Fault Modeling and Sealing

Seal or Leak?

A fault is not simply a barrier or a conduit; it can be either, and the answer controls whether the reservoir drains as one tank or several. The first control is juxtaposition: what the throw places against what across the fault plane. Where a permeable sand is thrown against another sand, fluids can cross, a leak window. Where sand is thrown against shale, the fault seals. Slide the throw in the widget and watch the seal-and-leak pattern along the fault change.

Shale Gouge and Smear

Juxtaposition is only the start. Even sand against sand can seal if shale has been smeared into the fault zone as the rock slipped. The shale gouge ratio (the proportion of shale in the interval that has slid past a point on the fault) estimates this: a high shale gouge ratio means a clay-rich, sealing fault. These estimates become a fault transmissibility multiplier, a number from zero (fully sealing) to one (open) applied to flow across the fault in the simulation.

Why It Matters

A sealing fault splits the reservoir into compartments that must each be drained by their own wells; a leaking fault lets them share. Mistaking one for the other is among the most expensive errors in field development, because it changes how many wells are needed and how the pressure behaves. Fault modeling is where the static framework first carries a dynamic consequence.