Making an Aquifer
Aquifer modeling is a method of simulating large amounts of water (or gas) connected to
the reservoir whereby it is not essential to know how the fluid moves in it, but rather how
it affects our reservoir.
There are several aquifer models: numerical, Carter-Tracy, Fetkovich, Constant flux,
Constant pressure (gas or water) and rainfall.
Each aquifer model has its own set of parameters and can be connected to the grid in
different directions: top down, bottom up, grid edges and/or fault edges.
To have better control over which cell needs to be connected, a series of options can be
used to limit the vertical extent and to restrict the connections to filtered cells only.
How to create an aquifer
1. Make a closed polygon using the Make/Edit Polygon process (we recommend using
the 2D window for this, since you will need to click outside the reservoir).
2. Open the Make Aquifer process.
3. Drop in the polygon.
4. Choose the drive direction.
5. Set the aquifer type and parameters.
Make Aquifer dialog settings
In this dialog you can define and connect aquifers to a given simulation grid.
The following options are available:
Create a new aquifer: this option allows you to make a new aquifer.
Edit the existing aquifer: this option allows you to modify an existing aquifer.
Both options allow you to select one of the following aquifer models: numerical, CarterTracy, Fetkovich, Constant flux, constant pressure gas, constant pressure/head water and
rainfall.
Connections tab
In this tab you define the aquifer’s connection to the grid. Connections are independent of
the aquifer model; therefore the information here does not change according to any
changes to the aquifer model.
The following options are available:
Area of interest: defines the area of interest to connect the aquifer, based on closed
polygons. Use the blue arrow to drop closed polygons, and use the button below the blue
arrow to remove polygons from the list.
Drive direction: defines the aquifer drive direction. You can select one or more of the
following options:
Top down: connected to the top cells of the grid.
Bottom up: connected to the bottom cells of the grid.
Grid edges: connected to the external side of the cells.
Fault edges: connected to the cells along a fault which has at least part of the fault face
not connected to any grid cell (see picture below).
Vertical Extent: optional setting which allows you to select top and/or bottom limit of the
connected cells. You can use a fixed depth, a surface or a contact.
Filter: optional check-box which allows you to connect only the displayed cells. If this
option is not checked, the whole grid is used. Note that cell selection is based on the cell
center of the top layer, even if that layer is not in the filtered cells; then it checks which of
those cells fall in the filtered selection.
Connected faces visualization in 3D window
Once you fill in the relevant data in the Connections tab and apply the changes, the
connected faces are generated and stored under the Aquifers folder for the grid.
You can visualize the connected faces in a 3D window by ticking the aquifer check-box.
Properties tab
In this tab the aquifer properties are defined. Each aquifer model requires a different set
of properties; hence this tab changes according to the aquifer model.
The parameters needed for the aquifer models are explained in the links below. For
detailed information about these models, please refer to the “ECLIPSE Technical
Description” manual, Chapter 4: Aquifer Modeling Facilities.
Numerical aquifer
This aquifer model is represented by a cell, or set of cells, where only the first cell is
connected to the reservoir. The set of cells defining the aquifer are connected together in
the following order: Reservoir  cell 1  cell 2  …  cell (n-1)  cell n.
To establish this aquifer model the following properties need to be defined:
Number of cells: select the number of cells to model the numerical aquifer.
Fluid model: when selected, this option allows you to drop a fluid model using the blue
arrow and take the water properties from it. If unchecked, it will take the water properties
based on the PVT region number (PVTNUM) of the cell.
Saturation function: this option allows you to drop a saturation function using the blue
arrow. If unchecked it will use the saturation function based on the saturation function
number (SATNUM) of the cell.
Transmissibility multiplier: you can change the calculated transmissibility using this
multiplier. This can be useful, for example, when performing history matching.
Each numerical aquifer cell needs the following properties:
Equilibrium: select this radio button to have the initial pressure in hydrostatic equilibrium
with the reservoir.
Initial pressure: select this radio button to type the initial pressure at datum depth.
