Pore Pressure Predictor (Eaton)

Predict formation pore pressure using Eaton's empirical method from sonic or resistivity logs. Calculate overpressure, equivalent mud weight (EMW), and visualize pressure vs depth relationships. Essential for well planning and drilling safety.

Eaton Method Pore Pressure Overpressure Well Planning

Input Parameters

Prediction Method

Eaton exponent: n = 3.0 for sonic

Measurement Depth

m
Depth of pressure prediction point

Sonic Log Data

m/s
Measured sonic velocity at depth
m/s
Expected velocity from normal compaction trend

Pressure Gradients

MPa/km
Typical: 22.6 MPa/km (1.0 psi/ft) for sediments
MPa/km
Typical: 10.05 MPa/km (0.44 psi/ft) for freshwater

Quick Scenarios

Results

Theory & References

Eaton's Method

Eaton's empirical relationship predicts pore pressure from deviations in log properties from normal compaction trends:

Sonic (velocity):

PP = σv - (σv - Pn) × (Vobs/Vnorm)3

Resistivity:

PP = σv - (σv - Pn) × (Robs/Rnorm)1.2

Where:

  • PP = Pore pressure
  • σv = Overburden stress
  • Pn = Normal (hydrostatic) pressure
  • Vobs, Robs = Observed values
  • Vnorm, Rnorm = Normal trend values

Normal Compaction Trend (NCT)

The NCT represents expected log values under normal pressure conditions. Key points:

  • Establishment: Define NCT from normally pressured shales in offset wells or shallow section
  • Velocity NCT: Typically increases with depth due to compaction
  • Resistivity NCT: Increases with depth as porosity decreases
  • Deviations: Underpressure → faster velocity, higher resistivity
  • Overpressure: Slower velocity, lower resistivity than NCT

Typical Exponents:

  • Sonic: n = 3.0 (most common)
  • Resistivity: n = 1.2 (for shales)
  • May vary by basin - calibrate to offset wells

Applications & References

Applications:

  • Well Planning: Predict pressure before drilling
  • Mud Weight Design: Calculate required EMW
  • Casing Points: Identify pressure transition zones
  • Real-time Monitoring: Update predictions while drilling
  • Wellbore Stability: Assess collapse/fracture risks

References:

  • Eaton, B.A., 1975, The equation for geopressure prediction from well logs: SPE 5544
  • Bowers, G.L., 1995, Pore pressure estimation from velocity data: Offshore Technology Conference, OTC 7630
  • Zhang, J., 2011, Pore pressure prediction from well logs: Petroleum Industry Press