratedMesh
  dim = 1
  nx = 3
  xmin = -1
  xmax = 1
[]

[GlobalParams]
  PorousFlowDictator = dictator
[]

[Variables]
  [./pp]
  [../]
[]

[ICs]
  [./pinit]
    type = FunctionIC
    function = x
    variable = pp
  [../]
[]

[Kernels]
  [./mass0]
    type = PorousFlowMassTimeDerivative
    fluid_component = 0
    variable = pp
  [../]
[]

[UserObjects]
  [./dictator]
    type = PorousFlowDictator
    porous_flow_vars = 'pp'
    number_fluid_phases = 1
    number_fluid_components = 1
  [../]
  [./pc]
    type = PorousFlowCapillaryPressureVG
    m = 0.5
    alpha = 1
  [../]
[]

[Modules]
  [./FluidProperties]
    [./simple_fluid]
      type = SimpleFluidProperties
      bulk_modulus = 1
      density0 = 1
      thermal_expansion = 0
    [../]
  [../]
[]

[Materials]
  [./temperature]
    type = PorousFlowTemperature
  [../]
  [./ppss]
    type = PorousFlow1PhaseP
    porepressure = pp
    capillary_pressure = pc
  [../]
  [./massfrac]
    type = PorousFlowMassFraction
  [../]
  [./simple_fluid]
    type = PorousFlowSingleComponentFluid
    fp = simple_fluid
    phase = 0
  [../]
  [./porosity]
    type = PorousFlowPorosityConst
    porosity = 0.1
  [../]
[]

[Postprocessors]
  [./total_mass]
    type = PorousFlowFluidMass
  [../]
[]

[Preconditioning]
  [./andy]
    type = SMP
    full = true
    petsc_options_iname = '-ksp_type -pc_type -snes_atol -snes_rtol -snes_max_it'
    petsc_options_value = 'bcgs bjacobi 1 1 10000'
  [../]
[]

[Executioner]
  type = Transient
  solve_type = Newton
  dt = 1
  end_time = 1
[]

[Outputs]
  execute_on = 'timestep_end'
  file_base = mass01
  csv = true
[]
(modules/porous_flow/test/tests/mass_conservation/mass01.i)

Recall that in PorousFlow, mass is lumped to the nodes. Therefore, the integral above is evaluated at the nodes, and a sum of the results is outputted as the PorousFlowFluidMass postprocessor. Using the properties given above, this yields:

Table 2: Nodal masses in the single-phase, single-component test

DensitySaturationNodal mass
-1-10.3678794410.7071067810.008671002
-0.333333333-0.3333333330.7165313110.9486832980.02265871
-0.333333333-0.3333333330.7165313110.9486832980.02265871
0.3333333330.3333333331.39561242510.046520414
0.3333333330.3333333331.39561242510.046520414
112.71828182810.090609394
Total0.237638643

MOOSE also gives the total mass as 0.237638643\,kg.

Single-phase, two-components

This is similar to the previous section, but has two fluid ocmponents components. The mass fraction is fixed at (2)

# checking that the mass postprocessor correctly calculates the mass
# 1phase, 2component, constant porosity
[Mesh]
  type = GeneratedMesh
  dim = 1
  nx = 3
  xmin = -1
  xmax = 1
[]

[GlobalParams]
  PorousFlowDictator = dictator
[]

[Variables]
  [./pp]
  [../]
  [./mass_frac_comp0]
  [../]
[]

[ICs]
  [./pinit]
    type = FunctionIC
    function = x
    variable = pp
  [../]
  [./minit]
    type = FunctionIC
    function = 'x*x'
    variable = mass_frac_comp0
  [../]
[]

[Kernels]
  [./mass0]
    type = PorousFlowMassTimeDerivative
    fluid_component = 0
    variable = pp
  [../]
  [./mass1]
    type = PorousFlowMassTimeDerivative
    fluid_component = 1
    variable = mass_frac_comp0
  [../]
[]

