Advanced Forecast

Advanced Forecast is a production optimization tool for creating and evaluating different forecasts for a single well. This analysis must connect to an existing analytical or numerical model created with the Harmony Reservoir module.

After you pair a model, you can generate forecasts with varying constraints. Since this is a production optimization tool, the expected workflow is to start with an existing, history-matched model, and then create forecasts from it.

Multiple forecasts can be compared within the worksheet, either by qualitative analysis of the plotted forecasts through time, or by quantitative analysis of forecast results such as expected ultimate recovery (EUR) and recovery factor (RF).

Advanced Forecast provides additional benefits beyond the ability to show multiple concurrent forecasts. One benefit is the prediction of liquid loading in gas forecasts. Another benefit is the ability to display an inflow performance relationship (IPR) for the reservoir at any point in the forecast.

Furthermore, if you have a history-matched analytical model, then the expected workflow is to create one or more wellhead-pressure forecasts for which you can specify the wellbore configuration, and the date at which your wellbore configurations change. You can also customize your tubing configuration within the worksheet (instead of navigating back to the Wellbore editor.) Note that wellhead-pressure forecasts are not possible for numerical models.

Note: This analysis works with your Harmony Optimize™ license.

This analysis has the following icons:

Delete — removes the currently selected inflow, outflow, gradient, or forecast.
Copy — creates a duplicate of the currently selected inflow, outflow, gradient, or forecast. The name is appended with the word "Copy".
/ Show / Hide — toggle between showing or hiding the inflow, outflow, gradient, or forecast.
/ Collapse / Expand — closes / opens the details for the inflow, outflow, gradient, or forecast. If you see a red triangle () in the top left of a collapsed analysis, you need to investigate the required parameters.

Analysis selector

The Available Analyses drop-down list at the top of the window is used to pair the Advanced Forecast worksheet with a previously created analytical or numerical model. After you select a model, a Model Forecast box is displayed at the top of the Forecast pane on the left-side, and your model's original history match and forecast are displayed in a plot to the right.

Note: The Model Forecast box is read-only and replicates the forecast constraints used in the parent model’s Forecast tab. This is an important distinction from forecasts created within the Advanced Forecast worksheet.

By selecting a different model, the worksheet changes to display advanced forecasts that are tied to the newly selected analytical or numerical model.

Note: Deleting the Advanced Forecast worksheet does not delete your forecasts; they can be viewed again by creating a new Advanced Forecast worksheet with the same model. Forecasts can be individually deleted either within the Advanced Forecast worksheet, or by deleting the source model itself.

Forecast pane

The Forecast pane on the left-side has the following items:

Add Forecast button — click this button to create a forecast. Each time you click this button another Forecast box is created.
Pressure Reference drop-down list — when controlling the pressure for forecasting an analytical model, select Sandface or Wellhead. For numerical models, only Sandface pressure can be used. For more information, see forecasting using wellhead pressure.
Allow Injection checkbox — a negative control rate (to forecast as injection) can be specified with analytical models. For more information, see the analytical analysis.
Additional Constraints link — opens a popup where additional constraints can be entered. For more information, see below.

Additional constraints

After you click this link, you can type your maximum rate and abandonment rate conditions. The available constraints depend on the fluid type, and can include the following:

Minimum Pressure — (p_min) specifies the minimum sandface / wellhead pressure based on your Pressure Reference selection from the drop-down list.
Maximum Pressure — (q)_max sets a maximum rate to be applied during the forecast. In order to maintain the maximum rate constraint, flowing pressure is adjusted.
Abandonment Rate — (q)_ab sets the abandonment rate for the forecast. When the abandonment rate is reached, the forecast ends.

