Seismic detection of cracks in carbonates associated with potash mining

Zimin Zhang, Robert R. Stewart

Brine inflow in a mine, resulting from cracks or fractures in overlying strata, can be a significant problem. This report investigates whether cracked or fractured rock, associated with potash mining in western Canada, might be detectable by multi-component seismic methods. Rock physics modeling was carried out to simulate cracked rocks overlying a potash ore zone. The Kuster-Toksz procedure modeled randomly distributed cracks while Hudson's formulation was used for aligned cracks in a carbonate interval (the Dawson Bay including the Second Red Bed Shale) overlying the Prairie Evaporites. We find that cracked rocks can display a significant velocity decrease for both P- and S-velocities. For aligned cracks, velocity anisotropy was also observed. Synthetic seismograms for these cracked media show some character change (time shifts, amplitude variation with offset) compared with uncracked responses. The results provide promise for the detection of cracked rock using multi-component seismic data and repeated surveys.