High Pressures And High Temperatures Research Articles

Formation of SiV centers by doping in bottom-up grown HPHT nanodiamonds and its implication for optical nanosensig

We investigate doping and formation of luminescent point defects in nanodiamond at high pressures and high temperatures (HPHT) in fluorine-containing hydrocarbon growth systems with an excessive content of dopant organosilicon component. It is shown experimentally that the average concentration of silicon-vacancy centers (SiV-) tends to increase proportionally to the diameter of the nanocrystals. Respectively, the local concentration of the dopant in a crystal linearly increases with the distance from the crystal center. This phenomenon is explained by competition between growth of a perfect crystal and doping. The kinetics of the crystal growth are determined by the diffusion of carbon containing precursors to the surface of the crystal and the doping takes place at a very high concentration of the dopant in the growth mixture and that is defined by the rate of the chemical reaction on the crystal surface. Electrodynamic effects in the nanocrystals affecting the observed intensity of the photoluminescence are also considered. Although these results are obtained using important for applications SiV- photo luminescent centers, they have much wider implications.

Correlated Kelvin-probe force microscopy, micro-FTIR and micro-Raman analysis of doping anisotropy in multisectorial boron-doped HPHT diamonds

Boron-doped diamond single crystals of cubo-octahedral habit have been obtained by temperature gradient method at high pressures and high temperatures (HPHT) in Fe-Al-B-C system, and multisectoral plates of different orientations have been produced. Spatial distribution of uncompensated boron impurity and surface potential through the interfaces of different growth sectors of diamond plates have been studied by scanning Fourier transform infrared (FTIR) and Raman micro-spectroscopy, as well as scanning spreading resistance microscopy (SSRM) and Kelvin-probe force microscopy (KPFM). FTIR mapping showed strongly non-uniform growth-sector dependent distribution of uncompensated boron impurity gradually decreasing in a sequence {111} → {110} → {113} → {001} from ~7 · 1018 cm−3 down to 2 · 1017 cm−3. Micro-Raman mapping is used to reveal the submicron distribution of structural quality and boron content through the interfaces of different growth sectors. The inter-sectoral jumps of the surface potential in the axial and radial directions of the growth sectors were studied by KPFM, their theoretical estimates are obtained, and the features of the band structure of the inter-sector interfaces are revealed. A high level of structural perfection of inter-sectoral boundaries without electrically active defects is demonstrated.

Modeling viscosity of methane, nitrogen, and hydrocarbon gas mixtures at ultra-high pressures and temperatures using group method of data handling and gene expression programming techniques

Accurate gas viscosity determination is an important issue in the oil and gas industries. Experimental approaches for gas viscosity measurement are time-consuming, expensive and hardly possible at high pressures and high temperatures (HPHT). In this study, a number of correlations were developed to estimate gas viscosity by the use of group method of data handling (GMDH)-type neural network and gene expression programming (GEP) techniques using a large data set containing more than 3000 experimental data points for methane, nitrogen, and hydrocarbon gas mixtures. It is worth mentioning that unlike many of viscosity correlations, the proposed ones in this study could compute gas viscosity at pressures ranging between 34 and 172 MPa and temperatures between 310 and 1300 K. Also, a comparison was performed between the results of these established models and the results of ten well-known models reported in the literature. Average absolute relative errors of GMDH models were obtained 4.23%, 0.64%, and 0.61% for hydrocarbon gas mixtures, methane, and nitrogen, respectively. In addition, graphical analyses indicate that the GMDH can predict gas viscosity with higher accuracy than GEP at HPHT conditions. Also, using leverage technique, valid, suspected and outlier data points were determined. Finally, trends of gas viscosity models at different conditions were evaluated.

Phase behavior and fluid interactions of a CO2-Light oil system at high pressures and temperatures

This paper investigates the phase behavior and mutual interactions between a light crude oil and CO2 at high pressures and high temperatures (HPHT). To do so, we have measured PVT properties of the CO2-oil system at HPHT using a PVT setup. We have also tried to present a detailed methodology for measuring PVT properties of CO2-oil systems and highlight the difficulties such as oil vaporization by CO2 during the experiments. A crude oil sample, collected from a Malaysian oil field, was used here. Our experiments indicated that, CO2 solubility in the oil increased at higher pressures when measured at a fixed temperature. Our experiments also showed that increasing the test temperature would reduce CO2 solubility in the oil, while its effect is more significant at higher pressures. The swelling factor (SF) measurements showed an increasing trend with pressure up to a certain value so-called extraction pressure, at which, the SF started to be reduced even became less than one. The measurements of oil viscosity indicated that CO2 dissolution in the oil sample could reduce the mixture viscosity up to 61%. The interfacial tensions between CO2 and the crude oil at different pressures were also measured while the results were used to estimate the minimum miscibility pressure (MMP) and the first contact miscibility (FCM) pressure. The IFT measurements at various pressures displayed a reduction trend as a result of more CO2 dissolution in the oil but with two different slopes. That is, at lower pressure values, the measured IFTs were sharply reduced with pressure, while the reduction rate of the IFT became less when pressures exceeded the extraction pressure. This study helps with determining the optimum pressure and temperature conditions of CO2-oil systems to have a minimum IFT, a maximum CO2 solubility and SF, and a minimum oil viscosity that are favorable for CO2-enhanced oil recovery projects. Additionally, the methodology presented here gives guidelines on how to design PVT experiments of CO2-oil systems for petroleum and chemical engineering applications.