Forecast options

Each input is required to create a forecast segment. A forecast can consist of one segment – or many – depending on the number of operational changes specified in the forecast. Options include the following:

Time — defines the length of each forecast segment and each timestep, and has the following inputs:
- Start Date — determines the start of the forecast. This can be any time between the earliest and most-recent historical production date. If no historical production exists, this value defaults to today’s date.
- Duration — sets the length of the forecast segment. This can either be set to months or days.
- End Date — sets the date at which the forecast segment terminates. If Start Date and Duration are populated, this input is calculated.
- Step Count — sets the spacing of the timesteps, and can be set to either Arithmetic or Logarithmic. The "Arithmetic step" spaces the number of timesteps equally over the total duration of the period. The "Logarithmic step" spaces the number of timesteps logarithmically (that is, increased density near the beginning of the forecast).
Control — defines how the operating conditions change over the forecast period, and has the following editable fields:
- Control Type — sets what is used to calculate the forecast. For the analytical model, the forecast can be run using either flowing pressure, or the rate being analyzed.
- Interpolation — can be set to either Step or Ramp. "Step" keeps the control type constant over the forecast period. "Ramp" varies the control type linearly from an initial value to a final value.
Sandface Pressure — if the Control Type is set to Pressure, and the Pressure Reference drop-down list is set to Sandface, the sandface flowing pressure is used to set the flowing pressure for the forecast segment. If Interpolation is set to Step, only the initial pressure is specified. If Interpolation is set to Ramp, initial and final pressure are specified.
Wellhead Pressure — if the Control Type is set to Pressure, and the Pressure Reference drop-down list is set to Wellhead, the wellhead flowing pressure is used to set the flowing pressure for the forecast segment. If Interpolation is set to Step, only the initial pressure needs to be entered. If Interpolation is set to Ramp, initial and final pressure need to be entered.
Rate — if the Control Type in a period is set to Rate, an editable field is displayed, and it is used to set the rate for the forecast period. If Interpolation is set to Step, only the initial rate's field is editable. If Interpolation is set to Ramp, initial rate and final rate are editable.
Ratios — these additional forecast constraints are only available under certain conditions.
- WGR — available when using a gas analytical model, and the Pressure Reference is set to Wellhead. By selecting the WGR checkbox at the top of the Forecast pane, additional input fields are displayed below the Control Type section. The WGR in the forecast segment can be set to either Step or Ramp.
- CGR — available when using a gas analytical model, and the gas type is set to Liquid-Rich Gas in the Properties editor, and the vaporized oil ratio correlation is set to Constant Rv also in the Properties editor, and the Pressure Reference is set to Wellhead. If these conditions are met, then selecting the Separate Recombined Gas checkbox at the top of the Forecast pane displays additional fields below the Control Type section. The CGR can be set to either Step or Ramp.
- GOR — available when using an oil analytical model, and the Pressure Reference is set to Wellhead. By selecting the GOR checkbox at the top of the Forecast pane, additional input fields are displayed below the Control Type section. The GOR in the forecast segment can be set to either Step or Ramp.
- WOR — available when using an oil analytical model, and the Pressure Reference is set to Wellhead. By selecting the WOR checkbox at the top of the Forecast pane, additional input fields are displayed below the Control Type section. The WOR in the forecast segment can be set to either Step or Ramp.

Customize Wellbore

This option is available when the Pressure Reference is set to Wellhead.

By clicking the Customize button, you can create and edit customized wellbore configurations. Options include: flow path, bottom depth of tubing, tubing, inner diameter, and tubing outer diameter.

Add Segment

You can add additional segments to the forecast. This can be used to schedule a change in a wellbore configuration, operating condition (for example, rate control vs. flowing pressure control), or additional fluid production (for example, WOR increase).

Subsequent forecasts must start at the date the preceding forecast ends. Segments can also be copied, deleted, expanded, and collapsed.

Forecast summary

When you click the Collapse icon (), a summary of the forecast is displayed. Results depend on the fluid type, but items could include the following:

EUR — expected ultimate recovery
Note: For wells with historical data, EUR is defined as the cumulative of the historical data up to the beginning of the forecast, after which time, the synthetic cumulative is calculated from the model until the end of the forecast.
RR — remaining recoverable
RF — recovery factor (as a percentage)
Duration — total duration of all forecast segments

Plots

There are two plots in the center of the window: a Forecast plot and an IPR / TPC plot. The Auto-scale checkbox fits the plot to the maximum viewable area of the screen.

