Thèses sur le sujet « HYDRALL »

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 25-27).
Clathrate hydrate formation and subsequent plugging of deep-sea oil and gas pipelines represent a significant bottleneck for ultra deep-sea production. Current methods for hydrate mitigation focus on injecting thermodynamic or kinetic inhibitors into the flow, heating the pipe walls, or managing the flow of formed hydrates. These methods are expensive and energy intensive. An alternative approach involves reducing the adhesion of hydrates to surfaces, ideally to a low enough level that the force of flow detaches them and prevents plug formation. Systematic and quantitative studies of hydrate adhesion on smooth surfaces with varying energies were conducted. Surface energies were quantified using van Oss-Chaudhury-Good analysis of advancing and receding contact angles of polar and nonpolar fluids. The strengths of hydrate adhesion to these surfaces were measured using a custom-built testing apparatus, and greater than 75% reduction in adhesion strength of Tetrahydrofuran hydrate was achieved on treated surfaces compared with bare steel. This reduction is achievable on surfaces characterized by low Lewis acid, Lewis base, and van der Waals contributions to surface free energy such that the work of adhesion is minimized. Hydrate adhesion strength was correlated with the practical work of adhesion, i.e. with [gamma]₁(1 + cos [theta]rec) , of a suitable probe fluid, that is, one with similar surface energy properties to those of the hydrate. These fundamental studies provide a framework for the development of hydrate-phobic surfaces, and may lead to passive enhancement of flow assurance and prevention of blockages in deep-sea oil and gas operations.
by Jonathan David Smith.
S.M.

Dans le domaine de la valorisation des dérivés de la biomasse, les réactions de transestérification suscitent un grand intérêt en raison de leur importance pour transformer des molécules plateformes biobasées. L'étude des paramètres clés régissant une réaction de transestérification modèle, catalysée par des solides de type silicate de magnésium, a été menée. L'ensemble des données expérimentales (XRD, XPS, DRIFTS, RMN) a démontré qu'une phase de silicate de magnésium hydraté (MSH) est présente à la surface des catalyseurs les plus actifs. Cette phase, possédant une structure proche de celle d'une argile mais avec des défauts et présentant des propriétés acido-basiques spécifiques, est capable d'activer à la fois l'alcool (sur des sites basiques) et l'ester (sur des sites acides). Ce résultat est confirmé par l'étude cinétique qui met en évidence un mécanisme Langmuir-Hinshelwood. En outre, il a été montré que l'eau coordonnée au magnésium situé sur le bord des feuillets des particules ou dans les défauts présents à la surface des silicates engendre des sites acides particuliers.Par ailleurs, une série de phyllosilicates de magnésium, a été testée dans la réaction de transestérification modèle. Le rôle de la taille des particules a été mis en évidence et les meilleurs résultats catalytiques ont été obtenus avec le talc et la laponite possédant des tailles de feuillet nanométriques. De plus, l'étude cinétique indique que la réaction de transestérification catalysée par la laponite, n’ayant seulement que des sites basiques, implique un mécanisme Eley-Rideal. Enfin, dans le cas de la laponite la dissociation de l’eau sur les sites basiques empoissonne la réaction
In the field of biomass derivatives valorisation, transesterification reactions have attracted numerous interest due to its importance to transform platform molecules. A study of the parameters governing the reactivity of magnesium silicate based catalyst in a model transesterification reaction was thoroughly undertaken. The set of experimental data (XRD, XPS, DRIFTS, NMR) demonstrated that a magnesium silicate hydrate (MSH) phase is formed at the surface of the most active silicates. It is thus concluded that this active phase, presented a clay-like structure with defects and specific acido-basic properties, is able to activate together the alcohol (over base sites) and the ester (over acid sites). This result fits with the kinetic study that implies the Langmuir-Hinshelwood mechanism. Moreover, the acid sites were revealed that are created from the water coordinated to magnesium located on the edge of the clay-like particles or in the defects present in the silicate layer.Besides, a series of phyllosilicates having the similar structure with MSH, were tested in the model transesterification reaction. The influence of the particles size was investigated and the best catalytic performances were obtained with talc and laponite with nanosheets. In addition, kinetic study indicates that the transesterification reaction on the laponite, with purely basic sites, undergoes Eley-Rideal mechanism. Finally, unlike the positive role of water on the formation of acid sites in MSH, on laponite, the dissociation of the water on basic sites poisons the reaction

The concept which led to the establishment of the research in natural gas hydrate production, was born by Dr. Robert Amin (currently Professor of Petroleum Engineering at Curtin University and Chair of the Woodside Research Foundation) and Alan Jackson of Woodside Energy. The intended research in this field is to establish the viability of utilizing a synthesised natural gas hydrate as a means to allow a cheaper form of transportation of natural gas from the wellhead to the customer in direct competition with liquefied natural gas (LNG). Natural gas exists in ice-like formations called hydrates found on or under sea-beds and under permafrost. Hydrates trap methane molecules inside a cage of frozen water, where the amount of hydrates trapped is dependent on surrounding formation pressure. The amount of natural gas trapped in hydrates is largely unknown, but it is very large. A number of scientists believe that hydrates contain more than twice as much energy as all the world's coal, oil, and natural gas combined, hence making it a viable option of fuel in the 21st century, in a world constantly seeking cleaner sources of energy. The feasibility of production of natural gas hydrates on offshore installations and onshore facilities makes this development a viable option. As such this technology requires detailed research and development in a laboratory environment coupled with a pilot plant construction for commercial operation. Current estimates for onshore based facilities for the production of hydrates show a cost reduction of approximately 25% compared with LNG plants of the same energy capacity.
There are two major issues which require detailed research and development in order to progress this technology. First is the enhancement of the hydrates production by the use of other additives, and second, the continuous production at near atmospheric pressures. Other research related to transport methodology and re-gasification will be essential for the overall success of this technology, however, this work is outside the scope of this research.

The concept which led to the establishment of the research in natural gas hydrate production, was born by Dr. Robert Amin (currently Professor of Petroleum Engineering at Curtin University and Chair of the Woodside Research Foundation) and Alan Jackson of Woodside Energy. The intended research in this field is to establish the viability of utilizing a synthesised natural gas hydrate as a means to allow a cheaper form of transportation of natural gas from the wellhead to the customer in direct competition with liquefied natural gas (LNG). Natural gas exists in ice-like formations called hydrates found on or under sea-beds and under permafrost. Hydrates trap methane molecules inside a cage of frozen water, where the amount of hydrates trapped is dependent on surrounding formation pressure. The amount of natural gas trapped in hydrates is largely unknown, but it is very large. A number of scientists believe that hydrates contain more than twice as much energy as all the world's coal, oil, and natural gas combined, hence making it a viable option of fuel in the 21st century, in a world constantly seeking cleaner sources of energy. The feasibility of production of natural gas hydrates on offshore installations and onshore facilities makes this development a viable option. As such this technology requires detailed research and development in a laboratory environment coupled with a pilot plant construction for commercial operation. Current estimates for onshore based facilities for the production of hydrates show a cost reduction of approximately 25% compared with LNG plants of the same energy capacity.There are two major issues which require detailed research and development in order to progress this technology. First is the enhancement of the hydrates production by the use of other additives, and second, the continuous production at near atmospheric pressures. Other research related to transport methodology and re-gasification will be essential for the overall success of this technology, however, this work is outside the scope of this research.

Waxes and hydrates formation are two major flow assurance challenges, imposing considerable costs for prevention and, in worst case scenario, pipeline blockage removal and deferred production. Employing remediation and prevention schemes for hydrate and wax related problems necessitates knowledge of their formation conditions as well as their amount. The main focus of this work is thermodynamic modelling of phase equilibria in systems prone to waxes, hydrates and combined wax−hydrate formation. Study of these complex mixtures requires the development of a robust multiphase flash calculation algorithm capable of identifying the correct number and nature of the phases in equilibrium. Such an algorithm is devised in this work based on the Gibbs free energy minimization concept. The algorithm is first applied to complex hydrate forming systems and then extended to combined wax-hydrate forming mixtures, enabling investigation of the mutual interactions between hydrates and waxes from the thermodynamics viewpoint. The new algorithm is fast and is capable of showing complex behaviours in hydrate and wax forming systems including stability of several wax phases or more than one hydrate structure at equilibrium conditions. In this work, an integrated thermodynamic model coupling three highly accurate schemes, i.e., the cubic plus association equation of state, UNIQUAC activity coefficient model and van der Waals and Platteeuw approach−to describe the non-idealities of the fluids, paraffinic solids (waxes) and hydrates, respectively−is implemented. Furthermore, the formation of waxes in high-pressure condition is thoroughly investigated, especially for highly asymmetric condensate-like systems. Accordingly, a modified thermodynamic model is presented for wax formation in high-pressure systems. Comparing with experimental solid-fluid equilibrium data of synthetic mixtures, the integrated model presents excellent agreement which demonstrates the reliability of the approach. Finally, the method available for the extension of the integrated model−which was based on synthetic mixtures−to real oil systems and especially for wax formation, are evaluated. Based on the analysis presented the best model is chosen and used for illustrating the combined wax-hydrate precipitation in a real crude oil.

The thermal properties of hydrate bearing sediments remain poorly studied, in part due to measurement difficulties inside the hydrate stability envelope. In particular, there is a dearth of experimental data on hydrate-bearing sediments, and most available measurements and models correspond to bulk gas hydrates. However, hydrates in nature largely occur in porous media, e.g. sand, silt and clay. The purpose of this research is to determine the thermal properties of hydrate-bearing sediments under laboratory conditions, for a wide range of soils from coarse-grained sand to fine-grained silica flour and kaolinite. The thermal conductivity is measured before and after hydrate formation, at effective confining stress in the range from 0.03 MPa to 1 MPa. Results show the complex interplay between soil grain size, effective confinement and the amount of the pore space filled with hydrate on the thermal conductivity of hydrate-bearing sediments.

