Unconventional multi-well model

With the unconventional multi-well (UMW) module, you can simulate multiple horizontal multifrac wells using the group numerical model to history-match producing wells and forecast future production. With this analysis, wells are considered to be parallel, with the same length, and to have the same number of fractures.

Note: This model works with your Harmony Reservoir™ license.

Before you start using the multi-well model, make sure that all required information is added to the Harmony Enterprise project:

Populate sandface locations for each well in the Attributes tab.
Populate well production data (rates and sandface pressures) in the Production editor for each well in the group.
Specify reservoir and fluid properties in the Properties editor of the group. When you create a new multi-well model, group reservoir properties are automatically applied.
Populating wellbore information (such as, a deviation survey, completion, and perforation data) is not required. However, we recommend populating this information because it helps to initiate the multi-well model with correct default settings.

We recommend that you perform analyses and/or modeling for individual wells prior to using the multi-well model. You can bring in parameters from individual well analyses as a starting point for the multi-well model.

By default, the Plots tab opens (with the Wells button selected) with a dashboard with four plots. For more information, see dashboard.

Model creation

To create an UMW model:

1. Create a group (in the Entity Viewer - Hierarchy or Entity Viewer - Custom) that contains all the wells you want to include in the model.

2. Launch the group for analysis. For more information, see selecting an entity for analysis.

3. Click the Group image and select Multiphase Multi-well Model, Unconventional.

You can create a Black Oil, Volatile Oil, or a Gas Condensate model:

Black Oil — accounts for gas dissolved in liquid, but does not account for liquid vaporized in gas; therefore, you should not create a Black Oil model for a group that has liquid-rich gas as a gas type.
Gas Condensate — used to create a multiphase model that accounts for liquid vaporized in gas. This model should only be used for groups that have liquid-rich gas as their gas type.
Volatile Oil — used to create a multiphase model that accounts for liquid vaporized in gas. The water phase can be turned off within the model.

Note: For more information, see modifications for the multiphase model.

Primary toolbar

The primary toolbar has the following icons:

Pull Defaults — select from these options:
- Group Properties — copies default values from the Properties editor of the group.
- Group Analysis — displays a sub-menu with all the other unconventional multi-well models for the group. (If there are no other unconventional multi-well models, this option is not displayed.) Selecting one of the existing models copies one multi-well model to another in the same group, which can be useful if you want to experiment with the copy of the model while preserving the original content. Note that the parameters on the Forecast tab are not copied.
- Selected Well Analysis — displays a sub-menu with all the analyses (that is, URM, analytical, and numerical) for the selected well. (If there are no other analyses, this option is not displayed.) Selecting one of the existing analyses, copies parameters of that analysis to the currently selected well.
- Another Well in this Model — displays a sub-menu with all the other wells in the same model. Select one of the wells to copy the calculation method, well parameters, and constraints from that well to the currently selected well (displayed in Wells under Selected Well).
Push Defaults — copies well parameters from the currently selected well to the one other well you select, or to All Wells in the model. Selecting Model Parameters copies all parameters set under the Plots Tab \ Wells; selecting Forecast Parameters copies parameters set under the Forecast tab for the currently selected well.
Synthesize — click this icon every time you want to history-match and create a forecast.
Stop Synthesize — stops the model's synthesize calculations.
Previous Well — jumps to the previous well.
Next Well — jumps to the next consecutive well.

Copy to / Paste from Clipboard — copies / pastes entity parameters from the clipboard.
Playback icons ()

After you click the Synthesize icon ( Synthesize icon ) in the primary toolbar and the calculations are complete, the icons listed below are enabled in the same toolbar. With these playback icons, you can see how pressures or saturations change through time. As you hover over your color-shaded plot, a tooltip displays the pressure or saturation value and unit.

Skip to Beginning — displays the property at time 0.
Step Back One Frame — view timesteps in reverse one frame at a time.
Play in Reverse — view timesteps in reverse. You can click this icon multiple times to increase the speed of the playback.
Stop — stops the playback process. As you hover over various cells in your well, the pressure or saturation is displayed.
Play — view timesteps from start-to-finish. You can click this icon multiple times to increase the speed of the playback.
Step Forward One Frame — view one frame at a time.
Skip to End — displays the last timestep.