[UserObjects]
  [./dictator]
    type = PorousFlowDictator
    porous_flow_vars = 'pp mass_frac_comp0'
    number_fluid_phases = 1
    number_fluid_components = 2
  [../]
  [./pc]
    type = PorousFlowCapillaryPressureVG
    m = 0.5
    alpha = 1
  [../]
[]

[Modules]
  [./FluidProperties]
    [./simple_fluid]
      type = SimpleFluidProperties
      bulk_modulus = 1
      density0 = 1
      thermal_expansion = 0
    [../]
  [../]
[]

[Materials]
  [./temperature]
    type = PorousFlowTemperature
  [../]
  [./ppss]
    type = PorousFlow1PhaseP
    porepressure = pp
    capillary_pressure = pc
  [../]
  [./massfrac]
    type = PorousFlowMassFraction
    mass_fraction_vars = 'mass_frac_comp0'
  [../]
  [./simple_fluid]
    type = PorousFlowSingleComponentFluid
    fp = simple_fluid
    phase = 0
  [../]
  [./porosity]
    type = PorousFlowPorosityConst
    porosity = 0.1
  [../]
[]

[Postprocessors]
  [./total_mass_0]
    type = PorousFlowFluidMass
  [../]
  [./total_mass_1]
    type = PorousFlowFluidMass
    fluid_component = 1
  [../]
[]

[Preconditioning]
  [./andy]
    type = SMP
    full = true
    petsc_options_iname = '-ksp_type -pc_type -snes_atol -snes_rtol -snes_max_it'
    petsc_options_value = 'bcgs bjacobi 1 1 10000'
  [../]
[]

[Executioner]
  type = Transient
  solve_type = Newton
  dt = 1
  end_time = 1
[]

[Outputs]
  execute_on = 'timestep_end'
  file_base = mass02
  csv = true
[]
(modules/porous_flow/test/tests/mass_conservation/mass02.i)

Table 3: Nodal masses in the single-phase, 2-component test

DensitySaturationNodal massNodal mass
-1-10.3678794410.70710678110.0086710
-0.333333333-0.3333333330.7165313110.9486832980.1111110.002517630.02014108
-0.333333333-0.3333333330.7165313110.9486832980.1111110.002517630.02014108
0.3333333330.3333333331.39561242510.1111110.005168930.04135148
0.3333333330.3333333331.39561242510.1111110.005168930.04135148
112.718281828110.090609390
Total0.114653530.12298511

MOOSE produces the expected answer.

Two-phase, two-components

A 1D model with two elements from is created, with two phases (0 and 1), and two fluid components (0 and 1). The phase densities are calculated using a constant bulk modulus fluid with bulk modulus of 1 Pa. The density at zero pressure is 1 kg.m for phase 0, and 0.1 kg.m for phase 1. The porepressure of phase 0 is held fixed at 1 Pa, and a constant capillary pressure of 0 is specified so that the pressure of phase 1 is also 1 Pa. This results in phase densities of kg.m for phase 0, and kg.m for phase 1.

Saturation of phase 1 varies linearly as , while porosity is 0.1 throughout. The mass fraction of species 0 in fluid phase 0 is specified as 0.3, while the mass fraction of species 0 in phase 1 is 0.55.

# Checking that the mass postprocessor correctly calculates the mass
# of each component in each phase, as well as the total mass of each
# component in all phases.
# 2phase, 2component, constant porosity

[Mesh]
  type = GeneratedMesh
  dim = 1
  nx = 2
  xmin = 0
  xmax = 1
[]

[GlobalParams]
  PorousFlowDictator = dictator
[]

[Variables]
  [./pp]
  [../]
  [./sat]
  [../]
[]

[AuxVariables]
  [./massfrac_ph0_sp0]
    initial_condition = 0.3
  [../]
  [./massfrac_ph1_sp0]
    initial_condition = 0.55
  [../]
[]