In this study
gas production by depressurization method from a hydrate reservoir containing free gas zone below the hydrate zone is numerically modeled through 3 dimensional, 3 phase, non-isothermal reservoir simulation. The endothermic nature of hydrate decomposition requires modeling to be non-isothermal
hence energy balance equations must be employed in the simulation process. TOUGH-Fx, the successor of the well known multipurpose reservoir simulator TOUGH2 (Pruess [24]) and its very first module TOUGH-Fx/Hydrate, both developed by Moridis et.al [23] at LBNL, are utilized to model production from a theoretical hydrate reservoir, which is first studied by Holder [11] and then by Moridis [22], for comparison purposes. The study involves 2 different reservoir models, one with 30% gas in the hydrate zone (case 1) and other one with 30% water in the hydrate zone (case 2). These models are further investigated for the effect of well-bore heating. The prominent results of the modeling study are: &
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In case 1, second dissociation front develops at the top of hydrate zone and most substantial methane release from the hydrate occurs there. &
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In case 2 (hydrate-water in the hydrate zone), because a second dissociation front at the top of hydrate zone could not fully develop due to high capillary pressure acting on liquid phase, a structure similar to ice lens formation is observed. &
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Initial cumulative replenishment (first 5 years) and the replenishment rate (first 3.5 years) are higher for case 2 because, production pressure drop is felt all over the reservoir due to low compressibility of water and more hydrate is decomposed. Compared to previous works of Holder [11] and Moridis [22], amount of released gas contribution within the first 3 years of production is significantly low which is primarily attributed to the specified high capillary pressure function.

This thesis studies the application of Statistical Association Fluid Theory (SAFT) in the prediction of hydrate formation conditions. The main objective is to develop a robust, reliable and purely predictive model for calculating the formation of single hydrates former gases. The current study is based on the use of the algorithm proposed by Englezos et al. (1991). Simplified SAFT (Fu & Sandler 1995) was employed to model the vapor and liquid phases as well as the van der Waals-Platteew model to represent the hydrate phase. The predictive ability of the model was investigated on single hydrate formers in the presence of inhibitors. With this end in mind, the inhibiting effects of methanol and ethylene glycol on methane, ethane, propane and carbon dioxide incipient hydrate forming were studied. The calculated results were compared to the experimental data obtained from the literature. A deviation of less than 10% in pressure or 1℃ in temperature was desired. Additionally, the phase equilibria of water-methanol, methanol-methaen, methanol-ethane and methanol-propane were also studied. Excellent results were obtained from incipient hydrate calculations and the SAFT equation of state was found to be highly capable of tackling non-ideal mixtures such as water-alcohol and water-alcohol-hydrocarbon systems. Estimation of the SAFT pure component parameters and the temperature range over which the SAFT parameters are estimated was found to be crucial. To overcome this issue, several parameters were estimated over various different temperature ranges, and the one which provided the smallest average absolute deviation was selected.

Reservoir fluids are usually saturated with water at reservoir conditions and may form gas hydrates in transfer lines, which potentially may plug the system. For long subsea pipelines, methanol injection is the practical means for preventing hydrate formation and for decomposing blockages. For efficient and economical pipeline design and operation, phase boundaries, phase fractions and distribution of water and methanol among the equilibrium phases of the system must be accurately known. The system comprising reservoir fluids, water and methanol demonstrates a complex multiphase behaviour and currently no quantitatively adequate description for it has been detailed in the open literature. The problem is addressed in this thesis by a consistent application of classical equilibrium thermodynamics. At ordinary operating conditions any combination of as many as six phases can be potentially present. For the description of the vapour and all liquid phases, we use one cubic equation of state with nonconventional mixing rules developed as part of this work. Classical thermodynamics together with the cell theory of van der Waals and Platteeuw were employed for the development of a general model for the calculation of heat capacities of gas hydrates. A consistent methodology has also been developed for obtaining the potential parameters of the cell model. Thereafter, application of the model demonstrates that for nearly spherical guest molecules the classical cell theory is a strictly valid description of gas hydrates. However, complex guest molecules distort the hydrate lattice, resulting in variation of the numerical values of certain parameters of the model. This work presents an efficient algorithm for the solution of the problem of the identity of the equilibrium phases in multiphase systems where gas hydrates are potentially present. The algorithm is based on the alternative use of two equivalent forms of the Gibbs tangent plane criterion and it is believed to be more appropriate for systems involving gas hydrate equilibria than previous methods. Application of the proposed algorithm in several regions of the phase diagram of both binary and multicomponent systems shows that it can be used reliably to solve any phase equilibria problem, including the location of phase boundaries. In summary this work presents a consistent, efficient and reliable scheme for multiphase equilibrium calculations of systems containing reservoir fluids, water and methanol. Favourable results have been obtained by comparison with diverse experimental data reported in the open literature and it is believed that the proposed correlation can be used reliably for pipeline design and operation.

Thesis (Ph. D.)--University of California, San Diego, 2005.
Title from first page of PDF file (viewed March 1, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

The goal of this diploma thesis is the estimation of the market value of the company HYDRAX s.r.o. as of 1. 1. 2010. The thesis is divided into two parts, the first one is theoretic and the second is analytic. To keep the valuation approach, the financial analysis was performed at first, that should consider the financial condition of the company and value the existence of going-concern in conjunction with the strategic analysis. The earnings prediction is another aim of the strategic analysis and this prediction is the starting point for the analysis and the prognosis of value generators and financial plan. The DCF equity method was applied for the valuation itself. The final estimation is determined by means of interval valuation emerging from the optimistic and pesimistic earnings alternative.

Gas hydrates are crystalline compounds made of gas and water molecules. Methane hydrates are found in marine sediments and permafrost regions; extensive amounts of methane are trapped in the form of hydrates. The unique behavior of hydrate-bearing sediments requires the development of special research tools, including new numerical algorithms (tube- and pore-network models) and experimental devices (high pressure chambers and micromodels). Hydraulic conductivity decreases with increasing variance in pore size distribution; while spatial correlation in pore size reduces this trend, both variability and spatial correlation promote flow focusing. Invading gas forms a percolating path while nucleating gas forms isolated gas bubbles; as a result, relative gas conductivity is lower for gas nucleation than for gas invasion processes, and constitutive models must be properly adapted for reservoir simulations. Physical properties such as gas solubility, salinity, pore size, and mixed gas conditions affect hydrate formation and dissociation; implications include oscillatory transient hydrate formation, dissolution within the hydrate stability field, initial hydrate lens formation, and phase boundary changes in real field situations. High initial hydrate saturation and high depressurization favor gas recovery efficiency during gas production from hydrate-bearing sediments. Even a small fraction of fines in otherwise clean sand sediments can cause fines migration and concentration, vuggy structure formation, and gas-driven fracture formation during gas production by depressurization.

The present thesis focuses on the intrinsic kinetics of clathrate hydrate formation to provide the fundamental data and modeling needed to predict hydrate growth. A novel hydrate growth model based on particle size distribution measurements and a concentration driving force was proposed. The reaction rate constant of propane hydrate formation was determined using the aforementioned model. The mole fraction of carbon dioxide and methane in the bulk liquid phase was measured at the onset of hydrate growth and thereafter in a semi-batch stirred tank crystallizer. It was found that the guest mole fraction in the bulk liquid phase increases with pressure, decreases with temperature and remains constant during at least the first thirteen minutes of the growth stage. Based on such measurements, an alternate formulation of the hydrate growth model, independent of the dissolution rate at the vapor-liquid water interface, was suggested. As a result, the reaction rate constant of both carbon dioxide and methane clathrate formation was determined and found to follow an Arrhenius-type relationship, increasing with temperature over a four-degree interval, while being insensitive to pressure over the range investigated. The temperature trend of the reaction rate constant of hydrate formation yielded positive activation energies for both carbon dioxide and methane hydrate growth. The carbon dioxide and methane solubility dependency on temperature in water under hydrate-liquid water and vapor-liquid water equilibrium was also demonstrated using fundamental thermodynamics.
La présente thèse traite de la cinétique de formation des hydrates de gaz afin d'établir les données et la modélisation nécessaires à l'étude de leur croissance. Un modèle cinétique pour la formation des hydrates de gaz, intégrant des mesures de taille de particules et une force d'entraînement de concentration, a été développé et utilisé pour calculer la constante de vitesse de réaction des hydrates de propane. Des mesures de la fraction molaire du composé gazeux dans la phase liquide, au moment de la formation des hydrates et tout au long de leur croissance, ont été obtenues pour le dioxyde de carbone et le méthane. Les résultats ont démontré que cette fraction molaire augmente avec la pression, diminue avec la température et demeure constante durant au moins les premières treize minutes de la phase de croissance. Ces mesures ont permis de modifier le modèle cinétique pour le rendre indépendant de l'interface vapeur-eau liquide. Également, il a été démontré que la constante de vitesse de réaction des hydrates de dioxyde de carbone et de méthane obéit à la loi d'Arrhénius, augmentant avec la température sur un intervalle de quatre degrés centigrades, en plus d'être constante pour l'écart de pression considéré. L'effet de la température sur la constante de vitesse de réaction a permis de calculer une énergie d'activation positive pour la croissance des hydrates de dioxyde de carbone et de méthane. Enfin, l'effet de la température sur la solubilité du dioxyde de carbone et du méthane dans l'eau, tant pour un équilibre hydrate-eau liquide que vapeur-eau liquide, a été démontré à l'aide de la thermodynamique.

