Geothermal re-injection performance evaluation using surveillance analysis methods

Re-injection, the key factor in the success or failure of a geothermal field, is an integral part of any geothermal field development. Modified Hall integral - derivative plot and Hearn plot are analytical injection surveillance methods that may be used to identify sub-par injection behavior due to problems such as scaling. Plotting injection volumes and pressures in an appropriate format along with operating injection well pressure gradients may highlight significant changes in geothermal injection well behavior. Uses and advantages of each method is discussed using data collected from liquid dominated Alasehir geothermal field located in western Turkey. Injection performance of four different injection wells were evaluated using Modified Hall integral - derivative and Hearn plots. After acidizing operations, Hall derivatives of these wells fall below the Hall integral lines showing improved injectivity. It has been also observed that addition of new wells affected Hall plot such that an increase in the Hall slope is observed indicating a decrease in transmissibility and/or an increase in skin. This decrease is possibly related to limited volume of the fracture system constraining the injectivity. Similarly, when a booster pump was implemented to increase the injection pressure Hall derivatives of almost all injection wells moved above the Hall integrals except for the one with the booster pump. Addition of booster pump does not show its expected effect in Hearn analysis compared to that of combined Hall integral and derivative analysis. It was concluded that the modified Hall approach is superior to the Hearn method because when Hall derivative is used in tandem with the Hall integral, it provides unambiguous diagnosis of an injection well's performance status.