Black-oil fluid model

Overview

In the black-oil model three pseudo-components, oil (o), gas (g) and water (w) are considered. These are assumed to be partitioned across three fluid phases, named liquid (l), vapor (v) and aqueous (a).

Phase behavior is characterized by the following quantities which are used to relate properties of the fluids in the reservoir to their properties at surface conditions.

$B_o$ : oil formation volume factor
$B_g$ : gas formation volume factor
$R_s$ : gas/oil ratio
$R_v$ : oil/gas ratio

By tables, that tabulate saturated and undersaturated oil and gas properties as functions of pressure and solution ratios.

Dead oil

In dead-oil each component occupies only one phase. Thus, the following partition matrix determines the components distribution within the three phases:

$\begin{bmatrix} y_{gv} & y_{gl} & y_{ga}\\ y_{ov} & y_{ol} & y_{oa}\\ y_{wv} & y_{wl} & y_{wa} \end{bmatrix} = \begin{bmatrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 1 \end{bmatrix}$

and the phase densities are

$\rho_{l} = & \, \frac{\rho_{o}^{STC}}{B_{o}} \\ \rho_{v} = & \, \frac{\rho_{g}^{STC}}{B_{g}}.$

Live oil

The live oil fluid model make no assumptions about the partitioning of the hydrocarbon components and the following composition matrix can be used

$\begin{bmatrix} y_{gv} & y_{gl} & y_{ga}\\ \\ y_{ov} & y_{ol} & y_{oa}\\ \\ y_{wv} & y_{wl} & y_{wa} \end{bmatrix} = \begin{bmatrix} \frac{\rho_{g}^{STC}}{\rho_{g}^{STC} + \rho_{o}^{STC} r_{s}} & \frac{\rho_{g}^{STC} R_{s}}{\rho_{o}^{STC} + \rho_{g}^{STC} R_{s}} & 0 \\ \\ \frac{\rho_{o}^{STC} r_{s}}{\rho_{g}^{STC} + \rho_{o}^{STC} r_{s}} & \frac{\rho_{o}^{STC}}{\rho_{o}^{STC} + \rho_{g}^{STC} R_{s}} & 0 \\ \\ 0 & 0 & 1 \end{bmatrix}$

whereas the densities of the two hydrocarbon phases are

$\rho_{l} = & \, \frac{\rho_{o}^{STC} + \rho_{g}^{STC} R_{s}}{B_{o}} \\ \rho_{v} = & \, \frac{\rho_{g}^{STC} + \rho_{o}^{STC} R_{v}}{B_{g}}$

See Petrowiki for more information.

Parameters

Both types are represented by <BlackOilFluid> node in the input. Under the hood this is a wrapper around PVTPackage library, which is included as a submodule. In order to use the model, GEOS must be built with -DENABLE_PVTPACKAGE=ON (default).

The following attributes are supported:

XML Element: BlackOilFluid

Name	Type	Default	Description
checkPVTTablesRanges	integer	1	Enable (1) or disable (0) an error when the input pressure or temperature of the PVT tables is out of range.
componentMolarWeight	real64_array	required	Component molar weights
componentNames	string_array	{}	List of component names
hydrocarbonFormationVolFactorTableNames	groupNameRef_array	{}	List of formation volume factor TableFunction names from the Functions block. The user must provide one TableFunction per hydrocarbon phase, in the order provided in “phaseNames”. For instance, if “oil” is before “gas” in “phaseNames”, the table order should be: oilTableName, gasTableName
hydrocarbonViscosityTableNames	groupNameRef_array	{}	List of viscosity TableFunction names from the Functions block. The user must provide one TableFunction per hydrocarbon phase, in the order provided in “phaseNames”. For instance, if “oil” is before “gas” in “phaseNames”, the table order should be: oilTableName, gasTableName
name	groupName	required	A name is required for any non-unique nodes
phaseNames	groupNameRef_array	required	List of fluid phases
surfaceDensities	real64_array	required	List of surface mass densities for each phase
tableFiles	path_array	{}	List of filenames with input PVT tables (one per phase)
waterCompressibility	real64	0	Water compressibility
waterFormationVolumeFactor	real64	0	Water formation volume factor
waterReferencePressure	real64	0	Water reference pressure
waterViscosity	real64	0	Water viscosity

Supported phase names are:

Value	Comment
oil	Oil phase
gas	Gas phase
water	Water phase

Example

<Constitutive>
  <BlackOilFluid name="fluid1"
                 fluidType="LiveOil"
                 phaseNames="{ oil, gas, water }"
                 surfaceDensities="{ 800.0, 0.9907, 1022.0 }"
                 componentMolarWeight="{ 114e-3, 16e-3, 18e-3 }"
                 tableFiles="{ pvto.txt, pvtg.txt, pvtw.txt }"/>
</Constitutive>