Saturation-Height on the Ogbon-1 Well
Learning objectives
- Lay the saturation-height model beside the log Archie Sw on the Ogbon-1 well
- See the model reproduce the logged saturation in the clean pay
- Recognize that a blind by-height model fails in the shale streaks
- Apply the saturation-height function per rock type, not by depth
The Model Meets the Log
The chapter ends by laying its product beside the logs. Chapter 7 produced a measured water saturation from the deep resistivity and Archie; this chapter produces a predicted one from height above the free-water level, with no resistivity at all. On the Ogbon-1 well the two are drawn in the same track, foot for foot.
Triumph and Caveat
In the clean oil sands the two curves lie exactly on top of each other: the saturation-height model reproduces the logged saturation foot for foot. That coincidence is the license to carry the model away from the well, into the inter-well volume where no resistivity exists, which is the whole reason the chapter built it. But applied blind, by height regardless of rock, the model predicts oil in the shale streaks the shale cannot hold, reading low where the logs read full water. Mask it to net reservoir and the two agree throughout.
The Lesson
The saturation-height function is a law per rock type, not a depth-only formula. It belongs to the reservoir rock the J-function calibrated; pointed at shale it is meaningless. Used correctly, one per rock type applied within net reservoir, it turns a handful of capillary-pressure cores into a field-wide saturation model, closing the loop from the pore throat of the first section to the reservoir volume the engineer will simulate.
References
- Worthington, P. F. (2002). Application of saturation-height functions in integrated reservoir description. Geological Society Special Publication, 215.
- Asquith, G. and Krygowski, D. (2004). Basic Well Log Analysis, 2nd ed. AAPG Methods in Exploration 16.