Borehole Geophysics Applied to the Study of Landfill Sites in Fractured Bedrock Terrains

Ferriz, Horatio; Pedler, William H.

doi:10.4133/1.2922683

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“…Drost et al (1968) developed and tested a scintillationcounter probe able to fit down a borehole that determined flow direction by tracing radioisotopic elements injected into the borehole. More recently, interest has focused on directly measuring ground water speed and direction using downhole instrumentation that requires no tracer (e.g., Cronk and Kearl 1990;Kerfoot et al 1991;Kearl et al , 1999Kearl 1997;Ferriz and Pedler 1999;Kearl and Roemer 1998;Wilson et al 2001;Beauheim 2000;Korte et al 2000;Pedler and Jepsen 2003). Examples of these types of instruments include the horizontal heat-pulse flowmeter (KVA flowmeter) (Kerfoot 1982;Kearl et al 1999;Melville et al 1985), the acoustic Doppler velocimeter (Kraus et al 1994), the laser Doppler velocimeter (Momii et al 1993), the fixed-point colloidal borescope (Kearl and Case 1992), and hydrophysical logging (Anderson et al 1993), which directly measure the horizontal component of velocity inside a wellbore.…”

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confidence: 99%

Simulations to Verify Horizontal Flow Measurements from a Borehole Flowmeter

et al. 2005

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This paper reports on experiments and simulations of subsurface flow from a slotted acrylic tube deployed in a sand-tank flow chamber for two different purposes. In the first instance, the slotted tube is used to represent a single fracture intersected by an uncased well. In the second instance, the slotted tube is used to represent a multislot well screen within a porous medium. In both cases, the scanning colloidal borescope flowmeter (SCBFM) measures ground water velocity within the well by imaging colloids traveling through a well to measure their speed and direction. Measurements are compared against model simulations. For the case of a slotted tube representing a single fracture, SCBFM and model results agree with respect to the flow direction and to within a factor of 1.5 for the speed near the well's center. Model and experimental agreement lend confidence that for an uncased well drilled in a fractured-rock medium, a calibrated SCBFM could be used to identify and quantify flowing features. Next, the SCBFM was deployed in a four-column multislotted casing with slots aligned with the flow direction. Another numerical model was developed to estimate the flow field within this well screen to evaluate the potential usefulness of employing the SCBFM in a screened well to estimate flow speed and direction in the surrounding porous medium. Results indicate that if the slots are not aligned with the flow, the SCBFM may only provide order-of-magnitude speed measurements and direction measurements with an uncertainty of approximately +/-25 degrees .

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