Dissertationen zum Thema „Carbonate“

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A petrofísica computacional é uma técnica que vem sendo utilizada cada vez mais na indústria do petróleo para caracterizar reservatórios e simular computacionalmente o seu comportamento físico. Através dessa técnica é possível caracterizar um elevado número de amostras, sob diferentes condições ambientais, em um tempo relativamente curto. Este trabalho propõe um modelo de estimativa de permeabilidade que utiliza parâmetros petrofísicos retirados de imagens de microtomografia de raios x (µCT) e os compara com parâmetros petrofísicos medidos em laboratório. Foi analisado um conjunto de 19 amostras com características deposicionais, diagenéticas e texturais diferentes entre si, pertencentes às bacias do Araripe, Potiguar e Sergipe-Alagoas. Delas, 14 são de calcário, 2 de tufa calcária, 2 de caliche e 1 de dolomito. Em laboratório foi utilizado um permoporosímetro a gás para medir os parâmetros porosidade e permeabilidade. As amostras de µCT foram adquiridas com resolução em torno de 2,0 µm. O conjunto de imagens criado foi tratado no software Avizo Fire e foram extraídos os parâmetros porosidade, permeabilidade, conectividade e diâmetro equivalente de poros. Um modelo estatístico foi estabelecido para predição da permeabilidade a partir dos parâmetros do espaço poroso extraídos das imagens de µCT. Os resultados indicam que a conectividade dos microporos, inferida a partir do cálculo do Número de Euler em imagens 3D, é o parâmetro que exerce maior influência na estimativa da permeabilidade, seguida pela porosidade dos macroporos e pela conectividade dos macroporos. O modelo preditivo proposto apresentou um coeficiente de determinação de 0,994, mostrando-se bastante confiável para o grupo de amostras investigado.
Computational petrophysics is a technique that has been increasingly used in the petroleum industry to characterize reservoirs and to simulate computationally its physical behavior. Through this technique it is possible to characterize a big number of samples, under different environmental conditions, in a relatively short time. This work proposes a model of permeability estimation that uses petrophysical parameters taken from x - ray microtomography images (µCT) and compare them with petrophysical parameters measured in the laboratory. It was analyzed a set of 19 samples with different depositional, diagenetic and textural characteristics, belonging to the Araripe, Potiguar and Sergipe - Alagoas basins. Of these, 14 are limestones, 2 of tufa limestone, 2 of caliche and 1 of dolomite. In the laboratory a gas permoporosimeter was used to measure the porosity and permeability parameters. µCT samples were obtained with a resolution of about 2.0 μm. The set of images created was treated in Avizo Fire software and the porosity, permeability, connectivity and pore diameter parameters were extracted. A statistical model was established to predict permeability from pore space parameters extracted from µCT images. The results indicate that the connectivity of micropores, inferred from the calculation of the Euler Number in 3D images, is the parameter that exerts the greatest influence in the estimation of permeability, followed by the porosity of the macropores and the connectivity of the macropores. The proposed predictive model presented a coefficient of determination of 0.994, being very reliable for the group of samples investigated.

En domaine de plate-forme carbonatée épicontinentale peu profonde, la production sédimentaire est étroitement liée aux variations eustatiques, au climat et à la position paleogéographique. Les périodes d’émersion constituent des phases de non-dépôt durant lesquelles l’arrêt de l’enregistrement sédimentaire peut être relayé par un enregistrement diagénétique. Les transformations associées aux discontinuités (réarrangement des porosités, modifications lithologiques, circulations tardives…) peuvent avoir un rôle déterminant sur les propriétés pétrophysiques des réservoirs carbonatés. La détection des surfaces d’émersion et des produits diagénétiques associés apparaît donc essentielle pour préciser la qualité des réservoirs, par (1) la compréhension des processus sédimento-diagénétiques aux limites de séquence, (2) la comparaison de données d’affleurement et de subsurface, et la caractérisation des géométries des réservoirs associés, (3) l’analyse de l’impact de la diagenèse associée à ces surfaces (amélioration ou détérioration des propriétés réservoir).La Formation Natih d’Oman (Albien sup. – Turonien inf.) se situe au sommet d’une épaisse série de plates-formes carbonatées peu profondes et de grande extension géographique (marge de la Néotéthys). La Formation Natih est subdivisée en quatre séquences majeures (3ème ordre) constituées d’unités transgressives tabulaires à faiblement inclinées (rampe à faciès boueux) et de prismes régressifs progradants plus inclinés (barrière bioclastique bien différenicée protégeant un domaine de lagon interne) (van Buchem et al. 2002). Ces séquences se terminent par une ou plusieurs surfaces d’émersion, pouvant être associées à des incisions (Grélaud et al. 2006). La présente étude porte sur l’analyse diagénétique de ces surfaces d’émersion par l’intégration de données de terrain (Foothills d’Adam, Jebel Akhdar) et de subsurface (carottes de forage et données de puits de champs pétroliers voisins).L’analyse diagénétique détaillée des affleurements et des données de subsurface repose sur l’étude de la chronologie relative et de la répartition spatiale des phases diagénétiques associées aux surfaces d’émersion. Elle démontre la mise en place d’une diagenèse précoce dans des conditions relativement arides qui se traduisent par l’absence de karstification et de phénomènes pédogénétiques bien développés sur la plate-forme émergée. Sous les surfaces, des circulations de fluides météoriques oxydants, alimentés par des recharges latérales, entrainent une dissolution précoce des minéralogies instables et la précipitation de ciments météoriques en domaine phréatique. Cette étude diagénétique est complétée par l’analyse des phases mésogétiques et télogénétiques qui permettent de contraindre la séquence diagénétique de la Formation Natih avec les grandes étapes de déformations tectoniques et d’enfouissement.A partir de ces résultats, les produits diagénétiques et leur impact sur l’évolution des réservoirs peuvent être caractérisés et interprétés pour chaque surface. Ils résultent d'interactions complexes entre des facteurs intrinsèques et extrinsèques comme la dynamique de l'aquifère météorique, le contexte paléogéographique et géodynamique au moment des émersions, la maturité du substrat... Ces paramètres sont effectifs au moment du dépôt et des émersions. Toutefois la préservation des produits éogénétiques peut-être fortement influencée par l'évolution au cours de l'enfouissement qui se caractérise par des phénomènes de compaction, cimentation ou dissolution
On epeiric carbonate platforms, sediment production and stratigraphic architecture are mainly controlled by sea-level variations, climate and palaeogeographic position. During periods of subaerial exposure, carbonate production/deposition stops and the sedimentary record can then be replaced by the diagenetic record. The diagenetic transformations associated to discontinuity surfaces (rearrangement of porosity distribution, lithological alteration, late fluid circulation …) may have a significant impact on carbonate reservoir properties. The characterization of subaerial exposure surfaces and associated diagenesis is therefore essential to understand and predict reservoir quality. It requires: (1) the study of the sedimentological and diagenetic processes at the sequence boundaries, (2) the integration and comparison of outcrop and subsurface data, including respective reservoir architecture, (3) the analysis of the diagenetic overprint related to these surfaces (enhancement or deterioration of reservoir properties).The Natih Formation (Late Albian – Early Turonian) is the last of a thick succession of Cretaceous epeiric carbonate platforms. It is subdivided into four third-order sequences. In each sequence, the transgressive phase is formed by flat to slightly sloping units (muddy ramp facies) whereas the regressive phase corresponds to a higher angle prograding carbonate ramp with a well developed bioclastic margin protecting an inner lagoon (van Buchem et al. 2002). These sequences are capped by one or several subaerial exposure surfaces, sometimes associated with incisions (Grélaud et al. 2006). The present study focuses on the diagenetic analysis of these emersion surfaces by the integration of outcrop (Adam Foothills, Jabal Akhdar) and subsurface data (neighbouring oil fields from the interior Oman).The detailed study of the lateral distribution and chronology of the diagenetic phases associated with emersion surfaces form the basis for the sedimentological and diagenetic model. The results highlight the development of a meteoric diagenetic system which was probably subject to relatively arid conditions, explaining the absence of karstification and pedogenetic features on the exposed platform. Below the emersion surfaces, the circulation of oxidizing meteoric fluids, laterally sourced, leads to the early dissolution of unstable minerals and the precipitation of meteoric cements in the phreatic domain.This diagenetic study is completed by the analysis of the mesogenetic and telogenetic phases, which allow to constrain the diagenetic sequence in relation with the main phases of deformation and burial of the Natih Formation.These results show the particularities of each subaerial exposure event in terms of diagenetic products and their impact on reservoir properties. They result from complex interrelations between external and intrinsic factors, such as the dynamics of meteoric aquifers, the geodynamic and paleogeographic context during exposure, chemical reactivity ... These are effective during deposition and subaerial exposure. However, the preservation of exposure-related diagenetic features may subsequently be influenced by burial evolution trough competition between compaction, cementation and dissolution

