A multicomponent, time-lapse investigation of fractures in a potash mining region.

Andrew Nicol and Don C. Lawton

ABSTRACT

Time-lapse seismic analysis is used to monitor changes in the subsurface which occur in between the acquisition of the baseline and monitor surveys. In this study, the analysis of two multicomponent seismic vintages is conducted in order to monitor any fracture-induced changes to the seismic anisotropy in a potash mining region. The Dawson Bay Formation, a fractured carbonate which unconformably overlies the Prairie Evaporite Formation, which contains significant potash ore deposits, is the focus of this study. The two vintages of PP and PS volumes were divided into four sub-volumes consisting of a stack containing a 45 degree aperture of source-receiver ray paths. The azimuthal time difference plots created from the PP seismic data show travel-time differences running parallel to the edges of the highest density mine workings. Seismic interpretation and Vp/Vs analysis suggest that random fracturing is present in the subsurface, and is creating a significant low velocity anomaly observed as an increase in travel-time in the PP and PS volumes, while exhibiting a low amplitude effect in both vintages of the PP volumes.

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