Coupled Geomechanics

Pressure Carries the Overburden

Flow and rock mechanics are coupled. The fluid pressure helps the rock frame carry the overburden, so as the reservoir depletes the effective stress $\sigma' = \sigma - P$ on the grains rises.

Permeability Closes First

The grains compact: porosity drops a little, but permeability, which lives in the narrow pore throats, drops a lot, often exponentially with stress, $k = k_0,e^{-\gamma,\Delta\sigma'}$. The reservoir throttles its own flow as it produces.

Compaction and Subsidence

The same compaction can reach the surface as subsidence, with famous cases at Ekofisk and Wilmington. A coupled simulator solves the stress and the flow together rather than holding the rock rigid.