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Module 3 - Functions

IntroductionIn this module, how to make fluid models (PVT), saturation functions (relative permeability and capillary pressure), and rock compaction functions in Petrel, will be covered.

PrerequisitesNo prerequisites are required for this module.

Learning ObjectivesIn this module you will learn:

• How to create a correlation based black oil fluid model• How to define the initial contact depths and pressure• How to create correlation based saturation functions• How to create rock compaction functions based on correlations• How to import fluid models and rock physics functions from

keyword files• How to edit and visualize the functions in Petrel

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Lesson 1 - Make fluid model

Make fluid model

The Make fluid model process allows you to create black oil models from correlations and to create compositional and thermal models. In this course, we will only use black oil models, but we will briefly explained how to create compositional models.

Correlation libraryThe correlation library we use incorporates many published correlations, some of which use the separator conditions as input. All of the correlations have been tested against an extensive database of actual PVT (pressure-volume-temperature) experiments at the Schlumberger Reservoir Fluids Center in Edmonton, Canada. Petrel selects which correlation to use based on the input data you provide – the API gravity, the reservoir pressure, etc.

The library contains about 70 black-oil correlations - including the ones most commonly used in the industry.

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Black Oil and Compositional Models

ECLIPSE Blackoil and FrontSim• Black oil simulators• One component of gas and oneof oil in both vapor and liquidphase

ECLIPSE Compositional• Compositional simulator• Both the vapor and the liquid phase consists of several components

Rv

Rs

There will always be two, or frequently three, phases present in the reservoir during its producing life (oil, gas, water). The proportions, the composition and the physical properties of the phases may change as production proceeds, and pressures change. All of the phases are considered compressible, although to different degrees.

In a black oil model, the temperature is assumed to be constant. Typical temperatures at reservoir conditions are 350K~77C~171F. Also, since both the liquid hydrocarbon phase and the vapor phase are assumed to consist of mainly one component, it is customary to name them the oil and gas phase, respectively. The compositional behavior is modeled by allowing some of the gas component to be dissolved in oil and some of the oil component to be vaporized in gas.

A compositional fluid model represents the hydrocarbon fluid by a set of components (typically 6-12 for reservoir simulation). An equation of state is then used to determine the physical properties of mixtures of these components as a function of pressure and temperature and the properties of the individual components.

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Appropriate Black Oil Models

Fits the Black Oil model.

Unsuited for black oil simulation (use Compositional simulation).

Approximated by Black Oil varying gas/oil and oil/gas ratios to mimic small compositional changes.

A: Dead Oil

D: Dry Gas

F: Wet Gas, Retrograde

E: Wet Gas

G: Near Critical Fluid

B: Live Oil, Initially

Undersaturated

C: Live Oil, Saturated

Temperature

Pressure

Phase diagramsThe hydrocarbon behavior in a reservoir is often described in terms of a phase diagram as showed in the illustration above. The phase diagram relates the fluid state to pressure and temperature in the reservoir. The upper line of the phase envelope represents the lowest pressure and temperature limit for the existence of a liquid phase. This line is called the bubble point line. The lower line represents the upper limit for pressure and temperature for the existence of a vapor phase. This line is called the dew point line. The area between the two lines is pressure and temperature conditions where both a liquid and a vapor phase is present simultaneously. The point where the bubble point line and the dew point line meet, is called the critical point. At this pressure and temperature condition, the vapor and the liquid properties are equal. Pressure-temperature conditions close to the critical point cannot be modelled using a black-oil model.

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Make a Fluid Model

2. Specify Model type.

1. Select Create newto define a new fluidmodel.

1

2

Note : All fluid models will be stored in the Input pane.

In the process dialog, you need to specify whether to make a black oil, compositional or thermal fluid model.

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Compositional Model1. Select equation of state

from the General tab.

2. Append a row for eachcomponent.1

2

Note: There is no support for tuning an equation of state to match laboratory measurements.

You can select pre-defined components from the drop-down menu.

3. Go to the Interactions tabto give interactions and to theSamples tab to give samples.

3

When you make a compositional model, you must first select an equation of state at the General tab. Note that there is no support for tuning the equation of state to laboratory measurements. For that, you will have to use PVTi and import the resulting matched equation of state.

When you add a new component on the Components tab, you need to type in the molecular weight and then click the Fill table button to fill in the rest of the table according to the equation of state. Note that if you later change the equation of state, you must return to the Components tab and click the Fill table button again.

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Make a default Compositional Model1. Select model type –

Compositional.

2. Use the drop-downmenu to specify default model.

1 2

All sub-tabs are filled with preset values.

Make a default Black Oil Model

2

1

1. Select Black oil as Model type.2. On the General tab, specify which

phases are required (enter required properties in the following tabs).

3. Or use one of the defaults.4. Specify an initial condition.

3

4

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There are four default black oil models to select from: Dead oil. Two phases, oil and water. Bubble point pressure lower

than minimum reservoir pressure, hence no gas will boil out of the oil.

Heavy oil+gas. Three fluid phases, oil, gas, and water. The oil has API gravity of 26.

Light oil+gas. Three phases, oil, gas, and water. A lighter oil with API gravity of 45.

Dry gas. Two fluid phases, gas and water. To make a default model, select one of the models from the drop-down list and go to the Initial conditions tab to specify the initial fluid contacts.

Make a model using the settings

General tab• Select phases.• Enter pressure and temperature

in the reservoir.

In addition to the four default fluid models, you can make black oil models by filling in the settings in the process dialog. Based on the settings, Petrel will select a model based on correlations.

The General tabIn the General tab, you specify which fluid phases that are present and also the reservoir pressure and temperature.

Reservoir conditions. This is where the minimum and the maximum pressure in the reservoir is specified. In addition, you must enter the temperature in the reservoir.

Separator conditions. Here you can specify the pressure and the temperature at separator conditions. Some of the correlations need information on separator conditions.

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The Gas tab

GasInformation on the gas phase composition entered here is used to select correlations.

CorrelationsLeave as Default to allow Petrel to select correlations based on your input.

Gas properties. Enter the density or the gravity of the gas phase. If you are defining a dry gas, you must type in the vaporized gas/oil ratio. You can also select which correlations to use or you can make Petrel select, based on the input you give.

If you have information on the concentration of each component of the gas phase, this can be entered here. Note that this option is only used to select which correlations to use, it does not mean that you are defining a compositional model.

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The Oil tab

Specify gravity and bubble point pressure.

Correlations -are reported on the Statisticstab of the fluid model

Oil properties. Here, you need to specify the oil density or the oil gravity (API gravity: The usual range starts with water density at 10 degrees and rises to volatile oils and straw colored condensate liquids around 60-70 degrees). In addition, you must enter the Bubble point pressure or the Solution gas/oil ratio at the oil/gas contact. Note that if the bubble point pressure you supply is lower than the minimum reservoir pressure, then no gas will boil out of the oil. Consequently, you get dead oil. Also, notice that unless you plan to give a depth dependent Solution gas/oil ratio, the bubble point pressure must be equal to the pressure at the gas/oil contact as specified in the Initial conditions tab.

You can either select correlations, or leave it to Petrel to select based on the input you give. Notice that the correlations that are used to make the fluid model are listed on the Statistics tab of the settings dialog for the fluid model.

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Initial conditions tab

1. From contact set.

2. Define in the table.

3. Add columns to thetable to add initial condition regions.

1

23

Initial conditions tabIn the Initial conditions tab, you can give the initial fluid contacts as well as the pressure and the capillary pressure at those contacts. This information is used in the simulator to calculate the initial pressure and phase saturations in every grid block.

For each fluid region, you must specify a reference depth (datum) and a corresponding pressure, gas-oil contact depth, and water contact depth (depending on which phases you have). In the Define simulation case process you will have the opportunity to associate each of these initial condition regions with a region of the grid.

There are two ways you can define your initial conditions:Contact set: If you have an existing contact set, you can select the

Use contact set option and drop in the contact set from the Petrel explorer. The option Target number of initial conditions will control how many regions to make from a contact set (for example, if a tilted surface is made in the

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Make contacts process). This algorithm is iterative and cannot guarantee to get exactly the number of targets specified. For example, if you enter 10, but there are only two distinct values in the surface, you will only get two regions.

