OPM - Reference Documentation for ewoms

Compositional Multi-Phase Model Based on Flash Calculations. More...

Collaboration diagram for Flash:

Files
file	flashproperties.hh
	Declares the properties required by the compositional multi-phase model based on flash calculations.

Classes
class	Ewoms::FlashBoundaryRateVector< TypeTag >
	Implements a boundary vector for the fully implicit compositional multi-phase model which is based on flash calculations. More...

class	Ewoms::FlashExtensiveQuantities< TypeTag >
	This template class contains the data which is required to calculate all fluxes of components over a face of a finite volume for the compositional multi-phase model based on flash calculations. More...

class	Ewoms::FlashIndices< TypeTag, PVOffset >
	Defines the primary variable and equation indices for the compositional multi-phase model based on flash calculations. More...

class	Ewoms::FlashIntensiveQuantities< TypeTag >
	Contains the intensive quantities of the flash-based compositional multi-phase model. More...

class	Ewoms::FlashLocalResidual< TypeTag >
	Calculates the local residual of the compositional multi-phase model based on flash calculations. More...

class	Ewoms::FlashModel< TypeTag >
	A compositional multi-phase model based on flash-calculations. More...

class	Ewoms::FlashPrimaryVariables< TypeTag >
	Represents the primary variables used by the compositional flow model based on flash calculations. More...

class	Ewoms::FlashRateVector< TypeTag >
	Implements a vector representing rates of conserved quantities. More...

Detailed Description

Compositional Multi-Phase Model Based on Flash Calculations.

This model assumes a flow of $M \geq 1$ fluid phases $\alpha$ , each of which is assumed to be a mixture $N \geq M$ chemical species (denoted by the upper index $\kappa$ ).

By default, the standard multi-phase Darcy approach is used to determine the velocity, i.e.

$\mathbf{v}_\alpha = - \frac{k_{r\alpha}}{\mu_\alpha} \mathbf{K} \left(\mathbf{grad}\, p_\alpha - \varrho_{\alpha} \mathbf{g} \right) \;,$

although the actual approach which is used can be specified via the FluxModule property. For example, the velocity model can by changed to the Forchheimer approach by

SET_TYPE_PROP(MyProblemTypeTag, FluxModule, Ewoms::ForchheimerFluxModule<TypeTag>);

The core of the model is the conservation mass of each component by means of the equation

$\sum_\alpha \frac{\partial\;\phi c_\alpha^\kappa S_\alpha }{\partial t} - \sum_\alpha \mathrm{div} \left\{ c_\alpha^\kappa \mathbf{v}_\alpha \right\} - q^\kappa = 0 \;.$

To determine the quanties that occur in the equations above, this model uses flash calculations. A flash solver starts with the total mass or molar mass per volume for each component and, calculates the compositions, saturations and pressures of all phases at a given temperature. For this the flash solver has to use some model assumptions internally. (Often these are the same primary variable switching or NCP assumptions as used by the other fully implicit compositional multi-phase models provided by eWoms.)

Using flash calculations for the flow model has some disadvantages:

The accuracy of the flash solver needs to be sufficient to calculate the parital derivatives using numerical differentiation which are required for the Newton scheme.
Flash calculations tend to be quite computationally expensive and are often numerically unstable.

It is thus adviced to increase the target tolerance of the Newton scheme or a to use type for scalar values which exhibits higher precision than the standard double (e.g. quad) if this model ought to be used.

The model uses the following primary variables:

The total molar concentration of each component: $c^\kappa = \sum_\alpha S_\alpha x_\alpha^\kappa \rho_{mol, \alpha}$
The absolute temperature $T$ in Kelvins if the energy equation enabled.

Files

Classes

Detailed Description