Evaluating efficiency and stability of calcite scaling inhibitors at high pressure and high temperature in laboratory scale

Reduction or prevention of scaling is commonly achieved by injecting scaling inhibitors into the geothermal circuit. Inhibitor-efficiency tests can be carried out in static or dynamic experiment set-ups allowing measurements at high pressures and high temperatures (HPHT). For these measurements, suitable analytical methods have to be selected depending on the nature of the scales and the specifics of the related sensors in a HPHT environment. In this study, a calcite scaling inhibitor was evaluated in static batch tests at HPHT conditions with respect to its inhibitory efficiency as well as its degradation behaviour. The inhibitor efficiency significantly decreases in comparison to ambient p,T-conditions. In a long-term stability experiment, a delayed partial degradation of the inhibitor at HPHT conditions could be observed.

Controlling lateral buckling of subsea pipeline with sinusoidal shape pre-deformation

It is common for subsea pipelines to operate at high pressures and high temperatures (HPHT) conditions. The build-up of axial force along the pipeline due to temperature and pressure differences from as-laid conditions coupled with the influence of the seabed soil that restricts free movement of the pipeline can result in the phenomenon called ‘lateral buckling’. The excessive lateral deformation from lateral buckling may risk safe operation of the pipeline due to local axial strains that potentially could be severe enough to cause fracture failure of welds or collapse of the pipeline. Engineered buckles may be initiated reliably during operation by using special subsea structures or lay methods which are expensive. This paper introduces and exemplifies a novel method that involves continuously deforming the pipeline prior to or during installation with prescribed radius and wavelength to control lateral buckling that could be a valuable modification of the practical design of offshore pipelines. Previous published work has shown that installation of a pipeline with such continuous deformations is feasible. The results from an example pipeline case described here show that the pipeline can be installed and operated safely at elevated temperatures without the need for other expensive buckle initiation methods.

Enhanced hardness of CVD diamond after high pressure and high-temperature treatments

The diamond thick layers prepared using chemical vapor deposition (CVD) methods have been treated at high pressures and high temperatures (HP-HT). It was found that the Vickers hardness of the HP-HT treated bulks was nearly two times as high as that of the starting CVD diamond samples. The hardness of the samples treated at 8 GPa and 1800°C is ∼80 GPa at a loading force of 49 N, close to that of the single-crystal diamond (∼100 GPa). In addition, the oxidation resistance of CVD diamond samples was also enhanced greatly after HP-HT treatments, and the diamondization of sp2 bonded carbon in the CVD diamond samples could occur at 7–8 GPa and 1600–1800°C. The HP-HT conditions of diamondization in our works are much lower than the case of the graphite-to-diamond direct transformation without the presence of catalyst (>15 GPa and 2000°C).

Brillouin scattering and x-ray diffraction of solid argon to 65 GPa and 700 K: Shear strength of argon at HP/HT

We performed simultaneous Brillouin scattering and x-ray diffraction measurements on solid argon at high pressures and high temperatures (HP/HT) in an externally heated diamond-anvil cell. From the measured acoustic velocities and densities, we derive the bulk elastic properties of solid argon up to 700 K at above 60 GPa. Our measured acoustic velocity results at room temperature are in agreement with previous Brillouin scattering results. However, the derived aggregate elastic moduli differ from previous studies. In particular, the shear modulus is significantly lower. Our HP-/HT-data show that the bulk modulus is almost insensitive to an increase of temperature (within the P-T-range of our study), whereas the shear modulus G measurably decreases with increasing temperature. We find that G(P,T) can be described by a polynomial of the form: G (P,T) = 5.8(9) GPa + 1.45(12)*(P − P0) – 0.007(2) GPa−1*(P − P0)2 – 0.01(.3) GPaK−1*(T − T0) – 0.0006(2) K−1*(P − P0)*(T − T0) (where the reference P/T-conditions are 4.3 GPa and 300 K). We use our results to estimate the shear strength of argon at HP/HT, which we find to be 0.8 GPa at 65 GPa, substantially lower than found in a previous study. Increasing temperature to 700 K reduces the shear strength to 0.5 GPa at 65 GPa.

