Characterizing fractured-zone flow using numerical flow-log models

Water-quality monitoring and hydraulic testing in fractured bedrock aquifers involves two important tasks: 1) identifying the hydraulically active fractures intersecting the borehole, and 2) inferring how the specific entry or exit ports in the borehole wall are connected to large-scale flow paths in the region surrounding the borehole. Effective characterization of fractured bedrock flow results when hydraulically active fractures and fracture zones are first identified using flow logs, and then the hydraulic properties of these active zones are given by subsequent hydraulic tests. A more difficult technical problem is relating the hydraulic properties of the few specific fractures that serve as borehole entry ports to the large-scale hydraulic properties of the surrounding rock mass. This problem is addressed through a generalized borehole flow model inversion formulated so that the boundary conditions at the outer edge of the boundary layer can be inferred from the properties of measured borehole flow.