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Nodal Analysis - Forecast

1. Overview

The FORECAST feature evaluates the long-term production response to changes in wellbore configuration and operating conditions while accounting for reservoir pressure depletion. Use it to compare future well performance without building a numerical reservoir model.

Applications include comparing differnt flowpath, different tubing sizes, evaluating changes in artificial lifts, and assessing the production impact of choke changes. Review the production forecast together with future inflow performance relationship (IPR) and vertical lift performance (VLP) curves to understand how a case performs as the reservoir depletes.

2. Basics

2.1. Current and Future Well Performance

An IPR describes reservoir inflow at a given reservoir condition. A VLP describes the wellbore pressure requirement for a given production rate and operating configuration. Their operating intersection relates the production rate to flowing bottomhole pressure (BHP).

FORECAST extends this analysis into the future. A configuration that performs well today may perform differently at lower reservoir pressure. Evaluate its production response over the forecast period and inspect the corresponding future IPR and VLP curves.

For the underlying inflow and wellbore relationships, see IPR/VLP.

2.2. Preparing the Analysis

Before comparing forecasts, review the well's production history, PVT description, pressure data, and wellbore configuration. Perform the Flowing Material Balance or Numerical Model to get the reservoir pressure profile.

The FORECAST tab includes Productivity Index Data and Material Balance / Tank Data panels. Review both when setting up the analysis. The starting inflow description and depletion assumptions should be consistent with the well's observed behavior.

For supporting workflows, see Bottomhole Pressure and Flowing Material Balance.

2.3. How the IPR Forecast Evolves

An IPR forecast links the initial inflow calibration to future reservoir pressure and wellbore conditions:

  1. Calibrate the current IPR. Recent well tests or the Multiphase Flowing Material Balance interpretation establish a representative starting inflow description.
  2. Forecast reservoir pressure. The depletion interpretation provides the average reservoir pressure at each future date. Conceptually, this pressure trajectory can be established using Flowing Material Balance or a pressure decline model.
  3. Update the IPR. With deliverability parameters held constant, decreasing reservoir pressure moves the IPR toward the origin and reduces the rate available at a given flowing bottomhole pressure.
  4. Intersect the IPR with the VLP. The intersection determines the operating rate and flowing BHP for the wellbore configuration and surface pressure at that date.

Repeating this process produces rate and flowing BHP profiles over time. Reviewing the future intersections also helps identify when the existing configuration may require an intervention to sustain production.

In a comparison that holds the reservoir interpretation fixed, each wellbore option uses the same IPR forecast but a different VLP response. A fixed VLP is a simplifying assumption: changes in water/gas ratio (WGR), oil/gas ratio (OGR), wellhead pressure (WHP), or wellbore configuration can change the VLP over time.

3. Inputs

3.1. Productivity Index Data

The Productivity Index Data panel establishes the starting reservoir inflow performance used in the forecast. It combines production rates and pressure data from a representative operating period with the selected IPR Type.

The user can select a Date to Fetch Production & Wellbore Data and a reservoir pressure source, such as Multiphase FMB. When data are available for the selected date, the panel uses the following sources:

Input Source and purpose
Liquid Rate / Gas Rate Production Data provides the rate used to establish inflow performance. The displayed rate input depends on the selected IPR type.
Gas/Oil Ratio Calculated from the Production Data input, where applicable.
Bottomhole Pressure Fetched from the Bottomhole Pressure feature and used as the flowing pressure for the selected operating point.
Reservoir Pressure Obtained from the selected reservoir pressure source and used with bottomhole pressure to establish the pressure drawdown.
Saturation Pressure Fetched from the PVT feature, where applicable to the selected IPR type.

The FETCH FROM IPR option allows the user to retrieve an existing IPR description. After retrieving or calculating the inputs, the user should inspect CURRENT IPR | VLP to confirm that the starting inflow response is representative of the well. The user also has the flexibility supply the input values. Rates and pressures should represent the same operating conditions.

The productivity calculation depends on the selected IPR Type. For Vogel (Oil + Water), the production rates and specified pressures are used to calculate the oil and water productivity indices, using the Vogel relationship for oil and a straight-line IPR for water. For C & n (Gas), the gas rate, reservoir pressure, flowing bottomhole pressure, and specified exponent n are used to calculate the gas deliverability coefficient C from the gas pseudopressure difference. The user should review the inputs before clicking RUN to calculate the productivity parameters for the selected IPR type.

3.2. Material Balance / Tank Data

The Material Balance / Tank Data panel describes the reservoir volume contacted by the well and the production already withdrawn from that volume. These inputs establish the starting depletion state for the forecast and should be consistent with the reservoir pressure used in Productivity Index Data.

When using Flowing Material Balance, the user selects a representative slope on the Flowing Material Balance plot. The contacted pore volume is the inverse of this slope. The selected interpretation should represent the production interval used to establish the forecast's starting conditions.

