| Abstract |
Understanding reservoir processes is critical to managing geothermal reservoirs. Production and re-injection of the produced brine cause pressure, temperature, enthalpy, and fluid chemistry changes in the reservoir. Monitoring the chemistry of the liquid being produced is an important surveillance activity that can provide information about these changes. In the Awibengkok (also known as Salak) geothermal field, routine geochemistry monitoring is conducted on a quarterly basis. Liquid geothermometry allows the temperature of reservoir fluid to be estimated from the fluid chemistry, especially at initial-state conditions. Comparing initial-state chemistry with historical changes shows that liquid geothermometers do not continually represent actual reservoir temperatures. However, the trends given by both the cation and silica geothermometers can be used to understand the processes occurring in the reservoir during production. A comparison of the trends given by the silica and cation (Na-K-Ca) geothermometers was conducted in some wells at Awibengkok geothermal field. It was determined that the fluid temperature values diverged as the field is produced and, therefore, provide clues to the active reservoir processes present at specific times. From the preliminary evaluation of geothermometry trends, coupled with the historical time plots of enthalpy and reservoir chloride concentration, two main reservoir processes are believed to be active in the Awibengkok geothermal reservoir: boiling and injection breakthrough. |