Reservoir testing and analysis are fundamental tools in understanding reservoir hydraulics and hence forecasting reservoir responses. The quality of the analysis is very dependent on the conceptual model used in investigating the responses under different flowing conditions. The use of reservoir testing in the characterization and derivation of reservoir parameters is widely established, especially in conventional oil and gas reservoirs. However, with depleting conventional reserves, the quest for unconventional reservoirs to secure the increasing demand for energy is increasing; which has triggered intensive research in the fields of reservoir characterization. Gas hydrate reservoirs, being one of the unconventional gas reservoirs with huge energy potential, is still in the juvenile stage with reservoir testing as compared to the other unconventional reservoirs. The endothermic dissociation hydrates to gas and water requires addressing multiphase flow and heat energy balance, which has made efforts to develop reservoir testing models in this field difficult. As of now, analytically quantifying the effect on hydrate dissociation on rate and pressure transient responses are till date a huge challenge. During depressurization, the heat energy stored in the reservoir is used up and due to the endothermic nature of the dissociation; heat flux begins from the confining layers. For Class 3 gas hydrates, just heat conduction would be responsible for the heat influx and further hydrate dissociation; however, the moving boundary problem could also be an issue to address in this reservoir, depending on the equilibrium pressure. To address heat flux problem, a proper definition of the inner boundary condition for temperature propagation using a Clausius-Clapeyron type hydrate equilibrium model is required. In Class 1 and 2, crossflow problems would occur and depending on the layer of production, convective heat influx from the free fluid layer and heat conduction from the cap rock of the hydrate layer would be further issues to address. All these phenomena make the derivation of a suitable reservoir testing model very complex. However, with a strong combination of heat energy and mass balance techniques, a representative diffusivity equation can be derived. Reservoir testing models have been developed and responses investigated for different boundary conditions in normally pressured Class 3 gas hydrates, over-pressured Class 3 gas hydrates (moving boundary problem) and Class 1 and 2 gas hydrates (crossflow problem). The effects of heat flux on the reservoir responses have been addressed in detail.

Thesis (MSc)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: A theoretical and experimental study was performed in order to identify factors that influence the propensity of compounds containing anionic functional groups that are commonly found on pharmaceutical drug compounds to form hydrates. A Cambridge Structural Database (CSD) survey was initially undertaken to determine the propensity of different pharmaceutically acceptable anions to form hydrates. The results showed that hydrate formation will take place more regularly when the polarity of the functional group increases. Furthermore, if the charge distribution is very concentrated over the polar groups, hydrate formation will occur more readily. This observation was further investigated by performing a series of potential energy surface (PES) scans for the hydrogen bond (H-bond) in the structure of N-(aminoiminomethyl)-N-methylglycine monohydrate (creatine monohydrate) with various Density Functional Theory (DFT) and Wave Functional Theory (WFT) methods. WFT is often also referred to as ab initio, which refers to the construction of the wave function from first principles when this theory is applied. The scans revealed that several strong and directional H-bonds with different geometrical parameters between the carboxylate group and the water molecule are possible, which suggests that the H-bond plays an important role in driving the formation of pharmaceutical hydrates. A total of 44 hydrate structures were identified that have pharmaceutically acceptable functional groups. Optimisations in the gas phase and in an implicit solvent polarisable continuum solvent model with a variety of solvents showed that there is a significant dependence of the H-bond interaction energy on the anionic group as well as the steric density of surrounding substituents. It was found that the M06-2X method utilising the 6-311++G(d,p) basis set outperformed the other methods that were tested when compared to optimisations performed with the benchmark MP2/aug-cc-pVTZ level of theory. Furthermore, the strength of the H-bond was measured in the 44 experimentally determined structures by using a total of five generalized gradient approximation (GGA) methods, of which two methods contained the DFT-D3 correction. The results of these DFT methods were subsequently compared to results obtained at the benchmark MP2/aug-cc-pVTZ level of theory. The M06-2X method was identified as the most economical method to calculate H-bond energies. It was also found that the H-bond interaction energy shows a substantial dependence on the electrostatic environment. This was observed by a significant decrease in H-bond strength as the relative permittivity of the solvent increases. The effect of steric density on the H-bond interaction energy was investigated by performing hydrogen bond propensity calculations. These values were then compared to the interaction energies of each structure and the results showed that the presence of large bulky substituents can lead to an increase in bond energy by forcing the anionic functional group closer to the water molecule. Contrastingly, the bulky group can also push the anionic group away from the water molecule and result in a decrease in bond energy. Approximate values for the amount of stabilisation offered to the H-bonding system by the surrounding crystalline environment were calculated by optimising the H-bond geometrical parameters of selected compounds with a combination of the M06-2X and MP2 methods utilising the 6-311++G(d,p) basis set. The H-bond interaction energies were then calculated at the M06-2X/6-311++G(d,p) level of theory and compared to the H-bond interaction energies in geometries that have been fully optimised. After these energies were compared and the crystal packing of each structure was investigated, it was found that the packing of some structures within the crystalline environment limits the number of H-bonds that can be formed between the water and the compound of interest. Full optimisation calculations result in structures with cooperative stabilisation, such that more than one H-bond is found between the two fragments. The effect of substituents on H-bond interaction energy was investigated by the addition of six electron-donating and electron-withdrawing groups on four aromatic compounds with different anionic functional groups, namely carboxylate, nitrogen dioxide, sulfonate and phosphonate. It should also be mentioned that the nitrogen dioxide is not an anionic functional group, but it was included as it is a neutral radical that often forms hydrogen bonds. A total of 80 structures were optimised with a combination of the M06-2X and MP2 methods utilising the 6-311++G(d,p) basis set. This was followed by counterpoise corrected single point calculations at the M06-2X/6-311++G(d,p) level of theory. The results showed that the H-bond interaction energy bears no relationship to the inductive strength or the inductive ability of the substituents, but rather the ability of these substituents to rotate the anionic functional group and allow cooperative stabilisation of the H-bond. Furthermore, AIM analysis was performed for the substituted H-bonded aromatic structure. The results showed that electron-donating groups that are placed at the para position yield stronger H-bonds, which is once again accompanied by cooperative stabilisation. Electron-withdrawing groups with sufficient inductive effects can result in a weaker H-bond when placed at the meta position. The effect of water activity (aw) on the hydrate crystal formation was investigated experimentally by performing a series of crystallisations in various solvent mixtures. These mixtures consisted of water mixed with acetone, ethanol and ethyl acetate. A total of three organic acids were used in crystal formation, namely pyridine-4-carboxylic acid (isonicotinic acid), N-amino-iminomethyl-N-methylglycine (creatine) and benzene-1,3,5-tricarboxylic acid. It was found that water activity affects the formation of the hydrate as well as the anhydrous product. Additionally, nucleation and super saturation plays a large role in crystal formation and can serve as an effective technique when the formation of crystals of an appropriate shape and size is required for further analysis.
AFRIKAANSE OPSOMMING: 'n Teoretiese en eksperimentele studie was uitgevoer om faktore te identifiseer wat die geneigdheid van verbindings met anioniese funksionele groepe wat algemeen gevind word op farmaseutiese dwelm verbindings om die hidraat produk te vorm, affekteer. 'n Opname van strukture in die Cambridge Strukturele Databasis (CSD) is onderneem om die geneigdheid van verskillende farmaseutiese aanvaarbare anione om hidrate te vorm te bepaal. Die resultate het getoon dat hidraatvorming meer gereeld plaasvind indien die polariteit van die funksionele groepe toeneem. Verder is daar ook opgemerk dat 'n gekonsentreerde ladingsverspreiding op die polêre groepe ook tot 'n toename in hidraat vorming sal lei. Hierdie waarneming is verder ondersoek deur 'n reeks potensiële energie oppervlak (PES) skanderings van die waterstof binding (H-binding) vir die struktuur van N-amino-iminometiel-N-metielglisien monohidraat (kreatien monohidraat) met verskeie Digtheids-Funksionele Teorie (DFT) en Golffunksie Teorie (WFT) metodes uit te voer. Die skanderings het getoon dat verskeie sterk, gerigte H-bindings met verskillende geometriese parameters tussen die karboksilaatgroep en die watermolekule kan vorm. Hierdie bevindinge lê klem op die belangrike rol wat H-bindings in die vorming van farmaseutiese koolhidrate speel. 'n Totaal van 44 hidraat strukture met farmaseutiese aanvaarbare funksionele groepe was geïdentifiseer. Optimaliserings is in die gas fase asook in 'n implisiete kontinuum polariseerbare oplosmiddel model met 'n verskeidenheid oplosmiddels uitgevoer. Die resultate het 'n beduidende afhanklikheid van die H-binding interaksie-energie op die anioniese groep asook die steriese afkskerming van omringende groepe getoon. Daar is bepaal dat die M06-2X metode wat saam met die 6-311++G(d,p) basisstel die mees akkuraatste resultate gelewer het in vergelyking met die ander DFT metodes asook die MP2/aug-cc-pVTZ maatstaf. Die H-binding se sterkte is vir hierdie strukture bereken deur vyf GGA metodes te gebruik, waarvan twee metodes van die DFT-D3 korreksie gebruik maak. Die resultate van die berekeninge met hierdie DFT metodes is daarna vergelyk met resultate verkry met die MP2/aug-cc-pVTZ maatstaf. Daar is gevolglik bepaal dat die M06-2X metode die mees ekonomiese metode is om H-binding energië te bereken. Die H-binding interaksie energie toon 'n aansienlike afhanklikheid op die diëlektriese konstante van die oplosmiddel aan. Hierdie waarneming is op grond van 'n beduidende afname in die H-binding interaksie-energie indien die relatiewe permittiwiteit van die oplosmiddel verhoog word gemaak. Die effek van steriese digtheid is ondersoek deur waterstofbindinggeneigdheid waardes te bereken. Hierdie waardes is met die interaksie-energië van elke struktuur vergelyk. Die resultate dui daarop dat steries digte groepe tot 'n toename in interaksie energie kan lei wanneer die anioniese funksionele groep nader aan die water molekule gestoot word. Verder is dit ook moontlik vir hierdie steries digte groepe om die anioniese groep weg van die water molekule te stoot en gevolglik 'n afname in interaksie energie te veroorsaak. Benaderde waardes vir die hoeveelheid stabilisering wat die omringende kristallyne omgewing aan die H-binding bied is bereken deur die H-binding geometriese parameters van geselekteerde verbindings met die M06-2X en MP2 metodes en die 6-311++G (d,p) basisstel te optimaliseer. Die H-binding interaksie-energië is gevolglik by die M06-2X/6-311++G(d,p) vlak van teorie bereken en met die H-binding energië in strukture wat volledige optimaliseer is vergelyk. Nadat hierdie waardes vergelyk is, is daar gevind dat die pakking van strukture in the kristallyne omgewing verhoed dat sekere H-bindings tussen die water molekule en die verbinding van belang kan vorm. Strukture wat volledig optimaliseer is, lei tot strukture wat in staat is om koöperatiewe stabilisering te ondergaan. Koöperatiewe stabilisering word gekenmerk deur die vorming van meer as een H-binding tussen twee fragmente. Die effek van substituente op die H-binding interaksie energie is ondersoek deur die bevoeging van ses elektrondonor- en elektronontrekkendegroepe op vier aromatiese verbindings, naamlike die karboksilaatgroep , stikstofdioksied , sulfonaat en fosfonaat. Dit moet ook genoem word dat stikstofdioksied nie 'n anioniese funksionele groep is nie, maar dit was wel ingesluit omdat dit ‘n neutrale radikaal groep is wat dikwels waterstofbindings vorm. 'n Totaal van 80 strukture optimiserings was uitgevoer met 'n kombinasie van die M06-2X en MP2 metodes wat gebruik maak van die 6-311++G(d,p) basisstel. Dit is gevolg deur interaksie-energie berekeninge op die M06-2X/6-311++G(d,p) vlak van teorie. Die resultate het getoon dat daar geen verband tussen die induktiewe vermoë van die substituente en die sterkte van die H-binding is nie, dit is eerder die vermoë van hierdie substituente om die anioniese funksionele groep te laat roteer wat toelaat dat koöperatiewe stabilisering van die H-binding kan geskied. Die AIM analise is op 'n gesubstitueerde H-binding struktuur toegepas. Die resultate het getoon dat elektrondonorgroepe wat by die para posisie geplaas word tot sterker H-bindings sal lei, wat weereens met koöperatiewe stabilisering vergesel word. Elektrononttrekkendegroepe met sterk induktiewe effekte kan tot 'n swakker H-binding lei indien hulle by die meta posisie geplaas word. Die effek van water aktiwiteit (𝑎w) op hidraatkristalvorming is deur die uitvoering van 'n reeks kristallisasies in verskeie oplosmiddelmengsels ondersoek. Hierdie oplosmiddel mengsels bestaan uit water met asetoon, etanol of etielasetaat gemeng. Kristallisasies is vir drie organiese sure, naamlik piridien-4-karboksielsuur, N-amino-iminometiel-N-metielglisien monohidraat en 1,3,5-benseen tri-karboksielsuur uitgevoer. Daar is gevind dat water aktiwiteit 'n invloed op die vorming van die hidraat en watervrye produkte kan hê. Daarbenewens, speel water aktiwiteit 'n belangrike rol in die nukleasie fase van kristalvorming en kan as 'n effektiewe tegniek dien om kristalle van 'n toepaslike vorm en grootte vir verdere analise te verkry.

