Designing a fit-for-purpose drilling fluid for high-pressure, high-temperature (HP/HT) operations is one of the greatest technological challenges facing the oil and gas industry today. Typically, a drilling fluid is subjected to increasing temperature and pressure with depth. While higher temperature decreases the drilling fluid’s viscosity due to thermal expansion, increased pressure increases its viscosity by compression. Under these extreme conditions, well control issues become more complicated and can easily be masked by methane and hydrogen sulfide solubility in oil-base fluids frequently used in HP/HT operations. Also current logging tools are at best not reliable since the anticipated bottom-hole temperature is often well above their operating limit. The Literature shows limited experimental data on drilling fluid properties beyond 350°F and 20,000 psig. The practice of extrapolation of fluid properties at some moderate level to extreme-HP/HT (XHP/HT) conditions is obsolete and could result in significant inaccuracies in hydraulics models. This research is focused on developing a methodology for testing drilling fluids at XHP/HT conditions using an automated viscometer. This state-of-the-art viscometer is capable of accurately measuring drilling fluids properties up to 600°F and 40,000 psig. A series of factorial experiments were performed on typical XHP/HT oil-based drilling fluids to investigate their change in rheology at these extreme conditions (200 to 600°F and 15,000 to 40,000 psig). Detailed statistical analyses involving: analysis of variance, hypothesis testing, evaluation of residuals and multiple linear regression are implemented using data from the laboratory experiments. I have developed the FluidStats program as an effective statistical tool for characterizing drilling fluids at XHP/HT conditions using factorial experiments. Results from the experiments show that different drilling fluids disintegrate at different temperatures depending on their composition (i.e. weighting agent, additives, oil/water ratio etc). The combined pressure-temperature effect on viscosity is complex. At high thresholds, the temperature effect is observed to be more dominant while the pressure effect is more pronounced at low temperatures. This research is vital because statistics show that well control incident rates for non- HP/HT wells range between 4% to 5% whereas for HP/HT wells, it is as high as 100% to 200%. It is pertinent to note that over 50% of the world’s proven oil and gas reserves lie below 14,000 ft subsea according to the Minerals Management Service (MMS). Thus drilling in HP/HT environment is fast becoming a common place especially in the Gulf of Mexico (GOM) where HP/HT resistant drilling fluids are increasingly being used to ensure safe and successful operations.

Transition metal oxides have been extensively studied during past decades. The purpose of this research was to synthesize new or little characterised transition metal oxides using high-pressure/high-temperature (HPHT) techniques. Various ternary vanadium oxides have been synthesised at ambient and high pressure conditions. All compounds have been studied by neutron and laboratory X-ray powder diffraction and magnetisation measurements. In some cases resistivity and synchrotron X-ray powder diffraction measurements were also carried out. The MnVO3 perovskite containing localized 3d5 Mn2+ and itinerant 3d1 V4+ states has been synthesised at 8 GPa and 1100°C. MnVO3 crystallises in Pnma space group (a = 5.2741(6) Å, b = 7.4100(11) Å, and c = 5.1184(8) Å at 300 K) and is metallic at temperatures of 2 – 300 K and at pressures of up to 67 kbar. Synchrotron X-ray powder diffraction study on the combined sample of several high pressure products showed slight variation in the stoichiometry of MnVO3. Incommensurate Mn spin order was discovered in the neutron powder diffraction measurements, which reveal a (0.29 0 0) magnetic vector below the 46 K spin ordering transition, and both helical and spin density wave orderings are consistent with the diffraction intensities. Electronic structure calculations show large exchange splittings of the Mn and V 3d bands, and (kx 0 0) crossings of the Fermi energy by spin up and down V 3d bands may give rise to Ruderman-Kittel-Kasuya-Yosida coupling of Mn moments, in addition to their superexchange interactions. The new compound CoVO4 has been discovered in a high pressure synthesis experiment. Magnetic susceptibility measurement, synchrotron X-ray and neutron powder diffraction studies were carried out. Refinements of the synchrotron X-ray and neutron data show CoVO4 to crystallise in space group Pbcn (a = 4.5012(2) Å, b = 5.5539(3) Å, and c = 4.8330(2) Å at 300 K (synchrotron X-ray data)). The magnetic susceptibility measurement reveals that Co3+ is most likely in a low spin state in CoVO4. Monoclinic brannerite type CoV2O6 was synthesised in ambient pressure. Neutron powder diffraction measurements were carried out and an antiferromagnetic order with an a x b x 2c supercell was observed below TN = 15 K. High spin Co2+ moments of magnitude 4.77(4) μB at 4 K lie in the ac plane and are ferromagnetically coupled within chains of edge-sharing CoO6 octahedra parallel to b axis. No structural transition is observed down to 4 K, but a magnetostriction accompanying antiferromagnetic order at TN = 15 K was discovered. A field-induced 1/3 magnetisation plateau and corresponding changes in the magnetic structure were studied by carrying out neutron powder diffraction measurements at 2 K in applied magnetic fields of 0, 2.5 and 5.0 T. Three collinear magnetic phases were observed as field increases; the above antiferromagnetic state with propagation vector (0 0 ½), a ferrimagnetic (¯⅓ 1 ⅓) phase, and a (0 0 0) ferromagnetic order. Co2+ moments of 4.4 - 5.0 μB have a large orbital component and are aligned close to the c-axis direction in all cases. Spin-lattice coupling leads to a magnetostriction and volume expansion as field increases. The ferrimagnetic phase accounts for the previously reported 1/3 magnetisation plateau, and demonstrates that monoclinic CoV2O6 behaves as an accidental triangular antiferromagnetic lattice in which further frustrated orders may be accessible. Orthorhombic columbite-type NiV2O6 and CoV2O6 compounds were synthesised at 6 GPa and 900°C. Metamagnetism and magnetic transitions were found in magnetic measurements. Powder neutron diffraction studies in zero and applied field were carried out. Both compounds were refined in space group Pbcn and the following lattice parameters were obtained at 300 K, CoV2O6: a = 13.4941(20) Å, b = 5.5736(9) Å, and c = 4.8082(8) Å and NiV2O6: a = 13.3725(17) Å, b = 5.5344(7) Å, and c = 4.8162(7) Å. Neutron powder diffraction studies in zero field did not reveal any magnetic peaks for either of the compounds but magnetic order emerges in applied fields between 1 and 4 T.

Pressure and temperature are two environmental variables that are increasingly being exploited by solid-state researchers probing structure-property relationships in the crystalline state. Modern high-pressure apparatus is capable of generating many billions of Pascals in the laboratory, and therefore can produce significantly greater alterations to crystalline materials than changes in temperature, which can typically be varied by only a few thousand Kelvin. Many systems such as single-molecule magnets exhibit interesting properties under low-temperature regimes that can be substantially altered with pressure. The desire by investigators to perform analogous single-crystal X-ray diffraction studies has driven the development of new high-pressure apparatus and techniques designed to accommodate low-temperature environments. [Ni(en)3][NO3]2 undergoes a displacive phase transition from P6322 at ambient pressure to a lower symmetry P6122/P6522 structure between 0.82 and 0.87 GPa, which is characterized by a tripling of the unit cell c axis and the number of molecules per unit cell. The same transition has been previously observed at 108 K. The application of pressure leads to a general shortening of O···H hydrogen bonding interactions in the structure, with the greatest contraction (24%) occurring diagonally between stacks of Ni cation moieties and nitrate anions. A novel Turnbuckle Diamond Anvil Cell designed for high-pressure low-temperature single-crystal X-ray experiments on an open-flow cryostat has been calibrated using the previously reported phase transitions of five compounds: NH4H2PO4 (148 K), ferrocene (164 K), barbituric acid dihydrate (216 K), ammonium bromide (235 K), and potassium nitrite (264 K). From the observed thermal differentials between the reported and observed transition temperatures a linear calibration curve has been constructed that is applicable between ambient-temperature and 148 K. Low-temperature measurements using a thermocouple have been shown to vary significantly depending on the experimental setup for the insertion wire, whilst also adding undesirable thermal energy into the sample chamber which was largely independent of attachment configuration. High-pressure low-temperature single-crystal X-ray diffraction data of [Mn12O12(O2CMe)16(H2O)4] (known as Mn12OAc) reveals a pressure-induced expulsion of the crystallized acetic acid from the crystal structure and resolution of the Jahn-Teller axes disorder between ambient pressure and 0.87 GPa. These structural changes have been correlated with high-pressure magnetic data indicating the elimination of a slow-relaxing isomer over this pressure range. Further application of pressure to 2.02 GPa leads to the expansion of these Jahn-Teller axes, resulting in an enhancement of the slow-relaxing magnetic anisotropy as observed in the literature. Relaxation of pressure leads to a resolvation of the crystal structure and re-disordering of the Jahn-Teller axes, demonstrating that this structural-magnetic phenomenon is fully reversible with respect to pressure. The space group of the Prussian blue analogue Mn3[Cr(CN)6].15H2O has been re-evaluated as R-3m between ambient pressure and 2.07 GPa using high-pressure single-crystal X-ray and high-pressure neutron powder data. Reductions in metal-metal distances and gradual distortions of the Mn octahedral geometry have been correlated with previously reported increases in Tc and declines in ferrimagnetic moment in the same pressure range. Increasing the applied pressure to 2.97 GPa leads to partial amorphization and results in a loss of long-range magnetic order as shown by the literature. The application of pressure (1.8 GPa) to the structure of K2[Pt(CN)4]Br0.24.3.24H2O (KCP(Br)) causes a reduction in the Pt intra-chain and inter-chain distances, and results in an enhancement of the overall conductivity under these conditions as demonstrated in the literature. Almost no changes occur to the high-pressure crystal structure upon cooling to 4 K, except in the Pt-Pt intra-chain distances which converge and suppress the Peierls distortion known to occur at 4 K, resulting in a comparatively greater electrical conductivity under these conditions.

Common brown colour in natural diamond forms by plastic deformation during storage in the subcontinental lithospheric mantle (SCLM). Dislocation movement generates vacancies, which aggregate into clusters of perhaps 30–60 vacancies. Positron annihilation lifetime spectroscopy (PALS) and electron energy loss spectroscopy (EELS) support such vacancy clusters as the cause of brown colour. Brief treatment in a high-pressure–high-temperature (HPHT) vessel at 1800–2700 °C can destroy the brown colour. There has been speculation that similar colour removal should occur continuously at depth in the SCLM. Diamonds are stored at 900–1400 °C in the SCLM, according to inclusion thermometry. The effect of temperature on the time required to destroy brown colour has been calculated from published data. The activation energy for the breakup of vacancy clusters is a critical component. The time required to destroy brown colour in the SCLM is significant at the scale of geological time. Brown diamonds should easily maintain their colour for millions of years during cooler mantle storage at or below about 1000 °C. Warmer temperatures toward the base of the lithosphere may be able to reduce or eliminate brown colour within thousands of years. The survival of brown colour in the lithospheric mantle does not require the colour to be formed late in the storage history nor does it require metastable storage in the graphite stability field. Crystal strain is preserved upon loss of brown colour during HPHT treatment. Inhomogeneous crystal strain was measured in 18 natural diamonds using micro-X-ray diffraction (μXRD) χ-dimension peak widths. There is a correlation between strain and depth of brown colour. None of the colourless diamonds examined have high strain, as should be expected for a diamond that has gained and lost brown colour. This suggests that removal of brown colour is not a common natural occurrence. Infrared spectroscopy was used to determine nitrogen concentration and aggregation state in 60 natural diamonds. A loose association was found between brown colour and lower total nitrogen content. Within single diamonds, regions with less nitrogen tend to exhibit more anomalous birefringence due to strain. Colour zoned diamonds tend to have less nitrogen in the darker brown regions. This supports the hypothesis that diamonds with less nitrogen are more susceptible to plastic deformation and the development of brown colour. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2009-09-17 17:10:11.078

Mixed metal oxynitrides have attracted attention due to their interesting chemical and physical properties in the past twenty years. In this thesis, four series of mixed metal oxynitrides have been investigated. The samples have been synthesized by both thermal ammonolysis and high pressure high temperature methods. The structural exploration covers perovskite, scheelite and pyrochlore types. The structural studies were carried out using powder X-ray and neutron diffraction, and magnetic and conducting properties have been explored. A series of new RZrO2N (R = Pr, Nd and Sm) perovskites were synthesized using high pressure high temperature methods (HPHT) via a direct solid state reaction of R2O3 with Zr2ON2. All three new phases crystallize in the orthorhombic Pnma perovskite superstructure, and the structural distortion increases with decreasing R3+ ionic radius. RZrO2N contains both R3+ and d0 Zr4+ and thus shows a potential for multiferroic properties. EuWO1-xN2+x perovskites with a wide range of nitrogen contents (-0.16 ≤ x ≤ 0.46) were synthesized by thermal ammonolysis of an oxide precursor Eu2W2O9. Ferromagnetic ordering below a Curie temperature TC =12 ± 1 K and negative colossal magnetoresistances (CMR) have been discovered in these samples. In particular, for the lowest doped sample, EuWO0.96N2.04, CMR ≥ 99.7% was observed at 7 K. The possibility of tuning the physical properties by altering the chemical composition has been demonstrated. A linear relationship between the lattice parameter and nitrogen content of EuWO1+xN2-x was observed. An investigation has been made of the Eu-Mo-O-N system. A new pyrochlore oxynitride series Eu2Mo2O6-xN2+2x/3 (0.20 ≤ x ≤ 2.25) was synthesized by ammonolysis of Eu2Mo2O7. A ferrimagnetic ordering and semiconducting behavior has been observed in these samples. A detailed structural study of SrMO2N (M = Nb, Ta) has been performed using variable temperature neutron and electron diffraction. Partial anion order has been observed in both samples up to 750 oC. It is consistent with cis-ordering of the two nitrides in each MO4N2 octahedron. At low temperatures, this order directs the tilting of the octahedron to form a pseudo-tetragonal superstructure. It creates zig-zag MN chains in two or three dimensions within the lattice. This principle can be used to predict the local structures of perovskite-related oxynitrides AMO3-xNx.

<p>Knowledge about the stability of phases and their relationships in the Fe-O system at high pressures and temperatures is essential in implications of the multifarious states of iron oxides for models of the evolution of the Earth. In this respect, the iron ferrite magnetite (FeFe₂O₄) plays a significant role since it participates in the control of geochemistry of ferric iron, and hence oxygen fugacity in the Earth`s deep interior.</p><p>High-pressure experiments on Fe₃O₄ were performed using the diamond anvil cell technique combined with the laser and electrical resistive heating. The approach based on the combination of the synchrotron x-ray diffraction with Raman spectroscopic measurements benefited from the complementarity of the two methods originating from the different sensitivity to a range of structural order. High-pressure transformation of magnetite to a dense polymorph of the CaTi₂O₄-type structure proceeds via an intermediate step of the decomposition into a mixture of oxides on a microscopic scale. The kinetic hindrance of the reaction of the decomposition effectively prevents a phase separation controlled by diffusion and restricts the formation of the daughter products to locally ordered structures in the strained lattice of magnetite.</p><p>Thermodynamic analysis of the observed phase transformations along with published results on the elastic properties and pressure-induced transitions of iron oxides has led to the reassessment of the phase diagram of Fe₃O₄. The pressure - temperature field of its stability with respect to the breakdown to a mixture of oxides FeO and Fe₂O₃, and to the transition to a high-pressure form, has been accordingly modified.</p>

Knowledge about the stability of phases and their relationships in the Fe-O system at high pressures and temperatures is essential in implications of the multifarious states of iron oxides for models of the evolution of the Earth. In this respect, the iron ferrite magnetite (FeFe2O4) plays a significant role since it participates in the control of geochemistry of ferric iron, and hence oxygen fugacity in the Earth`s deep interior. High-pressure experiments on Fe3O4 were performed using the diamond anvil cell technique combined with the laser and electrical resistive heating. The approach based on the combination of the synchrotron x-ray diffraction with Raman spectroscopic measurements benefited from the complementarity of the two methods originating from the different sensitivity to a range of structural order. High-pressure transformation of magnetite to a dense polymorph of the CaTi2O4-type structure proceeds via an intermediate step of the decomposition into a mixture of oxides on a microscopic scale. The kinetic hindrance of the reaction of the decomposition effectively prevents a phase separation controlled by diffusion and restricts the formation of the daughter products to locally ordered structures in the strained lattice of magnetite. Thermodynamic analysis of the observed phase transformations along with published results on the elastic properties and pressure-induced transitions of iron oxides has led to the reassessment of the phase diagram of Fe3O4. The pressure - temperature field of its stability with respect to the breakdown to a mixture of oxides FeO and Fe2O3, and to the transition to a high-pressure form, has been accordingly modified.

The high-pressure behaviour of the lanthanide series of metals has been the subject of study since the work of Percy Bridgman in the 1940s. Differences in said behaviour between the different lanthanide metals are attributed to the increasing occupation of the 4f electron shell as Z increases. Upon compression, or as Z decreases, the trivalent lanthanides (La to Lu, excluding Eu and Yb) undergo a common phase transformation sequence through various close packed structures: hcp → Sm-type (the structure adopted by samarium at ambient conditions) → dhcp → fcc → distorted fcc (d-fcc). Upon further compression, the lanthanide metals experience a first order transition to a "volume collapsed" phase. Many studies have focused on the low-Z members of the series, since the various phase transitions occur at much lower pressure where it is comparatively easy to collect high quality data. By contrast, the other members of the series have received comparability little attention, and there are even fewer reports of the structural behaviour of the lanthanide metals at high pressure and high temperature. This thesis contains the results of angle-dispersive x-ray powder diffraction experiments at high pressure and high temperature of the various members of the lanthanide metals. Ce has been the subject of many previous studies, but a systematic x-ray diffraction study of the fcc/d-fcc phase boundary has never been attempted. Furthermore, the location in P-T space of the high temperature fcc/bct/d-fcc triple point has only been inferred, due to the lack of data on the fcc/bct phase boundary at high temperature. The high-pressure high-temperature phase diagram of Ce is presented and discussed. La is unique amongst the lanthanide metals due to its empty 4f shell at ambient conditions. Despite this, La undergoes the common lanthanide transformation sequence up to the d-fcc phase, after which it undergoes a re-entrant transition back to the fcc phase at 60 GPa. The diffraction peaks of d-fcc La are shown in this thesis to undergo changes in intensity upon compression, indicating a transformation to the oI 16 structure found in Pr. La is one of the few elements whose behaviour has been unknown above 100 GPa, and results of La's structural behaviour upon compression to 280 GPa are presented and discussed. At 76 GPa, La begins a transition from the fcc phase to a new phase with the bct structure. Finally, the d-fcc→fcc re-entrant phase transition has been determined at various temperatures, and the d-fcc stability region has been mapped out. Finally, x-ray diffraction experiments were performed on Gd up to 100 GPa and ~700 K, to determine the structure of the d-fcc phase and the "volume collapsed" phase. While d-fcc Gd does not undergo pressure-induced changes similar to its low Z brethren, the d-fcc Gd remains stable up to 41 GPa at 700 K, putting a constraint on the d-fcc stability region. The data collected on Gd's "volume collapsed" phase cannot be fitted to the currently accepted mC4 structure. This has implications for our understanding of the lanthanide series as a whole, since most of of the heavier members, and some of the lighter lanthanides, are reported to adopt the mC4 structure.

Ce travail de thèse porte sur la synthèse de nouveaux matériaux nanostructurés sous conditions extrêmes de pression et de température (P > 5 GPa et T > 1000 °C). Les matériaux que nous étudions sont basés sur un élément particulier : le bore. Ces matériaux présentent des propriétés uniques. D'une part, les allotropes du bore présentent des duretés élevées et une grande inertie chimique. D'autre part, les alliages du bore (ou borures métalliques) présentent des propriétés variées, de la thermoélectricité (HfB2) à la supraconductivité (MgB2). La synthèse en sels fondus est utilisée afin d'obtenir des systèmes nanostructurés comprenant deux composants : des nanoparticules cristallines d'environ 10 nm de borures métalliques (HfB2 ou CaB6) comprises dans une matrice de bore amorphe.Le traitement sous haute pression et température est le seul permettant de cristalliser la phase amorphe. La conservation de la nanostructure initiale est démontrée. Plusieurs nouveaux matériaux sont ainsi synthétisés : des nanocomposites borure/borate (HfB2/HfB2O5 ou CaB6/CaB2O4) ou borure/bore (HfB2/?-B ou CaB6/?-B), premiers membres de nouvelles familles de nanomatériaux. Un précurseur de bore amorphe nanostructuré synthétisé en sels fondus est ensuite utilisé. Il est cristallisé sous haute pression et haute température. En sus de la première occurrence de bore epsilon nanostructuré, deux nouvelles phases riches en bore sont obtenues, dont la structure est en cours de résolution. En somme, ce travail conduit à une nouvelle méthode de synthèse à la frontière entre la chimie des nanomatériaux et la physique des hautes pressions et températures, à l'origine de nouveaux nanomatériaux et structures. / In this PhD work, we develop a way to prepare new nanostructured materials under extreme pressure and temperature conditions (P > 5 GPa et T > 1000 °C). The studied materials are based on a specific element: boron. Indeed, these materials have unique properties. On the one hand, boron allotropes exhibit high hardness and chemical inertness. On the other hand, metal-boron alloys (metal borides) span a wide range of properties, from thermoelectricity (HfB2) to superconductivity (TiB2). We use the synthesis in molten salts to reach nanostructured systems with two components: crystalline boride nanoparticles (ca. 10 nm) embedded in an amorphous boron matrix. High pressure high temperature treatments on these systems enable crystallisation of the amorphous component into unique phases, thus yielding new nanomaterials: boride/borate (HfB2/HfB2O5 or CaB6/CaB2O4) or boride/boron (HfB2/β-B or CaB6/β-B) nanocomposites, representing the first members of new nanomaterials families. In a final step, a specific nanostructured amorphous boron precursor is synthesised in molten salts. It is crystallised under high pressure and temperature. In addition to the first nanostructured occurrence of the epsilon-boron phase, we report two new boron-rich phases, which structure is under resolution. All in all, a new synthetic route is developed at the frontier of nanomaterials chemistry and high pressure and temperature physics, leading to new nanomaterials and structures.

This thesis project has focussed on the experimental study of simple molecular systems at extreme conditions. High-pressure and high-temperature techniques have been used in combination with Raman spectroscopy and X-ray diffraction diagnostics to characterise three simple molecular systems which are unified by the inclusion of nitrogen as a constituent element. The N2 molecule contains the only triple-bond amongst the elemental diatomics and is considered a model system for exploring the changes in structure and bonding induced by tuning pressure and temperature conditions. As such the nitrogen phase-diagram is a focus-point in current extreme conditions research and nitrogen has been found to exhibit a high-degree of polymorphism not observed in other simple molecular systems such as hydrogen or oxygen. Understanding molecular mixtures of nitrogen with other simple molecules at extreme conditions is significant to many scientific fields varying from chemistry to astronomy. The first system presented is the binary mixture of nitrogen and xenon which was studied as a function of pressure. The study constitutes the first comprehensive study of the xenon-nitrogen system at high-pressures. A new van der Waals compound was observed which underwent a phase transition at 14 GPa and was stable up to at least 180 GPa and 3000 K, conditions where pure nitrogen becomes amorphous. Optical measurements suggested possible metallization of the new compound around 120 GPa. The second system presented is the binary mixture of nitrogen and hydrogen which was studied both as a function of pressure and composition. Two known nitrogen-hydrogen structures were confirmed and a pressure-temperature path-dependent formation of hydrazine or ammonia was discovered. Additionally, one mixture was compressed to 242 GPa, the highest pressure investigated in the nitrogen-hydrogen system. The third system presented is the elemental nitrogen phase known as i-nitrogen, an elusive high-temperature polymorph which has hitherto eluded structure determination and proved challenging to access. i-nitrogen was successfully characterised as having an extraordinarily large unit cell containing 48 N2 molecules, making it the most complex molecular nitrogen structure to be determined unambiguously.