Carbonate cements in clastic rocks capture a geochemical record of burial processes. As such, much of our understanding of clastic diagenesis and subsurface microbial activity is influenced by studies of carbonate cemented horizons and concretions. Furthermore, their presence can have a significant impact on clastic reservoir quality. However, the formation of cement bodies is poorly understood. A part of this problem is that studies investigating carbonate cements have historically been limited by the δ18Ocarbonate being dependent on both the carbonate precipitation temperature and δ18Oporewater. Often, these variables cannot be constrained and one or the other has to be assumed to derive an interpretation, with significant implications for understanding the fluid history and timing or diagenetic processes. This PhD study applies a new geochemical palaeothermometry technique, "carbonate clumped isotopes", to constrain the temperature of the cement precipitation. With this, the δ18Oporewater can be back-calculated and the formation burial history of changes in δ13C and δ18Oporewater can be constrained. This thesis contains three studies using the clumped isotope technique to investigate carbonate cementation. The first examines outcrop carbonate cements in the Mancos Shale, Colorado, where changes in δ13C and δ18Oporewater are captured over a temperature range of 33-117 °C and placed into a burial history. The second study then examines a variety of cements and concretions from different formations around the world to determine the geochemical conditions necessary for cement precipitation, through trends in δ13C, δ18Oporewater and temperature. This reveals that the temperatures of cementation appears to be strongly controlled by the optimal temperature of activity for subsurface microbes. The final study then applies the technique to subsurface carbonate cements in cores from the Bruce Field, UK North Sea. This places carbonate cementation and the δ18Oporewater into the burial history of one of the reservoir formations. The results of this PhD demonstrate the usefulness of carbonate clumped isotopes for understanding clastic carbonate cementation burial histories, in outcrop and the subsurface. Furthermore, they provide an insight into the temperatures at which microbial processes occur during diagenesis and more generally, the chemical conditions common to carbonate cementation.

The carbon dioxide (CO2) system is the primary buffer in seawater which controls oceanic pH. Changes in the marine CO2 system affect a number of processes such as metal speciation, mineral saturation states, auditory responses in fish, and primary productivity rates. Increased atmospheric concentrations of CO2 from human activities (e.g. burning of fossil fuels, deforestation, and cement production) has led to a global decrease in surface ocean pH termed anthropogenic ocean acidification. One particular concern in response to increased oceanic CO2 is a substantial decrease in the calcium carbonate (CaCO3) saturation states, ΩCaCO3. The long-term physiological effects of ocean acidification and decreased ΩCaCO3 on marine biota are currently subjects of intensive global investigation. Consequently improved methods are needed to facilitate evaluations of the evolving CO2 system chemistry and the responses of marine organisms to those changes. Currently two of four measureable chemical parameters (pH, dissolved inorganic carbon, fugacity of CO2, and total alkalinity) are required for full characterization of the inorganic CO2 system; carbonate ion concentrations ([CO3 2-]) can, for example, be calculated from paired measurements of pH-DIC and pH-TA. The primary objective of this dissertation is to refine a method for directly determining [CO3 2-] using a single measurement, the distinctive ultraviolet absorbance spectra of Pb(II) species in seawater. The technique is fast, methodologically simple, and suitable for routine use in laboratory and shipboard studies. It is, as well, suitable for analyses using autonomous instrumentation. My studies began with an investigation of lead carbonate (PbCO3 0) complexation in synthetic media (at 25 °C between 0.001 to 5.0 molal ionic strength) to evaluate factors that control Pb(II) speciation, and thereby Pb(II) spectra, in seawater. Since laboratory investigations of Pb(II) speciation in seawater require potentiometric measurements of seawater pH, my dissertation includes development of a novel spectrophotometric method for calibrating pH electrodes directly in seawater. This spectrophotometric electrode calibration enables improved assessment of the extent to which electrode behavior is Nernstian and the influence of salinity on electrode calibrations. In addition, for the first time at sea, [CO3 2-] was directly determined in the Arctic and the Eastern Pacific Oceans using the Pb(II) method. These field studies allowed assessment of the consistency between direct [CO3 2-] determinations and carbonate determined using conventional CO2 system measurements. Finally, using techniques from my evaluation of lead speciation, as well as my electrode calibration development and field studies, additional laboratory studies were used to increase carbonate measurement sensitivity and applicability over a wider range of salinity.

Recent studies have demonstrated that marine bony fish (teleosts) precipitate inorganic calcium carbonate in their gut as a by-product of osmoregulation, subsequently excreting it into the open water column as loosely aggregated millimetre-scale pellet. These studies have primarily focused on physiological aspects of this process and the fate of resulting carbonates in pelagic settings, which is likely to be dissolution at depth. However, the implications of such carbonate production in shallow tropical and sub-tropical carbonate provinces has also begun to be considered, and it is thought that fish may contribute significant quantities of morphologically distinctive mud-grade high-Mg calcite in certain habitat settings. However, most studies of carbonate mud in modern subtropical settings do not report particles that are obviously fish-derived, and questions concerning fish-derived carbonate characteristics and post-excretion stability thus arise. The present work therefore provides more detailed characterisation of the carbonate products of an expanded range of Caribbean fish species and determines their short-term preservation potential in a sub-tropical carbonate province (the Bahamas). Following collection of carbonates from 22 fish species (all starved), precipitates were characterised using scanning electron microscopy and a suite of complimentary chemical analysis techniques. The form in which these carbonates are likely to be incorporated into surface sediments was investigated by disaggregating pellets and characterising the liberated particles by performing detailed image-based grain size analyses, with additional experiments demonstrating the likely rate and extent of pellet disaggregation by placing them in agitated seawater. Finally, short-term preservation potential was determined in a series of experiments whereby excreted precipitates were exposed to surface seawater and shallow subsurface porewater conditions for several months. Results indicate that, at the point of excretion, fish-derived carbonates are morphologically and mineralogically more varied than previously thought, although most morphotypes (e.g., ellipsoids, dumbbells, spheres, rhombohedra) are seemingly unique in shallow sub-tropical marine settings. ii High-Mg calcite, typically containing 20–35 mol% MgCO3, is the dominant product of about half the species investigated, but Mg calcite with lower MgCO3 contents (in the range 2–20 mol%) is also common, as is aragonite, which can represent up to 27 wt% of carbonates excreted by some species. In addition, amorphous magnesium carbonate (AMC) and magnesium-rich amorphous calcium carbonate (ACC), both of which are strongly hydrated, represent the dominant precipitation products of some species, with a hydrated crystalline phase (monohydrocalcite) occasionally accompanying the latter. A non-carbonate phase, brucite, is nearly ubiquitous as a volumetrically minor phase. Where analysed, all of these phases are further found to differ from other carbonate sediments in the Bahamas with regard to their stable carbon and oxygen isotope compositions; a consequence of the important role of metabolic HCO3 - in the precipitation process. Detailed grain size analyses indicate that most morphotypes are released from pellets upon disaggregation as individual mud-grade particles that retain their distinctive forms. However, extreme agitation can result in polycrystalline forms releasing their fibre-like components; these particles being less distinctive than their parent forms. In contrast, some particles are intergrown and do not disaggregate beyond particle clusters that are up to fine sand sized. Moreover, excreted pellets do not necessarily always disaggregate, with moderate agitation in seawater resulting in a significant proportion of carbonate being retained as intact pellets, albeit smaller (typically fine sand sized) and more well-rounded than initial pellets (typically fine to coarse sand sized). In quiescent settings pellet diminution is less extensive, and it is thus hypothesised that a significant proportion of fish-derived carbonates excreted in the Bahamas is preserved as sand-grade pellets. Despite the highly distinctive nature of fish-derived carbonates, particles that can be attributed to production by fish nevertheless remain elusive in studies of Bahamian surface sediments. It is thus necessary to invoke post-excretion processes of dissolution and/or recrystallisation to explain the apparent disparity between production rates and occurrence as sedimentary particles. Indeed, it is demonstrated here that AMC, brucite, and large quantities of ACC undergo complete dissolution in seawater within a few days of excretion, with the remaining ACC apparently crystallising to form fine sand-grade (50–200 μm diameter) polycrystalline calcite spheres over similar timescales. iii Monohydrocalcite, also undergoes complete dissolution or alteration (to calcite) during 3 month exposures to artificial seawater, and is predicted to alter in a similar manner in natural settings. Conversely, anhydrous crystalline phases remain largely unchanged after porewater and seawater exposures lasting several months, although two important post-excretion processes are observed. Firstly, high-Mg calcite ellipsoids appear to undergo partial dissolution (with preferential loss of MgCO3) and possible recrystallisation, and, based on these observations, it is predicted that longer exposure times will result in changes being pervasive, possibly obscuring the piscine origin of initial crystals. Secondly, carbonate pellets containing minor amounts of aragonite at the point of excretion appear, in some cases, to stimulate post-excretion growth of abundant aragonite needles that are morphologically similar to aragonite needles that dominate Bahamian carbonate muds. It is further apparent that these processes are inhibited in uncleaned samples, possibly due to surface adsorption of organic compounds, but the evidence after 3 month exposures indicates that inhibiting factors might eventually be overcome. Based on these results and modelling of carbonate excretion across shallow platform areas of the entire Bahamian archipelago, it is predicted that about 18 % of excreted carbonates will dissolve after excretion, while a further 53 % may alter beyond recognition within a very short period (perhaps on the order of years). Moreover, characterisation of carbonates produced by three species of normally feeding fish indicates they produce only amorphous carbonates, despite producing crystalline phases when starved. This difference, attributed to the inhibition of CaCO3 crystallisation by dietary phosphate, indicates that loss of fish-derived carbonate to dissolution might be considerably higher than 18 % under normal natural circumstances. The sedimentary significance of fish-derived carbonates thus remains enigmatic, but results presented herein indicate that they follow very different preservation pathways depending on their excreted form, and that they may make previously unrecognised contributions to: i) the carbonate sand fraction (as peloids); and ii) aragonite needle muds (as crystals grown post-excretion).