[ICs]
  [./pinit]
    type = ConstantIC
    value = 1
    variable = pp
  [../]
  [./satinit]
    type = FunctionIC
    function = 1-x
    variable = sat
  [../]
[]

[Kernels]
  [./mass0]
    type = PorousFlowMassTimeDerivative
    fluid_component = 0
    variable = pp
  [../]
  [./mass1]
    type = PorousFlowMassTimeDerivative
    fluid_component = 1
    variable = sat
  [../]
[]

[UserObjects]
  [./dictator]
    type = PorousFlowDictator
    porous_flow_vars = 'pp sat'
    number_fluid_phases = 2
    number_fluid_components = 2
  [../]
  [./pc]
    type = PorousFlowCapillaryPressureConst
    pc = 0
  [../]
[]

[Modules]
  [./FluidProperties]
    [./simple_fluid0]
      type = SimpleFluidProperties
      bulk_modulus = 1
      density0 = 1
      thermal_expansion = 0
    [../]
    [./simple_fluid1]
      type = SimpleFluidProperties
      bulk_modulus = 1
      density0 = 0.1
      thermal_expansion = 0
    [../]
  [../]
[]

[Materials]
  [./temperature]
    type = PorousFlowTemperature
  [../]
  [./ppss]
    type = PorousFlow2PhasePS
    phase0_porepressure = pp
    phase1_saturation = sat
    capillary_pressure = pc
  [../]
  [./massfrac]
    type = PorousFlowMassFraction
    mass_fraction_vars = 'massfrac_ph0_sp0 massfrac_ph1_sp0'
  [../]
  [./simple_fluid0]
    type = PorousFlowSingleComponentFluid
    fp = simple_fluid0
    phase = 0
  [../]
  [./simple_fluid1]
    type = PorousFlowSingleComponentFluid
    fp = simple_fluid1
    phase = 1
  [../]
  [./porosity]
    type = PorousFlowPorosityConst
    porosity = 0.1
  [../]
[]

[Postprocessors]
  [./comp0_phase0_mass]
    type = PorousFlowFluidMass
    fluid_component = 0
    phase = 0
  [../]
  [./comp0_phase1_mass]
    type = PorousFlowFluidMass
    fluid_component = 0
    phase = 1
  [../]
  [./comp0_total_mass]
    type = PorousFlowFluidMass
    fluid_component = 0
  [../]
  [./comp0_total_mass2]
    type = PorousFlowFluidMass
    fluid_component = 0
    phase = '0 1'
  [../]
  [./comp1_phase0_mass]
    type = PorousFlowFluidMass
    fluid_component = 1
    phase = 0
  [../]
  [./comp1_phase1_mass]
    type = PorousFlowFluidMass
    fluid_component = 1
    phase = 1
  [../]
  [./comp1_total_mass]
    type = PorousFlowFluidMass
    fluid_component = 1
  [../]
  [./comp1_total_mass2]
    type = PorousFlowFluidMass
    fluid_component = 1
    phase = '0 1'
  [../]
[]

[Executioner]
  type = Transient
  solve_type = Newton
  nl_abs_tol = 1e-16
  dt = 1
  end_time = 1
[]

[Outputs]
  execute_on = 'timestep_end'
  file_base = mass05
  csv = true
[]
(modules/porous_flow/test/tests/mass_conservation/mass05.i)

It is simple to calculate the total mass of each component in each phase using Eq. (1), the results of which are

Table 4: Masses in the 2-phase, 2-component test

SpeciesPhaseTotal mass Eq. (1)Total mass (MOOSE)
000.040774230.04077423
010.0074752750.007475275
0all0.048249500.04824950
100.095139860.09513986
110.0061161340.006116134
1all0.101255600.1012560

Constant fluid source

A fluid source of kg.m.s is introduced into a single element, and the PorousFlowFluidMass postprocessor is used to record the fluid mass as a function of time:

