关键词：
Hydrogeological properties
Sedimentary diagenesis
Geophysical methods
Paleocene
Canada
摘要：
The Paskapoo Formation is the primary groundwater supply in the province of Alberta, Canada. Fluvial sandstone channels form effective aquifers, although lateral continuity and yield can vary significantly over short distances. Borehole cores and geophysical logs from adjacent non-cored boreholes drilled in the Fox Creek area, at the northern edge of the Paskapoo Formation domain, enabled identification of intervals of friable sandstone with intervening tightly cemented sandstone. The combination of specific geophysical logs reveals the presence of highly cemented sandstone, which acts as a barrier and focuses groundwater circulation within permeable sandstone carrier beds. Multi-stage carbonate diagenesis, involving dissolution and precipitation in the presence of groundwater has generated the main physical properties of the aquifer. The sandstone is composed of quartz with feldspars and fragments of volcanic and carbonate rocks. Two types of porosity are recognized: primary depositional and secondary dissolution. The latter results from significant local dissolution by acidic groundwater of feldspars, volcanic rock fragments and carbonates. Within the secondary pores, various volumes of calcite cement can be present. delta O-18(VPDB) and delta C-13(VPDB) ratios indicate the cement has precipitated from groundwater with HCO3- derived from the dissolution of Paleozoic carbonate particles. The correlation of petrophysical core data with geophysical logs indicates that low permeability calcite cemented beds are characterized by a significant increase in values of resistivity, density and velocity, and elevated reflectivity in acoustic televiewer logs across sub-meter to meter-thick beds. Porosity logs derived from density logs correlate well with measured core porosity and provide complete vertical porosity profiles.
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