Chemical and Physical Indicators of Reservoir Processes in Exploited High-Temperature, Liquid-Dominated Geothermal Fields

Abstract

Experience in the long-exploited Cerro Prieto (Mexico) and Ahuachapan (El Salvador) geothermal fields shows that monitoring changes with time of fluid flow, enthalpy, reservoir temperatures (from silica and cation geothermometers), and reservoir chloride concentrations, can clearly indicate physical and geochemical processes occurring in the reservoir and wells. These processes include coldwater entry, near-well boiling, reservoir-wide boiling, production of injectate, scaling in the wellbore or in the formation, and entry of fluid through casing breaks or defective joints. The observed fluid changes provide warning of short-term problems related to well maintenance and long-term problems, such as reservoir cooling or drying loss of liquid superheating of steam), in time to take appropriate corrective actions.