Fracture Zone Characterization by Quantitative Analysis of Reflected Phases from Microseismic Waveform data
A. Oelke, S. Gutjahr, J. Kummerow, A. Reshetnikov, H. Asanuma, M. Häring and S.A. Shapiro
Event name: 78th EAGE Conference and Exhibition 2016
Session: Microseismic Event Detection and Analysis
Publication date: 31 May 2016
Info: Extended abstract, PDF ( 1.38Mb )
Price: € 20
Microseismic waveform data can provide detailed information on reservoirs. In our work, we re-process recordings of selected microseismic events from the geothermal reservoir Basel-1, in order to better characterize the reservoir. Coherent reflected phases are identified by clusterwise analysis of the waveforms, since clustered events illuminate structures in a similar way. Applying the Fresnel Volume Migration to several clusters, we image zones of high reflectivity in the vicinity of the borehole. From the ratio of reflected to direct wave, we assign a value of apparent reflectivity to each imaged reflector. Correcting for effects due to different ray paths of direct and reflected waves, we map the estimated reflection coefficients. Comparing the estimated values to the frequency- and angle-dependent reflection coefficient at a single fluid layer, we map the fracture width. Some of the reflectivity values indicate complex fluid-filled fractured zones, rather than single fractures. Under linear slip condition, a value for the normal compliance of the reservoir can be determined. In the Basel reservoir, we observe reflection coefficients of about 0.1, which means effective fracture widths in the range of centimeters.