Much progress has been made in understanding the physicomechanical properties of blended cement pastes of various formulations. However, unanswered questions abound, particularly as it concerns the long term chemistry of mineral distribution as clinker is diluted with progressively more supplementary cementitious materials (SCM's) and as a greater fraction of blending agent reacts with cement with time. This Thesis describes progress towards elucidating the mineralogical evolution mainly by isothermal equilibrium of known compositions. The evolution of mineralogy of two major systems: the calcium-alumina-silica-water (CASH) system and sodium-calcium-alumina-silica-water (NCASH) systems were studied at 20 – 85 °C, using ~70 compositions. Phase assemblage models have been developed for the systems, demonstrating the mode of occurrence and coexistence of phases with respect to temperature and composition. The coexistence of gels, one based on calcium silicate hydrate (C-S-H), the other based on aluminosilicate hydrate (A-S-H), and crystalline phases such as hydrogarnet solid solution, strätlingite and gismondine-Ca in the CASH system at 20 – 85°C, are illustrated. Transformation of gels to their corresponding crystalline phases has been predicted. Similarly, models are presented showing the mode of occurrence and coexistence of portlandite, alumina hydrate, silica, tobermorite, strätlingite, hydrogarnet solid solution, gismondine- type zeolite (Na,Ca)P solid solution, zeolite A, zeolite X, sodalite, etc., at temperatures 20 – 85 °C for the NCASH system. The stability and properties of the various crystalline CASH phases such as, hydrogarnet solid solution, strätlingite and gismondine, in relation to other phases relevant to cement hydration – such as C-S-H, AFts, AFms, gypsum and calcite – are characterized. The impact of sulfate, carbonate, alkali and solid solution on phase stability in systems relevant to aluminosilicate substituted cement paste are investigated. Concerns on long-term evolution of pH and its consequences to the passivation of cement-steel composite are discussed.

Gas hydrates pose economic and environmental risks to the oil and gas industry when plug formation occurs in pipelines. A novel approach using interfacial rheology was applied to understand cyclopentane clathrate hydrate formation in the presence of nonionic surfactant to achieve hydrate inhibition at low percent weight compared to thermodynamic inhibitors. The hydrate-inhibiting performance of low (<CMC), medium (≈CMC), and high (>CMC) concentrations of Span 20, Span 80, Pluronic L31, and Tween 65 at 2 °C on a manually nucleated 2 μL droplet showed a morphological shift in crystallization from planar shell growth to conical growth for growth rates below 0.20 mm ²/min. Monitoring the internal pressure of a droplet undergoing planar hydrate crystallization provided a strong correlation (up to R = –0.989) of decreasing interfacial tension to the shrinking area of the water-cyclopentane interface. Results from the high-concentration batch of surfactants indicated that while initial hydrate growth is largely suppressed, the final stage of droplet conversion becomes rapid. This effect was observed following droplet collapse from the combination of large conical growths and low interfacial tensions. The low-concentration batch of surfactants saw rapid growth rates that diminished once hydrate shell coverage was completed. The most effective surfactant was the high-concentration Tween 65 (0.15 g/100mL), which slowed hydrate growth to 0.068 mm²/min, nearly an order of magnitude slower than that found for pure water at 0:590 mm²/min. High molecular weight (1845 g/mol) and HLB (10.5) close to 10 contribute to a large energy of desorption at an interface and are believed to be the sources of Tween 65's hydrate-inhibiting properties.

According to the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4), fossil fuels are utilised to produce more than 80% of the world's energy and this is likely to remain unchanged in the nearest future, especially as industrialisation is pursued by such economic giants as China. Without substantial change in energy policies with primary focus on the development of sustainable technologies for power generation, mitigation of associated Green House Gas (GHG) emissions cannot be fully implemented, and will require continual improvement in order to achieve objectives set by the Kyoto protocol. Research and development in the field of Carbon Capture and Sequestration is therefore being thoroughly explored. In this work a new sustainable technology for CO2 capture from IGCC power stations is developed and discussed in detail. This technology is based on cryogenic condensation integrated with gas hydrate formation.With the massive global reduction in recoverable oil and the potential size in a few decades time, the accent started to shift towards the other available fossil fuels such as gas and coal. The amount of Natural Gas trapped in the form of solid hydrate sunk in the deep ocean and permafrost areas cannot be estimated precisely, however, the scientific community agrees that values in order of 1015 to 1017 cubic metres are realistic. This has caused overwhelming research into gas hydrates as storage media for different gases. Gas hydrates are highly organized crystalline structures with molecules of light gases encaged in a framework created by water molecules. They can form at any place where free water in intimate contact with hydrate forming gas is exposed to elevated pressures and low temperatures. The ability to store large quantity of gas per unit volume makes gas hydrates an attractive option for any application requiring gas preservation. One of such modern applications for gas hydrates has arisen from the global warming problem and addresses the potential capability to efficiently capture and safely store the CO2.Coal remains the main energy source in the world; for example, in Australia it is providing 40% of total energy and up to 80% of electricity (Cuevas-Cubria et al., 2010). The main advantages of coal over the other fossil energy resources are its abundance, its easy recoverability and lower cost. Massive pollution produced during burning of this fuel forced the creation of new technologies that allow for GHG reduction. Integrated Gasification Combined Cycle (IGCC) is the most favoured advanced option for energy recovery from a variety of sources, particularly coal, the so-called 'clean coal technology'. IGCC generates a high pressure shifted syngas stream composed essentially of Hydrogen and Carbon Dioxide. Historically, the CO2 was separated from rich sources (such as natural gas) via the Ryan-Holmes cryogenic condensation process. However, applied at the gas or oil refinery this method can consume up to 50% of the generated energy to bring the CO2 levels down to pipeline requirements which does not seem attractive in terms of cost of CO2 avoided. High temperatures utilised for coal gasification are also not favourable for the implementation of cryogenic condensation to an IGCC stream.On the other hand, high pressure and high CO2 content in the IGCC flue gas provide the ideal conditions for CO2 capture in the form of solid hydrates. This option has been investigated under the guidance of the US Department of Energy by a team of researchers (Los Alamos National Laboratory, Nexant, Inc., and SIMTECHE) since 1999 and at the Chinese Academy of Science. A few proof-of-concept reports can be found stating that the utilisation of the hydrate formation phenomenon for purification of gas streams is less energy intensive than any of the other existing CO2 capture methods. The ability to encapsulate significant amounts of gas in little space and relatively mild conditions of storage make the hydrates an extremely attractive option for easy handling of high rates of GHG emissions. However, this research is still on a laboratory scale.In this thesis a new method is developed for cost and energy efficient CO2 sequestration from IGCC sources based on a simple configuration. High feed pressure facilitates bulk removal of CO2 by cryogenic methods, and high energy recovery is achieved through process integration with hydrate formation. Liquid CO2 produced as a result of condensation carries most of the cold energy required for initial refrigeration, and the hydrate unit does not consume any substantial additional energy. Separated CO2 is characterised by high purity sufficient for utilisation in enhanced oil and gas recovery processes. The hydrate can be easily handled and stored. Although the focus is made on IGCC flue gas application, the method can be extended to other sources with high CO2 levels and supplied at high pressure.Additional value is brought to this research by extensive investigation of the phase behaviour of gas mixtures containing CO2. Particular attention is paid to the distinctive features of gas hydrates produced in different systems including mixtures with hydrocarbons and non-hydrocarbons in various concentrations and in the presence of chemicals dissolved in water. This knowledge will contribute to the future development in the field of hydrates and will be useful for both academic research and industrial application.

