MODIFYING AMBIENT DISSOLVED OXYGEN LEVELS TO LOCATE INTERSECTING FRACTURES AND DETERMINE BOREHOLE FLOW CONDITIONS IN BEDROCK WELLS

Investigating the complex nature of flow conditions in wells drilled in fractured crystalline rock requires sophisticated equipment and significant financial resources. Transmissive fractures are typically identified by optical televiewer and flow meter measurements under ambient and pumping conditions. Alternative water quality methods require replacing the water column with deionized water, increasing electrical conductivity by salt spikes or using chemical tracers. The use of substances not inherent to ground water may mandate their subsequent removal, rendering these methods laborious, time-consuming and impractical to perform in formations used for drinking water. Applying these water quality approaches in residential areas may face scrutiny and disapproval from surrounding communities. A new approach to locate hydraulically active fractures and ascertain vertical borehole flow is presented that utilizes dissolved oxygen as a benign tracer. Dissolved oxygen levels are elevated by injection of compressed air. The movement and dilution of dissolved oxygen is monitored to characterize the flow conditions. The method has the ability to detect minimal borehole flow rates and inflowing fractures under ambient conditions. The outflowing fractures are located by elevating dissolved oxygen in conjunction with slug tests. The location of transmissive fractures revealed by the method in two bedrock wells is in very good agreement with televiewer logs and heat-pulse flow meter measurements. The approach has proven to be effective, time-efficient and inexpensive. As such, the method is a promising alternative to conventional methods currently in use.