What Logs Measure — and What Interpretations Add

What Logs Measure — and What Interpretations Add

Well logs are not “honest.”

They are influenced by borehole conditions, tool physics, environmental effects, and measurement limitations.

Washouts, standoff, invasion, mud properties, rugosity, and depth control all leave fingerprints on the curves.

What logs provide are physical measurements:
radiation, density, acoustic travel time, electrical response.

Porosity, saturation, and net pay are not measured.
They are interpreted.

Interpretation adds value — but it also adds assumptions.

Models translate physical measurements into rock properties.
Cutoffs translate continuous curves into discrete decisions.

Most petrophysics problems don’t start with bad equations.
They start when interpretations are treated like observations.

Remembering what the tools actually measured — and where interpretation begins — prevents most downstream surprises.