Ted Dean writes about finding drilling targets with electrical resistivity imaging.
For example, Figure 6 illustrates a resistivity section from a community in the Blue Ridge province of Virginia. It is notoriously difficult to find high-yielding wells in the metamorphic rocks of the Blue Ridge. Twelve wells had previously been drilled in the community, several of which had been sited by a geologist using fracture trace analysis alone. Only six wells yielded sufficient water to bring into production, with yields ranging from 13,000 to 40,000 gallons per day (9 to 28 gpm). We conducted our own fracture trace analysis and suspected a topographic feature to be a fracture zone. We conducted electrical resistivity imaging and confirmed the topographic draw as a fracture zone as evidenced by vertical low-resistivity feature coincident with the valley. We recommended drilling on this feature, which resulted in a well yielding 114,000 gpd (79 gpm), almost three times the best yielding well located by fracture trace analysis alone.