Les systèmes sédimentaires carbonatés forment à la fois des archives géologiques uniques des changements globaux-locaux des enveloppes externes de la Terre et renferment plus de 75 % des réserves d'hydrocarbure conventionnelles. Ils sont complexes et très difficiles à comprendre et à prédire. Cette complexité à toutes les échelles spatio-temporelles rend nécessaire l'intégration de méthodes naturalistes et quantitatives pour les étudier. La modélisation numérique basée processus permet de réduire les incertitudes des prédictions des propriétés des réservoirs carbonatés.Le manuscrit présente une méthode de modélisation itérative des systèmes carbonatés de la stratigraphie à la sismique en intégrant la diagenèse. Cette approche est basée sur le couplage de plusieurs outils numériques et par une démarche de travail combinant la sédimentologie, la diagenèse, la physique des roches et la simulation sismique.L’approche de modélisation développée permet ainsi d’intégrer un grand nombre de données multi-échelles et multidisciplinaire au sein d’un modèle facilement partageable entre toutes les disciplines en géosciences. L’intégration de ces nombreuses données est facilitée par un continuum du modèle entre les différentes échelles d’espace et de temps (du bassin au réservoir). La sismique synthétique ainsi obtenue n’est pas une simple convolution géométrique, elle intègre les propriétés sédimentologiques et diagénétiques, permettant une analyse de la signification stratigraphique des réflecteurs sismiques. Cette approche innovante intègre les méthodes naturalistes et quantitatives nécessaires à la compréhension et à la prédiction des systèmes carbonatés
Carbonate sedimentary systems record both global and local geological changes of the outer envelope of the Earth and contain more than 75% of conventional hydrocarbon reserves. These carbonate systems show a great complexity at every spatial and temporal scales. To increase our ability to understand and predict such intricate natural systems, it is necessary to integrate naturalistic and quantitative methodological apporaches. Numerical process-based modeling (stratigraphic-sedimentary-diagenetic) reduces the uncertainty of prediction of carbonate reservoir properties. The manuscript presents a method of iterative modeling of carbonate systems from stratigraphy to seismic by integrating diagenesis. This approach is based on the coupling of numerical tools and a working approach combining sedimentology, diagenesis, rock physics and seismic simulation. Tests on case studies associated with scientific and industrial issues validated the method.The modeling approach that was developed during the thesis allows to integrate a large number of multi-scale and multidisciplinary data. Models can easily be shared between the disciplines of geosciences. The model continuum along different scales of space (from the basin to the reservoir) and time eases the integration of various data. The obtained synthetic seismic is not a simple geometric convolution, but an integration of sedimentological and diagenetic properties, which allows for an analysis of the stratigraphic significance of the seismic reflectors. This innovative approach integrates naturalistic and quantitative methods, which improve the understanding and prediction of carbonate systems and reservoirs

The calcination of calcium carbonate in a cement or a lime kiln uses approximately two to four times the theoretical quantity of energy predicted from thermodynamic calculation depending upon the type of the kiln used (1.4 x 10^6 Btu/ton theoretical to 6 x 10^6 Btu/ton actual). The objective of this research was to attempt to reduce the energy required for the calcination by 1. decreasing the calcination temperature of calcium carbonate, and/or 2. increasing the rate of calcination at a specific temperature. Assuming a catalytic enhancement of 20 percent in the industrial applications, an energy savings of 300 million dollars annually in the United States could be reached in the cement and lime industries. Three classes of compounds to date have shown a positive catalytic effect on the calcination of calcium carbonate. These include alkali halides, phospho- and silico-molybdate complexes, and the fused carbonates system.

Nuclear Magnetic Relaxation Dispersion (NMRD) is strongly sensitive to the microscopic wettability of oil and brine bearing carbonate rocks. Exploring a very large range of low frequency enables isolating the typical NMRD dispersion features, 1/T1Surf, associated to the different processes of molecular surface dynamics. This allows a separation of the surface and bulk microdynamics of oil and water even for a biphasic saturation of petroleum rocks. Several surface dynamical parameters were determined and related to the concept of microscopic wettability of oil and water in porous media.

The characterisation of karstified carbonate reservoirs is a challenging task due to: (a) Complex fault systems; (b) Amplitude anomalies (karst features) and (c) Strong heterogeneity. To deal with these difficulties, I have developed three techniques targeting at the karstified carbonate reservoirs from Tarim basin: (a) Fracture detection based on seismic coherence can be affected by dipping reflectors and noise. A robust algorithm is developed, where dip is used to eliminate the impact of dipping reflectors and a pseudo-multichannel appraoch is employed to improve robustness (good performance for S/N ratio greater than 2). (b) In the presence of karst fractures (strong amplitudes), seismic facies classification based on seismic trace shape may not analyse the weak amplitudes in the background strata. To combat this difficulty, I use the amplitude variation pattern (normalised seismic segment) as the input to avoid the potential impact of strong amplitudes and help to analyse the weak amplitude. (c) It is difficult to honour the lateral variation due to the strong heterogeneity in the karstified carbonate reservoirs. I adopt a Fourier integral method (FIM) in the stochastic inversion where the lateral variation is honoured based on the seismic trace similarity. After I have successfully developed and verified these methods listed above, I apply them together to characterise another carbonate reservoir. This case study has less number of existing wells (five). Explicitly, I apply in order: seismic coherence, seismic facies classification, FIM-based stochastic inversion, and the lithofacies classification. I use seismic coherence as prior knowledge in the classification, enabling to honour the localised dolomitization along faults and fractures. Finally, I propose three well locations for potential oil/gas production based on the classified facies and lithofacies probability (over 40%). My study shows that the algorithms can be employed for reservoir characterisation and provide improved results comparing with conventional methods.

Thesis (M.S.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1988.
Includes bibliographical references (leaves 82-85).
The sulfur content of planktonic and benthic foraminifera was measured in specimens recovered from deep-sea sediment cores and individuals grown in culture. A new method for measuring sulfur in foraminiferal calcium carbonate was developed, employing a high-resolution inductively coupled plasma-mass spectrometer. The sulfur measurements, expressed as sulfur-to-calcium (S/Ca) ratios in the foraminiferal shells, ranged from 0.26 to 6.0 mmol/mol. Most analyses fell in the range of 0.7 to 2.5 mmol/mol. Culturing experiments were conducted in the planktonic foraminifer G. sacculifer to test the hypothesis that S/Ca ratios in the foraminifer are inversely proportional to the carbonate ion concentration in the seawater in which they grow, and hence proportional to the pH of the seawater. The slope of the relationship between cultured G. sacculifer S/Ca and the pH of the seawater medium was -1.92 mmol mol-1/pH unit with a least squares linear correlation coefficient, r2=0.927. The S/Ca ratios of planktonic and benthic foraminifera from Holocene and last glacial period sediments were measured in an effort to use the established relationship of S/Ca and pH to calculate the ocean pH gradient between Holocene and glacial time. The results indicate the pH of global ocean deepwater was 0.10 to 0.15 pH units higher during glacial time than today. Smaller pH gradients were seen for some cores which may have been caused by circulation-induced water mass changes. Surface ocean changes in pH over the Holocene-glacial interval seem to vary from region to region, with up to an 0.2 pH unit increase at the Sierra Leone Rise in glacial time. Benthic foraminifera from coretops in the thermocline of the Little Bahama Bank were analyzed for S/Ca to examine the effects of hydrographic variables on S/Ca. The relationship of S/Ca to pH and [CO3=] has a positive slope, at odds with the expected negative slope from the previous results. The S/Ca results do correlate well with salinity, suggesting that salinity or other hydrographic parameters may also influence foraminiferal S/Ca ratios.
by Jeffrey Nicholas Berry.
M.S.

