AQUNUM

Recognised by the OPM Flow parserGRID

The AQUNUM keyword defines the properties of numerical aquifers, including which grid blocks in the model should be utilized as part of the numerical aquifer. Each row entry in the AQUNUM keyword defines one numerical aquifer. Note that a numerical aquifer may consists of more than one grid cell, in order to better describe the water influx from the aquifer to the grid.

Notes:

Where NX, NY and NZ are the dimensions of the model as defined on the DIMENS keyword in the RUNSPEC section.

The keyword is followed by up to MXNAQN records as defined on the AQUDIMS keyword in the RUNSPEC section

Each record is terminated by a “/” and the keyword should be terminated by a “/”.

Numerical aquifers are modeled as one-dimensional, with aquifer flow assumed to be in the direction defined by LENGTH, and flux out of the aquifer is through the cross sectional area defined by AREA. Note that, all the aquifer cells must be isolated from the reservoir cells, with only the AQUCON connections connecting to the actual reservoir cells.

The values entered on the AQUNUM keyword are used to calculate the aquifer's pore volume and the transmissibility between the aquifer and the connected cell faces defined on the AQUCON keyword. Thus:

The aquifer’s pore volume is always calculated from the data entered on the AQUNUM keyword using[Pore~ Volume = AREA times LENGTH times PORO]and any modifications to the host cell values performed in either the and any modifications to the host cell values performed in either the GRID or EDIT sections are always ignored for cells declared as numerical aquifers cells.

For the transmissibility calculation either the cross-sectional area (AREA) defined on the AQUNUM keyword may be used or the connecting cell cross-sectional area by setting the AQUOPT1 variable on the AQUCON keyword.

In order to fully define a numerical aquifer one has to define the aquifer properties via the AQUNUM keyword, and how the aquifer is connected to the reservoir using the AQUCON keyword in the GRID or SOLUTION sections.

Note

If the AQUCON keyword has been utilized in the run deck then OPM Flow will write the AQUIFERN array to the *.INIT file in order to visualize the aquifer connections in OPM ResInsight.

This is accomplished by setting the AQUIFERN value to 2^(AQUID-1) for cells connected to aquifer AQUID. If a cell is connected to multiple numerical aquifers then AQUIFERN is summed for all aquifers connected to a cell. Note that connecting cells to multiple aquifers is best avoided.

Finally for cells representing the numerical aquifers themselves, AQUIFERN is set to minus AQUID.

Using one aquifer cell should generally be sufficient, provided the aquifer properties are constant. However, employing multiple cells may be appropriate if the aquifer properties vary with distance or depth, which is not uncommon. Secondly, having multiple cells may help to minimize throughput-related convergence problems by increasing the pore volumes exponentially away from the reservoir cells. Typically, three to five aquifer cells are employed under theses circumstances.

The aquifer pore volume can be used to define the amount of pressure support; whereas the aquifer transmissibility will influence the responsiveness of the aquifer.

See also the AQUDIMS keyword in the RUNSPEC section that defines the numerical aquifer dimensions.

Records

One or more records, each terminated by /

Items per record

12

Parameters

Example

Given the following grid and aquifer dimensions in the RUNSPEC section:
--
-- MAX MAX MAX
-- NDIVIX NDIVIY NDIVIZ
DIMENS
96 58 28 /
-- AQF AQF AQF AQF AQF AQF AQF AQF
-- MXAQN MXNAQC NIFTBL NRIFTB NANAQU NCAMAX MXNALI MXAAQL
AQUDIMS
3 3 1* 1* 1* 1* 1* 1* /
The following numerical aquifer definition:
--
-- NUMERICAL AQUIFER DESCRIPTION
--
-- AQUID - LOCATION - AQF AQF AQF AQF AQF AQF PVT SATNUM
-- NUMBER I J K AREA LENGTH PORO PERM DATUM PRES TAB TAB
--
AQUNUM
1 1 3 28 5.20E03 2.0E3 0.05 0.3 1* 1* 1* 1* /
1 1 2 28 5.20E06 2.0E6 0.05 0.3 1* 1* 1* 1* /
1 1 1 28 5.20E09 2.0E9 0.05 0.3 1* 1* 1* 1* /
/
defines one numerical aquifer consisting of three cells. The connection to the grid cells would take the form of:
--
-- NUMERICAL AQUIFER CONNECTIONS
--
-- ID ---------- BOX --------- CONNECT TRANS TRANS ADJOIN
-- NUMBER I1 I2 J1 J2 K1 K2 FACE MULT OPTN CELLS
AQUCON
1 1  1 4 58 28 28 'K+' 1.3 1* 1* /
1 2 96 1 58 28 28 'K+' 1.3 1* 1* /
/
that creates a basal aquifer115
       Basal Aquifer: An aquifer located at the bottom of a geologic unit..
Basal Aquifer: An aquifer located at the bottom of a geologic unit.
| Note If the AQUCON keyword has been utilized in the run deck then OPM Flow will write the AQUIFERN array to the *.INIT file in order to visualize the aquifer connections in OPM ResInsight. This is accomplished by setting the AQUIFERN value to 2^(AQUID-1) for cells connected to aquifer AQUID. If a cell is connected to multiple numerical aquifers then AQUIFERN is summed for all aquifers connected to a cell. Note that connecting cells to multiple aquifers is best avoided. Finally for cells representing the numerical aquifers themselves, AQUIFERN is set to minus AQUID. |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

Manual source: parts/chapters/subsections/6.3/AQUNUM.fodt