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As macrófitas aquáticas possuem papel fundamental nos ecossistemas aquáticos participando dos processos de ciclagem de nutrientes, além de servirem como abrigo e alimento para muitas espécies de peixes e outros organismos. Dentre os principais métodos de controle de macrófitas está o controle químico com o uso de herbicidas. O objetivo deste estudo foi realizar o controle químico da macrófita Hydrilla verticillata com a aplicação isolada de diquat e hidróxido de cobre, e da mistura de diquat + 1% de hidróxido de cobre. O primeiro experimento para o controle da H. verticillata e da microalga Ankistrodesmus gracilis foi realizado em sala de bioensaio em recipientes plásticos de 1,5 litros, sendo todos os tratamentos testados eficientes no controle da macrófita e da microalga. Posteriormente, foram realizados experimentos em condições de microcosmos de concreto de 600 litros e em mesocosmos de concreto de 1200 litros, com o monitoramento de variáveis da qualidade da água (temperatura, oxigênio dissolvido, condutividade elétrica e pH), teor de clorofila a, demanda biológica de oxigênio (DBO) e demanda química de oxigênio (DQO) por um período de sessenta dias após a aplicação dos tratamentos. A mistura de diquat + 1% de hidróxido de cobre foi o tratamento mais eficaz no controle da macrófita Hydrilla verticillata para a maioria dos parâmetros analisados, havendo alteração nas variáveis de qualidade da água. Foram também realizados experimentos ecotoxicológicos para organismos não-alvo (Hyphessobrycon eques, Pomacea canaliculata, Lemna minor e Azolla caroliniana) com diquat, oxicloreto e hidróxido de cobre, onde a mistura de diquat + 1% de oxicloreto de cobre foi a mais tóxica para os organismos bioindicadores e a macrófita Lemna minor foi o bioindicador que apresentou a maior sensibilidade aos agroquímicos testados.
The macrophytes have a fundamental role in aquatic ecosystems participating in nutrient cycling processes, as well as serving as shelter and food for many species of fish and other organisms. Among the main weeds control methods is chemical control using herbicides. The aim of this study was the chemical control of the macrophyte Hydrilla verticillata with isolated application of diquat and copper hydroxide, and the mixture of diquat + 1% copper hydroxide. The first experiment for the control of H. verticillata and microalgae Ankistrodesmus gracilis was held in bioassay room in plastic containers of 1.5 liters, with all treatments tested effective in controlling macrophyte and microalgae. Subsequently, experiments were carried out under conditions of 600 liters concrete microcosms and in 1200 liters concrete mesocosms, with the monitoring of water quality variables (temperature, dissolved oxygen, electrical conductivity and pH), content chlorophyll a, demand biological oxygen (BOD) and chemical oxygen demand (COD) for a period of sixty days after the application of treatments. The mixture diquat + 1% copper hydroxide was the most effective treatment in Hydrilla verticillata of weed control for the majority of parameters, with change in water quality variables. Ecotoxicological experiments were also carried out for non-target organisms (Hyphessobrycon eques, Pomacea canaliculata, Lemna minor and Azolla caroliniana) with diquat, oxychloride and copper hydroxide, wherein the mixture of diquat + 1% copper oxychloride is more toxic to bioindicators organisms and macrophyte Lemna minor was bioindicador with the highest sensitivity to the tested pesticides.

Cette étude doctorale a consisté à décrire la dynamique géochimique de deux pockmarks à hydrates de gaz de la marge africaine en considérant deux approches différentes. La première zone d’étude, appelée Preowei, est située au large du Nigéria. Elle est caractérisée par un grand nombre de pockmarks de tailles différentes, plus ou moins proche les uns des autres. Les analyses géochimiques des échantillons de fluides interstitiels, combinées aux données géophysiques (séismiques) ont permis de mieux comprendre le schéma de migration des hydrocarbures pour un ensemble composé de quatre pockmarks très rapprochés. L’utilisation de ces données géochimiques dans un modèle de transport- réaction a conduit à une datation de plusieurs séquences de libération de gaz au sein de ces structures. Un schéma conceptuel décrivant les processus de formation et d’évolution temporelle des pockmarks a été proposé pour synthétiser les conclusions obtenues. Finalement, cette étude a montré que l’ensemble des pockmarks étudiés sont actifs depuis 2700 ans, qu’ils sont en phase de formation d’hydrates pour certains, et de carbonates pour d’autres. La deuxième structure étudiée est le pockmark Regab. Il est situé au large du Gabon, au nord du canyon sous-marin alimenté par le fleuve Congo. Il est caractérisé par la présence d’hydrates affleurant et une faune abondante et très variée sur toute sa surface. L’originalité de ce travail a été d’étudier la distribution de la mégafaune présente sur ce pockmark en fonction de la nature des fluides qui migrent dans le sédiment superficiel, et qui est libérés dans la colonne d’eau. Une attention particulière a été portée au méthane car c’est un élément central dans le cycle énergétique des microorganismes qui vivent en symbiose avec cette mégafaune. Trois nouveaux habitats ont été étudiés. Les données obtenues, associées à celle de la littérature ouverte, renforcent les conclusions des travaux antérieurs. Les Mytilidés ont besoin de très fortes concentrations de méthane pour se développer. Elles colonisent les zones de sortie de bulles et celle caractérisées par des hydrates affleurants. Les tapis bactériens sont associés à des zones où l’oxydation anaérobique du méthane se déroule dans le sédiment superficiel, avec une méthanogenèse dans la couche sous-jacente. Les Vésicomydé polychètes vivent dans des zones pauvres en méthane et sont très sensibles à sa variation de concentration
The present work describes the dynamics of two pockmark areas, off West Africa. The intention is to propose two different approaches to study the relationships between fluid migration and pockmarks. The first investigated area corresponds to a pockmark cluster called Preowei, located off Nigeria. Geochemical analyses and modeling were combined with seismic data to detail the hydrocarbon migration pattern at this area, with implication on both the pockmark formation and the evolution of their morphology. The proposed interpretation seeks to identify the conceptual bases of pockmark evolution over time at this area. It is argued that the cluster has been active for at least 2700 years, and it is still at the stage of hydrate formation for some pockmarks and carbonate formation for other. The second investigated pockmark, called Regab, is located off Gabon. It is a giant pockmark of 800-m diameter, characterized by an ecosystem rich in fauna, with a large variety of living species. The main core of the work done on this pockmark was focused on finding a link between the fluid chemistry and the spatial distribution of the living communities which populate it. This was achieved by combining new geochemical and bathymetric results with a well-compiled dataset from the literature

While global demand for energy is increasing, it is mostly covered by fossil energies, like oil and natural gas. Principally composed of hydrocarbons (methane, ethane, propane ...), reservoir fluids contain also impurities such as carbon dioxide, hydrogen sulphide and nitrogen. To meet the request of energy demand, oil and gas companies are interested in new gas fields, like reservoirs containing high concentrations of acid gases. Natural gas transport is done under high pressure and these fluids are also saturated with water. These conditions are favourable to hydrates formation, leading to pipelines blockage. To avoid these operational problems, thermodynamic inhibitors, like methanol or ethanol, are injected in lines. It is necessary to predict with more accuracy hydrates boundaries in different systems to avoid their formation in pipelines for example, as well as vapour liquid equilibria (VLE) in both sub-critical regions. Phase equilibria predictions are usually based on cubic equations of state and applied to mixtures, mixing rules involving the binary interaction parameter are required. A predictive model based on the group contribution method, called PPR78, combined with the Cubic – Plus – Association (CPA) equation of state has been developed in order to predict phase equilibria of mixtures containing associating compounds, such as water and alcohols. To complete database for multicomponent systems with acid gases, VLE and hydrate dissociation point measurements have been conducted. The developed model, called GC-PR-CPA, has been validated for binary systems and applied for different multicomponent mixtures. Its ability to predict hydrate stability zone and mixing enthalpies has also been tested. It has been found that the model is generally in good agreement with experimental data.

The aims of this research project were to assist in understanding hydrate formation, stability, and scientific aspects of CO2 storage as a liquid and CO2 hydrate. These have been addressed by two investigatory pathways: hydrate stability modelling and hydrate formation within sediments (in synthetic CO2 hydrates and natural methane hydrates). Developed computer models predict large regions offshore Western Europe with the potential to store considerable volumes of CO2 as a hydrate. Laboratory experiments have also shown CO2 hydrate to form rapidly and relatively easily in sandy sediments, cementing the sediment grains. In water-rich environments hydrate appears to create pore-filling cement impeding further CO2 flow to underlying sediments, which may aid trapping of an underlying liquid store. Fortunate acquisition of natural hydrate cores from Cascadia Margin also allowed investigation of natural methane hydrate formation; revealing a number of well-preserved methane hydrate morphologies, and complex brine filled pore networks within the hydrate, resulting from different rates of growth. Results highlight a number of research areas, which need addressing through further investigations. However, these preliminary investigations support CO2 storage as a hydrate as a potential feasible storage method, and this method should be pursued further as an emissions reducing mitigation strategy.