# checking that the mass postprocessor correctly calculates the mass
# 1phase, 1component, constant porosity, with a constant fluid source
[Mesh]
  type = GeneratedMesh
  dim = 3
[]

[GlobalParams]
  PorousFlowDictator = dictator
[]

[Variables]
  [./pp]
    initial_condition = -0.5
  [../]
[]

[Kernels]
  [./mass0]
    type = PorousFlowMassTimeDerivative
    fluid_component = 0
    variable = pp
  [../]
  [./source]
    type = BodyForce
    variable = pp
    value = 0.1 # kg/m^3/s
  [../]
[]

[UserObjects]
  [./dictator]
    type = PorousFlowDictator
    porous_flow_vars = 'pp'
    number_fluid_phases = 1
    number_fluid_components = 1
  [../]
  [./pc]
    type = PorousFlowCapillaryPressureVG
    m = 0.5
    alpha = 1
  [../]
[]

[Modules]
  [./FluidProperties]
    [./simple_fluid]
      type = SimpleFluidProperties
      bulk_modulus = 1
      density0 = 1
      thermal_expansion = 0
    [../]
  [../]
[]

[Materials]
  [./temperature]
    type = PorousFlowTemperature
  [../]
  [./ppss]
    type = PorousFlow1PhaseP
    porepressure = pp
    capillary_pressure = pc
  [../]
  [./massfrac]
    type = PorousFlowMassFraction
  [../]
  [./simple_fluid]
    type = PorousFlowSingleComponentFluid
    fp = simple_fluid
    phase = 0
  [../]
  [./porosity]
    type = PorousFlowPorosityConst
    porosity = 0.1
  [../]
[]

[Postprocessors]
  [./porepressure]
    type = PointValue
    point = '0 0 0'
    variable = pp
    execute_on = 'initial timestep_end'
  [../]
  [./total_mass]
    type = PorousFlowFluidMass
    execute_on = 'initial timestep_end'
  [../]
[]

[Preconditioning]
  [./andy]
    type = SMP
    full = true
    petsc_options_iname = '-ksp_type -pc_type -snes_atol -snes_rtol -snes_max_it'
    petsc_options_value = 'gmres bjacobi 1E-12 1E-20 10000'
  [../]
[]

[Executioner]
  type = Transient
  solve_type = Newton
  dt = 1
  end_time = 10
[]

[Outputs]
  execute_on = 'initial timestep_end'
  file_base = mass03
  csv = true
[]
(modules/porous_flow/test/tests/mass_conservation/mass03.i)

Mass conservation in a deforming material

A single unit element, with roller BCs on its sides and bottom, is compressed at a uniform rate: (3) Here is the vertical displacement and is time. There is no fluid flow and the material's boundaries are impermeable. Fluid mass conservation is checked.

# The sample is a single unit element, with roller BCs on the sides
# and bottom.  A constant displacement is applied to the top: disp_z = -0.01*t.
# There is no fluid flow.
# Fluid mass conservation is checked.
#
# Under these conditions
# porepressure = porepressure(t=0) - (Fluid bulk modulus)*log(1 - 0.01*t)
# stress_xx = (bulk - 2*shear/3)*disp_z/L (remember this is effective stress)
# stress_zz = (bulk + 4*shear/3)*disp_z/L (remember this is effective stress)
# where L is the height of the sample (L=1 in this test)
#
# Parameters:
# Bulk modulus = 2
# Shear modulus = 1.5
# fluid bulk modulus = 0.5
# initial porepressure = 0.1
#
# Desired output:
# zdisp = -0.01*t
# p0 = 0.1 - 0.5*log(1-0.01*t)
# stress_xx = stress_yy = -0.01*t
# stress_zz = -0.04*t
#
# Regarding the "log" - it comes from preserving fluid mass

[Mesh]
  type = GeneratedMesh
  dim = 3
  nx = 1
  ny = 1
  nz = 1
  xmin = -0.5
  xmax = 0.5
  ymin = -0.5
  ymax = 0.5
  zmin = -0.5
  zmax = 0.5
[]

