Mapping of alteration zones with seismic-amplitude data and well logs in the hard-rock environment of the Keefe Lake area, Athabasca Basin, Canada

Abstract

Optical televiewer (OTV) and full-wave sonic (FWS) data sets acquired in two boreholes from the Keefe Lake property of Atom Energy Inc. (AEI) provided a unique opportunity to study the lithologic units through analysis of P- and S-wave velocities and elastic rock properties derived from them (Poisson's ratio, lambda, and mu). This approach is a first attempt to describe petrophysical properties for the sandstone sediments and underlying crystalline Proterozoic rocks of the eastern Athabasca Basin. Wireline measurements penetrated through the entire (180-m) thickness of the basin fill and deep into the basement (357 m and 552 m), intersecting several fracture and alteration zones. Such zones are considered possible locations of uranium mineralization in the Athabasca Basin. Seismic attributes (amplitude envelope and cosine instantaneous phase) can be used in the hard-rock environment. The characteristic values of fracture and alteration zones can by analyzed by crossplotting the elastic properties derived from the FWS data. After insertion of the elastic-property logs into the closest seismic section, the probable spatial extents of three anomalous zones revealed in the vicinity of the boreholes are investigated. The results of amplitude-variation-with-offset (AVO) modeling carried out based on petrophysical properties obtained from the basement show that clay-filled fracture zones in the hard-rock environment of the study area are associated with increasing, anomalous AVO responses.