El desenvolupament de substitucions propargíliques catalitzades per metalls de transició o reaccions de tipus SN2 de carbonats cíclics propargílics i altres heterocicles relacionats proporcionen estratègies eficients per construir molècules i materials orgànics complexos. L’ús del coure és molt conegut per transformacions catalítiques de substitució propargílica asimètrica de carbonats cíclics substituïts amb alquins terminals a través d’intermedis de tipus Cu-al·lenilidè. Tot i així, les reaccions de tipus SN2 catalitzades per coure de carbonats cíclics substituïts amb alquins interns o heterocicles similars no han sigut explorades. Basant-nos en resultats recents del nostre grup, hem dissenyat una funcionalització descarboxilativa catalitzada per coure de carbonats cíclics substituïts amb alquins interns incorporats amb reactius de diboro(4) o sililborans. Aquesta nova transformació proporciona nous paradigmes de reactivitat oferint una gamma més àmplia de compostos útils sintèticament i, a la vegada, aporta informació addicional sobre el mode de funcionament del catalitzador. Un altre dels protocols amb un objectiu atractiu desenvolupats en aquesta tesis és la preparació de productes enantioenriquits mitjançant reaccions estereoespecífiques catalitzades per níquel. Tenint en compte que els compostos d’organosilici i d’organobor es caracteritzen per l'estabilitat, baixa toxicitat i la facilitat d’ús, creiem que el desenvolupament d'aquests compostos contribueix a ampliar la caixa d'eines sintètiques de la química orgànica oferint noves oportunitats de síntesis per a la química fina.
El desarrollo de sustituciones propargílicas catalizadas por metales de transición o reacciones de tipo SN2 de carbonatos cíclicos propargílicos y otros heterociclos relacionados proporcionan estrategias eficaces para construir moléculas y materiales orgánicos complejos. El uso de cobre es muy conocido para transformaciones catalíticas de sustitución propargílica asimétrica de carbonatos cíclicos sustituidos con alquinos terminales a través de intermedios de tipo Cu-alenilideno. Aun así, las reacciones de tipo SN2 catalizadas por cobre de carbonatos cíclicos sustituidos con alquinos internos o heterociclos similares son inexploradas. Basándonos en resultados recientes de nuestro grupo, hemos diseñado una funcionalización descarboxilativa catalizada por cobre de carbonatos cíclicos incorporados con alquinos internos con reactivos de sililboro o diboro(4). Esta nueva transformación proporciona nuevos paradigmas de reactividad ampliando la gama de compuestos sintéticamente útiles y, al mismo tiempo, brinda información adicional sobre el modo de funcionamiento del catalizador. Otro de los nuevos protocolos con un objetivo atractivo desarrollados en esta tesis es la preparación de productos enantioenriquecidos a través de reacciones estereoespecíficas catalizadas por níquel. Teniendo en cuenta que los compuestos de organosilicio y de organoboro se caracterizan por su estabilidad, baja toxicidad y fácil manejo, creemos que el diseño de estos compuestos contribuyen a ampliar las herramientas sintéticas de la química orgánica ofreciendo nuevas oportunidades de síntesis para la química fina.
The development of TM-catalyzed propargylic substitution or SN2'-type reactions of propargylic cyclic carbonates and related heterocycles has provided an efficient strategy to construct complex organic molecules and materials. Even though Cu catalysis has been shown to be very successful in promoting the asymmetric propargylic substitution of terminal alkyne-substituted cyclic carbonates via Cu−allenylidene intermediates, Cu-catalyzed SN2'-type reactions of internal alkyne-substituted cyclic carbonates or similar heterocycles remains unexplored. Based on previous reports and recent achievements in our group, we envisioned that the development of Cu-promoted decarboxylative functionalization of (internal) alkyne-substituted cyclic carbonates with silylboron or diboron(4) reagents would potentially provide new reactivity paradigms while giving additional insights into the operating mode of the catalyst and delivering a more ample range of synthetically useful compounds. In addition, new catalytic protocols that can foster the easy preparation of enantioenriched products via stereospecific Ni-catalyzed reactions would also be an attractive target. Considering that organosilicon and organoboron compounds are characterized by stability, nontoxicity, and easy handling, the development of these compounds is believed to contribute to amplify the synthetic toolbox of organic chemists offering new synthetic opportunities for a wide range of fine-chemical targets.

The aims of this study are to extend the established high-resolution sequence stratigraphic framework of the Madison Formation of Wyoming and southern central Montana to the correlative and genetically-related Mississippian carbonate ramp, ramp margin, and basin strata of the central Montana trough and Antler foreland basin in order to examine and discriminate the controls on depositional processes and the resulting stratigraphic architecture through space and time in tectonically-active settings. An outcrop-based, high-resolution sequence stratigraphic study of two ramp-to-basin transects, one in central Montana and the other in southwestern Montana and east-central Idaho, is conducted in order to examine these deposits across two coeval margins with differing subsidence, hydrodynamic, and physiographic configurations and histories. Independent measurements of system response to global and local forcings allows disentanglement of primary controls on deposition and allows us to gain understanding of the roles and interplay of these controls, in particular eustasy and tectonics, on the system's architectural development. Conversely, insight into the geodynamic evolution of western North America, glacioeustatic changes, and variations in global climate and oceanographic systems during the greenhouse-to-icehouse transition is gained. A series of high-resolution sequence stratigraphic cross-sections and time-slices are produced incorporating outcrop measured sections and measured sections previously collected by members of the Comparative Sedimentology Laboratory in a series of transects across the Madison ramp system. A new chronostratigraphic framework for Madison carbonates is developed by using Lower Carboniferous delta C-13 isotope excursions as isochronous tie points between ramp-top, margin, and basinal sections. These delta C-13 excursion events have been documented to be time-invariant globally due to global changes in ocean chemistry. The results of the study include resolution and discrimination of sequential foreland basin subsidence, carbonate sediment production and progradation, subsidence and uplift of foreland basin structures along a carbonate shelf edge, diachronous subsidence of discrete depocenters, and eustasy.

Reliable measurements of the thermodynamics of the carbonate system are needed to better understand the CO2 system in natural waters. New measurements of the carbonic acid pK1* and pK2* in seawater have been made over a wide range of temperatures (1 to 50°C) and salinities. The commonly used CO2 constants of Mehrbach et al., (1973) were limited to salinities (19 to 43) and temperatures (2 to 35°C). They cannot be used to study estuarine or fresh waters. The results of these measured pK1* and pK2* values are in good agreement with those determined using the Miami Pitzer equations (Millero and Pierrot, 1998). The results in this dissertation can be demonstrates the validity of the model that can be used to study the carbonate system in most natural waters. The so called Miami model is presently being used to examine the effect of ocean acidification on natural waters. The boric acid effect on the dissociation constants in seawater and NaCl solutions was tested. The addition of boric acid has little or no effect on pK1* values. However, the values of pK2*, decreases with the addition of small amounts of boric acid to ASW in agreement with the work of Mojica-Prieto and Millero, (2002). The addition of larger concentrations of boric acid cause the values of pK2* to increase. These effects have been attributed to the interactions of boric acid with the carbonate ion (CO32-) in seawater (Mojica-Prieto and Millero, 2002). The addition of boric acid to NaCl solutions in contrast, caused the values of pK1* and pK2* to decrease. This has been attributed to the interactions of borate ions with Mg2+ and Ca2+ in seawater. Further measurements in Na-Mg-Cl and Na-Ca-Cl solutions are needed to prove that this is the case. The boric acid effect on the carbonate constants indicate that an increase in boric acid has no affect on pK1*, but does change the values of pK2*. At low concentrations of boric acid, pK*2 decreases, and at higher concentrations it increases. These results indicate that boric acid has some ionic interactions with the carbonate ion. Similar studies in NaCl indicate that both pK1* and pK2* decrease when boric acid is added. The differences between seawater and NaCl may be related to the interactions of Mg2+ and Ca2+ with borate anions. Further studies of NaCl with additions of MgCl2 and CaCl2 are needed to examine the effects in detail. Preliminary studies on the effect of DOC on the carbonate constants are not definitive. The change of the DOC concentration from 50 to 100 µmol kg-1 has little effect on the values of pK1* and pK2*. Dilutions of seawater with artificial seawater are complicated by changes in the concentration of boric acid. Earlier studies indicated that DOC may cause the 8 mu-mol kg-1 increase in total alkalinity of seawater needed to balance the thermodynamics of the system (Millero et al., 2002). This may be partially due to the new values for the B/Cl ratio in seawater found by Lee et al., (2010) that increases the TA by ~ 6 µmol kg-1. Further studies are needed to examine the effect of humic compounds in estuarine waters on the carbonate system. Measurements of pH or pCO2 along with TA and TCO2 can be used to separate the effect of organic ligands on TA. If DOC measurements are also made, one can relate the effect to organic ligands that can accept a proton. The cruises in the Little Bahama Banks show for the first time the active precipitation of CaCO3 (Bustos-Serrano et al., 2009). This causes measured decreases of TA, TCO2 and pH and increases in pCO2 in the whitings. This is in contrast to earlier studies on the Grand Bahama Banks where no active precipitation of CaCO3 was every found (Morse et al., 2003; Millero et al., 2005). The differences appear to be due to the movement of fresh saturated seawater from the Gulf Stream into the LBB. The Gulf Stream water enters the GBB in the winter, and the precipitation occurs on the suspended sediment over the year. Observations are needed on the Grand Bahama Banks in the winter and throughout the year to prove that this is the case.

High resolution micro-CT images of porous rocks provide a very useful starting point to the development of pore-scale models of fluid flow and transport. Following a literature review covering recent results on the applicability of tomographic imaging to study reaction phenomena at the pore and core scales, this thesis presents a pore-scale streamline-based reactive transport model to simulate rock dissolution. The focus is on carbonate dissolution in CO2-saturated fluids. After injecting CO2-rich fluids into carbonate reservoirs, chemical reactions between the acidic fluid and the host rock are to be expected. Such reactions may cause significant variations in the flow and transport properties of the reservoir, with possible consequences for field development and monitoring. The interplay between flow and reaction exhibits a very rich behaviour that has not yet been fully understood, especially in the case of carbonate rocks, which possess a complex pore structure. The model is developed within a Lagrangian framework, where the advective displacement employs a novel streamline tracing method which respects the no-flow boundary condition at the pore walls. The method is implemented in the pore-space geometry reconstructed from micro-CT images of sedimentary rocks. Diffusion is incorporated with a random walk and fluid-solid reactions are defined in terms of the diffusive flux of reactants through the grain surfaces. To validate the model, simulation results are compared against a dynamic imaging experiment where a carbonate sample was flooded with CO2-saturated brine at reservoir conditions. The agreement is very good and a decrease of one order of magnitude in the average dissolution rate, compared to the rate measured in an ideal reactor, is explained in terms of transport limitations arising from the flow field heterogeneity. The impact of the flow heterogeneity in the reactive transport is illustrated in a series of simulations performed in rocks with different degrees of complexity. It is shown that more heterogeneous rocks, in the sense of flow heterogeneity, may exhibit a decrease of up to two orders of magnitude in the sample-averaged reaction rates, and that the flow rate is also an important factor when studying carbonate dissolution.

