Harmonic pulse testing is a technology that has similar capabilities as conventional well testing. It intends to determine the hydraulic parameters such as storativity and transmissivity. In comparison with well testing, pulse testing requires more time due to the number of pulses required. The advantage, however, is that it can be employed during ongoing field operations. This makes it an ideal monitoring tool. An EGS stimulation operation was performed in Pohang, South Korea, with the purpose to monitor the seismicity and to locate the activated zone for further stimulation treatments and drilling operations. The purpose was not to increase substantially the injectivity but we employed harmonic pulse testing to demonstrate its feasibility for monitoring injectivity. Prior to the stimulation, a test was performed to obtain the baseline properties. Then, tests were performed during injection cycles with increasing rates and pressures, in order to follow the development of injectivity. The particular test showed a slight increase of injectivity during the stimulation treatment, which was mostly lost after completion of the test. However, the test does show the great potential of the method and has taught us the critical operational parameters. These include the pulse durations, the accuracy of the switching moment and sampling rate of pressures and injection rates.

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