[GlobalParams]
  displacements = 'disp_x disp_y disp_z'
  PorousFlowDictator = dictator
  block = 0
[]

[Variables]
  [./disp_x]
  [../]
  [./disp_y]
  [../]
  [./disp_z]
  [../]
  [./porepressure]
    initial_condition = 0.1
  [../]
[]

[BCs]
  [./confinex]
    type = PresetBC
    variable = disp_x
    value = 0
    boundary = 'left right'
  [../]
  [./confiney]
    type = PresetBC
    variable = disp_y
    value = 0
    boundary = 'bottom top'
  [../]
  [./basefixed]
    type = PresetBC
    variable = disp_z
    value = 0
    boundary = back
  [../]
  [./top_velocity]
    type = FunctionPresetBC
    variable = disp_z
    function = -0.01*t
    boundary = front
  [../]
[]

[Kernels]
  [./grad_stress_x]
    type = StressDivergenceTensors
    variable = disp_x
    component = 0
  [../]
  [./grad_stress_y]
    type = StressDivergenceTensors
    variable = disp_y
    component = 1
  [../]
  [./grad_stress_z]
    type = StressDivergenceTensors
    variable = disp_z
    component = 2
  [../]
  [./poro_x]
    type = PorousFlowEffectiveStressCoupling
    biot_coefficient = 0.3
    variable = disp_x
    component = 0
  [../]
  [./poro_y]
    type = PorousFlowEffectiveStressCoupling
    biot_coefficient = 0.3
    variable = disp_y
    component = 1
  [../]
  [./poro_z]
    type = PorousFlowEffectiveStressCoupling
    biot_coefficient = 0.3
    component = 2
    variable = disp_z
  [../]
  [./poro_vol_exp]
    type = PorousFlowMassVolumetricExpansion
    variable = porepressure
    fluid_component = 0
  [../]
  [./mass0]
    type = PorousFlowMassTimeDerivative
    fluid_component = 0
    variable = porepressure
  [../]
[]

[AuxVariables]
  [./stress_xx]
    order = CONSTANT
    family = MONOMIAL
  [../]
  [./stress_xy]
    order = CONSTANT
    family = MONOMIAL
  [../]
  [./stress_xz]
    order = CONSTANT
    family = MONOMIAL
  [../]
  [./stress_yy]
    order = CONSTANT
    family = MONOMIAL
  [../]
  [./stress_yz]
    order = CONSTANT
    family = MONOMIAL
  [../]
  [./stress_zz]
    order = CONSTANT
    family = MONOMIAL
  [../]
[]

[AuxKernels]
  [./stress_xx]
    type = RankTwoAux
    rank_two_tensor = stress
    variable = stress_xx
    index_i = 0
    index_j = 0
  [../]
  [./stress_xy]
    type = RankTwoAux
    rank_two_tensor = stress
    variable = stress_xy
    index_i = 0
    index_j = 1
  [../]
  [./stress_xz]
    type = RankTwoAux
    rank_two_tensor = stress
    variable = stress_xz
    index_i = 0
    index_j = 2
  [../]
  [./stress_yy]
    type = RankTwoAux
    rank_two_tensor = stress
    variable = stress_yy
    index_i = 1
    index_j = 1
  [../]
  [./stress_yz]
    type = RankTwoAux
    rank_two_tensor = stress
    variable = stress_yz
    index_i = 1
    index_j = 2
  [../]
  [./stress_zz]
    type = RankTwoAux
    rank_two_tensor = stress
    variable = stress_zz
    index_i = 2
    index_j = 2
  [../]
[]

[Modules]
  [./FluidProperties]
    [./simple_fluid]
      type = SimpleFluidProperties
      bulk_modulus = 0.5
      density0 = 1
      thermal_expansion = 0
      viscosity = 1
    [../]
  [../]
[]