Gas Hydrates are a specific type of inclusion compound in which water molecules arrange themselves by hydrogen bonding to form cages accommodating a guest molecule of appropriate size. These compounds are thermodynamically stable at low temperatures (~ 0°C) and relatively high pressures. These conditions are typically found in deep oceans and make gas hydrates the most abundant hydrocarbon source on earth. Gas hydrates have also been investigated because they are known to plug oil pipelines. Experiments were carried out to determine how efficient VP/VC was at slowing down gas hydrate formation when compared to de-ionized water. Kinetics of formation of methane hydrate film was compared using two measurement methods: Microscopy and gas consumption. Experiments were conducted for each solution at temperatures and pressures ranging from 274-278 K and 5000-7000 kPa respectively. Gas consumption by the system and spatial movement of the hydrate film were monitored simultaneously. It was noticed that hydrate film growth measured by microscopy could be separated in two steps; initial and second growth stages. Initial growth rates measured were significantly higher than second growth rates (3 to 300 times higher). It is suspected that liquid saturation affects initial growth rates and initial film thicknesses. It was noticed that at 1 and 2°C, initial growth rates in presence of VP/VC were higher than with water. Initial growth rates with VP/VC were lower than those of water at 3°C. Results of initial film thicknesses show an inversely proportional trend with subcooling conditions. Second growth rates were shown to increase when hydrate formation driving force increased in presence of water. Results with VP/VC were significantly lower than with water and were not shown to depend noticeably on experimental conditions.
Les hydrates gazeux font partis de la catégorie des complexes d’inclusion. Ce type de molécule se forme lorsque des molécules d’eau se structurent par liaisons hydrogène pour former une cage pouvant accepter une molécule «invité» d’une grandeur appropriée. Ces complexes sont thermodynamiquement stable à basse temperatures (~ 0°C) et pressions relativement élevées. Ces conditions sont reproduites dans les fonds marins. Ceux-ci abritent une énorme quantité d’hydrates gazeux, ce qui en fait la plus grande source d’hydrocarbures sur terre. Les hydrates gazeux sont également étudiés parce qu’ils se forment dans les conduits transportant du gaz ou du pétrole causant plusieurs problèmes. Une série d’expériences a été réalisée afin de déterminer l’efficacité de VP/VC à ralentir la croissance d’hydrates par rapport à une solution d’eau déionisée. La cinétique de formation d’une pellicule d’hydrate a été comparée en utilisant deux méthodes d’analyse: la microscopie et la consommation de gaz par le système. Les pressions and températures examinées pour chaque solution variaient respectivement entre 5000-7000kPa et 274-276K. La consommation de gaz et la hauteur du film étaient suivies tout au long de l’expérience. Il a été remarqué que la période de croissance du film d’hydrates mesurée par microscopie pouvait être séparée en deux phases distinctes: la croissance initiale et la deuxième croissance. La vitesse de croissance initiale mesurée était significativement supérieure à celle de la deuxième croissance (3 à 300 fois supérieure). La saturation de la phase liquide est suspectée d’influencer les valeurs de vitesse de croissance initiale ainsi que la hauteur initiale du film. La vitesse croissance initiale mesurée avec VP/VC était plus élevée qu’en présence d’eau déionisée à 1 et 2°C. Les résultats à 3°C montraient une tendance inverse. Les estimations d

Polymorphism presents complex issues for the pharmaceutical industry from processing, regulatory, patenting and stability perspectives. It can be further challenging to control the same form throughout processing and development when it has the capacity to form a hydrate. Incorporation of water into the crystal lattice contributes to significant differences in solubility, stability and bioavailability of the active pharmaceutical ingredient (API). During processing and formulating steps, water is used in many procedures such as, recrystallisation, wet granulation, aqueous coating lyophilisation etc. This can trigger anhydrous to hydrate conversion and could be detrimental for bioavailability and stability of the product. The factors responsible for this type of transition such as, role of solvent, activity of solvent, thermodynamic stability of different forms, equilibrium conditions, processing induced transformations are investigated. Theophylline, a channel hydrate, is chosen as a model compound which exhibits both polymorphs and solvates. The value of water activity at which the theophylline monohydrate is thermodynamically stable form was investigated using solubility, cooling crystallisation and slurry experiments and found to be aw 2: 0.70 at 25 QC. Full characterisation of the solid state chemistry of theophylline has resulted in the discovery of a new, previously unreported, anhydrous form of theophylline, called Form IV. Using solubility, crystallisation, slurrying and thermal experiments, Form IV was found to be thermodynamically more stable than the currently known stable form, Form H. The crystal structure of Form IV and Form I was determined by single crystal :X-Ray diffraction technique. The crystal structures for Form IV and Form I are deposited in Cambridge Structural Database (CSD) with reference code BAPLOT03 and BAPLOT04 respectively. The experimentally observed stability behaviour was correlated with the structural features of solid forms and also with the energy calculations. The kinetic ally stable Form H serves as the intermediate for polymorphic and hydrate-anhydrate transformations as the catemer motif observed in Form II can easily propagate by forming a strong and directional hydrogen bonds. In contrast, the dimer of theophylline molecules as observed in Form IV needs the presence of solvent to link through other dimers only by weak interactions. This results in the generation of Form IV only via solvent mediated transformations. Solid state chemistry of hydrate forming compounds Theophylline has also been used here as a model compound to study eo crystallisation with various saturated, dicarboxylic acids. A new, eo crystal of theophylline with adipic acid was generated and using thermal methods and PXRD, the stoichiometry (1 :2, adipic acid: theophylline) is confirmed. The complex hydration-dehydration behaviour of theophylline was investigated. The samples subjected to different pharmaceutical processing conditions for hydration-dehydration, generated various .intermediate phases suggesting multiple dehydration mechanisms and the potential of phase transformations during processing of such kind of hydrate forming compounds. The sensitivity of thermal methods over other bulk methods such as PXRD, in detecting a small amount of phase impurity, has been highlighted.

Homogeneous single C-S-H gels have been prepared for the investigation of alkali binding potential and crystallisation. A distribution coefficient, R_d, was introduced to express the partition of alkali between solid and aqueous phases at 25°C. R_d is independent of alkali hydroxide concentration and depends only on Ca:Si ratio over wide ranges of alkali concentration. The trend of numerical values of R_d indicates that alkali bonding into the solid improves as its Ca:Si ratio decreases. Reversibility is demonstrated, indicating a possibility of constant R_d value of the material. Al has been introduced to form C-A-S-H gels and their alkali sorption properties also determined. Al substituted into C-S-H markedly increases R_d, indicating enhancement of alkali binding. However, the dependence of R_d on alkali concentration is non-ideal with composition. A two-site model for bonding is presented. Crystallisation both under saturated steam and 1 bar vapour pressure has been investigated. It has been shown that heat treatment by saturated steam causes crystallisation of gels. The principal minerals obtained were (i) C-S-H gel and Ca(OH)₂ at ~55°C, (ii) 1.1 nm tobermorite, jennite and afwillite at 85-130°C, and (iii) xonotlite, foshagite and hillebrandite at 150-180°C. Properties of crystalline C-S-H were also reported for reversible phase transformation, pH conditioning ability, seeding effect and solubility. At 1 bar pressure, crystallisation is slower than in saturated steam due to lower water activity. Tobermorite-like nanodomains develop during reaction at low Ca/Si ratios. In some Ca-rich compositions, Ca(OH)₂ is exsolved and occurs as nano-sized crystallites.

Thesis (S.M. in Geophysics)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 21-23).
I show that perchlorate hydrates, which have been indirectly detected at high Martian circumpolar latitudes by the Phoenix Mars Lander, have a dramatic effect upon the rheological behavior of polycrystalline water ice under conditions applicable to the north polar layered deposits (NPLD). I conducted subsolidus creep tests on mixtures of ice and magnesium perchlorate hexahydrate (MP6) of 0.02, 0.05, 0.10, and 0.47 volume fraction MP6. I found these mixtures to be increasingly weak with increasing MP6 content. For mixtures with by Hendrik J. Lenferink.
S.M.in Geophysics

Methane hydrates are frozen deposits of methane and water found in high pressure or low temperature sediments. When these deposits destabilize, large quantities of methane can be emitted into the atmosphere. This is significant to climate change because methane has 25 times more greenhouse gas potential than Carbon Dioxide. Worldwide, it is estimated there are between 2500 and 10000 gigatons of methane stored in hydrate deposits. This represents more carbon than all fossil fuels on Earth. It is estimated that between 200 and 2000 gigatons of methane are stored in hydrates in Arctic waters acutely vulnerable to greenhouse warming. Over the last decade, researchers have identified instances of hydrate destabilization that have already begun. To gain insight into the potential climatic effects widespread hydrate dissociation would have, researchers have examined hydrate dissociation during the Paleocene Eocene Thermal Maximum 55 million years ago as a geologic precedent. In this period, large-scale hydrate dissociation contributed to 5-8 degree Celsius warming worldwide. If such a climatic shift were to transpire today, impacts on society would be enormous. There is currently a debate in the scientific community as to whether the risk of methane hydrate dissociation is relevant to the present generation. One side argues that not enough methane could be emitted into the atmosphere from today’s hydrate sources to have a meaningful impact on climate warming, where the other side contends that more than enough methane could be emitted from present day hydrate deposits to cause significant impacts to the global greenhouse effect. Given the information currently known about hydrates, it is reasonable to conclude there is a moderate risk of widespread destabilization that could impact global climate change in the coming decades. Significant acceleration of the conversion to alternative energies and implementation of geoengineering strategies should be considered.

