DIFFAGAS

Recognised by the OPM Flow parserPROPS

The DIFFAGAS keyword defines the gas diffusion coefficients assuming a mass fraction formulation for each compositional component in the model and for each PVT region, for when the Molecular Diffusion option has been activated by the DIFFUSE keyword in the RUNSPEC section.

This keyword is optional as OPM Flow will automatically calculate the coefficients assuming the mole fraction formulation, as described by Sandve et al.1 Tor Harald Sandve, Sarah E. Gasda, Atgeirr Rasmussen, and Alf Birger Rustad. Convective dissolution in field scale CO2 storage simulation using the OPM Flow simulator. Submitted to TCCS 11 – Trondheim Conference on CO2 Capture, Transport and Storage Trondheim, Norway – June 21-23, 2021., if the DIFFAGAS and DIFFCGAS keywords are absent from the input deck. The keyword thus allows one to overwrite the automatically calculated values.

Tor Harald Sandve, Sarah E. Gasda, Atgeirr Rasmussen, and Alf Birger Rustad. Convective dissolution in field scale CO2 storage simulation using the OPM Flow simulator. Submitted to TCCS 11 – Trondheim Conference on CO2 Capture, Transport and Storage Trondheim, Norway – June 21-23, 2021.

The keyword should only be used if the CO2STORE or H2STORE keywords and either the GASWAT or the GAS and WATER keywords in the RUNSPEC section, have also been activated for the gas-water two component model.

See also the DIFFCGAS and DIFFCWAT keywords that assume the standard mole fraction formulation for diffusion rather than the mass fraction formulation assumed by the DIFFAGAS and DIFFAWAT keywords. The DIFFAGAS and DIFFAWAT keywords cannot be used in combination with the DIFFCGAS and DIFFCWAT keywords.

Note

This is an OPM Flow keyword used with OPM Flow’s CO2STORE or H2STORE and GASWAT keywords in the RUNSPEC section, and should not be confused with the version of the DIFFAGAS keyword used in the commercial compositional simulator that defines activity corrected diffusion coefficients.

Notes:

The keyword is followed by NTPVT tables as declared on the TABDIMS keyword in the RUNSPEC section.

Each record is terminated by a “/” and there is no “/” terminator for the keyword.

Note

The option has been tested in combination with the CO2STORE keyword, but not for the general case at this point.

See also the DIFFUSE keyword in the RUNSPEC section to activate the Molecular Diffusion option and the DIFFAWAT keyword in the PROPS section that defines the water diffusion coefficients for each compositional component in the model and for each PVT region. Finally, for gas-oil systems the DIFFC keyword in the PROPS section should be used.

Normally diffusion coefficients are measured in laboratory units, that is cm2/s, for ease of use, Table 8.3.31.2outlines the conversion factors for converting the laboratory measured diffusion coefficients to those used by the simulator.

Diffusivity Conversion Factors

Laboratory Measured Units

Conversion Factor

Simulator Units

1 cm2/s

92.9979 ft2/day

Field

8.64 m2/day

Metric

3600 cm2/hour

Laboratory

Table 8.3.31.2: Diffusivity Conversion Factors

Records

Fixed number of records

Items per record

2

Parameters

Example

The example below is based on field units, with NTPVT equal to three on the TABDIMS keyword.
--
-- PVT REGION GAS COMPONENT DIFFUSION COEFFICIENTS (OPM FLOW KEYWORD)
--
DIFFAGAS
-- CO2 IN WAT IN
-- GAS DF GAS DF
-- ------- -------
0.160 0.150 / PVT REGION NO. 01
0.165 0.155 / PVT REGION NO. 02
/ PVT REGION NO. 03
Here the third PVT region has no values for the two component diffusion coefficients, and therefore the simulator will use correlations to define the diffusivity coefficients for this PVT region.
| Note This is an OPM Flow keyword used with OPM Flow’s CO2STORE or H2STORE and GASWAT keywords in the RUNSPEC section, and should not be confused with the version of the DIFFAGAS keyword used in the commercial compositional simulator that defines activity corrected diffusion coefficients. |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Note The option has been tested in combination with the CO2STORE keyword, but not for the general case at this point. |
|-----------------------------------------------------------------------------------------------------------------------|
| Diffusivity Conversion Factors |                   |                 |
|--------------------------------|-------------------|-----------------|
| Laboratory Measured Units      | Conversion Factor | Simulator Units |
| 1 cm2/s                        | 92.9979 ft2/day   | Field           |
| 8.64 m2/day                    | Metric            |                 |
| 3600 cm2/hour                  | Laboratory        |                 |

Related keywords

Requires

GAS, WATER

Cannot be combined with

DIFFCWAT, DIFFCGAS

Manual source: parts/chapters/subsections/8.3/DIFFAGAS.fodt