[Materials]
  [./temperature]
    type = PorousFlowTemperature
  [../]
  [./elasticity_tensor]
    type = ComputeElasticityTensor
    C_ijkl = '1 1.5'
    # bulk modulus is lambda + 2*mu/3 = 1 + 2*1.5/3 = 2
    fill_method = symmetric_isotropic
  [../]
  [./strain]
    type = ComputeSmallStrain
  [../]
  [./stress]
    type = ComputeLinearElasticStress
  [../]
  [./vol_strain]
    type = PorousFlowVolumetricStrain
  [../]
  [./eff_fluid_pressure]
    type = PorousFlowEffectiveFluidPressure
  [../]
  [./ppss]
    type = PorousFlow1PhaseP
    porepressure = porepressure
    capillary_pressure = pc
  [../]
  [./massfrac]
    type = PorousFlowMassFraction
  [../]
  [./simple_fluid]
    type = PorousFlowSingleComponentFluid
    fp = simple_fluid
    phase = 0
  [../]
  [./porosity]
    type = PorousFlowPorosityConst
    porosity = 0.1
  [../]
  [./permeability]
    type = PorousFlowPermeabilityConst
    permeability = '0.5 0 0   0 0.5 0   0 0 0.5'
  [../]
[]

[UserObjects]
  [./dictator]
    type = PorousFlowDictator
    porous_flow_vars = 'porepressure disp_x disp_y disp_z'
    number_fluid_phases = 1
    number_fluid_components = 1
  [../]
  [./pc]
    type = PorousFlowCapillaryPressureVG
    m = 0.5
    alpha = 1
  [../]
[]

[Postprocessors]
  [./p0]
    type = PointValue
    outputs = 'console csv'
    execute_on = 'initial timestep_end'
    point = '0 0 0'
    variable = porepressure
  [../]
  [./zdisp]
    type = PointValue
    outputs = csv
    point = '0 0 0.5'
    use_displaced_mesh = false
    variable = disp_z
  [../]
  [./stress_xx]
    type = PointValue
    outputs = csv
    point = '0 0 0'
    variable = stress_xx
  [../]
  [./stress_yy]
    type = PointValue
    outputs = csv
    point = '0 0 0'
    variable = stress_yy
  [../]
  [./stress_zz]
    type = PointValue
    outputs = csv
    point = '0 0 0'
    variable = stress_zz
  [../]
  [./fluid_mass]
    type = PorousFlowFluidMass
    fluid_component = 0
    execute_on = 'initial timestep_end'
    use_displaced_mesh = true
    outputs = 'console csv'
  [../]
[]

[Preconditioning]
  [./andy]
    type = SMP
    full = true
    petsc_options_iname = '-ksp_type -pc_type -snes_atol -snes_rtol -snes_max_it'
    petsc_options_value = 'bcgs bjacobi 1E-14 1E-8 10000'
  [../]
[]

[Executioner]
  type = Transient
  solve_type = Newton
  start_time = 0
  end_time = 10
  dt = 2
[]

[Outputs]
  execute_on = 'initial timestep_end'
  file_base = mass04
  [./csv]
    type = CSV
  [../]
[]
(modules/porous_flow/test/tests/mass_conservation/mass04.i)

Note the use_displaced_mesh = true option in the PorousFlowFluidMass postprocessor: it is necessary to correctly compute the mass.

Under these conditions (4) Here is the fluid porepressure, which is at ; is the fluid bulk modulus; is the effective stress; is the drained bulk modulus of the material; is the shear modulus of the material; and is the height of the sample.

PorousFlow produces these results exactly, and, importantly, conserves fluid mass.

Mass computation with a saturation threshold in multi-component, multi-phase fluids

The PorousFlowFluidMass postprocessor may be used to compute the total mass of each component in each phase, as well as the total mass of each component in all phases. Furthermore, a saturation threshold may be set to only count the fluid above the threshold.