Plots tab

This tab displays four plots in a dashboard and has five buttons in the lower left: Wells, Reservoir, Layers, Volumes, and Options. If you do not see all these buttons, click >> and select Show All Buttons.

Wells

When you click the Wells button, parameters for all wells, the selected well, geometry, permeabilities etc. are displayed.

Currently, the wells within the UMW model are considered to be parallel, with the same length, and with the same number of fractures. Therefore, the following parameters are shared between all wells:

L_e — effective horizontal well length. By default, this field is populated based on the perforations that are set up in the Wellbore editor for each well in the group, but you can edit it.
n_f — number of fractures.
x_wL1 — the distance from the first well to the left reservoir boundary.
x_wRn — the distance from the last well to the right reservoir boundary.
x_e — extent of the reservoir in the x-direction. This value cannot be edited directly, but can be changed by changing x_wL1, x_wRn, and x_sp for individual wells.
y_e — extent of the reservoir in the y-direction. By default, y_e = L_e.
Note: Setting y_e > L_e makes calculations significantly slower. (In the case when y_e = L_e, all fracture stages of the model are identical, and we can make use of the symmetry to increase calculation speed.) If matrix permeability is low, we recommend setting y_e = L_e. If matrix permeability is relatively high and contributions from the portions of the matrix that are beyond the wellbore are significant, you can set y_e > L_e to include these contributions. You may also consider running the model with y_e = L_e during the history-matching process, and setting y_e > L_e only to calculate the model's forecast.

The rest of the parameters in Wells are set up on a per-well basis. Select a well from the Selected Well drop-down list to set or modify parameters related to that particular well. (You have to set up parameters for each well for the multi-well model to be valid.)

Include — by default, all wells in the group are included in the model. Deselect Include to exclude the selected well from the model. If the well is excluded, you still need to set up valid parameters for it: the geometry of the well region is still being used to generate a grid used in the model. However, if the well is excluded, its production is not taken into account, and permeability for the whole well region (including fracture and SRV) is modeled to be equal to the matrix permeability (k_matrix).

Geometry

x_f — fracture half length. Set this field if you want to model a symmetrical fracture with an SRV region extending along the whole fracture. Otherwise, set x_fL, x_fR, x_SRVL, and x_SRVR in the Advanced Geometry section.
y_SRV — half SRV in the y-direction.

Permeabilities

k_SRV — SRV (inner zone) permeability.
F_CD — dimensionless fracture conductivity.
k_fw_f — fracture conductivity. Fracture conductivity and dimensionless fracture conductivity are related by:
F_CD = k_fw_f / (k_SRVx_f). You can set any of these two parameters (F_CD or k_fw_f), and the other one is calculated based on the parameter you set.

Advanced Completion Geometry

x_sp — the horizontal distance to the next wellbore.
x_fL, x_fR — use these parameters to set a non-symmetrical fracture. The left wing of the fracture (x_fL) and the right wing of the fracture (x_fR) can be different (see geometry above).
x_SRVL, x_SRVR — use these parameters to set up an SRV that extends less than, or beyond the x_f (see geometry above).

Vertical Resolution

Parameters in the Vertical Resolution section are used to set up z-values for well locations and completions. Use this section when wellbores are located at different depths, and when SRV and fractures do not extend through the entire thickness of the reservoir. When you set non-default vertical resolution, the model is correspondingly gridded in the vertical direction. In this case, fluid flow is modeled in three dimensions, taking into account k_z/k_xy and gravity.

z_w — vertical distance from the bottom of the reservoir to the wellbore.
z_fU — extent of the fracture (up).
z_fD — extent of the fracture (down).
z_SRVU — extent of SRV (up).
z_SRVD — extent of SRV (down).

Other parameters

Calculation Method for Production — set if the selected well is to be operated at rate, or at pressure control.
Calculation Method for Injection — if you have injection rates for your well in the Production editor, the Calculation Method for Injection section is enabled, and you can set controls to be used during injection.

