Investigation of Factors Affecting the Hydraulic Conductivity of a Fractured Sandstone
Abstract
An understanding of groundwater flow is essential in many aspects of mining. This is especially true for the sandstones of the Manitou Falls Formation, which overlie uranium deposits in the Athabasca Basin of northern Saskatchewan. Experience has shown that the hydraulic conductivities of these sandstones can be relatively high, especially in zones containing natural fractures, thus leading to potentially problematic groundwater inflow rates. This thesis presents the results of a study of hydraulic conductivity of the Manitou Falls Formation, in which detailed core logging and laboratory testing were undertaken for samples from two boreholes at the McArthur River mine site. Results from the logging and laboratory testing were interpreted in context provided by multiple packer tests conducted in these boreholes. Through core logging, indicators of conductive zones were identified. These indicators include fracture orientation (sub-vertical fractures were found to have more of an impact on conductivity than horizontal fractures), infilling, and staining. The laboratory testing program involved the measurement of hydraulic conductivities of fractured core samples across a span of effective confining pressures representative of in-situ conditions. Changes in fracture aperture were simultaneously recorded at each confining pressure level. It was found that theoretical relationships between aperture change and fracture conductivity represent the observed behavior of the samples reasonably well when fracture roughness is accounted for. The laboratory testing also confirmed the effects of fracture staining and infilling on hydraulic conductivity inferred from core logging and packer testing results.
The results provide insights into the mechanisms underlying flow in fractured intervals of the Manitou Falls Formation, and provide guidance for selecting intervals to investigate during future packer testing in this formation.