585 research outputs found
A simple model of precipitation squeeze treatments
No full textScale inhibitors are retained within porous media by the two main mechanisms of “adsorption” (G) and “precipitation” (?). In previous experimental and modelling work, we have demonstrated for static (equilibrium) “apparent adsorption” tests where the system exhibits either (a) adsorption only or (b) it is in the coupled adsorption/precipitation (G/?) regime. A complete model of SI retention must have (i) an equilibrium description of the coupled G/? process (Kahrwad et al, 2008); (ii) a kinetic model of coupled G/? which correctly limits to the equilibrium case (i.e. the kinetics must be consistent with the equilibrium G/? model as t -> ¶); (iii) the full kinetic G/? model must then be embedded in a transport model for flow through porous media. Some progress towards this full model has been made and reported previously (Sorbie, 2010; Vazquez et al, 2010). The full coupled kinetic G/? model is comprehensive and is currently being verified by experiment. However, this full model is quite complex and difficult to understand. Therefore, in this paper, we present a new simple model of kinetic precipitation (?) which explains some key features of this process. This work will present 3 key new findings, as follows: (i) a very simple mathematical explanation of the mechanism and observations in kinetic precipitation; (ii) some simple but novel analytical formulae which describe the process; (iii) a worked field scale radial kinetic precipitation examples is presented which demonstrates how to estimate whether a given field system is close to or far from precipitation/dissolution equilibrium. This simpler model represents an end-member where a precipitating SI system is described by a solubility (Cs) and a dissolution rate, ?. In most practical cases, some level of adsorption is also superimposed upon this behaviour but this is neglected in this simple model. However, understanding the behaviour of this idealized system does give us some mechanistic insights and some simple practical formula for precipitation squeeze design purposes
Redemption in the work of Francis Stuart
Get PDFThe idea of redemption is central to an understanding of the work
of Francis Stuart. Through an examination of its development and
expression, it is possible to demonstrate the integrity of his work and
its distinctive qualities. Such a demonstration is necessary because
Stuart's writing has been subjected to comparatively little scholarly
inquiry, although reviews of his work, especially that produced since
1949, suggest that it is impressive and important.
First, a general background to Stuart's work, a discussion of the
special problems associated with reading it, and a summary of his corpus
is provided. This indicates that the idea of redemption is important to
his earliest writing. The state of redemption is shown to be a
necessary apotheosis for Stuart's outcast heroes; it involves spiritual
suffering through which may be found a sense of reintegration and a
higher reality. This is expressed through interrelated themes such as
those of gambler, artist and ordinary man; mystic and criminal; sacred
and profane love; and spirituality and the mundane. The nature of the
redemptive experience is further elaborated by distinctive, complex
motifs, especially the hare, the ark and the woman-Christ. Their
recurrence provides an important element in the unity of Stuart's work.
Because Stuart's idea of the outcast raises important biographical
questions, an examination of the relationship between Stuart's life and
his work is made. Finally, the way in which the idea of redemption
exists in the language structures of Stuart's novels is examined, with
especial reference to his most recent work, The High Consistory. The
thesis shows that the development of the these of redemption
demonstrates the integrity of Stuart's work
An experimental and numerical study of the kinetics of barium sulphate in flowing systems
Get PDFThe formation and deposition of mineral scales, such as barium sulphate (BaSO4) and
calcium carbonate (CaCO3), is a common problem in many industrial and life science
processes. This is caused by chemical incompatibility due to either the mixing of
incompatible aqueous solutions or due to changes of the physical conditions, usually
temperature and pressure. Many laboratory studies have been conducted using techniques
broadly classified into batch and flowing tests to understand the reaction and mechanisms.
