Constitutive Models

Constitutive models describe relations between various physical quantities. In a physics simulation they are used to model the response or state of material (solid, fluid, or a mixture) as a function of input variables.

In GEOSX constitutive models are listed in <Constitutive> block of the input XML file. Each type of model has its own XML tag and each model must be assigned a unique name via name attribute. Names are used to assign models to regions of the physical domain via a materialList attribute of the <ElementRegion> node, see Element: ElementRegions. In some cases, physics solvers must also be assigned specific constitutive models to use, see Physics Solvers.

Typical <Constitutive> and <ElementRegions> block will then look like:

<Problem>
  ...
  <Constitutive>
    <PoroLinearElasticIsotropic name="shale"
                                defaultDensity="2700"
                                defaultBulkModulus="61.9e6"
                                defaultShearModulus="28.57e6"
                                BiotCoefficient="1.0"/>

    <CompressibleSinglePhaseFluid name="water"
                                  referencePressure="2.125e6"
                                  referenceDensity="1000"
                                  compressibility="1e-19"
                                  referenceViscosity="0.001"
                                  viscosibility="0.0"/>
  </Constitutive>

  <ElementRegions>
    <ElementRegion name="region1"
                   cellBlocks="cellBlock1"
                   materialList="water shale"/>
  </ElementRegions>
  ...
</Problem>

There are several types of constitutive models that differ in their input and output variables. Currently supported constitutive models are:

• Solid Models
  • Linear elastic isotropic solid model
  • Linear elastic anisotropic solid model
  • Linear poroelastic isotropic solid model
  • Linear poroelastic anisotropic solid model
• Fluid Models
  • Compressible single phase fluid model
  • Black-oil fluid model
  • Compositional multiphase fluid model
  • CO2 and brine models
• Relative Permeability Models
  • Brooks-Corey relative permeability model
  • Three-phase relative permeability model
• Capillary Pressure Models
  • Brooks-Corey capillary pressure model
  • Van Genuchten capillary pressure model