Abstract

Understanding aquifer architecture is critical for managing groundwater resources in western Canada. Recent regulations have yielded abundant new gamma-ray well-log data from the principal aquifer in Alberta, the Paleocene Paskapoo Formation. A major obstacle to utilizing this data is the fact that gamma-ray measurements in the shallow subsurface are made through surface casing, which suppresses gamma-ray readings and effectively prohibits stratigraphic characterization. Here we describe and demonstrate a relatively simple and efficient method for normalizing gamma-ray data from stratigraphic horizons that are behind surface casing and apply this method to the Paskapoo Formation in west-central Alberta. The gamma-ray normalization procedure adjusts the cased gamma-ray values so that high and low percentile values of the resulting gamma-ray statistical distribution are equal to those of the non-cased values. The effectiveness of this procedure is demonstrated by comparing the normalized gamma-ray values from cased intervals with those from nearby wells without casing. Good matches between these wells, as well as the transition between normalized curves at the base of cased zones and the gamma-ray curves at the uppermost portion of uncased zones, suggest this methodology is effective for studying the Paskapoo Formation. The normalized curve allows cased and uncased intervals to be correlated, enabling improved stratigraphic characterization and mapping of fluvial sand bodies behind surface casing. This new data provides the framework for better characterization of aquifer dimensions and the derivation of stratigraphic parameters used to constrain hydrogeological models and enhance groundwater recovery.

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