Using Microseismicity to Image the Structure of the Basel Geothermal Reservoir

We apply our microseismic imaging approach to waveforms recorded during and after the stimulation of the Geothermal Reservoir below Basel, Switzerland (2006). Firstly, the hypocenter of the microseismic events is precisely located. Secondly, these events are treated as a "pseudo-active" seismic sources and the reflections within the recorded wavefield are processed by using a directional migration algorithm in order to construct a high resolution image of the illuminated subsurface region. Since the number of the located events is much larger than the number of sensors we swap sources and receivers. Thus, one can consider the system as several "sources" and a cloud of spatially distributed "receivers". We obtain two images from two different downhole sensors. The first one is a large scale fault system in the vicinity of the injection borehole which is compared to the existing results. Second one is a high resolution image of the microseismic cloud interior. There are several reflectors which can be associated with the first and second order cracks revealed in the vicinity of the injection well open hole interval. The strongest reflectors in the image consistent with cracks orientation in the borehole.