Modelling fluid replacement
In Amplitude vs. Offset modelling, as seismic waves reflect off an interface, the amplitude of the reflected wave is affected by the amount and type of fluid that occupies the pore space of the rock.
GeoSyn applies Gassman's equation to model this using a P sonic, shear sonic, and density log. You change the water saturation to apply different scenarios to your model. The available pore space not saturated with water is assumed to contain oil and gas.
Click for in-depth details on how fluid replacement modelling is implemented in GeoSyn.
To model fluid replacement:
1. From the Edit menu, select Log editing (
).
OR
Double-click the log
OR
Right-click the log and select Log editing.
The Log Editor
dialog box opens.
2. In the toolbar
beside the Log Editor,
click the Fluid Replacement Modelling
tool (
).
The Fluid Replacement Wizard (Input and output logs, depth range)
dialog box opens.
3. GeoSyn automatically populates the Input logs and Output logs drop-down lists if the required logs are available in your model; otherwise, click Create Missing Log Types to display the Generate Logs for Well... dialog box and select the log types to create, and then click Create after noting the following:
Click the log types to create in the left column and ensure Maintain link check box is cleared so that changes made to the derived log aren't overwritten by the parent log.
Click Edit to the right of a log type to display the Edit the Derivation Equation for Log dialog box and modify the equation used to derive the log.
Click Duplicate Key Logs to create exact copies of existing logs in your model for the input logs. You might do this if you want to keep a pristine copy of the original logs.
4. Click Next.
The Fluid Replacement Wizard (In-situ
reservoir properties)
dialog box opens.
5. Using the image in the top-left of the Matrix and Pore Fluids tabs, click to place the white circle in the mineralogy and pore fluid zones that most closely define the rock properties in the subsurface.
Click Workshop to display either the Minerals Calculator or the Batzle and Wang Fluid Properties Calculator dialog boxes and select criteria more specific to your zone of interest.
6. Click Next.
The Fluid Replacement Wizard (Calibrate shear log for water saturations < 100%) dialog box opens if the water saturation defined using the previous dialog box is less than 100%. This option compensates for the fact that the shear log is frequently derived from a sonic log using Castagna's formula. Castagna's formula requires a correction when gas is present in the zone of interest. Select the check box and click Next.
The Fluid Replacement Wizard (FRM
Modelling: Set new water saturation)
dialog box opens.
7. Ensure the above
dialog box doesn't overlap the Log
Editor displaying the well for which you're modifying water saturation,
and then using the Log Editor, drag the mouse to select the area of interest as depicted below.
The Depth Range fields are updated in the Fluid Replacement Wizard.
To define the area of interest using formation tops instead, click Tops to display the Depth Range from Tops dialog box, where you select the top and bottom formations for the zone.
8. Click the thumbnail or drag the green circle to the desired fluid composition and then click Close to complete the wizard and apply the changes.