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Four-dimensional studies of fluid-rock interaction
Get PDFSuccessful management of hydrocarbon reservoirs, geothermal energy extraction
sites, radioactive waste and CO2 storage sites depends on a detailed knowledge
of fluid transport properties, porosity and permeability. Amongst deformation
processes, fluid-rock interaction plays an important role in controlling the
petrophysical properties of a rock. The presence of fluids in the rocks induce chemical
and physical changes in compositions and texture, affecting porosity and permeability,
hence influencing dynamic transport properties and fluid flow. Fluid-rock interaction
processes have been deeply investigated in nature and in numerous experimental
and numerical modelling studies. However, these studies lack a spatio-temporal
characterization of the dynamic evolution of porosity and reaction microfabrics. There
is no clear understanding of the spatio-temporal evolution of these properties in three
dimensions, and how this evolution affects fluid percolation in the rock. Computed
X-ray micro-Tomography (μCT) was applied to investigate these processes in three
dimensions and observe their evolution in time (4DμCT). The combination of μCT
with 2D analytical techniques (e.g. scanning electron microscope, SEM, electron
microcrobe, EMPA, electron backscatter diffraction, EBSD) furthermore enables the
extrapolation of the information gained from 2D analyses to the 3rd an 4th dimension
(4D μCT).
The thesis investigates two different categories of fluid-rock interaction
processes, by using 4DμCT to monitor the evolution of mineral reactions (in the
first case) and porosity (second case) in relation to strain and time. In the first
case study, natural rock samples were analysed. The samples show a compositional
change along a strain gradient from olivinic metagabbros to omphacite-garnet bearing
eclogites in a ductile shear zone. Synchroton-based x-ray microtomography (sμCT)
was applied to document the 3D evolution of garnets along the strain gradient (which
represent the 4th dimension). The 3D spatial arrangement of garnet microfabrics can
help determine the deformation history and the extent of fluid-rock interaction active
during deformation. Results from the sμCT show that in the low strain domain,
garnets form a large and well interconnected cluster that develops throughout the
entire sample and garnet coronas never completely encapsulate olivine grains. In the
most highly deformed eclogites, the oblate shapes of garnets reflect a deformational
origin of the microfabrics. EBSD analyses reveal that garnets do not show evidence
for crystal plasticity, but rather they highlight evidence for minor fracturing, neo-nucleation
and overgrowth, which points to a mechanical disintegration of the garnet
coronas during strain localisation.
In the second case study, pressure-solution processes were investigated using
NaCl as rock-analogue, to monitor the evolution of porosity and pore connectivity in
four dimensions, providing a time-resolved characterization of the processes. NaCl
samples were uniaxially compacted and μCT scans were taken at regular interval
times to characterize the evolution of grain morphologies, pore space and macro-connectivity
of the samples. Different uniaxial loads, as well as different bulk sample
compositions (phyllosilicates and/or glass beads) were used to investigate their effect
on the process. Greater uniaxial loads, and the presence of phyllosilicates within
the deforming NaCl columns were found to enhance pressure-solution processes.
The pore space becomes highly disconnected in the presence of phyllosilicates, with
important implications for fluid percolation and dynamic transport properties. Mean
strain rates, calculated from volumetric Digital Image Correlation (3D-DIC) analyses,
were found to be higher where phyllosilicates were located. The combination of μCT
with volumetric DIC and SEM imaging proved to be an efficient analytical method
for investigating the dynamic behaviour of porosity and permeability during ongoing
pressure-solution processes.
The results showed that fluid-rock interaction critically modifies the rocks at the
pore/grain scale, with important consequences on dynamic fluid transport properties.
The combination of μCT with classical 2D techniques provided a better understanding
on the dynamic evolution of transport properties and fluid percolation during fluid-rock
interaction processes, allowing the characterization in three dimensions of
reaction microfabrics and porosity
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Experimental evidence that viscous shear zones generate periodic pore sheets
Get PDFIn experiments designed to understand deep shear zones, we show that periodic porous sheets emerge spontaneously during viscous creep and that they facilitate mass transfer. These findings challenge conventional expectations of how viscosity in solid rocks operates and provide quantitative data in favour of an alternative paradigm, that of the dynamic granular fluid pump model. On this basis, we argue that our results warrant a reappraisal of the community's perception of how viscous deformation in rocks proceeds with time and suggest that the general model for deep shear zones should be updated to include creep cavitation. Through our discussion we highlight how the integration of creep cavitation, and its Generalised Thermodynamic paradigm, would be consequential for a range of important solid Earth topics that involve viscosity in Earth materials like, for example, slow earthquakes.Applied Geophysics and Petrophysic
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
4-dimensional study of dissolution precipitation creep in oedometric compaction experiments of NaCl-biotite aggregates
Get PDFUnderstanding the dynamic evolution of hydraulic rock properties and the
associated deformation mechanisms is a crucial factor in establishing the potential
of groundwater resources, geological repositories as well as fossil fuel reservoirs.
Chemical compaction by dissolution precipitation creep (DPC) is a major ductile
deformation mechanism in the Earth’s upper crust that affects the porosity and
permeability of its host rock and therefore influences transport properties and fluid
flow herein. However, investigations of the process were in the past limited to
observations on natural samples, laboratory experiments and numerical modelling,
either lacking a temporal or spatial component or the validation of the model by
direct observations. The link between space and time only became possible recently
with the implementation of X-ray computed microtomography (microCT) in the
earth sciences. By means of microCT imaging time-resolved, three-dimensional data
(4D datasets) can be used to investigate the dynamic spatio-temporal evolution of
hydraulic properties and the effect of mechanical-chemical feedback mechanisms.
This thesis investigates slow chemical compaction mechanisms and their
influence on porosity in NaCl-biotite rock-analogues. Oedometric compaction
experiments on samples of different compositions and structures (layered vs.
homogeneous) were conducted and time-resolved (4D) microtomographic data used
to capture the dynamic evolution of the transport properties with progressing
compaction. Furthermore, emphasis was placed on the effect of phyllosilicates
upon deformation by dissolution precipitation creep, which is generally regarded to
reinforce the process.
Percolation analysis in combination with advanced digital volume correlation
techniques showed that the presence of phyllosilicates influences the dynamic
evolution of the porosity in the samples by promoting a reduction of porosity in
their vicinity to the point of disconnecting the pore volume. However, the absence
of strain localisation around those phyllosilicates and a homogeneous distribution
of axial shortening across the samples invites a renewed discussion of the effect of
phyllosilicates on dissolution precipitation creep, with a particular emphasis on the
length scales of the processes involved.
The results presented in this thesis, are among the first spatial-temporal data
sets resolved on the microscale that demonstrate the crucial role of dissolution
precipitation creep for the dynamic evolution of fluid transport properties. In addition
to that, they encourage discussing classical theoretical models of diffusive transport
and give an insight into the remaining challenges of experimental dissolution
precipitation creep, especially concerning the nucleation and growth of stylolites
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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