Geomechanics · Module G5
Calibrating the Model
A mechanical earth model built only from correlations is a hypothesis. This module uses the measurements a well already has, formation pressure tests for pore pressure and leak-off or formation integrity tests for the minimum horizontal stress, to fit the model's free parameters. It covers pairing test depths with log samples, excluding doubtful points in the open, and reporting the misfit before and after.
- Level
- Intermediate
- Position
- Module 5 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
- What pressure tests and leak-off tests each constrain
- Converting test depths to true vertical depth
- Matching tests to log samples within a depth tolerance
- A least-squares fit of the Eaton exponent
- Fitting tectonic strain to leak-off data
- Depleted points, outliers and over-fitting
Learning outcomes
After the module you should be able to:
- Fit the Eaton exponent and tectonic strain to measurements and report the misfit.
- Report the misfit of a model before and after calibration
- Explain why a leak-off pressure is not the minimum horizontal stress
A short preview
Calibration is a fitting problem with a small, noisy data set. Suppose five sand pressure points exist and an uncalibrated model misses them by +0.6, +0.4, +0.7, +0.5 and −0.9 ppg. The first four agree that the model is off in the same direction, but the fifth comes from a sand that has already been produced and depleted. Keeping it pulls the fit towards a compromise that suits none of them; excluding it, with the reason written down, gives a model that honours the other four and a record a reviewer can check.
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.