Focused packer testing using geophysical tomography and CCTV in a fissured aquifer

Double packer testing is a commonly used technique in hydrogeology for assessing vertical spatial variations of permeability in a borehole. In fractured rock systems, spatially continuous fractures are typically major transmissive features that control groundwater flow and solute transport. Efficient, cost-effective packer testing of fractured rock aquifers can be conducted by focusing the packer test on hydraulically conductive zones, defined using borehole geophysical techniques. The combined use of cross-borehole electrical imaging and borehole television (CCTV) as methods for focusing the packer test was applied to a limestone aquifer. CCTV identified features exposed in the borehole whereas Electrical Resistivity Tomography (ERT) revealed their spatial continuity and probable hydraulic significance. Whole borehole pumping tests were conducted to provide a check on the effectiveness of these methods as tools for guiding the packer test. Results from a set of boreholes in a fissured aquifer revealed the transmissivity estimates obtained from the whole borehole pumping test to be close to the sum of transmissivities obtained from focused packer testing of features identified using CCTV and ERT. The hydraulic properties of the aquifer were hence defined whilst avoiding intensive packer testing of the entire length of the boreholes.