Datum depth: check the box to specify the aquifer reference depth. The default value is
cell depth.
Permeability: aquifer permeability. This parameter cannot be defaulted.
Porosity: check the box to specify the aquifer porosity. The default value is cell porosity.
Cross sectional area: This value can be larger than the cell cross-sectional area.
Length: This value can be larger than the cell length.
The aquifer cell volume is calculated using porosity, cross-sectional area and length.
Carter Tracy aquifer
The Carter-Tracy aquifer model is a simplified approximation to a fully transient model,
which avoids the need for superposition. The model uses tables of dimensionless time
versus a dimensionless pressure influence function. The default table is for an infinite
reservoir with constant terminal rate as given by Everdingen and Hurst.
The list of properties needed to define this aquifer model is as follows:
Equilibrium: select this radio button to have the initial pressure in hydrostatic equilibrium
with the reservoir.
Initial pressure: select this radio button to type the initial pressure at datum depth.
Datum depth: aquifer reference depth
Permeability: aquifer permeability
Porosity: aquifer porosity
Total compressibility: aquifer total (rock and water) compressibility
External radius: aquifer external radius
Thickness: aquifer thickness
Angle of influence: the angle subtended by the aquifer boundary from the center of the
reservoir, measured in degrees.
Salt concentration: initial salt concentration. This value is relevant either for Brine option,
or if Salt-sensitivity option in Polymer Flood is activated, otherwise it is ignored.
Fluid model: use the blue arrow to drop a fluid model from which the aquifer will take
the water pressure properties.
Fetkovich aquifer
The Fetkovich aquifer model uses a simplified approach based on a pseudo-steady-state
productivity index and material balance relationship between the aquifer pressure and the
cumulative influx.
The properties needed to define this aquifer model are as follows:
Equilibrium: select this radio button to have the initial pressure in hydrostatic equilibrium
with the reservoir.
Initial pressure: select this radio button to type the initial pressure at datum depth.
Datum depth: aquifer reference depth
Volume: initial aquifer water volume
Total compressibility: aquifer total (rock and water) compressibility
Productivity index: aquifer productivity index, which is: total influx rate per unit pressure
difference.
Salt concentration: initial salt concentration. This value is relevant either for the Brine
option, or if the Salt-sensitivity option in Polymer Flood is activated, otherwise it is
ignored.
Fluid model: use the blue arrow to drop a fluid model from which the aquifer will take
the water pressure properties.
Constant flux aquifer
A constant flux aquifer model has its water flux specified directly by the user, instead of
being calculated by an analytic aquifer model. The water flux can be modified over time
by entering the corresponding values in the Time tab.
The properties needed to specify this aquifer are:
Spatially constant flux: select this radio button to specify a constant inflow value.
Spatially variable flux: select this radio button to use an inflow map.
Flux: aquifer water inflow rate per unit area of connected cell face. It can be either a
value (constant) or a map (variable). When using a map, make sure it covers all the
simulation grid area.
Number of bins: this setting is only needed when using spatially variable flux and it is the
number of regions into which you want to divide the flux map. It uses the minimum and
maximum values of the whole map to perform the calculation, so if the map is too large
compared to the simulation grid area the region values may not be representative. It may
then be better to use a smaller map. When selecting Apply, a grid property is generated,
and its name follows the convention: “[aquifer name] regions using [map name]”.
Salt concentration: Initial salt concentration. This value is relevant either for the Brine
option, or if the Salt-sensitivity option in Polymer Flood is activated, otherwise it is
ignored.
Time tab: allows you to change Flux and Salt concentration properties over time. If no
values are entered here it is assumed that the aquifer does not change during the
simulation.
Regions tab: activated only when using spatially variable flux. This tab shows you a
spreadsheet with a list of generated regions, and their pressures at initial state and in each
time defined in Time tab. Review this table to find the appropriate Tolerance value.
Constant pressure gas model
A constant pressure gas model is an analytic aquifer that uses a pressure boundary at the
connected cell faces, and represents an infinite gas reservoir (a gas “aquifer”). The
development of this model was primarily intended for a reservoir connected to the
atmosphere. The gas pressure can be modified over time by entering the corresponding
values in the Time tab.
