PRESSURE GRADIENT ANALYSISClick Through Guide

ANALYSIS OF PRESSURE DATA

Hydrocarbon columnAn estimate of the maximum potential height of the

hydrocarbon column can be made with knowledge of

the fluid density and the difference between the pore

pressure(overpressure) and the fracture gradient

Predict FWL and CompartmentsUsing Pressure data interpretation can be made on

the Free Water Level in the Reservoir. In addition

comparison of gradients can indicate

compartmentalization

Seabed correctionPressure data from wells throughout the basin need to be depth

corrected in order to calibrate regional pressure data sets

Pressure Gradient Analysis Features

Pressure Data Loading and QC

• Load Pressure data and meta

data

• QC with guide lines and marker

• QC with well data

• Load Guidelines

• Export to Petrel

Pressure Data Interpretation

• Interpret Pressure Profiles

• Interpret Fluid Contacts

• Export Contacts

Pressure Profile Prediction

• Predict fluid profiles

• Predict hydrocarbon fill

Seabed Correction

• Import / Edit seabed level

• Remove Seabed effect

• Re apply new seabed level

LOAD AND QC PRESSURE DATA

Import Pressure data from ASCII and QC together

with Well Logs, Zones and Guidelines

INTERPRET AND CREATE CONTACTS

Interpret Fluid Gradient and Contacts. Create Contacts and Save

Pressure Data to Petrel

PRESSURE PROFILING AND HYDROCARBON FILL

• Predict Pressure gradients between an interpreted Apex and a Spill Point

• Create Hydrocarbon Fill between Fracture Gradient and OverPressure Gradient

HC Limits between

the Fracture (max)

and Pore

Pressure(min)

Pressure Data Loading and QCLoading

To import Pressure data from a spreadsheet you need only a Well Name – Which must match a Well in

Petrel, a depth and a pressure measurement

The rest are optional values which can be used as meta data on the plot.

This data can then be loaded via an ASCII loader or pasted into the loader

Pressure Data Loading and QCLoading

Match up the corresponding

columns using Ignore to leave

empty

Well Name, Depth and Pressure

are the required fields.

Pay close attention to the Depth

mode chosen to import. Available

options are TVDSS, TVD and MD

Pressure Data Loading and QCQC

Once Loaded the data will appear

on the Pressure plot (Pressure vs

Depth)

The first couple of things you might

want to adjust is the Scales and

Units of the plots and the display of

the points. This can be done from

the display options of the main

toolbar.

On the main toolbar you can also

find a legend button which will help

to annotate the plot

Data can also be filtered by any of

the attributes specified on loading,

i.e. Well Name, Pressure Type,

Foramtion etc.

Changes points display

and axis scales

Should you also define a

Zone Log (wells) and a

3D Gird, more filter

options will appear

Pressure Data Loading and QCQC

The plot can also be further

annotated to add some extra

context to the plot.

Firstly a set of Well Tops can be

defined to indicate markers or

zones on the plot

In addition to this, a Well Logs

track can be added to give a

visual QC i.e. to distinguish

sands from shales

Pressure Data Loading and QCExport to Petrel

Normally the Pressure Points are

stored as part of the Tool on the

Petrel input tree and can be only be

used inside of the Pressure

Gradient Tool.

However a export to a Well Point

Set can be done to enable display

of the Data in the Well Section

Window

Pressure Data InterpretationActive Data

The main function of the

Interpretation mode is to fit a best fit

gradient line to a set of visible and

active data.

Data can be made visible by use of

filters discussed in the previous

sections.

Data an also be set inactive by use

of the eraser tool found on the main

tool bar. This method also allows

the user to select and delete points

Pressure points can also be edited

by double clicking on it.

Eraser Tool – Make data inactive and

delete

Pressure Point Properties

Filters

Pressure Data InterpretationCreate Best Fit

Once data has been filtered, a best

fit gradient can be created by

clicking the create best fit icon.

Once created a Gradient Lines

folder will be displayed on the tree

of the Pressure Gradient Tool.

The slope of the line will determine

which label or fluid type to which

the line belongs.

Once created, gradient line can be

adjusted by the two end points

(length), the mid point( position)

and by the stem of the line (slope).

The definitions which govern the

lines properties can be adjusted in

the Gradient Lines settings

Adjustment points of the Gradient Line

Gradient Lines object

Gradient Lines Properties

Pressure Data InterpretationView and Flattening

Picking out Hydrocarbon Gradients

can be made easier by applying a

flattening to the hydrostatic

gradient.

The effectively makes the

hydrostatic water gradient vertical

so other gradient become more

visible.

This tool can be found on the main

toolbar.

Pressure Data InterpretationMake Contacts

If multiple gradients have been

interpreted they can be projected

together to predict fluid contacts.

Extend the lines vertically so that

they cross, then click the scissors

icon from the main toolbar.

A fluid contact is then annotated on

the plot and listed in the legend.

Information about the contact can

also be found in the Settings of the

gradient lines.

This include the error in the contact

depth which is calculated by

summing the error bars from each

gradient. Be sure that the error bar

for each gradient cover the spread

of the data.

Pressure Data InterpretationMake Contacts

Once interpreted, a fluid contact

can then be generated for any 3D

Grid in Petrel.