Reservoir

When you click the Reservoir button, you can specify parameters that are used for the entire reservoir model.

If the model has more than one layer, some of the parameters in the Reservoir tab are read-only because they are defined per layer. To set up parameters for each of the layers, click the Layers button and set parameters there.

k_matrix — matrix (outer zone) horizontal permeability within the well region of the selected well.

k_z/k_xy — the ratio of vertical permeability to horizontal permeability. (This ratio is only being applied to k_matrix.)

To include the effect of adsorbed gas, click the Adsorption checkbox. Adsorption parameters are set up for the entire reservoir. Note that this option cannot be used for models that include oil or condensate. For more information, see Langmuir isotherm.

To include the effects of changing formation compressibility and permeability with pressure, click the Geomechanical checkbox. Geomechanical parameters are set up for the entire reservoir. For more information, see geomechanical reservoir models.

Fluid type selection

Click the checkboxes for the fluid phases you want to include in your model: Gas, Oil, and/or Water.

Layers

When you click the Layers button, layers for the reservoir are displayed. If your model has only one layer, layer parameters are read-only because the layer is the same for the entire reservoir. Therefore, click the Reservoir button and set parameters there.

Toolbar

The Layers toolbar has the following icons:

Add New Layer Below the Selected Layer — opens the Add Layer dialog box where you type a name for the new layer to be added below your currently selected layer.
Remove Selected Layer — deletes your currently selected layer. You are not prompted to confirm your decision.

To rename a layer, right-click it.

Selected Layer section

To view or modify parameters of a particular layer, select the layer from the Selected Layer drop-down list. All of the parameters displayed below are for the selected layer.

Formation Crossflow — this option is available for all layers except for the top one. This option is used to define whether there is communication between the layers through the matrix (formation crossflow), or if the layers are separated by an impermeable layer (gap), and are only communicating through a fracture or SRV.

If this checkbox is selected, this implies that there is communication between the layers in the reservoir through the matrix.
If the checkbox is deselected, you can model a gap between the currently selected layer and the one above it; type the height of the gap in the Gap Above field. You can view the gap in the XZ view (side view) of the schematic.

Volumes

When you click the Volumes button, read-only values for Reservoir, Well, and Layer are displayed. You can switch which Well and/or Layer is displayed by selecting from the drop-down list.

Options

When you click the Options button, initialization and gridding parameters are displayed.

Initialization

Initialization parameters are displayed only when the model has more than one grid in a vertical direction (for example, when the model has multiple layers).

z_ref — this is the distance from the bottom of the reservoir to the reference depth for p_I. Initial pressure for the reservoir (p_I) is defined in Reservoir. By default, it is assumed that the value of the initial pressure corresponds to the middle of the reservoir’s pay. However, you can change the reference depth at which p_I is defined. For example, if you set z_ref =0 ft and p_I=5000 psi(a), it means that initial pressure at the bottom of the reservoir is equal to 5000 psi(a).

After the initial pressure is set at the reference depth, initial pressure at each of the model's grid cells is calculated according to the options set under Initial Pressure Distribution:

p = p_I — the initial pressure in each cell is equal to p_i.
p = p_I + ρ_mix g ∆h — the pressure in each cell is calculated as described in the figure below. Each individual pressure difference is calculated as: ∆p = ρ_mix g ∆h, where ρ_mix is the mixture density and is calculated as:
where only mobile phases are included in both summations.
p = p_I + ρ_MMob g ∆h — the pressure in each cell is calculated as described in the figure below. Each individual pressure difference is calculated as ∆p = ρ_MMob g ∆h, where ρ_MMob is the density of the most mobile phase in the cell.

We recommend setting up the model such that the phases are segregated (that is, each cell has only one mobile phase, with lighter phases above). In this case, the second and third options reduce to: ∆p = ρ g ∆h, where ρ is the density of only the mobile phase in the cell. Selecting either the second or third option results in initializing the system to be in hydrostatic equilibrium. If you decide to set up the model such that the phases are not segregated, the model will not be in equilibrium, no matter what option you select. (The phases start segregating due to gravity as a part of the model's simulation.) Depending on the case, distributing pressures using one of the available options may help to initialize the model to a state that is close to hydrostatic equilibrium.

