7 Uncertainty Analysis - Part 2

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7. Static Uncertainty Analysis – Part 27. Static Uncertainty Analysis – Part 2

Edit WorkflowEdit Workflow

The automatically generated Uncertainty Workflow by Petrel may have some property missing because it is not included in the “Volume Calculation” For example :

The height above contact, which is needed for evaluating Saturation will not be included in Uncertainty Workflow because it does not appear in the Volume Calculation.

Permeability may also be excluded for the same reason. If water saturation is calculated based on the J-Function, then permeability must be included.

Missing process need to be included by Editing the Workflow.

Editing Workflow requires skill and understanding of Workflow Editor

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Edit WorkflowEdit Workflow

Sensitivity AnalysisSensitivity Analysis

Sensitivity Analysis is the analysis of uncertain variables toward the objective variable (e.g., STOIP or EUR)

Sensitivity Analysis can also be done for Sensitivity of the Process

The result of sensitivity analysis can be viewed as the histogram, known as Sensitivity Plot, as well as the Tornado Plot Tornado Plot is only available for PETREL

2010 or later

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Sensitivity PlotSensitivity Plot

Tornado PlotTornado Plot

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$Seed Variable$Seed Variable

The $Seed Variable is used to generate multiple realization for the same model. In order to be able to reproduce the model,

Seed Number should be provided to the program.

Same Seed number can be supplied for both Facies and Petrophysical Properties Modeling.

If variables are varied in uncertainty analysis it is better not to make variability in seed number. On the other hand, if none of the variables are

varied, $Seed should be used

Exercise 8Exercise 8

Objective : To be able to perform basic Uncertainty Analysis

by changing fluid contact

Task : Calculate Volume for the base case Generate Uncertainty Workflow Vary fluid contact using uncertainty of +/- 10 ft

from the base case Determine P10-P50-P90, from histogram and from

worksheet Reproduce the P10-P50-P90 models.

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Including Discrete Uncertain Properties

Including Discrete Uncertain Properties

Accessing specific Data Row

The data can be accessed using ForLoop Statement


Objective : Be able to include different Saturation-Height

function to capture the uncertainty of Capillary Pressure Data

Task : Generate the minimum and maximum curves of

Sw-Height function for each rock type Generate workflow to include the uncertainty of the

above curves Determine P10-P50-P90 (from histogram and from

worksheet)

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Objective : To understand the Experimental Design

sampling technique

Task : Use the two level ED and three level ED for

Exercise 9 to get the Uncertainty Analysis


Objective : To understand Sensitivity Analysis

Task : Perform Sensitivity Analysis (by variable and

by process) for Exercise 9.

Generate the Sensitivity Plot as well as the Tornado Plot

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Uncertainty Best Practice(Petrel Help File)


Duplicate Model before Running Uncertainty Analysis Workflow

Be cautious when running structural uncertainty on a model that contains properties.

It is generally recommended to untick the Copy option on the command With 3D grid. Using the Copy option may cause the uncertainty run to fail or may lead to undesired results.



For workflows that include a depth conversion step, always make sure you are using the correct velocity model and depth grid.

Use Latin-Hypercube option in the Monte-Carlo sampler.

The use of nested loops in the base case workflow is not recommended. In particular, the Define simulation case and Volume calculation commands should not be placed inside a nested loop.

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The output sheet automatically generated at the end of the execution of an optimization workflow is not stored in a Petrel project. It is then good practice, to copy the content of this output spreadsheet and store it in a file, for example by using an external spreadsheet application or text editor.

Always ensure the project is backed up! When defining the distributions of variables,

particular attention has to be paid to the Min and Max arguments. Min has to be strictly smaller than Max. If the variable has a negative range, the variable with the bigger absolute value is the lowerlimit and has to be entered as Min.



Running Uncertainty and optimization can generate a lot of cases on the Cases pane, if all these cases have large amounts out output (either simulation output or volumetric output), problems with disk storage can occur, it is good practise to review the out selected before running large number of cases.

7 Uncertainty Analysis - Part 2

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