Theory 31/Earth, Climate & Energy /Geothermal energy
Geothermal Fades by Permeability
Decline is modelled as heat depletion. The wells may be clogging.
Geothermal output declines because permeability falls as the reservoir cools and minerals precipitate, so sustainable extraction rate is set by a critical flow above which permeability damage outpaces heat extraction.
01The evidence
Geothermal fields show output decline that is faster than heat depletion alone predicts, and decline correlates with flow rate.
02The tension
Models treat the reservoir as a heat exchanger and predict decline from thermal drawdown, which misses the permeability feedback.
03The mechanism
Cooling water dissolves and reprecipitates minerals, and the precipitation clogs pore throats. The rate depends on flow, because flow delivers the supersaturated fluid.
That makes flow rate the control, and predicts an optimum below which heat extraction dominates and above which clogging does.
04What this is not
Those models predict from heat. This predicts from permeability, which explains faster-than-thermal decline.
05Predictions
- P1Decline should track flow rate.
- P2An optimum flow should exist.
- P3Permeability should fall faster at high flow.
06Refutation
Decline tracking thermal drawdown at controlled flow would restore the heat model.
07What it changes
It would change how geothermal fields are operated.