Gridding Parameters

After you set your reservoir dimensions, well locations, and well completion parameters, the UMW model creates an appropriate grid to get accurate results with minimal calculation time. To display gridding, right-click the schematic plot and select Show Grid Cells.

Usually, the default gridding settings work well, but in some cases, you may want to adjust the gridding options by changing gridding parameters.

There are three predefined gridding options: Coarse, Medium, and Fine. When the Recommended option is enabled, one of the pre-defined options is automatically selected based on model parameters.

Alternatively, you can deselect Recommended and set your gridding manually. For example, you may want to use Coarse gridding while history-matching the model, and then switch to Fine gridding after the match is done.

If you need even more flexibility, you can select the Custom option and edit each gridding parameter individually. If you select this option, refer to the schematic of a model's grid and description of individual gridding parameters below:

The fracture has a cell containing the wellbore and its size is fixed. The rest of the fracture is divided into equal cells with an x-dimension approximately given by ΔX_f.
The SRV regions have arithmetic gridding in the x-dimension (approximately given by ΔXY_srv) and geometric gridding in the y-dimension (given by Min_srvXY, Ratio_srvXY, and Max_srvXY).
The matrix is split into a number of partitions (defined by the locations and SRV-boundaries of all the wells), and then each partition is gridded individually.
Partitions that have SRV regions adjacent to them have geometric gridding starting at the boundary with the SRV region. This is done to capture large pressure gradients in such areas. (Geometric gridding is governed by Min_matrixXY, Ratio_matrixXY and Max_matrixXY).
In other cases, matrix partitions have arithmetic gridding (the size of the cells are approximately equal to the ΔXY_matrix for the partitions that are adjacent to SRV regions, and are approximately equal to 2*ΔXY_matrix for other matrix partitions.)
Local grid refinements (LGRs) are added for those corners of matrix partitions that are touching SRV corners. The size of the local grid refinement is defined by LGRSize_matrix. The refined grid within those LGR areas is built by continuing grid lines from the adjusting partitions (that are gridded geometrically). Every n_{LGR matrix} – th line is being continued.
Local grid refinements are also added for the portions of the SRV that are touching fracture tips. The size of the LGR is defined by LGRSize_SRV. The refined grid within those LGR areas is built by continuing grid lines from the adjusting partitions (that are gridded geometrically). Every n_{LGR SRV} – th line is being continued.

Dashboard

In the dashboard, there are four plots.

You can switch which plots (that is, XY Schematic, Ratios, Well Rate Time, Total Rate Time, XZ Schematic, and YZ Schematic) are displayed in the dashboard by clicking the Change Plot button in each plot's toolbar.

Note: If you maximize a plot in the dashboard, you are not able to switch the plot until you minimize its view. For a description of common icons, see plot toolbars.

Ratios plot

This plot displays historical and simulated ratios for the selected well.

Well Rate Time plot

This plot displays historical and simulated rates and pressure for a single well. To show or hide gas / oil / water, click the appropriate icon(s): .

Be aware that you can switch views with this icon:

/ Switch to Rate vs Time / Switch to Cumulative vs Time — toggle between these two views.

To switch wells, you can:

Click the arrows in the main toolbar.
Select a different well from the Select Well drop-down list.

Total Rate / Cum Time plot

This plot displays the total historical and simulated rates / cumulative production for the entire reservoir, and the reservoir pressure. To show or hide gas / oil / water, click the appropriate icon(s): .

Be aware that you can switch views with this icon:

/ Switch to Rate vs Time / Switch to Cumulative vs Time — toggle between these two views.

Schematic plot

This plot displays a schematic view of the reservoir shape, and the location of the wells within it. After you run the model, you can use the same plot to view distribution of cell properties (pressure, saturation of any phase or permeabilities) at any timestep.

You can have schematic plots displaying XY, XZ, or YZ cross-sections. If more than one cross-section is displayed, each cross-section has blue arrow tips indicating the location of the other cross-sections.