The work presented in this thesis is concerned with the nucleation and growth of calcium carbonate (CaCO3). CaCO3 deposition on fabrics during the washing process is a major problem, causing fabric damage and harshness. It is important to understand the mechanism of CaCO3 nucleation in order to control its precipitation. The extent of crystallisation on different model fabrics was first investigated in order to understand the principal factors governing the crystal deposition. Surface topography of the fabrics such as the presence of steps and kinks was found to be the dominating factor for the nucleation of CaC03 crystals under the experimental conditions.

Molten Carbonate Fuel cells are high temperature fuel cells suitable for distributed generation and combined heat and power, and are today being installed on commercial basis in sizes from 100kW to several MW. Novel applications for MCFC which have attracted interest lately are MCFC used for CO2 separation from combustion flue gas, and high temperature electrolysis with reversible fuel cells. In the first application, the intrinsic capability of the MCFC to concentrate CO2 from the cathode to the anode side through the cell reaction is utilized. In the second application, the high operating temperature and relatively simple design of the MCFC is utilized in electrolysis, with the aim to produce a syngas mix which can be further processed into hydrogen of synthetic fuels. In this thesis, the effect on fuel cell performance of operating a small lab-scale molten carbonate fuel cell in conditions which simulate those that would apply if the fuel cell was used for CO2 separation in combustion flue gas was studied. Such operating conditions are characterized especially by a low CO2 concentration at the cathode compared to normal operating conditions. Sulfur contaminants in fuel gas, especially H2S, are known poisoning agents which cause premature degradation of the MCFC. Furthermore, combustion flue gas often contains sulfur dioxide which, if entering the cathode, causes performance degradation by corrosion and by poisoning of the fuel cell. This makes poisoning by sulfur contaminants of great concern for MCFC development. In this thesis, the effect of sulfur contaminants at both anode and cathode on fuel cell degradation was evaluated in both normal and in low CO2 simulated flue gas conditions.      The results suggested that the poisoning effect of SO2 at the cathode is similar to that of H2S at the anode, and that it is possibly due to a transfer of sulfur from cathode to anode. Furthermore, in combination with low CO2 conditions at the cathode, SO2 contaminants cause fuel cell poisoning and electrolyte degradation, causing high internal resistance. By using a small lab-scale MCFC with commercial materials and standard fuel cell operating conditions, the reversible MCFC was demonstrated to be feasible. The electrochemical performance was investigated in both fuel cell (MCFC) and electrolysis cell (MCEC) modes. The separate electrodes were studied in fuel cell and electrolysis modes under different operating conditions. It was shown that the fuel cell exhibited lower polarization in MCEC mode than in MCFC mode, and a high CO2 concentration at the fuel cell anode reduced the polarization in electrolysis mode, which suggested that CO2 is reduced to produce CO or carbonate.
Smältkarbonatbränsleceller (MCFC) är en typ av högtemperaturbränsleceller som är anpassade för kombinerad el- och värmeproduktion i mellan-till stor skala. Idag installeras MCFC på kommersiell basis i storlekar mellan 100kW och flera MW. En ny typ av tillämpning för MCFC som har väckt intresse på senare tid är användandet av MCFC för CO2-avskiljning i kombination med konventionell elproduktion genom förbränning. En annan ny tillämpning är högtemperaturelektrolys genom användandet av reversibla bränsleceller. I det första fallet utnyttjas att CO2 kan koncentreras från katod- till anodsidan, vilket sker genom cellreaktionen för MCFC. I det andra fallet utnyttjas den höga arbetstemperaturen och den relativt enkla cell-designen för att använda reversibla MCFC till elektrolys, med syfte att producera en syngas-blandning som kan förädlas till vätgas eller till syntetiskt bränsle. I denna avhandling studeras effekten på bränslecellens prestanda genom att operera en MCFC i lab-skala med driftförhållanden som simulerar de som förväntas uppkomma om bränslecellen användes för CO2-avskiljning ur rökgaser från förbränning. Dessa driftförhållanden karaktäriseras av låg CO2-koncentration på katodsidan jämfört med normal drift. Svavelföroreningar i bränsle, speciellt H2S, är kända för att orsaka förgiftning av anoden, vilket i sin tur försämrar bränslecellens prestanda. Dessutom innehåller rökgaser ofta SO2, vilket antas orsaka korrosion och förgiftning av katoden. Detta gör effekten av svavelföroreningar till ett prioriterat ämne för utvecklingen av MCFC. I denna avhandling undersöks effekten av svavelföroreningar på både anod- och katodsidan, i normala driftförhållanden och i förhållanden med låg CO2 som simulerar användandet av rökgaser för CO2-avskiljning. Resultaten tyder på att effekten av förgiftning med SO2 på katoden liknar den med H2S på anoden, och att detta kan vara orsakat av en transport av svavel från katod till anod. Vidare, i kombination med låg CO2 koncentration på katoden så orsakar SO2-föroreningar elektrolytdegradering, vilket orsakar hög inre resistans. Genom att använda en liten MCFC i lab-skala med kommersiella material och standardförhållanden för MCFC påvisades att reversibla smältkarbonatbränsleceller kan vara ett lovande koncept. Den elektrokemiska prestandan av både cell och separata elektroder undersöktes både som bränslecell (MCFC)och vid elektrolys (MCEC). Resultaten visade att cellen uppvisade lägre polarisation vid elektrolys än som bränslecell, och att ten hög CO2-koncentration på det som är bränslecellens anodsida gav upphov till en minskad elektrodpolarisation, vilket indikerar att CO2 reduceras för att producera CO eller karbonat.

QC 20141028

Since the early 1970's there have been a number of investigations into the preparation of dense sintered hydroxyapatite for medical applications. However, there have been few studies reporting the production of sintered carbonate apatite, which resembles more closely the composition of human bone mineral. This work has studied the precipitation, processing and sintering of carbonate apatites. Crystallisation variables such as temperature and bicarbonate ion concentration have been investigated in order to determine some effects on the size, morphology and composition of carbonate apatite precipitates. By employing the correct conditions, nanoscale precipitates have been produced that have enabled the use of a colloidal filtration route in processing. The effect of sintering atmosphere, green density, and carbonate content were investigated isochronally over a range of temperatures. Isothermal experiments demonstrated the evolution of microstructure and changes in density with time. Results from this study indicated that translucent 99.9% relative density carbonated hydroxyapatite could be produced by sintering in an atmosphere of carbon dioxide and water. Water was found to enhance densification in carbon dioxide furnace atmospheres. The temperature at which maximum densification occurred decreased with carbonate content. Bloating was found to be related to carbonate content as larger expansions were observed in higher carbonate content materials. The partial pressure of water did not effect the composition of the carbonate apatite, whereas the green composition did, contrary to the findings of other workers.

This thesis presents the results of computer simulation studies of impurity incorporation in calcite and the aggregation of calcite particles, using a combination of classical computational techniques based on interatomic potentials, namely molecular mechanics and molecular dynamics simulations. Firstly, the atomistic simulation techniques have been employed to investigate the thermodynamics of mixing in calcite with seven divalent cationic impurities (Mg2+, Ni2+, Co2+, Zn2+, Fe2+, Mn2+ and Cd2+), based on the calculation of all inequivalent site occupancy configurations in 2 × 2 × 1 and 3 × 3 × 1 supercells of the calcite structure. In addition to the enthalpy of mixing, the configurational entropy and mixing free energy have also been calculated, providing an insight into the mixing behaviour as a function of the temperature for a series of carbonate solid solutions. The calculations have revealed that the solubility of the cationic impurities in calcite is largely related to the cationic coordination distance with oxygen. Secondly, the aggregation process has been investigated implementing classical computational techniques, and especially the interaction of a calcite nanoparticle with the major calcite surfaces, where the adhesion energy and optimised geometries of a typical calcite nanoparticle on different surfaces in vacuum and aqueous environment have been calculated. The results show the orientation of a nanoparticle is a key factor that effects the interactions, besides the size and structure of the nanoparticle. The most stable aggregated configuration occurs when the lattices of the nanoparticle and the surface are perfectly aligned. Finally, a number of symmetric calcite tilt grain boundaries have been constructed to act as models of two calcite nanoparticles, after collision has occurred but before growth has a chance to commence. Molecular dynamics simulations were then employed to study the stability of these tilt grain boundaries and the growth of a series of calcium carbonate units at the contact points in the pure and hydrated calcite tilt grain boundaries. The calculation have proved that the initial incorporation of a CaCO3 unit is preferential at the obtuse step in a grain boundary, and the growth velocity of the acute step is 1.3 to 2.1 times higher than that of the obtuse step, once the initial growth unit has been deposited on the steps. This study has evaluated the conditions required for the growth of new calcium carbonate materials in the calcite tilt grain boundaries.

