Modifying Borehole Dissolved Oxygen Levels as a Tool in Deciphering Fracture Flow Conditions

This research was undertaken to develop new low-cost methods that use elevated dissolved oxygen (DO) as a means to characterize fracture flow conditions in bedrock wells. The low background DO levels were elevated by two wellbore aeration systems designed in the study. Subsequently, the wellbore DO was profiled under ambient conditions or during a slug test which simulated pumping conditions. The method successfully located transmissive fractures under ambient and stressed (slug test) conditions. Changes in DO concentration with time were used to estimate wellbore flow rates. The results from tests conducted in two fractured crystalline wells compared favorably with previously performed geophysical logging and flow meter tests. The method presents a promising low-cost alternative to geophysical characterization methods. Additionally, the use of elevated DO to decipher the connectivity between two fractured bedrock wells was evaluated in a series of pumping tests. However, the method did not provide definitive information and requires further testing. The DO borehole tracer method developed in this study would be particularly useful over other chemical tracers in wells used for drinking water where issues of toxicity arise