Hydrostratigraphic characterization of intergranular and secondary porosity in part of the Cambrian sandstone of the cratonic interior of North America: improving predictability of hydrogeologic properties.


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February 2006


The Upper Cambrian interval of strata in the cratonic interior of North America has a long history of inconsistent hydrogeologic classification and a reputation for marked and unpredictable variability in hydraulic properties. We employed a hydrostratigraphic approach that requires hydraulic data to be interpreted within the context of a detailed characterization of the distribution of porosity and permeability to arrive at a better understanding of these rocks. As a first step, we constructed a framework of hydrostratigraphic attributes that is a depiction of the spatial distribution of both rock matrix and secondary porosity, independent of hydraulic data such as pumping-test results. The locations of hundreds of borehole geophysical logs and laboratory measurements of rock sample matrix porosity and permeability were mapped on detailed (mostly 1:100,000 or greater), conventional, lithostratigraphic maps. Stratigraphic cross-sections, based on hundreds of natural gamma logs and thousands of water-well records, have provided a markedly improved depiction of the regional distribution of rock matrix hydrostratigraphic components. Borehole, core and outcrop observations of secondary porosity were also tied to detailed stratigraphic sections and interpolated regionally. As a second step, we compiled and conducted a large number of hydraulic tests (e.g., packer tests and borehole flowmeter logs) and analyzed thousands of specific capacity tests (converted to hydraulic conductivity). Interpretation of these data within the context of the hydrostratigraphic attributes allowed us to produce a new hydrogeologic characterization for this stratigraphic interval and gain important insights into geologic controls on hydraulic variability. There are a number of assumptions inherent in most previous hydrogeologic investigations of these strata, such as equivalency of lithostratigraphic and hydrogeologic units and the dominance of intergranular flow in sandstone, that are not consistent with our results. A particularly importa


Bedding-Plane Fractures, Groundwater, Sandstone, Dual Porosity, Hydraulic Conductivity

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Sedimentary Geology, Vol. 184, no. 3-4 (2006-02-15).