Assessing attenuation, fractures, and anisotropy using logs, vertical seismic profile, and three-component seismic data: heavy oilfield and potash mining examples

Zimin Zhang

ABSTRACT

Integrated geophysical studies in two areas (the Ross Lake heavy oilfield, Saskatchewan, and a Saskatchewan potash mine) are described in this thesis. Multicomponent seismic processing and interpretation, rock physics modeling, and well log analysis are carried out to develop detailed descriptions of a heavy oil reservoir and fractures which can pose problems in potash mining.

In the Ross Lake oilfield, the VSP data provide a reliable time-depth correlation, image around the borehole, and real amplitude AVO gather for delineating the sand channel reservoir. The relationship between seismic wave attenuation and rock properties is investigated for shale and sandstone using zero-offset VSP data. Interval Q values from VSP data for the P wave and shear wave correlate interestingly with petrophysical variables. Q values increase with P- and S-velocities and decrease with Vp/Vs and porosity. Shaly sandstone shows more attenuation than pure shale and sandstone.

Simulation of fractures in the rocks overlying the potash ore displays a significant velocity decrease and anisotropy for both P- and S-velocities. Seismic interpretation of the time-lapse 3C-3D surveys indicate noticeable amplitude changes and push-down effects at the Dawson Bay Formation and underlying formations in 2008 survey compared with 2004 survey, especially on radial data. Vp/Vs and seismic curvature attributes also outline the fractured zones. The analysis on anisotropic modeling seismic data suggests that by searching for seismic anisotropy, shear-wave splitting on the multicomponent seismic data, we may also be able to delineate the fracture orientation and intensity in the potash mining area.

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