Identification of Fracture Zones in Geothermal Field Based on Microseismic Events

Abstract

This paper describes the identification of fracture zones in geothermal field based on microseismic events with see hypocenter distribution. An important step in hypocenter determination is how to determine the phases of P- and S-wave arrival times at all stations. In this study, we applied filtering techniques (i.e. band-pass and low-cut filters) to suppress noise and conducted S-transform analysis to improve the picking quality of unclear P- and S- wave arrival times. The initial locations of microseismic events were determined using the Geiger Adaptive Damping (GAD) method. We selected microseismic events with time residuals i.e. the difference between S-wave arrival time (ts) and P-wave arrival time (tp) less than 2 seconds. Our preliminary results show that the initial events are distributed in the central southwestern parts and northeastern parts of the seiemographic station network. The events seem to be more clustered in the same region at depths of 0-1 km below the mean sea level (MSL) in the central part, at depths of 0-2 km below MSL in the northeastern part and at depths of 0-8 km below MSL in the southwestern part of the station network. Epicenter distribution has a pattern which can be interpreted with predominantly NE-SW strike direction as shown by the rose diagrams. A major fracture is observed at depths of about 1200-1300 m. For future work, we will add more data coverage and conduct seismic tomography to determine 3D seismic velocity structure. We expect to be able to further improve the accuracy of the hypocenter relocation by using the resulting 3D velocity model and to identify detailed fracture zones in the study area.