Input Description
Initial Reservoir Pressure Reservoir pressure before depletion, distinct from the current reservoir pressure used to establish inflow performance.
Cum Oil Production to Date Oil produced up to the date used to initialize the forecast.
Cum Water Production to Date Water produced up to the date used to initialize the forecast.
Cum Gas Production to Date Gas produced up to the date used to initialize the forecast.
Contacted Pore Volume Reservoir pore volume represented by the material balance interpretation.
Contacted OGIP Original gas in place within the contacted reservoir volume.
Contacted OOIP Original oil in place within the contacted reservoir volume.
Contacted OWIP Original water in place within the contacted reservoir volume.
Drainage Area Area associated with the contacted reservoir volume.
Rock Compressibility Describes how the reservoir pore volume changes with pressure.

OOIP, OGIP, and OWIP denote original oil, gas, and water in place, respectively; HCPV denotes hydrocarbon pore volume. Original in-place volumes describe the initial inventory, rather than the remaining inventory at the forecast start.

Before running the forecast, the user should review the cumulative production values, contacted volumes, and displayed units. Contacted pore volume is expressed at reservoir conditions, while the oil, gas, and water inventories use their respective displayed volume units. Keeping these inputs consistent with the selected material balance interpretation helps ensure that the forecast starts from a representative depletion state.

4. Forecast Workflow

4.1. Open Forecast and Review the Starting Conditions

  1. Open the well and navigate to Nodal Analysis → FORECAST.
  2. Review Productivity Index Data and Material Balance / Tank Data.
  3. Inspect CURRENT IPR | VLP and check whether the starting inflow and wellbore response are representative of the operating conditions being modeled.

Resolve unexplained differences between the starting case and observed performance before using the forecast to evaluate an intervention.

4.2. Add a Case and Define the Forecast Schedule

The Forecast Schedule window defines how wellhead pressure, production ratios, and wellbore configuration change during a case.


  1. Click MODIFY CASES in the Forecast Cases table to configure the cases to compare.
  2. Add a case in the left panel and enter a descriptive Forecast Schedule Name.
  3. Review the Correlation, Critical Rate Correlation, Rate Constraint Type, and Line Color.
  4. In WHP / Configuration, specify the pressure schedule and select the wellbore configuration for each segment.
  5. Review the production-ratio schedules.
  6. Use the + and - controls beside SEGMENTS to adjust the number of segments. Review each segment's Forecast Function, Segment End Date, Segment End Time, initial and final values, and decline input.
  7. Inspect the Forecast Profile plot to confirm the timing and magnitude of the changes, then click SAVE.


Each segment represents a period with a defined trend. For example, a forecast can retain the Current wellbore configuration for an initial period and switch to smaller tubing in a subsequent WHP / Configuration segment. Segment dates should reflect the planned intervention timing.

4.3. Add or Edit Wellbore Configurations

The ADD / EDIT WELL CONFIGURATION option in the Forecast Schedule window allows the user to prepare configurations for the planned operating changes.


  1. Click ADD / EDIT WELL CONFIGURATION.
  2. Select an existing configuration or click + to add a configuration.
  3. Enter a descriptive name. COPY CURRENT CONFIGURATION provides a starting point based on the current wellbore setup.
  4. Review Casing Data and Tubing Data, including depths, diameters, and roughness.
  5. Select the Flowpath and Artificial Lift Method. Review other applicable inputs, including Compute Through, Gauge Depth, and Choke, and complete the inputs required by the selected lift method.
  6. Click SAVE to return to the Forecast Schedule and assign the configuration to the appropriate WHP / Configuration segment.

The artificial lift selections include None, Jet Pump, Gas Lift, ESP, Rod Pump, and Plunger lift (GAPL, PAGL). Each configuration should represent the equipment and operating conditions being evaluated. For more information on each artificial lift, see Artificial Lift Methods

4.5. Save Different Forecast Cases

A wellbore configuration describes the equipment and flowpath. A forecast case combines configurations with pressure and production-ratio schedules, allowing the user to compare complete operating plans.

  1. Click MODIFY CASES and use the + button in the left case panel to add a case.
  2. Enter a descriptive Forecast Schedule Name, such as, Tubing Installation, or Lower WHP.
  3. Define the schedules and assign the appropriate wellbore configurations as described in sections 4.2 and 4.3 above.
  4. Repeat for each alternative cases.
  5. Click SAVE. The saved cases appear in the Forecast Cases table.

After saving changes, the user must run the affected cases to calculate the updated forecast. The Show checkboxes and Show All Cases control which results appear on the plot.


4.6. Inspect Future IPR and VLP Curves

Select FUTURE IPR | VLP and use the Date or Day selector to inspect the forecast at a future time. Compare the displayed reservoir pressures and IPR/VLP curves for the cases of interest.

Use this view to connect changes in the production forecast with changes in reservoir inflow and the wellbore operating point. Compare cases at the same date or day.

4.7. Identify the Intervention Window

The user can inspect successive dates in FUTURE IPR | VLP to identify when the forecast operating point approaches liquid-loading conditions or no longer has an intersection on the stable side of the VLP. The operating gas rate should also be compared with the applicable critical rate, such as the Turner rate, to assess whether liquids can continue to unload.

An IPR/VLP intersection alone does not establish that the well can unload liquids. A forecast operating point below the critical rate may indicate a need for intervention before the curves cease to intersect. The user can compare changes in tubing size, artificial lifts, or compression and evaluate both the resulting production profile and the duration of sustained operation.