In this study, we focused on the dynamic (kinetic) deposition of barium sulphate arising from
the mixing of 2 incompatible brines. The mechanism of barium sulphate (barite) deposition is
often assumed to be a one-step reaction in which the ions in the bulk fluid directly deposit
onto a surface. However, there is strong evidence in the literature that barium sulphate may
deposit through an intermediary nanocrystalline phase which we refer to as BaSO4(aq) in this
work. This initial nucleation species or nanocrystalline material (BaSO4(aq)) may remain
suspended in the aqueous system and hence may be transported through the system before it
ultimately deposits on a surface
In this work, we have formulated a barite formation/deposition model which includes both of
these mechanisms noted above, i.e. (i) barite formation in solution of a nanocrystalline
precursor which may be transported and deposited at an interface and (ii) the direct kinetic
deposition of barite from the free ions in solution.
The kinetic approach is most important in flowing conditions, since the residence time in a
given part of the macroscopic system (e.g. in a pipe or duct) may be shorter than the time
required to reach the full equilibrium state of the system. A CFD study is carried out by solving the Stokes equations to accurately model the local
residence time, species transport, and calculate the hydraulic and mass transfer layers.
Geometry alteration due depositing barite is also an important phenomenon to consider and
model in a flowing system. This is rarely done in mineral deposit calculations, especially with
a full kinetic deposition model, but it is included in our model. The geometry change affects
both hydraulic and mass transport layers in the vicinity of the depositing surface and may
often change the deposition regime in terms of the balance of dominant mechanism which
applies. The effect of geometry change on the local residence time is investigated through
performing a ramping up of the flow rate and explicitly deforming the geometry as the
deposition occurs.
We also performed and report experiments on two levels to gain information on the kinetics.
First, we studied the kinetics of incompatible brines using batch tests. Second, we developed
a laboratory experimental flow cell that enabled us to (i) use different flow geometries
through 3D printing, (ii) visualise the deposition process as it happens, and (iii) understand
the rates of the reactions by analysing the effluent from the system. We used three different
categories of geometries including a (i) simple flow channel, (ii) simple constrictions with
different configurations to enforce different mixing regimes, and (iii) more complicated
geometry with different constriction sizes. This allowed us to investigate the hypothesis
developed in the modelling work. The visual findings from laboratory experiments show the
deposition growth happens in the normal direction of the flow, and as the local residence time
reduces, the deposition tends to move further down the line. This is true in all three different
geometries investigated, showing the concept of the diffusion penetration length.
Our results from the modelling and experimental work, show that in the laminar flow regime,
the extent of deposition on a surface is limited by the diffusion penetration length (δ) referred
to above. This means that there will be more deposits at lower flow rates, where the diffusion penetration length is larger. In this case, since the diffusion penetration length is relatively
larger, the deposition mechanism will be kinetics-limited. As the deposition reduces the flow
path cross-section area near the inlet vicinity, the velocity increases. Thus, the hydraulic layer
becomes smaller, resulting in a smaller diffusion penetration length, which causes the
deposition location to move towards the end of the flow path, where the velocity is still lower.
In this case, since the diffusion penetration length is relatively smaller, the deposition process
will be more transport-limited. The results of this study have the potential to contribute to the
development of more effective strategies for preventing scaling in a wide range of industrial
processes
Beauty for the Present: Mill, Arnold, Ruskin and Aesthetic Education
Get PDFThe present thesis examines the idea of aesthetic education of three eminent Victorians: John Stuart Mill, Matthew Arnold and John Ruskin. By focusing on the essence of what they meant with ‘the cultivation of the beautiful’ and, more importantly, the way their ideas of beauty informed their criticism of society, my study aims to contribute to our understanding of the idea of aesthetic education in the Victorian context and, further, to participate in a recent debate about the nature of beauty and aesthetic education.
