An extensive program of tracer tests has been carried out to monitor the performance of the production/injection scheme in the Awibengkok geothermal field. Initially, tests using fluorescein dye were conducted in almost all of the 20 wells used as injectors. These tests yielded excellent data detailing the timing and direction of injectate flow, indicating strong lateral permeability and depth controls. It became clear, however, that fluorescein, even after application of the published thermal decay corrections, was not behaving conservatively as a tracer. While fieldwide bulk chloride mass balance calculations required first year injectate returns averaging 30%, the average fluorescein recovery, corrected for thermal decay, was only around 3%. In response to this the family of naphthalene sulfonate (NSA) tracers was employed to try to acquire more conservative tracer recovery data. Results from four recent tests using these tracers showed returns in the same production wells and same first arrival times as the fluorescein tests. Recovered concentrations are on average about eleven times as high as in the fluorescein tests. This is generally consistent with chloride mass balance and suggests that the NSA tracers are giving us the best overall quantitative view of injectate flow and recovery in the field.

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