Richard A Jepsen | Search PubMed

PubMed2006

Uncertainty in experimental techniques for measuring sediment erodability.

There are many experimental methods currently utilized to measure sediment erodability and stability. When utilizing any of the available methods or devices to characterize erodability, one must understand the inherent uncertainty associated with each technique in relation to the application or expected measurement need. In addition, while some uncertainties are unique to a particular measurement device or technique, other uncertainties arise from variation in sediment conditions or properties. Several widely used devices and techniques are discussed with respect to their uncertainties and applicability for certain measurements. Finally, suggestions will be made on how to reduce uncertainty and manage it in model development.

Conservation of Natural Resources↗

PubMedDate not supplied

Simulations to verify horizontal flow measurements from a borehole flowmeter.

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 .

Colloids↗