Microseismic Reflection Imaging of Stimulated Reservoirs and Fracture Zones

In this work we present an approach which uses waveforms from induced seismicity to build a detailed high resolution image of a stimulated reservoir. The idea of Microseismic Reflection Imaging (MRI) is to treat a located microseismic event as an active seismic source and to apply migration techniques adapted from reflection seismics. To image microseismic reflection data we perform a number of preprocessing steps and use a directional migration approach. To obtain polarization of reflected waves, we consider auto- and cross-variances of a seismogram within a time window. We also apply a hodogram linearity threshold as a criterion to exclude parts of seismograms with unreliable polarity estimates. The MRI approach is applied to the data from the stimulation of EGS at Basel, where microseismic waveforms were recorded at 6 shallow (about 200 m) and the deep (2.5 km) receivers. We show separate images of PP and SS reflections for different receivers. Finally, we provide a joint interpretation of obtained images and event locations. We discuss how microseismic reflection imaging can complement to surface seismic imaging, what the reflectors in microseismic reflection image can tell us about the stimulated reservoir and how these images can contribute to the reservoir characterization.