Firstly in the Filter Tab, enter the 3D

Grid that you wish to use

Next active a Gradient Line folder

from the Pressure Gradient Input

Tree.

Next Enter the name for a new

Contact St in the Contacts Tab

Then click Make contacts

• Import / Edit Seabed Level• When importing pressure data, sea bed level can be imported as a coloum in the ASCII loader. Once in the PGA tools the seabed

level can also be edited in the Well Settings

• Remove effect of Seabed• In order to calibrate regional pressure data, the seabed level needs to be corrected for each well. This is done by selecting the seabed

correction mode. Lithostatic gradient will be set to 0 and pressure data corrected.

• Re apply new level• Applying a new seabed level allows the assessment of new prospects. The new seabed level is set in the guidelines settings.

Points will be shifted down according to the new level. Lithostatic gradient will start from the new depth. Trap apex and Spill point will be unaffected.

Seabed CorrectionWorkflow

• Import / Edit Seabed Level• When importing pressure data, sea bed level can be imported as a coloum in the ASCII loader. Once in the PGA tools the seabed

level can also be edited in the Well Settings

Seabed CorrectionWorkflow

• Remove effect of Seabed• In order to calibrate regional pressure data, the seabed level needs to be corrected for each well. This is done by selecting the seabed

correction mode. Lithostatic gradient will be set to 0 and pressure data corrected.

Seabed CorrectionWorkflow

• Re apply new level• Applying a new seabed level allows the assessment of new prospects. The new seabed level is set in the guidelines settings.

Points will be shifted down according to the new level. Lithostatic gradient will start from the new depth. Trap apex and Spill point will be unaffected.

Seabed CorrectionWorkflow

• To begin the Pressure Profiling workflow, create a Prediction Set by clicking the create Prediction Icon

• This will create serval items which can be used in the Profiling/Prediction Workflows

• Lithostatic Gradient• Fracture Gradient• Over Pressure Gradient• Sea Bed Level• Apex / Trap Apex• Spill Level• Predicted Hydrocarbon Column

Pressure ProfilingWorkflow

Interpreting of these items allows two main workflows it be achieved:

i) Profiling of the Fluid Gradients

ii)Prediction of Hydrocarbon Columns

• Lithostatic Gradient - Lithostatic pressure is the vertical pressure due to the weight of the rock only. Used as a guideline and as a definition for the Fracture Gradient.

• Fracture Gradient - The pressure required to induce fractures in rock at a given depth. Used as a guideline and also limits the potential hydrocarbon fill – Upper Limit.

• Overpressure Gradient - Subsurface pressure that is abnormally high, exceeding hydrostatic pressure at a given depth. Used as a guideline and also limits the potential hydrocarbon fill – Lower Limit

• Seabed Level – Level of the Seabed – Used for correction of the gradients i.e. Lithostatic

• Apex Level – Upper depth of the potential Trap or Reservoir – Used to Calculate Hydrocarbon Column Height and Upper Limit of Pressure Profile

• Spill Level – The lower depth of the potential Trap or Reservoir - Sued to Calculate Hydrocarbon Column Height - Used to Calculate Hydrocarbon Column Height and Lower Limit of Pressure Profile

Pressure ProfilingDefinitions

*Definitions from AAPG Wiki and SLB Oilfield Glossary

• In the Depth / Pressure Plot the different guidelines can be adjusted to account for local conditions. The different guidelines can be defined in different ways.

• Lithostatic Gradient – Can be defined as a Pressure with Depth Change Or loaded form Leak Off Test data or defined/adjusted manually using a draw mode

• Fracture Gradient – Can be defined as a % of the Lithostatic Gradient, a Pressure with Depth or Loaded from pressure data

• Over Pressure Gradient – Starts a single Pressure but can be trimmed between Apex and Spill.

Pressure ProfilingAdjusting Guidelines

In pick mode the Lithostatic Gradient

can be adjusted manually ASCII Loader for loading LOFT Data as

Lithostatic or Fracture Gradient

Pressure ProfilingPressure Profile Prediction

When a Prediction set is created a spill and apex is automatically added to the plot, these can be adjusted by moving them up and down the plot or by using the Settings Dialog of the Prediction set.

A pressure profile is also automatically added between the Trap and Spill

The fluid phase of the reservoir can also be adjusted in the settings of the Prediction Set. The users can choose to have both fluid types and adjust the properties of those fluids.

Pressure ProfilingHydrocarbon Fill Prediction

With all the inputs defined, the prediction set will automatically calculate a Hydrocarbon Column

This will be demined between the Trap Apex and the Spill.

However, subsurface properties dictate that you cannot fill above the Fracture Gradient(The point at which the rock fractures) or below the Over Pressure Gradient.

These two physical boundaries will limit the fill.

In this example we have filled from out Trap down but expect less fill than interpreted from our spill point as we cross the Overpressure Gradient at a shallower depth.

ADDITIONAL TOOLS

Some additional tools can be found on the main toolbar

• Sea Bed Correction – Adjust the gradient based on the seabed level

• Annotations – Adds an annotation to the plot

• Change Guideline Units – The plot units for Guidelines can be changes and can include By Density

• Change Symbol and Colour – Changes the Well Symbol and Colour

Thank you for your attention!

Support.geo@cegal.com

+47 52 04 00 00

SUPPORT CONTACTS