Chapter One focuses on John Stuart Mill’s concept of ‘feeling’ in a series of essays. I will demonstrate how Mill’s idea of ‘aesthetic education’ was an ‘education of feelings,’ and moreover, how this idea was integrated into his literary criticism, his later critique of democratisation, his description of an ideal liberal society and even his own style of writing. Chapter Two contains a comparative study of Matthew Arnold and Friedrich Schiller. Through a rereading of Arnold, I will argue that his idea of aesthetic education is essentially Schillerian and that their resemblance consists primarily in their stress on the importance of aesthetic unity for modern life, which was becoming increasingly fragmentary and multitudinous. Chapter Three examines John Ruskin’s idea of aesthetic education and concentrates particularly on the cultivation of perception. Perception, as I shall show, was pivotal in Ruskin’s idea of aesthetic education. Just as what happened in Mill and Arnold, the emphasis on the education of seeing continued from his early writings well into his art and social criticisms. It not only differentiated him from his fellow art critics; the conviction that people should perceive with a pure heart also enabled him to link observation of artistic details with moral criticism of contemporary society and, thereby, to turn the cultivation of the beautiful into a moral-aesthetic experience
Immiscible fingering in porous media under different wetting conditions and its role in polymer flooding
No full textImmiscible viscous fingering occurs when a low viscosity fluid immiscibly displaces a
high viscosity fluid. In the field of geoenergy, this is typically a major problem whether
in gas storage or in oil recovery. When water is injected into the reservoir to aid recovery,
it can finger through a viscous oil, leaving large volumes bypassed and giving early water
breakthrough – neither of which is ideal from an economic or carbon footprint viewpoint.
Three major questions present themselves with regard to viscous fingering in such
systems: how can fingering be modelled correctly?; how can fingering be evaluated in
the laboratory?; and how can it be remedied? These are the 3 main areas of research that
will be addressed in this thesis.
A novel simulation methodology is used to directly model viscous fingers using standard,
commercial numerical simulators. In this work, this approach is validated against
literature experiments at a range of unstable viscosity ratios (μo/μw ~400 to 7,000). It is
then applied to model conventional core flood experiments, conducted as part of this
thesis, where μo/μw = 100. The simulation method is then used to upscale the core flood
results using scaling theory to a series of conceptual and sector models of the Captain
reservoir, which is currently undergoing polymer flooding in the North Sea.
The same numerical method is used to demonstrate how laboratory scale unstable
displacement experiments are sensitive to the suppression of viscous fingering by
capillary dispersion. This is then shown to occur even under extremely weak wetting
conditions. Using scaling theory, it is then shown how fingering “remerges” as the system
size is increased towards the field scale. These observations are then further supported by
carrying out laboratory 2D slab flood experiments under different wetting conditions for
an unstable immiscible displacement with viscosity ratio μo/μw = 100. The systems studied
include a weakly water-wet case which shows an apparently stable front, while the
equivalent weakly oil-wet system is highly fingered. By applying scaling theory, it is
demonstrated that capillary forces must be made negligible at the laboratory scale in order
to maintain the same viscous-capillary force balance which applies at the field scale
system.
Finally, the well-established enhanced oil recovery technique of polymer flooding is re-evaluated in the context of these findings. It is demonstrated both by simulation and
experiment that the principal increased recovery mechanism of the polymer is through viscous crossflow. This mechanism is shown to be responsible for the large and very rapid
response in oil recovery on polymer injection – even in highly viscous systems (>2,000
mPa.s) - as bypassed oil crossflows into established water channels (fingers). This
mechanism is evident in the laboratory when viscous fingers are allowed to form (viscous-dominated) and supports the conjecture that both polymer flooding and water flooding
are best examined without the stabilising effect of capillarity.
