Well logging methods in groundwater surveys of complicated aquifer systems: Bohemian Cretaceous Basin

Geophysical well logging methods (including borehole flow logging) can significantly contribute to a detailed understanding of hydrogeological conditions in basins with complicated sedimentary structure in studies undertaken to make optimal use of water sources, or to protect those resources from contamination. It is a common practice to delineate geological and hydrogeologic conditions at the scale used in geological maps and surface surveys. However, there is a need for more detailed descriptions of basin structure for many tasks related to water resources management and hydrologic research. This paper presents four specific examples of boreholes in complex hydrogeologic settings where useful information was provided by geophysical logging: (1) identification of large-scale upward cross-flow between aquifer horizons in an open borehole; (2) confirmation of continuous permeability throughout a long borehole interval; (3) identification of leakage into a test well via a defective casing joint; (4) evidence for downward flow in open boreholes; and (5) identification of permeable beds associated with water inflows during aquifer tests. These borehole geophysical measurements provide important information about the detailed lithological profiles of aquifers (especially in the absence of core), enabling the optimization of groundwater monitoring, resource use, and wellhead protection activities.