Geomechanics · Module G4
Pore Pressure Prediction
Overpressure leaves a signature in shale: porosity stays higher than the burial depth would suggest, so sonic slowness and resistivity move away from their normal trends. The module shows how to fit a normal compaction trend on shale points only, how the Eaton ratio method and the Bowers effective-stress method convert the departure into pressure, and what these methods are blind to.
- Level
- Intermediate
- Position
- Module 4 of 8
- Video
- About 16 minutes, narrated
- Format
- Narrated video lesson with captions and slide reading view; with the certified option, a quiz whose pass unlocks the next module.
What the module covers
- Disequilibrium compaction and fluid expansion
- Fitting a normal compaction trend on shales only
- Eaton's method for sonic and resistivity
- Bowers' method and unloading
- Keeping pore pressure between hydrostatic and overburden
- Why depleted sands do not show on trend methods
Learning outcomes
After the module you should be able to:
- Read pore pressure from a fitted shale compaction trend, with method and limits stated.
- Fit a normal compaction trend and justify its depth window
- State the method and exponent behind any pore pressure curve
A short preview
Eaton's sonic method scales the gap between overburden and hydrostatic pressure by how far the shale slowness has moved from its trend. At 12,000 ft TVD, suppose overburden is 11,400 psi and hydrostatic pressure 5,580 psi. If the trend predicts 90 µs/ft but the shale reads 110, the ratio 90/110 cubed is 0.548, so pore pressure is 11,400 − 0.548 × 5,820 ≈ 8,210 psi, or 13.2 ppg. With an exponent of 2.5 instead of 3 the result falls to about 12.6 ppg, which is why the exponent needs calibrating against measured pressures.
Who it is for
Drilling, completion and reservoir engineers, petrophysicists and geoscientists who build or review pore pressure and wellbore stability predictions for well planning.
Prerequisites: None required; working familiarity with well logs helps. The hands-on steps use the Geomechanics workspace, available from the Professional plan.
Take the module in the Learning Hub
Geomechanics: Specialty course, sold separately: eight modules that build a calibrated 1D mechanical earth model from logs, from elastic properties and pore pressure to the mud weight window and its range. The lesson opens in the Learning Hub once the track is purchased; graded quizzes and the certificate come with the certified option.