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!
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