Lithology model for PPP

The Lithology Model for PPP form (1D Model > Pore Pressure > Tools) allows you to create a second lithology model that can be used as input for pore pressure prediction calculations in the Compaction Analysis and Bowers Method workflows. The ability to generate a second lithology model means that you are not forced into adjusting your original lithology model for use in the pore pressure calculations; you can simply create a new lithology model on this form, edit the settings as needed for pore pressure modeling and select it in the relevant modeling steps. Note that, despite using this second lithology model for your pore pressure calculations, the original lithology model calculated in the Lithology sub-strip is carried into the Wellbore Stability workflow.

The model is generated by selecting a composite log for input. Once the input log has been selected, the calculated zones and segments can be edited using the Zonation Model for PPP view.

To create a lithology model for PPP

1. Choose the calculation type, Automatic or Manual (vertical) and Manual (inclined). The selection here depends largely on the availability of markers and a wellbore schematic, as well as the manner in which you want to handle the lithology definition.
   • Automatic  This option uses the markers and the wellbore schematic as inputs to calculate the zonations.
   • Manual (vertical)  For wells with a vertical trajectory, if marker and/or wellbore schematic data is unavailable, or if you prefer to create the zonations by hand, select Manual (vertical). This will allow you to create custom zones by clicking and dragging selection boxes in the Zonation Model track. For more, see Automatic versus Manual calculation below.
   • Manual (inclined)  If you are building the model for an inclined well, you can select this option and interpret the zones using the custom trend editor . See Automatic versus Manual calculation below for more information.
2. For the lithology model source choose one of the composite logs.
3. You can specify which models should be updated with the selection of the composite log: the Zonation Model and/or the Lithology Model. By default, the boxes for both options are checked, and both the Zonation Model and Lithology Model will be updated.
Important  Making changes to the zonation model calculation type or lithology model source will cause an update to the zonation model. If the lock icon shows unlocked (green), changes will occur automatically if, for example, the calculation type is changed from Automatic to Manual, or if you select a lithology log instead of a composite log as the source.
4. Click (Re)Calculate to calculate the new lithology model.
5. Click Show button to open the Zonation Model for PPP form where you can define the low, high and discriminator values for the selected zonation log, and lithology types for each zonation.
6. Once you are satisfied with your lithology model you can select it as an input in the Compaction Analysis and Input Logs and Filtering (Bowers Method) forms.

Automatic and Manual calculation of zonation segments

Depending on your available data you will select either Automatic or Manual calculation.

Automatic  The zonation model is calculated based on the existing marker and well schematic information. This method applies a lithology discriminator that determines the lithology type over the depth interval of the zone; the discriminator is applied vertically to the data. This discriminator, and the 0% and 100% shale volume bounds, can be changed in the Zonation Model track by clicking and dragging them to the desired position if you feel an adjustment is needed. You can find more information on the Zonation Model track in the Zonation Model view topic. Whether the lithology column automatically updates depends on the Automatic Update settings, which are defined in the Auto-Update Settings form or by clicking the lock icons in the Lithology Model form to turn auto-updates on or off.

Manual (vertical) For vertical wellbores, zonation segments are created by hand by clicking and dragging a box in the Zonation Model (similar to the manner in which you compose logs). After drawing the box around the area that you want to create a zone from, double-click the selection box to form the new zonation segment. The new segment will appear on the Zonation Model form, where you can review and fine-tune the segment settings. The Zonation Model form can also be used to create zones, instead of using the graphical interface, by specifying the start and stop depths for the zone. Like the Automatic approach, a lithology discriminator is applied to the entire zone when it is drawn to determine the lithology type of the zone, and runs vertically through the data.

Manual (inclined)  For inclined wellbores, an approach that applies a vertical lithology discriminator to your data may not make sense or may fail to produce an accurate lithology representation, due to the trajectory of the wellbore. To handle this, the Manual (inclined) mode allows you to draw custom lines through your data in the Zonation Model track. To create your interpretation, select the Manual (inclined) mode and begin by clicking in the track where you want to begin your custom line, then click to add turning points as you interpret down the data. A double click signals the end of the line. You can also click and drag the individual nodes to reposition them, if necessary. You may draw as many lines as needed. Note that if you draw or adjust a line so that it overlaps an existing line, the application will account for this and adjust the existing line to avoid the occurrence of an overlap. These custom lines serve as both the extent of the zone and the discriminator; a zone is created for each custom line you draw in the track. The image below exhibits and example interpretation of the discriminator line, and the corresponding zones that are created and defined on the Zonation Model form.