The properties needed to specify this gas model are:
Spatially constant pressure: select this radio button to specify a constant pressure value.
Spatially variable pressure: select this radio button to use a pressure map.
Pressure: gas pressure. It can be either a value (constant) or a map (variable). When using
a map, make sure it covers all the simulation grid area.
Number of bins: this setting is only needed when using spatially variable pressure. It is
the number of regions into which you want to divide the pressure map. It uses the
minimum and maximum values of the whole map to perform the calculation, so if the
map is too large compared to the simulation grid area the region values may not be
representative. It may then be better to use a smaller map. When selecting Apply, a grid
property is generated, and its name follows the convention: “[aquifer name] regions using
[map name]”.
Datum depth: gas “aquifer” reference depth
Productivity index: total influx rate per unit pressure difference.
Fluid model: use the blue arrow to drop a fluid model from which the “aquifer” will take
the gas pressure properties.
Time tab: allows you to change Pressure property through time. If no values are entered
here it is assumed that the aquifer does not change during the simulation.
Regions tab: activated only when using spatially variable pressure. This tab shows you a
spreadsheet with a list of generated regions, and their pressures at initial state and in each
time defined in Time tab. Review this table to find the appropriate number of bins to
represent the spatial variability.
Constant pressure/head water aquifer
A constant pressure water aquifer is an analytic model that uses a pressure boundary at
the connected cell faces. It represents an infinite water aquifer (or a rechargeable aquifer).
You can specify either a pressure at datum depth or a head depth of the aquifer.
Head depth is the water level of the aquifer connected to the atmosphere (for example, if
your aquifer is connected to a lake you should use the water lake level as head depth);
and the simulator will convert this value to pressure using the formula
Where the density  is taken from the water pressure properties (Fluid model).
The water pressure (or head depth) can be modified through time, by entering the
corresponding values in the Time tab.
The properties needed to specify this aquifer model are:
Pressure: select this radio button to specify aquifer pressure at datum depth.
Head: select this radio button to specify aquifer head depth.
Spatially constant pressure (head): select this radio button to specify a constant pressure
(head) value.
Spatially variable pressure (head): select this radio button to use a pressure (head) map.
Pressure: aquifer pressure at datum. It can be either a value (constant) or a map (variable).
When using a map, make sure it covers all the simulation grid area.
Number of bins: this setting is only needed when using spatially variable pressure and it
is the number of regions into which you want to divide the pressure map. It uses the
minimum and maximum values of the whole map to perform the calculation, so if the
map is too large compared to the simulation grid area, the region values may not be
representative. It may then be better to use a smaller map. When selecting Apply, a grid
property is generated, and its name follows the convention: “[aquifer name] regions using
[map name]”.
Datum depth: aquifer datum depth
Productivity index: total influx rate per unit pressure difference.
Salt concentration: initial salt concentration. This value is relevant either for Brine option,
or if Salt-sensitivity option in Polymer Flood is activated; otherwise it is ignored.
Fluid model: use the blue arrow to drop a fluid model from which the aquifer will take
the water pressure properties.
Time tab: allows you to change pressure (head) property through time. If no values are
entered here it is assumed that the aquifer does not change during the simulation.
Regions tab: activated only when using spatially variable pressure (head). This tab shows
you a spreadsheet with a list of generated regions, and their pressures (head depths) at
initial state and in each time defined in Time tab. Review this table to find the appropriate
number of bins to represent the spatial variability.
Rainfall aquifer
A rainfall aquifer model is a special case of a constant flux aquifer, where the flux rate
shows monthly variation. The monthly water flux can be modified over time by entering
the corresponding values in the Time tab.
The properties needed to specify this aquifer are:
Monthly flux: aquifer water inflow rates per unit are at the connected cell face. You need
to enter a value for each month.
Time tab: allows you to change the Monthly flux properties through time. If no values are
entered here it is assumed that the aquifer does not change during the simulation.