In addition, the findings of this thesis cast doubt on the conventional methods of
“measuring” relative permeability in the laboratory for application in adverse viscosity
ratio immiscible displacements in the field
Recommended from our members
Notis Musycall: Essays on Music and Scottish Culture in Honour of Kenneth Elliott
No full textKenneth Elliott is widely acknowledged as the leading scholar in the field of early Scottish Music. As
performer, deviser of radio programmes and countless concerts, and as author on the history and criticism of
Scottish music, Kenneth has done much to promote Scottish ‘art music’ of the period up to 1800. This
volume of essays, offered to him on the occasion of his 75th birthday, covers a variety of themes from the
medieval era through to the 20th century, and embracing music, art and Scottish culture, history, religion and
literature
New developments on the analysis of scale inhibitors
No full textScale inhibitors (SI) are used to control oilfield scale formation and the ability to analyse these species is very important such that SI concentrations as low as 0.5ppm active need to be measured accurately. If phosphorus is present in the SI molecule, then ICP based methods may be used for analysis. However, the oil industry’s increasing requirement to be environmentally friendly means that polymeric ‘green’ scale inhibitors are now increasingly being used, which raises issues over detection techniques i.e. ICP vs. wet chemical techniques. ICP detection for scale inhibitors is generally easier but, if it cannot be used, then at least time-saving improvements to wet chemical techniques are extremely beneficial. In this paper, we describe a range of analytical approaches which we have been using recently to improve chemical SI assay, especially at low near threshold levels (a few ppm active of SI). Progress is reported in 5 areas of SI analysis as follows: (1) Assay of sulphonated copolymer (VS-Co) was not possible by straightforward analysis without extensive dialysis and sample preparation. However, calibrations and repeats of a similar accuracy to the C18 were found for VS-Co using amino-propyl (NH2) cartridges and the Hyamine method (the Rhodia Method). (2) The Oasis® 2x4 method has been applied to SI analysis and this is able in principle to assay all types of polymeric scale inhibitors. This method has been used to detect a VS-Co scale inhibitor (SI) in a wide variety of different brine salinities from distilled water (DW) to high salinity formation waters (e.g. a Heron type FW). Although achievable under these different conditions, there was a significant decrease in the absorbance signals recorded with increasing salinity which was not significantly improved by a higher capacity sorbent cartridge. (3) Various elements have been assayed in the oil phase using ICP. Calibrations and accurate repeats within 5-10% error were achieved. After solving compatibility issues, the concentration of an oil-tolerant SI was determined successfully using calibrations and accurate repeats over a range of 0-10 ppm and 0-2500ppm active SI. (4) A matrix-matching Hyamine technique has been developed which allows any chloride ion effects on the chelating process between the Hyamine and SI to be negated, allowing accurate analysis of low polymeric SI concentrations. (5) ICP and wet chemical techniques have been able to accurately detect a P-tagged co-polymer type SI. The ability to apply 2 independent analytical methods to a given species offers some important advantages when more than one SI is deployed in a field system. In this work, we show excellent correlation between the wet chemical and ICP assay methods for this P-tagged SI. This study updates and adds to the set of analytical methods and procedures reported for scale inhibitor analysis by this group almost 20 years ago (Graham et al, 1993, 1994, 1995, 1996; Sorbie et al, 1992) and described in our FAST (Flow Assurance and Scale Team) Laboratory Procedures Manual (Sorbie and Boak, 2006)
New developments in the analysis of scale inhibitors
No full textScale inhibitors (SIs) are used to control oilfield scale formation, and the ability to analyze these species is very important such that SI concentrations as low as 0.5-ppm active need to be measured accurately. If phosphorus is present in the SI molecule, then inductively-coupled-plasma (ICP) -based methods may be used for analysis. However, the oil industry's increasing requirement to be environmentally friendly means that polymeric "green" SIs are now being used more, which raises issues concerning detection techniques (i.e., ICP vs. wet-chemical techniques). ICP detection for SIs is generally easier, but if it cannot be used, then at least time-saving improvements to wet-chemical techniques are extremely beneficial. In this paper, analytical approaches are described that have been used recently to improve chemical SI assay, especially at low near-threshold levels (a few ppm active of SI). Progress is reported in five areas of SI analysis: 1. Assay of sulfonated copolymer (VS-Co) was not possible by straightforward analysis without extensive dialysis and sample preparation. However, calibrations and repeats of accuracy similar to that of the C18 were found for VS-Co using amino-propyl (NH2) cartridges and the Hyamine method. 