Pore Pressure module
Purpose
The Pore Pressure module enables users to calculate the pore pressure in the shale intervals using the Eaton sonic and resistivity methods. Pressure can be calculated as either instantaneous or accumulated.
Primary Outputs
The following curves are the primary interpretations made in this module.
| Curve Name | Description |
|---|---|
| PORE_PRESSURE_FINAL | Pore pressure via selected method |
| OVERPRESSURE | Pressure above hydrostatic |
| HYDROSTATIC | Hydrostatic pressure |
| OVERBURDEN | Lithostatic pressure |
Discussion
The user has options for entering the hydrostatic and lithostatic pressure gradients. Lithostatic will preferably be calculated from the density curve if available. These two curves are useful calibration points and are displayed in the pressure track.
The Vclay Cutoff parameter allows the user to set what is considered “clay” for the purposes of the Eaton methods, which only calculate pore pressure in clay-rich intervals. Everything greater than or equal to the value will be used for calculations and will be highlighted in red on the Vclay track.
The Final Pore Pressure Method allows the user to select which results will be used when calculating overpressure and when moving into the Geomechanics and 1D Geomechanical Earth Model modules.
The parameters for the Eaton and Modified Eat methods are available for each method.
The results are all shown on the second track from the right along with the hydrostatic and lithostatic pressures. The Overpressure curve is a composite of the hydrostatic pressure gradient and the overpressure from the final pore pressure method, if present.
Users should keep in mind that:
- When evaluating pore pressure it is important to ensure that you are able to match the hydrostatic pressure in zones that are not suspected to be overpressured. This is a valuable anchor point.
- The Eaton methods should only be applied to shales. The Eaton resistivity method almost always underestimates pressures in organic shales because of the excess resistivity due to hydrocarbon presence.
- Pore pressure can either be calculated as accumulated or as instantaneous - there are use cases for each.
Here is an additional tutorial video.
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