Scale formation in domestic appliances is a widespread problem in the UK. This project has focussed on calcium carbonate scale formation in electric showers. A literature survey identified that CaCO; deposition on heated surfaces could be controlled by chemical or non chemical methods, each with various degrees of effectiveness. One of the most effective control methods was the addition of chemicals, although this may not be the most suitable option for the domestic environment. So here the chemical inhibitors tested were used for a benchmark for all the other studies. Two laboratory tests were involved t allow u to study CaCO; precipitation and scale formation. The effect of chemical additives on CaCO; precipitation was investigated using a jar tester. The longest delay to precipitation was obtained by polyacrylic acid dosing, closely followed by zinc. To study CaCO; formation on a heated surface, a rapid scaling test was developed. This test was conducted at 42°C and 70°C to examine and compare a range of treatment options, including chemical dosing, electrolytic, magnetic and electronic water conditioning and low fouling surfaces. From the options examined, the most successful was electrolytic dosing of zinc/copper media with over 95% reduction in scaling at both temperatures. Further, the use of low fouling surfaces, such as Diamond - like carbon coating could also potentially be used in electric showers. Reduction in scaling achieved on this surface was on average 68%. Surface properties of the materials were analysed using an atomic force microscope and their relationship with the scaling behaviour of the surfaces examined. The scaling rates at both temperatures typically increased with increasing adhesion force but no clear relationship was found between the roughness of the surfaces and their scaling behaviour. The relationship between CaCO3 precipitation and scale formation in synthetic solution and natural hard water was also explored here. The induction period in natural hard water was 55 minutes longer and the scaling rate 40% lower than i synthetic hard solution of similar composition. In addition, two shower test rigs, one based at Cranfield University and the other in Attleborough were used in this study. These were used primarily to enable the compilation of background data on scale formation in electric showers, where it was found that the design of the unit has a significant influence on the scale formation. The test rig was also used t test the strategies identified during the laboratory phase of the work. It was found that electrolytic zinc dosing reduced scaling by up to 54%, depending on the shower unit design.

Great challenges remain in our understanding of biomineralisation which impede the design and production of a new class of materials. Recent studies have suggested that calcium carbonate clusters are stable in solution before nucleation, and that these participate in the formation of amorphous calcium carbonate (ACC). The structure and stability of these clusters has not been fully determined. Furthermore, the dehydration of stable ACC before crystallisation remains ambiguous. Exhaustive computational searches have been carried out to provide a sample of clusters up to the sizes suggested for particles persisting before nucleation. A large sample of clusters were simulated at high concentration in water using molecular dynamics (MD). The results suggest that cluster stability is a balance between ionic coordination and ion hydration. At high concentration clusters are generally dynamic in the lower limit of stability, forming chains to which ions frequently aggregate and dissolve. Free energy calculations showed a transition in the favoured coordination levels with cluster size. One dimensional Umbrella Sampling calculations showed that at small sizes a collection of clusters with low average cation–anion coordination were thermodynamically stable. For systems containing sixty ions and above, more compact clusters with internal water, close to the stoichiometries identified for stable hydrated ACC in vivo, were lower in free energy. From MD simulations at experimental concentrations and pH, while dynamic ordering was found, ion pairs dominated in solution and the largest clusters observed contained no more than four ions. These findings, combined with the data at high concentration, allow for a re-evaluation of the proposed nucleation mechanisms for calcium carbonate from solution. ACC simulations identified water–filled channels within the ionic framework. Percolating clusters were found when H2O/CaCO3 was greater than 0.75–0.8. The ACC system fitted well with the percolation theory on a simple cubic site lattice for water, and critical exponents showed a good fit to the theoretical values. Non–standard diffusion was found for water, with a “jump” mechanism of diffusion observed and a cascade of molecule displacements within channels. This original result allows new light to be shed on the dehydration mechanism of ACC.

Prediction of fluid pressure before drilling, using geophysical methods helps the industry a lot in saving human life, drilling hazards, and equipments.There are several geophysical methods available to predict the fluid pressure before drilling but the most commonly used in the industry are those based on seismic velocities. However, seismic velocities methods are applied on clastic reservoirs with the assumptions that the pressure mechanism is due to mechanical compaction. A major exploration challenge is to successfully predict the presence of high pressure zones in the carbonate reservoirs. Carbonate reservoirs have a more complicated internal structure than clastic reservoirs. The main objective of this study is to predict the carbonate reservoir properties such as porosity and fluid pressure. The new prediction methods that I used in this thesis are called the artificail intelligent algorithms. These algorithms are better than the conventional geophysical methods because of their ability to explore complex relationships between the input seismic attributes and the predicted properties. The algorithms include artificial neural networks and group methods of data handling. Empirical equations from seismic prediction methods were used to transform velocities to fluid pressure. High resolution velocites (wavefrom tomography) proved that better prediction can be achieved when using better input velocity. The velocity methods performed a nice prediction when used with clastic seismic data but proved to give unreliable results when used with the carbonate seismic data. This was because of the difficult internal structure of carbonate reservoirs. The neural network methods proved that they are robust in clustering and segmenting the input carbonate seismic data. The usage of more input seismic attributes made the neural network methods better than the conventional velocity methods. Also, this gave the neural network methods more information about the same physical reservoir property. Among the different seismic attributes used in the experiment, seismic inversion and coherence attributes showed good reaction to high pressure zones. Porosity results from the supervised neural network method were used as a guide to the unsupervised neural network method to predict fluid pressure. The group method of data handling algorithm is performed here for the first time with seismic data to predict the reservoir properties. The new method showed faster and easier prediction than the neural network methods. The automation of the new method yields to better porosity and pore pressure prediction.

The aim of this work is to improve our knowledge of nutrients influence in the fossil record of the Miocene. The studied succession were analyzed trough a multidisciplinary approach encompassing paleontology, sedimentology and geochemistry in order to extract information and disclose the existing relation between fossil skeletal assemblages and nutrient abundance. The Miocene has been a turning point for our Planet evolution. During the Miocene the ocean circulation finally become comparable to the present-day situation. A further decrease in temperature brought climatic condition very close to those of the present. Land and marine life were fairly modern and many present-day ecosystems arose in the Miocene. Lower Miocene is also the oldest period in which the principle of taxonomic uniformity can be safely applied. Miocene is the first Epoch of modern Earth and therefore is the perfect setting to study, on a geological time frame, ecological processes and draw conclusions useful in the comprehension of present-day ecosystems. While many other works have tried to analyzed productivity and nutrient fluctuation in deep water sediments, this is one of the first attempt to approach the problem in shallow water setting. Shallow water biota is deeply influenced by variation in nutrient supply and may record these differences. Even thought chemical analyses may be sizebly biased by diagenesis in coarse-grained shallow-water sediment, with certain techniques and accurate combination of different groups of data it is possible to unveil precious information. The studied succession of the Pietra da Cantoni Limestone Group of the Tertiary Piedmont Basin and of the Sandy Molasse Unit of the Sommières Basin are both of Burdigalian age and they were close-by during the Miocene. They were also both characterized by an heterozoan skeletal assemblage and the abundance of coralline algae and taxa of suspension-feeder. They were chosen to minimize climatic and geographical variability and to concentrate over productivity. Nutrient-rich waters have left a clear imprint on the fossil record by influencing the marine biota. These traces may be brought to light and used to improve our knowledge of the nutrient cycle of the Earth.

Observations of modern carbonate depositional environments and their accompanying depositional models have been used for decades in the reconstruction and interpretation of ancient carbonate depositional environments and stratigraphic successions. While these Holocene models are necessary for interpreting their more ancient counterparts, they inherently exclude important factors related to the erosion, diagenesis, and ultimate preservation of sediments and sedimentary structures that are ubiquitous in shallow marine carbonate environments. Andros Island, Bahamas is an ideal location to examine the validity of Holocene conceptual models, where geologically young (Late Pleistocene) limestones can be studied immediately adjacent to their well-documented modern equivalents. For this study, two 3D ground-penetrating radar (GPR) datasets (200 MHz and 400 MHz) were collected at a schoolyard in northwest Andros. These surveys reveal the geometries and internal characteristics of a peloidal-oolitic sand wave and tidal channel in unprecedented detail. These two prominent features are underlain by low-energy lagoonal wackestones and packstones, and are bordered laterally to the northwest by wackestones-packstones intermixed with thin sheets of peloidaloolitic grainstone. A deeper radar surface is observed at approximately 6 m depth dipping gently to the west, and is interpreted to be a karstified exposure surface delineating the base of a complete depositional sequence. Interpretation of the 3D radar volumes is enhanced and constrained by data from three cores drilled through the crest and toe of the sand wave, and through the tidal channel. This study is the first of its kind to capture the complex heterogeneity of a carbonate depositional package in three dimensions, where various depositional environments, sedimentary structures, and textures (mudstone to grainstone) have been preserved within a small volume.The results from this study suggest that the degree of vertical and lateral heterogeneity in preserved carbonate successions is often more complex than what can be observed in modern depositional environments, where sediments can generally only be observed in two dimensions, at an instant in time. Data from this study demonstrate the value of using two overlapping GPR datasets at differing resolutions to image the internal characteristics of a complete carbonate depositional package in three dimensions. From these datasets, a depositional model similar to other Holocene and Pleistocene carbonate depositional models is derived.