These toolbar icons are unique to this plot:

Shaded plot display mode — this drop-down list becomes available after the model has been synthesized. Use this drop-down list to select which property you want to display in each grid cell. You can select one of the following properties to display it: Pressure, Saturations (color scheme based on saturations of all three phases), Gas Saturation, Oil Saturation, Water Saturation, or Permeability.

Set Cross Section Location — by default, all XY Schematics have a cross-section drawn through the middle of the pay. However, you can set the cross-section to be drawn at any given distance, Z, from the bottom of the reservoir. (Similarly, you can set the desired locations for cross-sections for ZX and YX Schematics.)

For information on common plot icons, see plot toolbars.

After you click the Synthesize icon ( Synthesize icon ) in the primary toolbar, the synthesis proceeds. Lines representing simulation results are drawn as the simulation progresses.

Position lines indicate calculation progress. The shaded plot displays the distribution of pressure or saturation at the timestep that has just been calculated (as indicated by the time-stamp in the lower left corner, which displays the exact date and time). After the calculation is completed, these Position lines can be dragged to the moment in time you want to examine more closely, and all plots are synchronized.

If you find that the color scale for your shaded plot needs adjusting, right-click the legend and select Customize Color Scale, and then enter customized min and max values. To revert back to the default min and max values, right-click the legend and select Reset Color Scale.

Context menu

Right-clicking the reservoir view for your wells lists these options:

Show Grid Cells — displays a grid layout on your schematic.
Show Shaded Plot (after Synthesizing) — displays the plot after the synthesis process is completed.
Show Scale Gridlines — show / hide gridlines with a scale marker.
Show Dimensions — show / hide dimensions on the right-side of the plot.
Show Cross-section Locations — show / hide cross-sections.
Show Layers — show / hide layers. This option is displayed, if more than one layer exists.
Different Colors for SRV and matrix — when this option is selected, the SRV and matrix are displayed in a different color from the rest of the schematic. When this option is deselected, the entire schematic is displayed in white.
Show Single Fracture Schematic — displays a close-up view of the fracture. You can toggle back to Show Entire Model Schematic.

Forecast tab

This tab has the same features as the numerical Forecast sub-tab, but you have the option to display all wells in the group, or individual wells.

Forecast Plot

If All Wells is selected in the Select Well drop-down list, the Forecast plot displays group-level rates and reservoir pressures. If one of the wells is selected in the Select Well drop-down list, the Forecast plot displays rates and flowing pressures for that selected well.

Forecast Options

Use the Select Well drop-down list to pick any individual well or All Wells. Select one of the wells to see forecast settings for just that well in the Forecast table, or select All Wells to see forecast settings for all the wells together.

The Forecast Start Date is set for the entire model (the forecast for all the wells starts at this given date).

The values in the Duration column are shared between all the wells in the model.

Forecast Constraints are applied for all of the wells in the model.

After you set up a valid forecast and synthesize it, the Forecast Results table displays EUR, RR, RF, and historical volumes for each well for each of the fluid phases available in the model.

Forecast injection

To forecast injection for any well, select one of these options from Control Type drop-down list:

Gas Inj Rate — the forecast at a given gas injection rate.
Water Inj Rate — the forecast at a given water injection rate.
Pressure (Inj Gas) — the forecast at a given sandface flowing pressure. (This pressure is reached by injecting gas.)
Pressure (Inj Water) — the forecast at a given sandface flowing pressure. (This pressure is reached by injecting water.)

Note: In order for the above options to be available, the corresponding fluid phase must be selected when you click the Reservoir button.

Injection constraints are applicable when at least one of the wells has an injection forecast.

(p_inj)_max — sets a maximum sandface flowing pressure during the forecast. In order to maintain the maximum flowing pressure, the injection rate is adjusted.
(q_ginj)_max — sets a maximum gas injection rate during the forecast. In order to maintain the maximum rate constraint, flowing pressure is adjusted.
(q_winj)_max — sets a maximum water injection rate during the forecast. In order to maintain the maximum rate constraint, flowing pressure is adjusted.

Toolbar

This toolbar has the same common icons described in plot toolbars.

Tables tab

This tab displays calculation results in a tabular format.