# Checking that the mass postprocessor correctly calculates the mass
# of each component in each phase, as well as the total mass of each
# component in all phases. Also tests that optional saturation threshold
# gives the correct mass
# 2phase, 2component, constant porosity
# saturation_threshold set to 0.6 for phase 1

[Mesh]
  type = GeneratedMesh
  dim = 1
  nx = 10
  xmin = 0
  xmax = 1
[]

[GlobalParams]
  PorousFlowDictator = dictator
[]

[Variables]
  [./pp]
  [../]
  [./sat]
  [../]
[]

[AuxVariables]
  [./massfrac_ph0_sp0]
    initial_condition = 1
  [../]
  [./massfrac_ph1_sp0]
    initial_condition = 0
  [../]
[]

[ICs]
  [./pinit]
    type = ConstantIC
    value = 1
    variable = pp
  [../]
  [./satinit]
    type = FunctionIC
    function = 1-x
    variable = sat
  [../]
[]

[Kernels]
  [./mass0]
    type = PorousFlowMassTimeDerivative
    fluid_component = 0
    variable = pp
  [../]
  [./mass1]
    type = PorousFlowMassTimeDerivative
    fluid_component = 1
    variable = sat
  [../]
[]

[UserObjects]
  [./dictator]
    type = PorousFlowDictator
    porous_flow_vars = 'pp sat'
    number_fluid_phases = 2
    number_fluid_components = 2
  [../]
  [./pc]
    type = PorousFlowCapillaryPressureConst
    pc = 0
  [../]
[]

[Modules]
  [./FluidProperties]
    [./simple_fluid0]
      type = SimpleFluidProperties
      bulk_modulus = 1
      density0 = 1
      thermal_expansion = 0
    [../]
    [./simple_fluid1]
      type = SimpleFluidProperties
      bulk_modulus = 1
      density0 = 0.1
      thermal_expansion = 0
    [../]
  [../]
[]

[Materials]
  [./temperature]
    type = PorousFlowTemperature
  [../]
  [./ppss]
    type = PorousFlow2PhasePS
    phase0_porepressure = pp
    phase1_saturation = sat
    capillary_pressure = pc
  [../]
  [./massfrac]
    type = PorousFlowMassFraction
    mass_fraction_vars = 'massfrac_ph0_sp0 massfrac_ph1_sp0'
  [../]
  [./simple_fluid0]
    type = PorousFlowSingleComponentFluid
    fp = simple_fluid0
    phase = 0
  [../]
  [./simple_fluid1]
    type = PorousFlowSingleComponentFluid
    fp = simple_fluid1
    phase = 1
  [../]
  [./porosity]
    type = PorousFlowPorosityConst
    porosity = 0.1
  [../]
[]

[Postprocessors]
  [./comp0_phase0_mass]
    type = PorousFlowFluidMass
    fluid_component = 0
    phase = 0
  [../]
  [./comp0_phase1_mass]
    type = PorousFlowFluidMass
    fluid_component = 0
    phase = 1
  [../]
  [./comp0_total_mass]
    type = PorousFlowFluidMass
    fluid_component = 0
  [../]
  [./comp1_phase0_mass]
    type = PorousFlowFluidMass
    fluid_component = 1
    phase = 0
  [../]
  [./comp1_phase1_mass]
    type = PorousFlowFluidMass
    fluid_component = 1
    phase = 1
  [../]
  [./comp1_total_mass]
    type = PorousFlowFluidMass
    fluid_component = 1
  [../]
  [./comp1_phase1_threshold_mass]
    type = PorousFlowFluidMass
    fluid_component = 1
    phase = 1
    saturation_threshold = 0.6
  [../]
[]

[Executioner]
  type = Transient
  solve_type = Newton
  nl_abs_tol = 1e-16
  dt = 1
  end_time = 1
[]

[Outputs]
  execute_on = 'timestep_end'
  file_base = mass06
  csv = true
[]
(modules/porous_flow/test/tests/mass_conservation/mass06.i)