L’evoluzione temporale e spaziale delle piattaforme carbonatiche e delle biocostruzioni è controllata dall’interazione di fattori globali (clima, variazioni eustatiche), regionali (tettonica) e fattori ambientali locali (nutrienti, penetrazione della luce e profondità) che influiscono sulle variazioni dell’accomodamento e la natura delle carbonate factories. La riorganizzazione delle placche tettoniche legata all’apertura della Tetide Alpina e le variazioni climatiche hanno influenzato direttamente le successioni carbonatiche Giurassiche, le quali registrano uno dei maggiori momenti di abbondanza e distribuzione di reef a coralli, spugne e microbialiti. Questo studio si focalizza sulla successione carbonatica del Giurassico Medio-Superiore della Sardegna orientale e la sua evoluzione nello spazio e nel tempo in termini di composizione e architettura delle facies, caratteristiche della carbonate factory e geometria del profilo deposizionale attraverso quattro fasi deposizionali. Le caratteristiche sedimentologiche e l’età di queste fasi deposizionali sono state approfondite attraverso dettagliate analisi di facies e microfacies, analisi geochimiche, diagenetiche e degli isotopi dello stronzio, nuovi dati biostratigrafici e precedenti studi litostratigrafici. La fase 1 (Calloviano-Oxfordiano medio) è caratterizzata da una rampa carbonatica dominata da grani rivestiti costituita da shoals a ooidi nella rampa interna e packstone peloidali nella rampa media e esterna. La fase 2 (Oxfordiano superiore-Kimmeridgiano superiore) registra l’evoluzione di una rampa carbonatica caratterizzata dalla presenza di tre tipi di biocostruzioni distribuite lateralmente lungo il profilo batimetrico, le cui caratteristiche sono controllate dall’interazione tra energia idrodinamica dell’ambiente e penetrazione della luce. Le biocostruzioni di tipo 1 (spessore 45 m, larghezza 100 m) sono costituite da boundstone e rudstone-grainstone a coralli e stromatoporoidi e colonizzano la rampa media prossimale. Le biocostruzioni di tipo 2 (spessore: 1-2 m, larghezza: 3-4 m) consistono di corpi lenticolari costituiti da boundstone a coralli, spugne calcaree e bivalvi diceratidi (compresi stromatoporoidi e spugne chetetidi) associati a packstone-grainstone bioclastici ed occupavano la rampa media distale. Le biocostruzioni di tipo 3 (1 m di spessore e pochi metri di larghezza) sono costituite da boundstone a spugne calcaree e silicee e coralli associati a packstone-grainstone bioclastici ed occupavano la rampa media distale e la rampa esterna. L’evoluzione dalla fase 1 alla fase 2 è legata all’espansione globale dei reef a coralli, stromatoporoidi, spugne calcaree e silicee e microbialiti durante il periodo Oxfordiano medio-Kimmeridgiano superiore dovuto ad una risalita eustatica e a variazioni climatiche. La fase 3 (Kimmeridgiano superiore) è successiva ad un abbassamento relativo del livello marino probabilmente dovuta a tettonica estensionale testimoniata da una superficie di esposizione subaerea al di sopra della fase 2. Durante la fase 3 nella rampa interna prossimale si sono depositate facies peritidali, mentre la rampa media distale è dominata da facies con grani rivestiti rimaneggiati (ooidi e oncoidi). L’età della fase 3 è stata revisionata rispetto ai lavori precedenti e assegnata al Kimmeridgiano superiore sulla base delle analisi sugli isotopi dello stronzio e nuovi dati biostratigrafici, in particolare in base alla presenza del foraminifero bentonico Alveosepta jaccardi. Il tetto della fase 3 è caratterizzato da un altro evento di esposizione subaerea registrato anche in coevi sistemi deposizionali Tetidei con una unconformity regionale attribuita a tettonica estensionale. L’inizio della fase 4 (Titoniano) è caratterizzato da depositi bacinali trasgressivi seguiti dalla ripresa della carbonate factory di reef. Questa fase è caratterizzata da un cambiamento della geometria deposizionale da rampa carbonatica a piattaforma ad alto rilievo con uno slope alto circa 70 m e inclinato di 3-15°. I depositi bacinali della fase 4 sono costituiti da mudstone, wackestone e siltstone e brecce litoclastiche con clasti risedimentati da meccanismi di debris flow e provenienti da ambienti meno profondi. Grainstone bio-intraclastici, wackestone con Clypeina jurassica, wackestone e floatstone con oncoidi e packstone/grainstone peloidali sono risedimentati da ambienti di piattaforma interna. Le brecce di debris-flow includono anche clasti provenienti da biocostruzioni Titoniane sviluppate durante la fase 4, differenti dalle biocostruzioni Oxfordiano-Kimmeridgiane della fase 2. Boundstone a coralli, spugne calcaree e microbialiti e boundstone a Bacinella irregularis costituivano biocostruzioni in ambienti ben illuminati di bassa profondità al margine della piattaforma della fase 4, mentre biocostruzioni nella parte superiore dello slope erano costituite da boundstone a spugne calcaree, Crescentiella morronensis e coralli e boundstone a spugne silicee. La trasgressione e la ripresa della carbonate factory di reef all’inizio della fase 4 sono state attribuite al Titoniano inferiore in accordo con nuovi dati biostratigrafici grazie al ritrovamento di ammoniti nelle facies bacinali. Questi eventi deposizionali sono stati probabilmente innescati da contemporanea instabilità tettonica e innalzamento eustatico che hanno favorito l’instaurarsi di condizioni ottimali per lo sviluppo dei reef della fase 4. I principali fattori di controllo dell’evoluzione della successione carbonatica Calloviano-Titoniano della Sardegna orientale sono: i cambiamenti globali delle carbonate factories con lo sviluppo di biota di reef (Oxfordiano superiore), la tettonica estensionale regionale registrata sul margine Europeo della Tetide Alpina che ha influenzato cambiamenti relativi del livello marino e accomodamento (Kimmeridgiano superiore) e innalzamenti globali del livello marino (Oxfordiano superiore e Titoniano inferiore). L’evoluzione diagenetica per ogni fase deposizionale è stata ricostruita tramite analisi petrografiche, in catodoluminescenza e analisi degli isotopi stabili di carbonio e ossigeno. Le facies della fase 1 sono caratterizzate da dolomitizzazione avvenuta durante la diagenesi di seppellimento, costituita da dolomite luminescente zonata formatasi nella porzione inferiore della successione nei pressi del basamento Ercinico e da cemento calcitico blocky e microsparite precipitati in ambiente di seppellimento o durante la telogenesi meteorica. Le facies deposte durante la fase 2 sono caratterizzate da cemento fibroso isopaco precipitato durante la diagenesi marina precoce, dolomitizzazione di seppellimento e cemento calcitico blocky e microsparite precipitati in ambiente di seppellimento o durante la telogenesi meteorica. Le facies della fase 3 sono caratterizzate da cementazione marina precoce da parte di cemento fibroso isopaco nelle facies di rampa media e da cementazione meteorica vadosa precoce da parte di cemento micritico a menisco e pendant nelle facies di piattaforma interna. La parte superiore delle facies della fase 3, nei pressi della superficie di esposizione subaerea, è caratterizzata da dolomitizzazione dovuta a brine evaporitiche in ambiente supratidale come dimostrato dalle caratteristiche petrografiche e dalla composizione isotopica di carbonio e ossigeno. Cemento calcitico blocky, cemento equigranulare a grana fine e microsparite precipitati in ambiente di seppellimento o di telogenesi meteorica caratterizzano le facies di fase 3. Le facies deposte durante la fase 4 sono caratterizzate da cementazione precoce marina con cemento fibroso isopaco e meteorica vadosa con cemento micritico a menisco. Anche le facies di fase 4 sono dolomitizzate per via dell’effetto di brine evaporitiche nei pressi della superficie di esposizione subaerea. Inoltre sono caratterizzate da cemento blocky e microsparite precipitate in ambiente di seppellimento e durante la telogenesi meteorica. Questo studio mette in luce come la tettonica globale e regionale, l’eustatismo e i cambiamenti delle carbonate factories influenzano l’evoluzione dei sistemi deposizionali carbonatici e lo sviluppo dei reefs durante il Giurassico integrando dati di terreno, petrografici, biostratigrafici, diagenetici e geochimici. I risultati hanno implicazioni nella comprensione di come le piattaforme carbonatiche e gli organismi costruttori di reef rispondono ai cambiamenti ambientali, climatici e di accomodamento nel record geologico.
The evolution through time and space of carbonate platforms and reefs is controlled by the interplay of global (climate, eustasy), regional (tectonic) and local environmental (nutrient levels, light penetration) factors affecting changes in accommodation and in the nature of the carbonate factories. Major tectonic plate reorganizations related to the opening of the Alpine Tethys and climatic fluctuations affected Jurassic carbonate successions, which recorded one of the major peaks in the Phanerozoic for the abundance of coral, sponge and microbialite reefs. This study focuses on the eastern Sardinia well-exposed Middle-Upper Jurassic carbonate depositional system that evolved in time and space in terms of facies composition and architecture, characters of the carbonate factory and geometry of the depositional profile encompassing four depositional phases. Detailed facies and microfacies analyses, diagenetic and geochemical investigations and new biostratigraphic data and strontium isotope analyses allowed to better constrain the distinctive sedimentological characteristics and age of these depositional phases, building upon the lithostratigraphic framework published in previous studies on eastern Sardinia carbonate succession. Phase 1 (Callovian-middle Oxfordian) was characterized by the development of a coated-grain dominated carbonate ramp with inner ramp ooidal shoals and peloidal packstone in middle to outer ramp. Phase 2 (late Oxfordian-late Kimmeridgian) recorded the evolution of a reef-bearing carbonate ramp characterized by three types of build-ups laterally distributed along the depositional profile, reflecting water depth increase and the interplay of water energy and light penetration. Type 1 build-ups (45 m thick, 100 m wide) consisted of coral-stromatoporoid boundstone and coral-stromatoporoid rudstone-grainstone and colonized proximal middle ramp settings. Type 2 build-ups (1-2 m thick, 3-4 m wide) were lens-shaped build-ups made of coral-calcareous sponge-diceratid boundstone, including stromatoporoids and chaetetid sponges associated with bioclastic packstone-grainstone developed in deeper, distal middle ramp settings. Type 3 build-ups (1 m thick and few metres wide) consisted of calcareous and siliceous sponge-coral-microbialite boundstone associated with bioclastic packstone-grainstone colonizing distal middle to outer ramp settings. The evolution from phase 1 to phase 2 was related to the global expansion of coral, stromatoporoid, calcareous and siliceous sponge and microbialite reefs during the middle Oxfordian-late Kimmeridgian due to eustatic sea-level rise and climatic fluctuations. Phase 3 (late Kimmeridgian) followed a sea-level fall likely driven by regional extensional tectonics recorded by a subaerial exposure surface at the top of phase 2 likely due to fault block uplift. During phase 3 peritidal facies accumulated in the proximal inner platform setting, whereas coated grain dominated facies (ooids and oncoids) were deposited as reworked grains in the more distal middle ramp domains. Differently from previous studies, the age of phase 3 was assigned to late Kimmeridgian according to strontium isotope and biostratigraphic data based on the occurrence of the foraminifer Alveosepta jaccardi rather than to the Tithonian. The top of phase 3 is marked by another event of subaerial exposure, also recorded in coeval Tethyan depositional settings as a regional unconformity attributed to extensional tectonics. The beginning of phase 4 (Tithonian) is characterized by transgressive basinal deposits followed by the recovery of a reefal carbonate factory. Phase 4 recorded a change in depositional geometry from a carbonate ramp to a higher-relief platform with a slope (about 70 m high and 3-15º steep). Basinal deposits consisted of mudstone, wackestone and siltstone and lithoclastic breccia with resedimented clasts from shallower environments through debris-flow mechanisms. Bio-intraclastic grainstone, wackestone with Clypeina jurassica, wackestone to floatstone with oncoids and peloidal intraclastic packstone to grainstone were resedimented from inner platform depositional environments. Debris-flow breccias include also lithoclasts of boundstone facies representing Tithonian bioconstructions developed during phase 4, different from the upper Oxfordian-upper Kimmeridgian phase 2 build-up types. Coral-calcareous sponge-microbialite boundstone and Bacinella boundstone constituted build-ups in well-illuminated shallow-water settings at the margin of phase 4 platform. Calcareous sponge-Crescentiella-coral boundstone and calcareous and siliceous sponge boundstone formed build-ups in the deeper upper slope and were resedimented into the adjacent basinal setting. The transgression and recovery of the reefal carbonate factory at the beginning of phase 4 were dated to the early Tithonian due to ammonite biostratigraphic data from the basinal deposits. These depositional events were coeval and possibly triggered by tectonic instability during the eustatic sea-level rise that promoted optimal conditions for reef growth during phase 4. The evolution of eastern Sardinia Callovian-Tithonian carbonate succession was controlled by global changes in the dominant carbonate factory with the onset of reef-building biota (late Oxfordian), regional extensional tectonics affecting the European margin of the Alpine Tethys that controlled relative sea-level changes and accommodation (late Kimmeridgian) and global eustatic rises in sea-level (late Oxfordian and early Tithonian). Petrographic, cathodoluminescence and carbon and oxygen stable isotope analyses allowed reconstructing the diagenetic evolution of each depositional phase. Phase 1 facies were characterized by replacive burial dolomitization of zoned luminescent dolomite close to the Hercynian basement and precipitation of blocky calcite cement and microsparite in burial environment and during meteoric telogenesis. Phase 2 facies were characterized by isopachous fibrous cement during early marine diagenesis, burial dolomitization and precipitation of equant blocky calcite and microsparite cement in burial and meteoric telogenetic diagenetic environments. Facies deposited during phase 3 were affected by early marine isopachous fibrous cement (middle ramp facies) or early meteoric vadose cementation by micritic meniscus and pendant cement (inner platform facies). The upper part of phase 3 succession, close to the subaerial exposure surface at the top, is characterized by fabric replacive dolomitization due to evaporitic brines in supratidal settings as inferred from the carbon and oxygen stable isotope signature. Precipitation of equant blocky calcite, fine-grained equant calcite and microsparite took place during burial diagenesis and telogenesis. Phase 4 facies are characterized by early marine (isopachous fibrous cement) and meteoric vadose (micritic meniscus) cementation. Fabric replacive dolomitization took place in the lower part of phase 4 facies close to the subaerial exposure surface due to possibly evaporitic brines. Blocky calcite cement and microsparite precipitated in burial environment and during meteoric telogenesis. This study, integrating field data, petrographic, biostratigraphic, diagenetic and geochemical stable isotope analyses, highlights how regional tectonics, eustasy and carbonate factory changes affected the evolution of a Jurassic carbonate depositional system and reef growth. These findings have implications for the understanding of the responses of carbonate platforms and reef-building biota to environmental, climate and accommodation changes in the geological record.