Table: If you not using contact set, you can enter the details of each initial condition in a table. The table consists of a column for each initial condition region; columns can be added or removed using the usual Petrel table manipulation buttons.

By default, the gas-oil contact is set as Datum. Also, the pressure at Datum is defaulted using a pressure gradient of 0.0981 bar/m over the depth given by (surface elevation - datum depth). To enter a specific pressure or datum depth, select the check box.

Note that unless you plan to give a depth table for solution gas/oil ratio and bubble point pressure, the pressure at the gas-oil contact must be equal to the bubble point pressure input, specified on the General tab.

Make contacts

Make contacts is the process where the contacts to be used in the Volume calculation and Simulation processes are made

To keep the fluids in a stair step condition, you will need to define the model as such (with an active aquifer, capillary pressure, etc). If you just put a tilted surface for the contact, and then run the simulator, the fluid will gradually slump down to a flat contact.

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To use contacts as input to the Make fluid model processes, you must define them in a separate process in Petrel, called Make contacts. The purpose of this is to be able to enter different types of contacts, such as constant values, dipping contacts and surfaces, and you can choose to use different contacts for each zone and each segment or the same contacts for the entire 3D model.

Another purpose of contacts is to visualize them together with one of the horizons. This will show the contact contour on the surface together with colored intervals for each hydrocarbon interval. This is useful when displaying the aerial extent of the hydrocarbon intervals.

Make contactsDefine fluid contacts

1. Append the number of contacts.

2. Define the contact type and name.

3. Define the contact level.

Can be a different value/surface for each segment and zone.

1 2

3

Make contacts - Procedure1. Open the Make contact process.2. Choose to Create new contact set.3. Enter the type of contacts to be created, and change the name

(if other than default).4. Enter the contact level.

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Contact level• Can be a constant value or a surface. To enter a constant

value, type the value directly into the cell. If it is a surface, select the little check box and use the blue arrow to copy the surface that represents the contact into the cell.

• To use different contacts for each segment and zone, clear the options Same for all zones and Same for all segments.

Fluid variations with depth

Right-click an Initial condition and select Spreadsheet to enter a depth table.

Specify the bubble point or the Rs value at each depth. If you specify one, then the other is calculated using the correlations.

Vertical variations in PVT must be given in a spreadsheet.

Composition of oil is frequently a function of depth• Solution gas/oil ratio (Rs) or Bubble point pressure (Pb• Vaporized oil/gas ratio (Rv) or dew point (Pd)

(No correlations available to create vaporized oil PVT – input manually or import)

To model the variation with depth, you have to fill in the Spreadsheet located under the Initial condition sub-folder of the fluid model folder. You can specify the bubble point or the Rs value at each depth. If you specify Pb, then Rs will automatically be calculated and vice-versa, using the correlations the fluid model is based on.

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Entering a depth table is optional. If a table is not entered, the dissolved gas concentration in under-saturated oil is set equal to the saturated Rs value at the gas-oil contact everywhere. This is the Rs value that you specified on the General tab when you made the fluid model.

If the bubble point pressure (specified on the General tab of the Make fluid model process) is not equal to the pressure at the gas-oil contact (as specified on the Initial conditions tab), a depth table is required. At any position in the reservoir, the Rs value derived from an Rs or Pb versus depth table, is subject to an upper limit equal to the saturated value at the local pressure, since the Rs value cannot exceed this.

Spreadsheets

You can view/edit a fluid model in spreadsheet format.

You can copy and paste to/from existing tables.

By right-clicking the oil or gas phase of the fluid model, you can access the data in a spreadsheet format. Data can be copied/pasted from/to those spreadsheets from Excel.

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Fluids data can be plotted in a function window.

Plotting

Import

Black oil models exported from PVTi can be imported.

The status of the import is reported in the message log.

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You can import fluid models generated in PVTi, or you can import Eclipse keyword files.

Exercises – Make fluid modelThere are several ways to create a fluid model in Petrel. You can use the Make fluid model process to generate a fluid model from correlations, you can import data or you can define a fluid model by using spreadsheets.

Exercise Workflow• Make a black oil fluid model• Reviewing fluid model settings• Import a keyword fluid model• Plot the fluid model

Exercise DataIn this exercise, we will continue to use the project from the previous exercise.

