User-defined Average Porosity and Net-

to-Gross determination per zone from

well tops in Petrel.

2014 Schlumberger. All rights reserved.

An asterisk is used throughout this presentation to denote a mark of Schlumberger.

Other company, product, and service names are the properties of their respective

owners.

Dataset

Gullfaks field description

Offshore oilfield in the Norwegian North Sea.

Exploration began in 1974.

Gullfaks reservoirs : Brent group Middle Jurassic sandstones

Lower Jurassic & Upper Triassic sandstones

Data content:

3 wells, well logs, well tops

Objective

How to create attributes in Petrel from continuous & discrete logs for well top zones

How to create attributes average porosity zone attribute using the insert new

attribute option

How to generate Net-to-gross per zone from facies

Gridding the zone attributes to generate maps for average properties

This is an important workflow as it allows for quick QC on imported well log data prior to

their use in exploration workflow.

Workflow

Import well logs and well tops (created well tops can also be used)

Create average continuous and discrete attributes for zones between two well tops

Grid zone attributes to generate surfaces for petrophysical properties

Generated grids can then be employed in volume calculations, modeling and used as

input for petrophysical analysis in other software

Well data display and QC

1. Display wells and well logs in a new WSW

2. QC logs and adjust log value limits

3. Display created or imported well tops

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Creating average porosity attribute per zone (1)

1. Expand attributes under well tops folder to view Petrel pre-defined well top attributes 2. Right click on attributes

3. Select new attribute to be created e.g. Continuous, discrete, boolean, string etc.

4. In the setting dialog, rename the attribute & select the appropriate template porosity 5. Click Apply.

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Creating average porosity attribute per zone (2)

In the Attributes operations tab,

1. Select To the zones at level (this generates average porosity between an

upper and lower well top)

2. Select porosity as the log to be used for

attribute computation. For porosity,

select treat log as lines and Arithmetic

as the average method to be used

3. Click Run this generates the attribute

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Displaying calculated average porosity attribute

1. Calculated attribute (porosity) is stored in the well tops folder under the attribute object.

2. Toggle on average porosity attribute to display it in the well section window. Note: the

calculated attribute defines the porosity between the a well top and the one below it.

Average porosity maps

1. Convert the active attribute to points for the different zones (right click on the zone

between 2 well tops and select convert the active attribute to points)

2. Using the point data and selecting Isochore as the algorithm method, gridded surfaces

of the zone attribute are created in the make/edit surface process.

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Average porosity maps

Attribute map not

created for Zone 1

(Base Cretaceous

and Top Tarbert).

Average porosity maps

Net-to-Gross (NTG) per Zones from well tops.

1. Right click on attributes .

2. Select insert new attribute

3. Expand the drop-down list and select discrete attribute and click ok

4. Give an appropriate name to the attribute, select facies as the template, click apply.

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Deriving calculated zone NTG attribute

Calculated attribute (Zone NTG) is stored in the input pane under well tops attributes

Toggle on Zone NTG attribute to display it in the well section window.

In the Attributes operations tab,

1. Select To the zones at level (this generates the net-to-gross for zone 1)

2. Select an appropriate facies log as the

log to be used for attribute computation.

3. For NTG, select treat log as lines and

Most of as the average method to be

used. NTG is a discrete property,

selecting most of gives preference to the highest occurring facies per zone.

4. Click Run this generates the attribute

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Displaying derived zone Net-to-Gross

1. Calculated attribute (porosity) is stored in the well tops folder under the attribute object.

2. The facies with the most proportion is assigned to the zone between two well tops.