Characterizing the declining CO2 emissions from Turkish geothermal power plants

Turkish geothermal fluids have substantially higher carbon dioxide content due to the unusual geologic setting of the geothermal fields in the country. Typical emission factors at power plant commissioning range from 1,000 to 1,300 g/kWh that is almost 10 times higher than the global average emission factor for geothermal projects of 121 g/kWh. Despite unusually high initial CO2 emission factors most, if not all, Turkish geothermal power plants have experienced gradual decline of CO2 emission with time based on available data. Declining CO2 emissions from 13 Turkish geothermal power plants located at Büyük Menderes and Gediz Graben are systematically investigated using geothermal power plant and well data. The average emission of these GPPs is 595.92 CO2 /kWh respectively, which is significantly lower than 2015 average (887 g/kWh). Simple predictive models based on decline curve analysis (DCA) of the CO2 emission data collected from several geothermal power plant developers that allow prediction of CO22 emissions from geothermal power plants over the project lifetime are developed. The DCA method provides a good fit of the CO2 emission data for geothermal power plants and the CO2 production data for individual wells. Using DCA models future CO2 production rates of wells and geothermal power plant emissions located were estimated. It has been observed that the declining CO2 content of the fluid is linked to degassed brine that is reinjected into the reservoirs; however, due to lack of chemical and tracer test data it is not possible to confirm such hydraulic connections except for some fields. The rate of the decline is different between different power plants depending on the size of the geothermal field and the degree of hydraulic connection between injectors and producers. The emission decline rate of power plants changes from 5.59% to 9.99% per year