Applications of Distributed Temperature Sensing in Subsurface Hydrology

Read, Tom Oliver Trevett (2016) Applications of Distributed Temperature Sensing in Subsurface Hydrology. Doctoral thesis, University of East Anglia.

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In the study of dynamic subsurface processes there is a need to monitor temperature and
groundwater fluxes efficiently in both time and space. Distributed Temperature Sensing
has recently become more accessible to researchers in Earth Sciences, and allows
temperatures to be measured simultaneously, at small intervals, and over large distances
along fibre optic cables. The capability of DTS in conjunction with heat injection to detect
groundwater fluxes, is assessed in this thesis using a combination of numerical modelling,
laboratory tests, and field trials at the Ploemeur research site in Brittany, France. In particular,
three methodological approaches are developed: thermal dilution tests, point heating,
and the hybrid cable method. A numerical model was developed to assess the sensitivity
range of thermal dilution tests to groundwater flow. Thermal dilution tests undertaken at
Ploemeur showed lithological contrasts, and allowed the apparent thermal conductivity to
be estimated in-situ, but failed to detect previously identified transmissive fractures. The
use of DTS to monitor in-well vertical flow is then investigated. This is first using a simple
experiment deploying point heating (T-POT), which tracks a parcel of heated water
vertically through the borehole. The method allowed for the relatively quick estimation
of velocities in the well. The use of heated fibre optics is then trialled, and through a
field test was shown to be sensitive to in-well vertical flow. However, the data suffered
from a number of artefacts related to the cable installation. To address this, a hybrid cable
system was deployed in a flume to determine the sensitivity relationship with flow angle
and electrical power input. Additionally, a numerical model was developed, which suggested
a lower limit for velocity estimation due to thermal buoyancy. With the emergence
of Distributed Acoustic Sensing, fibre optics may become an increasingly practicable and
complete solution for monitoring subsurface processes.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Users 7376 not found.
Date Deposited: 17 Jun 2016 12:52
Last Modified: 17 Jun 2016 12:52


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