Blocking Well Logs

From Centimetres to Metres

A log records facies every fifteen centimetres or so, far finer than a grid cell is thick. Before the log can condition the model it has to be blocked, or upscaled: each cell takes a single facies derived from the many log samples within it, usually the one that is most common.

The Cost of Coarsening

Majority blocking keeps the bulk facies right, but any bed thinner than a cell is outvoted and vanishes. The blocked net-to-gross then drifts from the true log value, and the drift grows as the cells get thicker. The widget shows thin sands disappearing as you coarsen the cell.

Resolve What Carries Flow

The real danger is that a thin but continuous high-permeability streak can dominate flow yet be erased by blocking, leaving the model to misjudge connectivity. The cell thickness has to resolve the beds that matter. Blocking is the bridge from log scale to model scale, and getting it wrong starts the model off biased.