2. The Oasis®2×4 method has been applied to SI analysis, and this is able to assay all types of polymeric SIs in principle. This method has been used to detect a VS-Co SI in a wide variety of different brine salinities from distilled water (DW) to high-salinity formation waters (FW) (e.g., a Heron-type FW). Although achievable under these different conditions, there was a significant decrease in the absorbance signals recorded with increasing salinity that was not significantly improved by a higher-capacity sorbent cartridge. 3. Various elements have been assayed in the oil phase using the ICP method. Calibrations and accurate repeats within 5 to 10% error were achieved. After solving compatibility issues, the concentration of an oil-tolerant SI was determined successfully using calibrations and accurate repeats over a range of 0 to 10 ppm and 0 to 2,500 ppm active SI. 4. A matrix-matching Hyamine technique has been developed that allows any chloride-ion effects on the chelating process between the Hyamine and SI to be negated, allowing accurate analysis of low-polymeric SI concentrations. 5. ICP and wet-chemical techniques have been able to accurately detect a P-tagged (phosphorus-tagged) copolymer-type SI. The ability to apply two independent analytical methods to a given species offers some important advantages when more than one SI is deployed in a field system. In this work, excellent correlation is observed between the wet-chemical and ICP assay methods for this P-tagged SI. This study updates and adds to the set of analytical methods and procedures reported for SI analysis almost 20 years ago (Graham et al. 1993,1995a, 1995b, 1996; Sorbie et al. 1992) and are described in our Flow Assurance and Scale Team (FAST) laboratory procedures manual (Sorbie and Boak 2006).</p
Coupled adsorption/precipitation experiments:1. Static results
No full textThe mechanism of retention of scale inhibitors (SI) within the reservoir formation is central to a squeeze treatment having a long lifetime. Scale inhibitors are retained within porous media by the two main mechanisms of adsorption (G) and precipitation (?). There is not complete agreement in the literature about when we should use one mechanistic description or another, and indeed both can occur together as coupled adsorption/precipitation (G/?). Previously a general model of coupled (equilibrium) adsorption/precipitation has been derived and the agreement between the model and experiment was very good (Kahrwad et al., 2008). This model was subsequently extended to derive a consistent dynamic coupled G/? model for simulating non-equilibrium (kinetic) coupled processes of any type (Sorbie, 2010). This latter model has not yet been fully validated, but the work in this paper and its companion paper (Paper 2: Ibrahim et al, 2010) provides the type of data required in order to do this. In this paper (Paper 1), new static experimental adsorption/precipitation measurements are presented for two phosphonate inhibitors, DETPMP (a penta-phosphonate) and OMTHP (a hexa-phosphonate) using sand, kaolinite and siderite as the mineral phases. These experiments were carried out at a range of adsorbent mass (m)/ fluid volume (V)/ ratios and it is the “apparent adsorption”, Gapp vs. the final scale inhibitor concentration, cf, which is measured and plotted. By observing how the Gapp vs. cf, curves vary for different values of the (m/V) ratio, this indicates whether we are in the purely adsorbing (G) or in the coupled adsorption/precipitation (G/?) regime (Kahrwad et al., 2008). For these static apparent adsorption tests, m = 10g, 20g and 30g samples of each mineral were used (with a fixed volume of SI solution, V = 80ml) to analyse the apparent adsorption behaviour. In addition, related pure precipitation/compatibility tests were carried out in the absence of any minerals in the bulk solutions. The experimental results for both phosphonate scale inhibitors show good agreement with the theory in different regions of pure adsorption and coupled adsorption/precipitation. These results show clearly how such laboratory measurements should be carried out to determine both the levels of SI retention and the precise retention mechanism. This paper characterizes the systems used in subsequent dynamic adsorption/ precipitation sand pack floods which are reported in a related paper (Ibrahim et al., 2012) and which will be used in future to validate fully dynamic coupled G/? flow models (Sorbie, 2010)
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