A tracer methodology for identifying ambient flows in boreholes

Area of Science:

• Hydrogeology
• Environmental Science
• Geophysics

Background:

• Characterizing aquifer properties requires understanding water movement within boreholes.
• Identifying vertical flow, inflow, and outflow depths is crucial for groundwater resource management.
• Conventional logging methods may not always detect all hydraulically active fractures.

Purpose of the Study:

• To demonstrate the efficacy of Single Borehole Dilution Tests (SBDTs) for identifying vertical flow and fractures.
• To establish SBDTs as a simple, cost-effective field method for hydrogeological investigations.
• To determine the location and rate of water inflow, outflow, and cross-flow within boreholes.

Main Methods:

• Computer simulations were employed to model tracer profile patterns under various flow conditions.
• Field tracer tests utilized saline tracers, applied both continuously and at specific depths.
• Single Borehole Dilution Tests (SBDTs) were conducted under natural hydraulic head conditions.

Main Results:

• SBDTs successfully identified flowing fractures at the boundaries of vertical flow sections.
• The method detected changes in vertical flow rates and pinpointed depths with consistent tracer concentration decreases.
• Results confirmed SBDTs' ability to locate fractures potentially missed by temperature and conductance logging.

Conclusions:

• SBDTs provide a valuable, simple, and economical tool for characterizing borehole hydraulics and aquifer connectivity.
• The technique effectively identifies hydraulically active fractures without the need for borehole pumping.
• SBDTs enhance the understanding of groundwater flow paths and aquifer properties.