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Geotechnical News • June 2013
43
THESIS ABSTRACTS
Heat Transfer in Waste-Rock Piles
Constructed in a Continuous Permafrost
Region
Hoang Nam Pham
Hoang Nam Pham, University of Alberta, nhpham@ualberta.ca
This study is a part of a field experiment constructed at the
Diavik Diamond Mines in northern Canada to investigate
water flow, geochemical reactions, thermal and gas transport
within unsaturated piles of mine waste rock in a continuous
permafrost. Diavik waste rock is categorized by its sulfur
content: Type I rock, Type II rock and Type III rock. Three
experiment waste-rock pile of 15 m high were constructed
to achieve the project objective. Two undercover test piles
were referred to as Type I test pile (Type I rock) and Type
III test pile (Type III rock). The third test pile is covered test
pile in which the Type III rock is covered by a layer of 1.5
m till and 3 m Type I rock. Three drill holes of 40 m depth
in a 80 m high pile were also instrumented to reexamine the
results of the test piles. This thesis focuses on the thermal
aspects of the project.
Thermal measurements in the uncovered piles implied the
importance of wind on heat transport. Temperatures within
the piles were found to decrease with time and permafrost
aggradation near the base and in the bedrock foundation. At
the covered pile, temperatures at and below the till cover
were frozen. There was no significant impact of wind on
temperatures below the cover and heat influx across the
cover was small. Bedrock foundation temperature of the
covered pile showed a small cooling trend and less fluctua-
tion compared to bedrock foundation of the uncovered piles.
Linear stability analysis for the onset of natural air convec-
tion in waste-rock piles with physical properties based on
Diavik waste rock was also performed. The results indicate
that oxidation can create sufficient temperature gradients (or
buoyancy forces) to trigger natural air convection.
Ground temperatures of three 40 m drill hole in the 80 m
high full-scale pile showed that conduction was dominated
and the pile was cooling. According to numerical simula-
tions, using air convection cover (ACC) the 80 m high pile
will be frozen for the next 100 years under a proposed cli-
mate warming for the site. Furthermore, numerical simula-
tions also showed that ACC can maintain frozen condition
within waste-rock piles even though there was a heat release
due to sulfide oxidation. This heat release may create natural
air convection within waste-rock piles which aids in its
removal.
Supervisor: D.C. Sego, University of Alberta, Civil &
Environmental Engineering, Edmonton, Alberta, Canada T6G 2G7,
T: 780-492-2176, F: 780-492-8198
Design, Deployment, Performance and
Assessment of Downhole and Near Surface
Monitoring Technology for Geological CO
2
Storage
Gonzalo Zambrano-Narváez
Gonzalo Zambrano-Narváez, University of Alberta,
E: gonzalo@ualberta.ca
Early carbon storage research and development efforts in
Canada and elsewhere began with “value-added” proj-
ects such as CO
2
-enhanced oil recovery or CO
2
enhanced
coalbed methane, where the increase in production helps to
offset the costs of CO
2
and of its potential long-term stor-
age. These projects provide a valuable opportunity to assess
appropriate measurement, monitoring, and verification
protocols foe the geological storage component of carbon
capture and geological storage technologies. Measurement,
monitoring, and verification operations provide confidence
that CO
2
has been injected and stored in an environmentally
sound and safe manner. Multiple, integrated monitoring
instrumentation systems are being deployed in CO
2
field
demonstration research projects around the world and will
provide experience that can be used in regulatory regimes
for future commercial CO
2
sequestration scale projects. The
Pembina field was chosen from several fields within Alberta,
Canada, for a geological CO
2
storage monitoring pilot study,
in which the injection of CO
2
was combined with EOR. As
part of the project, an existing wellbore within the study
area was used as a dedicated observation well. The design
and initial results during cementing of this observation well
were reviewed. The experience of implementing monitoring
technologies was analyzed in order to assess existing knowl-
edge for deploying downhole instrumentation used for men-
toring and verification of CO
2
movements in the subsurface.
Analysis indicates that the observation well allows direct
monitoring and measurements at reservoir level of multiple
variables through geophysical, geochemical, and geome-
chanical instrumentation, as well as the opportunity to carry
out wellbore integrity studies under “in-situ” conditions. A
post-cement job and completion analysis that couples down-
hole measurements, analytical and numerical simulation
was conducted to improve future installations. Downhole
pressure gauges captured the dynamics of cement displace-
ment and were key elements during post-cement job review
and assessments of future well integrity. This research also
include the performance assessment of the surface tiltmeter
array, an indirect-near-surface measurement technology,
deployed in CSEMP – a CO
2
enhanced coal-bed methane
pilot project located also in the Pembina Field. The experi-
ence and analyses gained from the installations provide
valuable insight for CO
2
geological storage monitoring and
risk/performance assessment.
Supervisor: R.J. Chalaturnyk, University of Alberta, Civil &
Environmental Engineering, Edmonton, Alberta, Canada T6G 2G7,
T: 780-492-2176, F: 780-492-8198