Tornado Charts

What Drives the Range

Monte Carlo gives the range; the tornado chart says what causes it. Each input is swung to its low and high case while the others stay at base, and the resulting span of STOIIP is drawn as a bar. Sorting the bars longest at the top down gives the tornado shape.

Target the Widest Bar

The longest bar is the input the volume is most sensitive to, the one that dominates the uncertainty. That is where effort pays off: an appraisal well, a better seismic inversion, or a core measurement that narrows that input shrinks the whole range the most. Narrowing a short bar barely moves the answer.

The Ranking Can Change

The ranking depends on how uncertain each input is, not just on how the equation responds. Tighten the porosity range in the widget and its bar pulls in, and once it is small enough another input takes over as the top driver. Tornadoes are recomputed as appraisal reduces uncertainties, redirecting effort to whatever dominates next.