Characterization of a Multilayer Aquifer Using Open Well Dilution Tests

Abstract

An approach to characterization of multilayer aquifer systems using open well borehole dilution is described. The approach involves measuring observation well flow velocities while a nearby extraction well is pumped by introducing a saline tracer into observation wells and collecting dilution vs. depth profiles. Inspection of tracer profile evolution allows discrete permeable layers within the aquifer to be identified. Dilution profiles for well sections between permeable layers are then converted into vertical borehole flow velocities and their evolution, using an analytic solution to the advection-dispersion equation applied to borehole flow. The dilution approach is potentially able to measure much smaller flow velocities that would be detectable using flowmeters. Vertical flow velocity data from the observation wells are then matched to those generated using a hydraulic model of the aquifer system, "shorted" by the observation wells, to yield the hydraulic properties of the constituent layers. Observation well flow monitoring of pumping tests represents a cost-effective alternative or preliminary approach to pump testing each layer of a multilayer aquifer system separately using straddle packers or screened wells and requires no prior knowledge of permeable layer depths and thicknesses. The modification described here, of using tracer dilution rather than flowmeter logging to obtain well flow velocities, allows the approach to be extended to greater well separations, thus characterizing a larger volume of the aquifer. An example of the application of this approach to a multilayer Chalk Aquifer in Yorkshire, Northeast England, is presented.

Induced Temperature Gradients to Examine Groundwater Flowpaths in Open Boreholes

“…One of the primary objectives of these different techniques in fractured rock aquifer systems is to locate and distinguish between the hydraulically active and inactive groundwater flow zones. Care is also needed with the use of tracer dilution tests (West and Odling 2007;Maurice et al 2011) as it involves the addition of salt or dyes into the aquifer which may affect the water quality and future investigations at the site. Some of the challenges with the use of inflatable packers and flowmeters are the sensitivity of the instruments to low groundwater flow rates and achieving a tight seal between the packer system and the drill hole wall.…”

Altering Dissolved Oxygen to Determine Flow Conditions in Fractured Bedrock Wells

“…; Brainerd and Robbins ), and multi‐well pumping tests (Marine ; Novakowski et al. ; West and Odling ). Difficulties associated with tracer behavior have been presented in numerous studies (Feuerstein and Selleck ; Smart and Laidlaw ; Shiau et al.…”

Variable‐Density Flow and Transport Simulation of Wellbore Brine Displacement

“…Borehole dilution tests using a variety of tracers (e.g., radioactive tracers, dyes, and brines) have been conducted since the 1950s (e.g., Brainerd and Robbins 2004, Drost et al 1968; Halevy et al 1967; Michalski and Klepp 1990; Moser and Neumaier 1957; Ogilvi 1958; Palmer 1993; Pitrak et al 2007; West and Odling 2007). Fundamentally, borehole dilution tests involve the injection of a tracer into a borehole and monitoring the tracer concentration in the well as it is changed by interaction between ground water flow in the aquifer and the borehole.…”

“…They are easy to perform; they can be quick to perform depending on the flow properties of the ground water system being tested; and depending on the tracer used the results may be easily and effectively monitored. Furthermore, according to West and Odling (2007), wellbore fluid displacement tests can potentially detect lower flow rates than flowmeter tests.…”