Forecast plot

This plot is used to display various production forecasts for comparison. Color-coding matches the fluid types; red for gas, blue for water, green for oil / condensate, and purple for recombined gas. Brown denotes flowing sandface pressure.

Historical data points are displayed using dots, whereas forecast-series data is displayed using lines. For gas wellhead forecasts, the transition from a solid to a dashed line denotes the transition between operating above and below the critical liquid loading rate, respectively.

Multiple forecasts can be displayed at the same time, but only one forecast can be selected. The forecast is denoted by a dark blue border around its forecast box in the Forecast pane. Thicker lines are displayed for the fluid rates and the flowing-pressure series. Active, but deselected forecasts, are displayed with thinner lines on the plot. By right-clicking the plot, you can copy the selected forecast's tabular values for pasting to another application (for example, Excel).

The vertical blue "Time / Date selector" is used to specify a forecast step at which to calculate the IPR curve (and outflow for wellhead forecasts) in the IPR / TPC plot at the bottom of the window. This Time / Date selector can be moved by clicking-and-dragging either the line, or the annotation at the top of the line, or by interacting with the annotation itself. The annotation has two states: a minimal display when the mouse is not hovering over the Forecast plot, and a full display when the mouse is hovering over the Forecast plot.

IPR / TPC Preview Plot

This plot is used to display the IPR curve for the selected forecast at the time specified by the Time / Date selector. You can select either a correlation-based or model-based IPR from the drop-down list.

Correlation-based IPR

After you select Correlation-based IPR, the IPR is created using a Simplified C,n correlation (assuming an ‘n’ value of 1) for gas wells, and a Vogel IPR correlation for oil wells.

If the Pressure Reference is set to Wellhead, a TPC is displayed using the wellbore configuration used at the time specified by the Time / Date selector. The intersection of the IPR and TPC correspond to the operating point and the resultant rate and flowing sandface pressure at the Time / Date selector-specified time. If the operating point is below the critical liquid loading rate, the operating point is red.

By right-clicking the plot, you can copy the inflow and outflow curves in tabular format, to be pasted to another application (for example, Excel).

Model-based IPR (not applicable to numerical models)

After you select Model-based IPR, the IPR is calculated directly from the analytical model you created.

The IPR is calculated using 32 individual forecasts that are performed on the analytical model.
Each of the 32 forecasts is performed at constant pressure, with the pressures being equally spaced from reservoir pressure to minimum pressure.
Each forecast is performed for one month (31 days, with 31 steps).
The final rate and flowing sandface pressure from each forecast are used to build the IPR.

By right-clicking the plot, you can copy the inflow and outflow curves in tabular format, to be pasted to another application (for example, Excel).

Send To button

After clicking this button, you can send / push IPRs and TPCs from the Advanced Forecast worksheet to an IPR / TPC worksheet (that is, Gas IPR / TPC, Oil IPR / TPC). This exports the IPR (and TPC) displayed on the IPR / TPC Preview plot. The pushed curves are displayed on the destination worksheet as read-only Custom Table Inflow and Outflow analysis panes.

You can select an existing IPR / TPC worksheet (which matches the primary fluid of the Analytical model), or create and type a name for a new worksheet in the Send To dialog box.

You can send either one IPR, or up to 10 IPRs at one time with a manually specified number of forecast steps between subsequent IPRs. If the selected Forecast is set to Wellhead, then you can send a TPC corresponding to the wellbore configuration and wellhead flowing pressure observed at the specified forecast step.

After an IPR is sent to an IPR / TPC worksheet, a confirmation dialog box opens. Navigate to the destination worksheet to view your pushed Inflow analysis pane.

After a curve is pushed from the Advanced Forecast worksheet, this curve is a standalone analysis. There is no synchronization between the Advanced Forecast or the Analytical model, and the resultant Inflow and/or Outflow analysis panes. For this reason, additional information is displayed on a pushed curve.