Self-Potential Anomaly Changes at the East Mesa and Cerro Prieto Geothermal Fields

Abstract

Repetitive self-potential (SP) surveys recently completed, over two producing geothermal fields, Cerro Prieto and East Mesa, ten years after the original surpleted over two producing ge veys gave us an unprecedented oppormnity to see whether SP changes over the fields are dated to pnssure gradients associated with massive fluid movements; is., production, injection and natural recharge. A strong cornlation between SP and production was observed at Cerro Prieto where the anomaly position has shifted eastward, and where we were able to model the new anomaly on the basis of actual production rates and the hydrogeology. On the other hand, we were unable to explain the East Mesa anomalies on the basis of what we presently know about production rates and the hydrogeology of that system.