Make a black oil model from correlationsIn this exercise, we will create a black oil fluid model based on correlations using the Make fluid model process in Petrel. The output from the process is a fluid model that can be used by the simulator.

Exercise steps1. From the Processes pane, open the Simulation folder and

open the Make fluid model process.2. Select Create new fluid model.3. Click on the Use presets button and select Light oil + gas

from the drop-down menu. Observe that the process window is filled with default values.

4. On the General tab, change the Maximum pressure to 460 bar.

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5. Inspect the Gas tab, accept the default settings.6. Select the Oil tab. Change the Bubble point pressure to 200

bar.7. Go to the Initial conditions tab. To specify the initial

reservoir conditions for the model, you can either drop in a contact set or you can enter a table of contact depths and pressures. In this exercise, we will use the table and enter a value for the gas-oil contact to -1600m and the water contact to -2600 m.

8. Enter a pressure at datum (the gas-oil contact) of 200 bar.

9. Click OK in the Make fluid model process dialog.

If the datum depth lies above the gas-oil contact, the pressure refers to the gas phase.

If the datum depth lies below the water-oil contact, the pressure refers to the water

phase. Otherwise, the pressure refers to the oil phase.

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Reviewing fluid model settingsIn this exercise, we will inspect the settings for the fluid model we just created to see how we can edit and change the model.

Exercise steps1. In the Input pane you can now see that a Fluids folder has

been added. This is where the fluid models are stored.2. Expand your fluid model inside the Fluids folder and then

right-click on Oil and select Spreadsheet from the context menu. This opens a spreadsheet view of the oil properties that vary with pressure.

Import a keyword fluid modelIn this exercise, we will import a fluid model from a keyword file. This file can be an included file to the simulation deck, or the main .DATA file of the simulation deck.

Exercise steps1. Right-click on the Fluids folder and select Import (on

selection). Navigate to the ImportData > Functions > FLUID.INC file, and click Open to do the import.

2. On import, you may get a message that some keywords were not imported. You can find those keywords in the Message log. These keywords do not contain PVT data.

3. After importing, a new fluid model is added to the Fluids folder in the Input pane. Check the imported data by using the Settings panel and the spreadsheets.

4. The fluid you imported does not have an initial condition, hence, an initial condition must be added before the fluid can be used in a simulation model.

Plotting the fluid modelIn this exercise, we will plot the fluid model in a function window.

Exercise steps1. Insert a New function window from the Window menu,

and select the check box next to Oil formation volume factor in the Oil folder of the imported Black oil model 1.

2. Use the Select/pick mode tool and click anywhere on

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any of the curves. The property name and value appear in the status bar. If you cannot see the status bar, enable it with the View > Status bar command.

3. Deselect to view the Oil formation volume factor and select the check box next to Oil viscosity instead.

4. Any changes made in any of the settings panels and spreadsheets will be reflected in what you see in the function window.

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Create multiple viewports – OptionalIn this exercise, we will set up a new plot window with four function viewports so we can make a report of the fluid model and inspect more data in one view.

Exercise steps1. Insert a New plot window from the Window menu.2. There are two ways to create multiple viewports in the plot

window:a. Go to the Windows pane and find the inserted plot

window. Open the settings for Plot window 1 [Any] and go to the Setup multiple viewports tab.

Or,b. From the toolbar, click on the New object in window

button on the toolbar and select Create/align multiple viewports.

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3. In the settings for ‘Plot window 1 [Any]’ dialog, select Function viewport(s) from the New viewport type drop-down menu. Define Number of rows: 2 and Number of columns: 2. Then click the Setup viewports button

and close the settings window by clicking OK.

4. You should now have four function viewports ready to use for plotting the line data. The active viewport is shown with a red border. Click inside a function viewport to make it active.

5. As an example, select the following data to plot from the Light oil + gas fluid model:a. Top left viewport: Oil formation volume factor.b. Top right viewport: Oil viscosity.c. Bottom left viewport: Pressure and the fluid contacts from

Initial condition 1.d. Bottom right viewport: Gas formation volume factor. 6. You should have a plot window similar to the one shown

below:

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