Gas hydrate deposits are known to store vast amounts of methane, and occur worldwide in marine and permafrost regions. Methane emissions driven by hydrate dissociation may contribute to submarine slope failures, geohazards to deep water infrastructures, and possibly climate change. Alternatively, hydrates are perceived as a viable energy resource. These environmental and economic implications mean that gas hydrate research is of both academic and industrial interest. To determine the environmental impact or economic potential of gas hydrate accumulations in any given geologic setting with a high level of confidence, it is mandatory to acquire lithological and geophysical information for a well-constrained joint interpretation. Robust delineation and quantification of gas hydrate structures is not a trivial task, due to inherent uncertainties from the absence of information regarding the physical properties of the reservoir of interest. In this thesis, I develop a rigorous joint interpretation scheme using marine controlled-source electromagnetic (CSEM), seismic and core data coupled by effective medium modelling, for the detection, delineation, and quantification of marine gas hydrate structures. The study area for this research is the CNE03 pockmark, situated on the Norwegian continental slope, Nyegga region, offshore Norway. The CNE03 pockmark is underlain by a pipe-like structure, where gas hydrate and free gas coexist. Marine CSEM data and sediment cores were acquired from the CNE03 pockmark, integrated and interpreted with collocated high-resolution two-dimensional seismic reflection and three-dimensional tomographic seismic data. The CNE03 pipe-like hydrate structure is detected and characterised using unconstrained and seismically constrained CSEM inversions of data obtained by ocean bottom electric field receivers (OBE). The unconstrained CSEM inversions detected the CNE03 pipe-like structure satisfactorily though with undefined and diffusive margins, which is mitigated by the seismically constrained inversions that improved the delineation of the CNE03 boundaries significantly. High-resolution resistivity imaging of the CNE03 pipe-like structure is achieved by a combined CSEM inversion of both the OBE and 3-axis towed electric field receiver (Vulcan) data. Robust quantification of hydrate content within the CNE03 structure is derived by comparison between CSEM and seismic datasets with joint elastic-electrical effective medium modelling scheme. The work I present in this thesis provides an integrated approach to elucidate both structural and fluid properties of sub-seafloor gas hydrate and free gas deposits. The joint interpretation framework applied here could also be utilised to map and monitor seafloor mineralisation, freshwater reservoirs, carbon capture and storage sites, and near-surface geothermal systems.

Thesis (Ph. D.)--University of California, San Diego, 2008.
Title from first page of PDF file (viewed Nov. 19, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 135-147).

Thesis (Ph.D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2008.
Committee Chair: J. Carlos Santamarina; Committee Member: Carolyn D. Ruppel; Committee Member: Costas Tsouris; Committee Member: Glenn J. Rix; Committee Member: J. David Frost

En France, les matériaux à base de ciment sont utilisés comme matrice de conditionnement des déchets nucléaires de faible et moyenne activité. La radiolyse de l'eau est due aux déchets nucléaires stockés dans les matériaux. La formation de ses produits radiolytiques tels que le gaz H₂ doit être évaluée pour des raisons de sécurité. Les silicates de calcium hydratés (C-S-H) représentent le principal produit (50%) d'hydratation du ciment Portland (CP). L’objectif de cette étude est de comprendre les mécanismes radiolytiques de la production d'hydrogène dans les C-S-H, d'étudier l'effet d'impuretés (telles que des ions alcalins, hydroxydes ou nitrates supplémentaires) sur la production de gaz H₂ dans les C-S-H et d'examiner l'existence d'interactions entre les phases principales (C-S-H et portlandite) du ciment Portland. Après avoir caractérisé les échantillons par diverses techniques, ils ont été soumis à différents types d'irradiation (faisceaux gamma et électrons et ions lourds (HI) pour déterminer leur rendement radiolytique en H₂, G(H₂). Dans les C-S-H, il a été démontré que, sous irradiation gamma, la production d’H₂ est indépendante de la teneur en eau et que les C-S-H produisaient autant d’H₂ que la même masse d’eau. Ainsi, le mécanisme de production d’hydrogène est très efficace dans les C-S-H. La comparaison entre les résultats obtenus sous rayons gamma et ceux obtenus sous HI implique qu’il n'y a pas ou peu d'effet de transfert d’énergie linéique (TEL) dans les C-S-H. Ainsi, les réactions de recombinaison semblent limitées. L’introduction d’ions nitrates dans la structure des C-S-H induit une diminution importante du G(H₂). L’irradiation des hydrates de C2S et C3S constitués majoritairement de C-S-H et de portlandite indique qu’il n’y a pas de phénomènes de transfert d’énergie entre ces phases. Enfin, les expériences de spectroscopie par résonance paramagnétique électronique (RPE) ont permis de proposer des mécanismes radiolytiques dans les C-S-H. L’ensemble de ces résultats nous permettent de mieux comprendre les effets d’irradiation dans les ciments
In France, cementitious materials are used as conditioning matrix of low level and intermediate level nuclear wastes. Water radiolysis occurs due to the nuclear wastes stored in the materials. The formation of its radiolytic products such as H₂ gas must be evaluated for safety reasons. Calcium silicate hydrate (C-S-H) is the main product (50%) of hydration of Portland Cement (PC). The aim of this study is to understand the radiolytic mechanisms of the hydrogen production in C-S-H, to investigate the effect of impurities (such as alkali ions, additional hydroxides or nitrates ions) on H₂ gas production in C-S-H and to examine if interactions exist between different main phases (C-S-H and portlandite) in cement matrix. After using various characterization techniques, samples were submitted to different types of irradiation (gamma rays and electrons and heavy ions (HI) beams) to determine their H₂ radiolytic yield, G(H₂). In C-S-H system, it has been shown, under gamma irradiation, that G(H₂) does not depend on water content, moreover, C-S-H system itself produce efficiently H₂ gas. The comparison between the results obtained under gamma rays and that obtained under HI implies: there is no/ low LET effect in C-S-H. While with nitrate ions in C-S-H, a large decrease of G(H₂) is observed. Irradiation of C2S and C3S hydrates mainly composed of C-S-H and portlandite shows that here is no energy transfer phenomena between these two phases. Finally, the electron paramagnetic resonance (EPR) spectroscopy experiments have enabled proposing radiolytic mechanisms. All these results help us to understand the radiation effects in cements

Thermophysical properties (dissociation enthalpy, heat capacity, metastability) and compositional properties (hydrate number, free water and fractionation) of natural gas hydrate were studied experimentally on samples that contained large amounts of ice. Methods for continuous hydrate production and sampling, and for quantification of the properties were developed. Hydrate was produced from a natural gas of ethane (5 %mol) and propane (3 %mol) in methane.

A low temperature scanning calorimetry method was developed to measure dissociation enthalpy, heat capacity, hydrate number and free water (ice). During the analysis, the hydrate samples were pressurized to 1.7 MPa with methane and the system operated between the hydrate equilibrium curves of methane and the hydrate forming natural gas. A sample conditioning procedure eliminated thermal effects of desorption as the ice melted. Desorption occurred since the samples were produced and refrigerated to 255 K under a natural gas pressure of 6-10 MPa, but were analyzed and melted under a methane pressure of 1.7 MPa.

A low temperature isothermal calorimetry method was developed to quantify the metastability properties. Metastability was confirmed for temperatures up to 268 K and quantified in terms of the low dissociation rate.

Fractionation data were obtained in the range 3.0 to 7.5 MPa and for subcoolings between 2 and 16 K. High pressure and large subcooling is desirable to suppress fractionation. A fractionation model was proposed. The model coincides with the van der Waals-Platteeuw model for zero subcooling. No fractionation is assumed for hypothetical hydrate formation at infinite driving force (subcooling). Between these two extremes an exponential term was used to describe the fractionation. The model predicted fractionation with an accuracy of about 1%abs corresponding to 1-10%rel.

Gas hydrate is a naturally occurring crystalline compound formed by water molecules and encapsulated gas molecules. The interest in gas hydrate reflects scientific, energy and safety concerns - climate change, future energy resources and seafloor stability. Gas hydrates form in the pore space of sediments, under high pressure and low temperature conditions. This research focuses on the fundamental understanding of hydrate bearing sediments, with emphasis on mechanical behavior, thermal properties and lens formation. Load-induced cementation and decementation effects are explored with lightly cemented loose and dense soil specimens subjected to ko-loading; the small-strain stiffness evolution inferred from shear wave velocity measurement denounces stiffness loss prior to structural collapse upon loading. Systematic triaxial tests address the intermediate and large strain response of hydrate bearing sediments for different mean particle size, applied pressure and hydrate concentration in the pore space; hydrate concentration determines elastic stiffness and undrained strength when Shyd>45%. A unique sequence of particle-level and macro-scale experiments provide new insight into the role of interparticle contact area, coordination number and pore fluid on heat transfer in particulate materials. Micro-mechanisms and necessary boundary conditions are experimentally analyzed to gain an enhanced understanding of hydrate lens formation in sediments; high specific surface soils and tensile stress fields facilitate lens formation. Finally, a new instrumented high-pressure chamber is designed, constructed and field tested. It permits measuring the mechanical and electrical properties of methane hydrate bearing sediments recovered from pressure cores without losing in situ pressure (~20MPa).

Gas hydrate consists of guest gas molecules encaged in water molecules. Methane is the most common guest molecule in natural hydrates. Methane hydrate forms under high fluid pressure and low temperature and is found in marine sediments or in permafrost region. Methane hydrate can be an energy resource (world reserves are estimated in 20,000 trillion m3 of CH4), contribute to global warming, or cause seafloor instability. Research documented in this thesis starts with an investigation of hydrate formation and growth in the pores, and the assessment of formation rate, tensile/adhesive strength and their impact on sediment-scale properties, including volume change during hydrate formation and dissociation. Then, emphasis is placed on identifying the advantages and limitations of different gas production strategies with emphasis on a detailed study of CH4-CO2 exchange as a unique alternative to recover CH4 gas while sequestering CO2. The research methodology combines experimental studies, particle-scale numerical simulations, and macro-scale analyses of coupled processes.

The objective of this study is to determine hydrate formation conditions of methane- hydrogen sulfide mixtures. During the study, an experimental work is carried out by using a system that contains a high-pressure hydrate formation cell and pressure-temperature data is recorded in each experiment. Different H2S concentrations and both brine and distilled water are used in the experiments and the Black Sea conditions, which are suitable for methane-hydrogen sulfide hydrate formation are examined. Considering the pressure-temperature data obtained, hydrate equilibrium conditions are determined as well as the number of moles of free gas in the hydrate formation cell. The change in the number of moles of free gas in the hydrate formation cell with respect to time is considered as a way of determining rate of hydrate formation. Effects of H2S concentration and salinity on hydrate formation conditions of methane-hydrogen sulfide mixtures are also studied. It is observed that an increase in the salinity shifts the methane-hydrogen sulfide hydrate equilibrium condition to lower equilibrium temperatures at a given pressure. On the other hand, with an increase in H2S concentration the methane hydrogen sulfide hydrate formation conditions reach higher equilibrium temperature values at a given pressure. After the study, it can be also concluded that the Black Sea has suitable conditions for hydrate formation of methane hydrogen sulfide mixtures, considering the results of the experiments.

The objective of this study is to determine hydrate formation conditions of a multicomponent polymer based drilling fluid. During the study, experimental work is carried out by using a system that contains a high-pressure hydrate formation cell and pressure-temperature data is recorded in each experiment. Different concentrations of four components of drilling fluid, namely potassium chloride (KCl), partially hydrolyzed polyacrylicamide (PHPA), xanthan gum (XCD) and polyalkylene glycol (poly.glycol) were used in the experiments, to study their effect on hydrate formation conditions.

This thesis is divided into several parts. The first part deals with hydrate theory and where hydrates form in the gas-and oil-dominated systems. A review of how hydrate plugs is formed and a method for removing hydrate plugs safely is also included.Simplified HYSYS models of the upstream part of Ormen Lange and Snøhvit gas fields on the Norwegian Continental Shelf constituted the basis for answering the second part of the task. Data from private conversations, reports, slide presentations, and other documents were used to create the models.Based on the models, calculations were made on the injection rate and storage capacity of mono ethylene glycol (MEG) on Ormen Lange and Snøhvit. The same models and calculation methods were used to determine injection rates for both methanol (MeOH) and MEG on the same fields. All the results combined with literature were then used to compare the inhibitors’ properties to determine which one was best suited for use on the current fields. During rate calculations several cases were made to determine which factors have the greatest impact on the amount of inhibitor needed.It was found that hydrates are formed on the pipe wall in gas dominated pipelines, while they are formed in the bulk flow in oil-dominated systems. The heat transfer coefficient and the seabed temperature have great influence on the amount of inhibitor needed. MEG-rate and storage capacity on Snøhvit are very large. Ormen Lange needs a larger inhibitor injection rate than Snøhvit. MEG is better suited than MeOH as an inhibitor of long-distance multi-phase tie-backs such as Ormen Lange and Snøhvit.

Gas hydrates are crystalline compounds with cage-like structures formed by hydrogen-bonded water molecules hosting guest molecules such as light hydrocarbons and CO₂. They are known to: • represent a potential reserve of natural gas embedded in seabed and permafrost sediments • pose a flow assurance challenge to the oil and gas industry Molecular dynamics simulations are employed to study the processes of gas hydrate decomposition and inhibition. To mimic the porous environment of the real gas hydrate reservoirs, hydroxylated silica surfaces are included in the simulations and placed in contact with hydrate and water. Water molecules wet the silica surfaces and form a meniscus, confirming the hydrophilic properties of the hydroxylated silica surface. It is found that the silica surface alters the characteristics of the confined water up to ~6 Å away from the surface. The decomposition of methane hydrate in the presence of silica surfaces, 34 to 40 Å apart, follows a concerted behavior where layers of hydrate cages at the curved dissociation front collapse almost simultaneously. The rate of hydrate dissociation in contact with a silica surface is faster compared to that of a hydrate phase just in contact with bulk water. Additionally, the decomposition leads to the formation of methane-rich regions (nano-bubbles) in the liquid water phase. In more realistic simulations, gas reservoirs are added to the simulations to determine whether the formation of nano-bubbles is a general feature of the hydrate decomposition process. It is found that the nano-bubbles can form under simulation conditions where the dissociation rate is faster than the diffusion rate, thus generating dissolved methane mole fractions of greater than 0.044 that would lead to bubble nucleation. Finally, the binding mechanism of the alpha-helical 37 amino acid residue winter flounder antifreeze protein, which is a candidate as a kinetic hydrate inhibitor to methane hydrate, is determined to be the result of cooperative anchoring of the pendant methyl groups of the threonine and two alanine residues, four and seven places further down in the protein sequence, to the empty half cages at the hydrate surface.
Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate

The presence of inhibitors delayed hydrate nucleation and decreased the overall formation of methane/ethane/propane hydrate compared to pure water system. However, the two classes of inhibitors: chemical (Polyvinylpyrrolidone (PVP) and industrial inhibitor: H1W85281) and a biological (Type I and III antifreeze protein (AFP)) were distinguished by the formation of hydrates with different stabilities. A single hydrate-melting peak was seen with the AFP-III and this was consistent after re-crystallization. In contrast, multiple hydrate melting events were observed in the presence of the chemical inhibitors. In stirred reactor, onset of hydrate decomposition occurred earlier in the presence of the inhibitors compared to water controls. However, depending on the type of inhibitor present during crystallization, hydrate decomposition profiles were distinct, with a longer, two-stage decomposition profile in the presence of the chemical inhibitors. The fastest, single-stage decompositions were characteristic of hydrates in experiments with either of the AFPs. Powder X-ray diffraction and nuclear magnetic resonance spectroscopy showed that structure II hydrates dominated, as expected, but in the presence of the chemical inhibitors structure I was also present. Raman spectroscopy confirmed the complexity and the heterogeneity of the guest composition within these hydrates. However, in the presence of AFP-III, hydrates appeared to be relatively homogeneous structure II hydrates, with weaker evidence of structure I. When individual gas cage occupancies were calculated, in contrast to the near full occupancy of large cages with these inhibitors, almost 10% of the large cages were not filled when hydrates were formed in the presence of AFP-III, likely contributing to the easy decomposition of such hydrates seen in DSC and stirred reactor experiments. These results argue that thought must be given to inhibitor-mediated decomposition kinetics when designing and screening of new kinetic inhibitors. This is a necessary practical consideration for industry in cases when due to long shut in periods; hydrate formation may be unavoidable even when inhibitors are utilized. This heterogeneity suggests that using these chemical inhibitors (PVP and H1W85281) may present a special challenge to operators depending upon the gas mixture and environmental conditions, and that AFPs may offer a more predictable, efficacious solution in these cases.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
Uma combinação de fatores geológicos e econômicos exige que as empresas produzam petróleo e gás em campos com profundidades de água cada vez maiores. Muitas das vezes não é econômico, ou no pior dos casos impraticável, instalar uma plataforma sobre os cabeçotes dos poços, por isso acaba se tornando comum transportar petróleo e gás através de amarras submarinas que podem ser de até 145km ou mais. Geralmente isso significa que as temperaturas são baixas o bastante e as pressões altas o suficiente para tornar aquele ambiente dentro do que chamamos de envelope de formação de hidrato e ações deverão ser tomadas afim de evitar os plugs de hidrato. Como resultado, a indústria foi forçada a intensificar sua pesquisa em químicos e sistemas que evitasse a formação da estrutura cristalina. Uma dessas pesquisas em estudo é a avaliação de um fluido modelo, emulsão A/O, analisando suas principais características e verificando as propriedades reológicas da estrutura cristalina em formação. Para tornar a pesquisa viável, este hidrato é formado a pressão atmosférica utilizando moléculas hóspedes que proporcionam essa formação em tal pressão e baixa temperatura. Logo, é utilizada uma substância líquida chamada ciclopentano, que substituirá o gás natural e irá proporcionar a formação do hidrato nestas novas condições. Dessa forma, este trabalho apresentou diferentes emulsões A/O, de acordo com a porcentagem de água, e reologia do hidrato formado para cada uma delas.
A combination of geological and economic factors requires companies to produce oil and gas in fields with increasing water depths. It is often impractical to install a platform over the heads of the wells, so it is becoming common to transport oil and gas through underwater moorings that can be up to 145 km or more. Usually this means that the temperatures are low enough and the pressures high enough to make that environment into what we call a hydrate formation envelope and actions should be taken to avoid the hydrate plugs. As a result, the industry was forced to intensify its research into chemicals and systems that prevented the formation of the crystalline structure. One of these researches is the evaluation of a model fluid, A / O emulsion, analyzing its main characteristics and checking the rheological properties of the crystalline structure in formation. To make the search feasible, this hydrate is formed at atmospheric pressure using guest molecules that provide such formation at such pressure and low temperature. Therefore, a liquid substance called cyclopentane is used, which will replace the natural gas and will provide the formation of the hydrate under these new conditions. In this way, this work presented different A / O emulsions, according to the percentage of water, and rheology of the hydrate formed for each of them.

Hydrate formation in oil and gas pipelines can be troublesome and often, without a proper remediation, the formation of hydrates can lead to a pipe blockage. As hydrate formation is a non-isothermal process, the modelling of the thermodynamic behaviour of the phases within the flow is proposed. A single energy equation has been formulated and verified with parametric analyses. A new hydrate kinetics routine, based on a two-step hydrate formation mechanism, in an oil-dominated flow is proposed. The first step involves the mass transfer of gas from the free gas phase into the oil (gas dissolution rate) and the second step is the mass transfer of the dissolved gas into the water (gas consumption rate). Suitable models in the form of transport equations for each mechanism, together with appropriate closure relations to account for the agglomeration of hydrate particles and hydrate slurry viscosity, are formulated. Both the energy equation and the hydrate kinetics routine were integrated into an existing in-house research code, TRIOMPH (Transient Implicit One-Dimensional Multiphase). The model was tested and validated against two flow loop experiments, and has shown good agreement. Advancement over the only other existing model in predicting hydrate formation in the heavily slugged hypothetical pipe, has also been shown, giving the current model versatility in simulating both slug and non-slug cases.