Reflection Imaging of EGS Reservoirs Using Microseimicity as a Source

Abstract

The authors have been developing a new variation of passive reflection technique, where microseismic multiplets are used as a source (multiplet reflection imaging using microseismicity: multiplet RIM). Closely similar waveform and precisely determined hypocenter of the multiplet can be effectively used to image structures inside/around the seismically activated EGS reservoirs. In the multiplet RIM, artifacts and blurred reflection image due to limited number of sources and detectors is suppressed by identification of relative/absolute time of arrivals of reflected phase from the multiplets and new concept of inversion.

The multiplet RIM has been applied to a data set collected at Soultz, France. The coherence index, which is a measure of arrival of reflected phase in the multiplet RIM, suggested that coherent reflected phase among the multiplets were successfully identified. The reflection image showed that there are possible reflectors at the bottom of shallow reservoir and surrounding zone. The index of reflectivity along a borehole at the site was consistent with results from FMI and PTS logging.