In the history of a reservoir, after the period of primary production, about 30 to 40%, of the original oil in place may be produced using a secondary recovery mechanism. Polymer injection, which is classified as a tertiary method, can be applied to the remaining oil in place. In this thesis, oil/water relative permeabilities, effect of polymer injection on end point relative permeabilities and residual oil saturations in heterogeneous carbonate reservoirs were investigated. Numereous core flood experiments were conducted on different heteroegneous carbonate cores taken from Midyat Formation. Before starting the displacement experiments, porosity, permeability and capillary pressure experiments were performed. The heterogeneity of the cores are depicted from thin sections. Besides the main aim stated above, effect of flow rate and fracture presence on end point relative permeability and on residual oil saturation and were investigated. According to the results of the displacement tests, end point hexane relative permeability increased when polymer solution was used as the displacing phase.Besides, end point hexane relative permeability increased with polymer injection and fracture presence.

Autocausticizing, a new method to regenerate sodium hydroxide from the sodium carbonate, is intended to replace the conventional Kraft Recovery System which uses calcium hydroxide produced in a lime kiln for this purpose. It is defined as the self-induced expulsion of carbon dioxide bound in the smelt by using certain amphoteric oxides. Thus autocausticizing can eliminate the need for a lime cycle and hence reduce the Kraft process capital and operating costs. The reactions between sodium carbonate and a number of amphoteric oxides have been reported in the literature. Patents have been issued on the use of titanium dioxide, iron oxide and sodium borates for this purpose. The sodium borates have the advantage of a high reaction rate, but are totally soluble and must be carried throughout the whole Kraft cycle. In this research colemanite (calcium borate) which is mined as a cheap mineral in California and in Turkey was studied as an autocausticizing agent. Since it is partially soluble and most likely can be recycled, it would eliminate the problems associated with the use of soluble borates. Experiments were performed both isothermally and under constant heating rate conditions. Isothermal studies were made with Ti0₂, alumina and colemanite to compare their performances as autocausticizing agents at 900°C and 1000°C for various reaction times in an electric furnace. The second group of experiments was made using a differential Chermogravimetric (TG) analyzer. In these experiments mixtures with 20 to 80 weight percent colemanite in sodium carbonate were heated at a constant heating rate of 10°K/min in the range of 190-1000°C. The results indicate that two reaction were involved. Above the stoichiometric colemanite concentration the colemanite and sodium carbonate had reacted completely by a temperature of about 700°C. Above that temperature the impurities in the colemanite appeared to catalyze the decomposition of sodium carbonate if the colemanite concentration was less than the stoichiometric amount needed. TG data were analyzed for the first and second reactions between the temperature ranges of 190-700°C and 700-1000°C respectively. Kinetic models were developed In terms of the reaction order, activation energy and frequency factor. The first reaction was found to be zero order on sodium carbonate concentration. The results also showed that the activation energy and frequency factor were functions of the colemanite concentration in the mixtures. As a result the rate was affected by the amount of colemanite used. The same was true for the second reaction except the reaction was first order. The concentrations predicted for the isothermal tests by the model were compared with the results of the isothermal study for various colemanite concentrations. Reasonable agreement was found except for the values at lower conversions, which might be due to the Increased importance of the diffusion of CO₂ from the mixtures in the case of Isothermal runs. It was also found that it is possible to obtain conversions as high as 85 percent with 40 percent colemanite in 20 minutes. Promising results were obtained from the recycle tests as well.
Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate