A successful cement job results in complete zonal isolation while saving time and money. To achieve these goals, various factors such as well security, casing centralization, effective mud removal, and gas migration must be considered in the design. In the event that high-pressure and high-temperature (HPHT) conditions are encountered, we must attempt to achieve permeability in the set cement to prevent gas migration and to prevent any other fluid passing through to collapse the entire structure. Therefore, the design of the cement must be such that it prevents: Micro-annuli formation Stress cracking Corrosive fluid invasion Fluid migration Annular gas pressure In HPHT cases, we need more flexible cement than in conventional wells. This cement expands more at least 2 to 3 times more in some special cases. The stress in the cement is strongly connected with temperature and pressure, as well as lithology and in-situ stress. If we can define a method which connects the higher temperature to the lower stress field, we would have the solution for one side of the equation, and then we could model the pressure (stress principles) at the designated depth and lithology. Since the stress is so dependent on temperature, the temperature variation must be accurately predicted to properly design the fluid and eliminate excessive time spent waiting on cement. In addition, a post-job analysis is necessary to ascertain zonal isolation and avoid unnecessary remedial work. By increasing the flexibility of the set cement (lowering the Young's modulus), we can reduce the tensile stress in the cement sheath during thermal expansion. This could be a solution to the problem of cement stability in high temperature cases. Here we report the use of the finite-element method (FEM) to investigate the stress fields around and inside the cement, and to forecast the time of failure and its affect on cement integrity. This method is more powerful than conventional stability methods since complex boundary conditions are involved as initial conditions and are investigated simultaneously to more accurately predict cement failure. The results of this study show the relevant dependency of stress principles with temperature and pressure. These results clarify the deformation caused by any disturbance in the system and the behavior of under-stress locations based on their relative solid properties.

A successful cement job results in complete zonal isolation while saving time and money. To achieve these goals, various factors such as well security, casing centralization, effective mud removal, and gas migration must be considered in the design. In the event that high-pressure and high-temperature (HPHT) conditions are encountered, we must attempt to achieve permeability in the set cement to prevent gas migration and to prevent any other fluid passing through to collapse the entire structure. Therefore, the design of the cement must be such that it prevents: Micro-annuli formation Stress cracking Corrosive fluid invasion Fluid migration Annular gas pressure In HPHT cases, we need more flexible cement than in conventional wells. This cement expands more at least 2 to 3 times more in some special cases. The stress in the cement is strongly connected with temperature and pressure, as well as lithology and in-situ stress. If we can define a method which connects the higher temperature to the lower stress field, we would have the solution for one side of the equation, and then we could model the pressure (stress principles) at the designated depth and lithology. Since the stress is so dependent on temperature, the temperature variation must be accurately predicted to properly design the fluid and eliminate excessive time spent waiting on cement. In addition, a post-job analysis is necessary to ascertain zonal isolation and avoid unnecessary remedial work. By increasing the flexibility of the set cement (lowering the Young's modulus), we can reduce the tensile stress in the cement sheath during thermal expansion. This could be a solution to the problem of cement stability in high temperature cases. Here we report the use of the finite-element method (FEM) to investigate the stress fields around and inside the cement, and to forecast the time of failure and its affect on cement integrity. This method is more powerful than conventional stability methods since complex boundary conditions are involved as initial conditions and are investigated simultaneously to more accurately predict cement failure. The results of this study show the relevant dependency of stress principles with temperature and pressure. These results clarify the deformation caused by any disturbance in the system and the behavior of under-stress locations based on their relative solid properties.

Modeling the performance of high-pressure, high-temperature (HPHT) natural gas reservoirs requires the understanding of gas behavior at such conditions. In particular, gas viscosity is an important fluid property that directly affects fluid flow through porous media and along production flowlines. Accurate measurements of gas viscosity at HPHT conditions are both extremely difficult and expensive. Unfortunately, the correlations available today do not have a sufficiently broad range of applicability in terms of pressure and temperature since no measured gas viscosities at HPHT are currently available. Thus the correlation accuracy may be doubtful for the prediction of gas viscosity at HPHT conditions. An oscillating-piston viscometer was used to measure the viscosity of mixtures of nitrogen and methane, and mixtures of CO2 and methane at a pressure range of 5,000 to 25,000 psi, and a temperature range of 100 to 360 degrees F. The viscosity of mixtures of nitrogen and methane, and mixtures of CO2 and methane measured to take into account of the fact that the concentration of non-hydrocarbons increase significantly in HPHT reservoir. The recorded measured data were then used to evaluate the reliability of the most commonly used correlations in the petroleum industry. Measured gas viscosity data at HPHT conditions suggest that the most common gas viscosity correlations return up to 9% relative error in gas recovery factor, which translates into a significant error in estimating the ultimate recovery for large HPHT natural gas reservoirs. Thus, the current gas viscosity correlations need to be adjusted to estimate gas viscosity at HPHT conditions. New gas viscosity correlations constructed for HPHT conditions developed based upon our experiment data provide more confidence on gas viscosity. A rolling ball viscometer was also used to assess its capability to measure gas viscosity. Using gas instead of liquid to calibrate a rolling ball viscometer over the entire pressure and temperature range of interest appears to be satisfactory. Optimizing tube inclination angle and ball/tube diameter ratio prevents turbulent flow effects around the ball, thus enhancing the accuracy of the measurement. The proposed calibration method was then verified with pure CO2 at a pressure range of 4,000 to 8,000 psi, and a temperature range of 98 to 240 degrees F. Consequently, rolling ball viscometer was introduced as a good candidate to measure the gas viscosity; however it has not been tested at HPHT conditions yet.

In order to keep up with the world’s energy demands, oil and gas producing companies have taken the initiative to explore offshore reserves or drill deeper into previously existing wells. The consequence of this, however, has to deal with the high temperatures and pressures encountered at increasing depths. For an oil well to maintain its integrity and be produced effectively and economically, it is pertinent that a complete zonal isolation is achieved during well completion. This complete zonal isolation can be compromised due to factors that come into play when oil well cement experiences cyclic loading conditions which can lead to fatigue failure as a consequence of extensive degradation of the microstructure of the cement material depending on stress levels and number of cycles. There have been a lot of research and experimental investigations on the mechanism of fatigue failure of concrete structures but the fatigue behavior of oil well cement is still relatively unknown to engineers. Research in the area of oil well cement design has led to improved cement designs and cementing practices but yet many cement integrity problems persist and this further strengthens the need to understand the mechanism of cement fatigue. This research seeks to develop a better understanding of the performance of the casing cement bond under HPHT well conditions that can lead to best practices and a model to predict well life. An analytical model, which can be used to evaluate stresses in the cement sheath based on actual wellbore parameters, was developed and combined effectively with finite element models to evaluate the fatigue and static loading behavior of a well. Based on the findings of this investigation, the mechanical properties of the casing, cement and formation as well loading conditions play a very big role in the static and fatigue failure of well cement. Finally, recommendations for future work on this subject were also presented in order to understand all tenets of cement fatigue and to develop governing equations.

Estimation of viscosities of naturally occurring petroleum gases provides the information needed to accurately work out reservoir-engineering problems. Existing models for viscosity prediction are limited by data, especially at high pressures and high temperatures. Studies show that the predicted viscosities of natural gases using the current correlation equations are about 15 % higher than the corresponding measured viscosities at high pressures and high temperatures. This project proposes to develop a viscosity prediction model for natural gases at high pressures and high temperatures. The project shows that commercial gas viscosity measurement devices currently available suffer from a variety of problems and do not give reliable or repeatable results. However, at the extremely high pressures encountered in high pressure and high temperature reservoirs, the natural gases consist mainly of methane as the hydrocarbon constituent and some non-hydrocarbon impurities. Available viscosity values of methane were used in the development of a correlation for predicting the viscosities of naturally occurring petroleum gases at high pressures and high temperatures. In the absence of measurements, this correlation can be used with some confidence.

This thesis presents work undertaken using Synchrotron and Laboratory based techniques in parallel on the Chemical State and Luminescence Imaging of Natural and Synthetic Diamond. X-ray absorption spectroscopy (XAS) techniques have revealed information on the chemical structure and bonding within brown and variegated type Ia, IIa, CVD and high-pressure, high-temperature (HPHT) treated diamonds. XAS, Raman, X-ray Excited Optical Luminescence (XEOL) and Photoluminescence (PL) are some of the techniques that have been applied to characterise and investigate the cause of the brown colouration. The XAS measurements have been undertaken in imaging mode with the capabilities of correlating the luminescence image with the brown regions in partial luminescence yield (PLY) and total luminescence yield (TLY). OD-XAS spectrums have been obtained at non-brown and brown regions and have revealed a higher concentration of sp2-bonded carbon present at the brown sites. Raman spectroscopy utilized in imaging mode also supports this discovery.

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.

Abstract A range of di®erent high-quality single crystal diamonds synthesized under high pressure and high temperature (HPHT) conditions have been studied in view of their potential as candidates for specialized electronic devices with emphasis on particle detectors. The studies incorporated a long range of spectroscopic and electronic characterization techniques. Special attention was given to electronic properties and device performance re- lated to the electrical contacts applied, the type and the concentration of impur- ities and the crystallographic defects present. The electronic response of a dia- mond detector as far as impurities are concerned is predominantly determined by the single substitutional nitrogen (SSN) and boron acceptors. Di®erent tech- niques were used to assess the role of such impurities in the diamond crystals stud- ied, as well as to study the dynamics due to the interaction of such impurities with each other (compensation). Hence, the electron spin resonance (ESR) and the current-deep level transient spectroscopy (I-DLTS) techniques were used in this re- spect to extract the information concerning activation energies, nitrogen-boron dy- namics, and the nitrogen and boron concentrations. ii iii It was found that the SSN content was below 1013 cm¡3 with this result giving the approximate concentration of boron acceptors, being the same value as of that of the SSN, or slightly above. Maximum activation energies of boron acceptors were extracted from three di®erent regions in the bulk of the diamond. The values were approximately 0.311 eV § 0.0027 eV in the center region, 0.308 eV § 0.007 eV in the intermediate region and 0.29 eV § 0.007 eV at the edge region, respectively. The maximum activation energy when boron is fully compensated is about 0.37 eV. Properties of ohmic and Schottky contacts as a function of concentration of SSN and boron acceptors were investigated using Current-Voltage characteristic and photo- current measurements. Di®erent surface treatment conditions and di®erent types of diamonds (IIa, IIb and Ib) were used. Electronic properties as a function of contacts were assessed for high purity synthetic type IIa diamond detector, incorporating a time of °ight (TOF) UV laser set-up. The maximum hole collection distance at room temperature was found to be 91.00 cm, the maximum transient time for holes was about 1.00 ms and the e±ciency was approximately 41%, with contacts made of Ti/Pt/Au-Ru. When Ru-Ru contacts are applied, the maximum hole mobility and the velocity were extracted at room temperature to be about 17963.44 cm2V¡1s¡1 and 5.02 £107 cms¡1, respectively, and the e±ciency of the device is about 30%. The maximum applied external electric ¯elds with Ru-Ru contacts were increased to about 1.32 times that at low temperature and to about 1.84 times that at room temperature. iv Large signals generated by ®-particles from 228Th were obtained without using amp- li¯cation. However, a full analysis of the pulse was not possible due to the narrow bandwidth of the electronic probes used. In a detector made of type Ib diamond, with SSN concentrations of about 50 ppm, it was found that regions in the bulk exhibiting better charge collection properties contained small concentrations of uncompensated boron impurity. On the other hand, the di®erence in the concentrations of SSN between the two type Ib diamonds, with about 50 ppm and about 200 ppm of SSN concentrations, respectively, resulted in approximately 70 ps di®erence in the transit time between two detectors made of these diamonds. Keywords: Synthetic diamond, detector, HPHT, type Ib, type IIa, single substitutional ni- trogen, SSN, ESR, ARP, I-DLTS, metallization, uncompensated boron impurity, crystallographic defects, rise and decay times, charge carrier life time, charge carrier mobility, carrier mean free path , charge collection distance, carrier Schubweg.

In the life of a well, the cement sheath not only provides zonal isolation but also supports casing and increases casing-collapse resistance. Due to the high-pressure, high-temperature (HPHT) conditions, the cement sheath plays an important role in maintaining wellbore integrity. During the production process in HPHT wells, the pressure differential inside the casing and the surrounding formation is larger than the conventional wells. The stress induced by fluid withdrawal in highly compact reservoirs can cause the cement and the casing failure in these wells. These present a greater challenge to the wellbore integrity than the conventional wells. To have reliable data, extensive experimental work on Class G cement was carried out to measure the principal parameters for mechanical structural calculations. The experiment was also set up to simulate conditions under which cement low-cycle fatigue failure could occur. Zero-based cyclic pressure was applied to the casing in the cement low-cycle fatigue test. Three types of cement (72-lbm/ft3, 101-lbm/ft3 and 118-lbm/ft3) were cured and tested at 300ºF to study the cement mechanical properties under high-temperature conditions over the long term. The tests included a 1-year mechanical properties measurement such as compressive strength development; i.e., Young’s modulus and Poisson’s ratio. Finite element methods (FEM) were used to study the casing buckling deformation characteristics of reservoir compaction in some south Texas wells. The 2D and 3D FEM models were built to study the effects of mechanical properties and reservoir compaction on HPHT well integrity. As the confining pressure increases, the cement shows more plasticity and can withstand more pressure cycles. The cement with a higher Poisson’s ratio and lower Young’s modulus showed better low-cycle fatigue behavior. Casing collapse resistance is very sensitive to void location, cement Poisson’s ratio, cement Young’s modulus, and pore pressure. Casing eccentricity and voids shape have minor effect on the casing-collapse resistance. Casing shear failure, tension failure, and buckling failure are the most likely failure modes in reservoir compaction. For different casing wall thickness, the critical buckling strain is almost identical. This study presents a better understanding of casing failure and cement failure in HPHT wells. The results of the study will help improve cement and casing design to maintain wellbore integrity that can in turn be expected to extend throughout the life of the well.

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.