High pressure synthesis and investigation of single crystals of metastable boron phases

In the present work we have confirmed the existence of the tetragonal boron phase T-50 that was disputed for more than a half of a century. This phase was reproducibly synthesized at high pressures and high temperatures (HPHT) in the form of single crystals and its structure was refined based on single-crystal synchrotron X-ray diffraction data. We also present here a previously unknown rhombohedral boron phase synthesized in a limited HPHT field. Its structure was solved based on in house single-crystal X-ray diffraction data and found to be similar to that of boron carbide. After hitherto known stable α-B, β-B, and γ-B polymorphs, T-50 and the newly obtained rhombohedral boron phases were designated in the present work as δ-B and ϵ-B, correspondingly. From the experimental evidences, both the phases are considered as metastable.

Understanding of the shape-controlled synthesis of strip shape diamond under high pressure and high temperature conditions

We present the shape-controlled synthesis of strip shape diamond with stretched crystal faces along {100} or {111} direction and larger length-to-radius ratio than the conventional diamond in the designed NiFe–C system at high pressures and high temperatures (HPHT). A series of synthetic experimental results on the strip shape diamonds were obtained at different pressures and temperatures. Under the constant pressure condition, the morphology of the strip shape diamond varied with the increase of temperature obviously. Fourier transform infrared (FTIR) micro spectroscopy and Raman spectroscopy revealed that the various locations of crystal face have different nitrogen impurity concentration, and internal strain and defects in these strip shape crystals. According to these results, it can be concluded that the difference of growth rates at various crystal faces results in different crystal morphologies. Based on the growth characteristics, we suggest that composition segregation of the metal film around the growing crystal induces the formation of strip shape diamond.

Transformação do nitreto hexagonal de boro em nitreto cúbico de boro com o catalisador magnésio

A importância do Nitreto cúbico de Boro (cBN) reside em processos de usinagem de metais ferrosos de elevada dureza. Apesar do cBN ser superado pelo diamante em termos de dureza, ele é mais resistente a oxidação provocada pelo ferro sob altas temperaturas em torno de 700ºC. Os cristais de cBN podem ser obtidos pela síntese a partir da mistura de Nitreto hexagonal de Boro (hBN), aplicando altas pressões e altas temperaturas (HPHT), durante um determinado tempo. Para facilitar os processos de transformação do hBN em cBN, podem ser utilizados um ou mais catalisadores, tais como o magnésio, lítio e bário e outros. No presente trabalho o magnésio na forma de partículas de até 53µm foi utilizado como catalisador nas tentativas de síntese de cBN. Com o objetivo de identificar os parâmetros de síntese (HPHT) que possibilitam a obtenção de partículas de cBN, foram feitas calibrações de temperatura e pressão na prensa hidráulica de 630 toneladas utilizada nos experimentos. As sínteses foram realizadas, utilizando a mesma temperatura para quatro pressões de 5,0; 6,0; 7,0; e 8,0 GPa, durante 5 minutos. E logo após as sínteses foram obtidas imagens por microscopia eletrônica de varredura (MEV) de cada amostra fraturada, o que mostrou algumas formações de cBN.

High-pressure / High-temperature Synthesis and Characterization of Boron-doped Diamond

Bulk samples (with volumes up to ~ 7.5 mm3) of boron-doped diamonds (BDD) were synthesized by means of direct reaction between boron carbide and graphite in a multianvil apparatus at high pressures and high temperatures (HPHT). X-ray diffraction data revealed the presence in BDD of a very small amount of a highly boron-enriched phase (B50C2) and traces of the B13C2 used as an initial material. The absence of B50C2 in the product of treatment of pure B13C2 under the same HPHT conditions suggests that boron-rich carbides exsolute from diamond on quenching leading to boron depletion of the diamond matrix. These observations imply that boron solubility in diamond increases at high pressure and high temperature. This result may have important implications for the understanding of the mechanism of boron incorporation into diamond at HPHT synthesis and for the interpretation of the data on superconductivity of polycrystalline BDD.

An Ultrasonic Device for Nondestructive Testing of Oilwell Cements at Elevated Temperatures and Pressures

Summary This paper describes a measuring technique and a hardware system that automatically monitors and records the complete history of compressive strength development and initial set of oilwell cement slurries under high pressures and high temperatures (HP/HT). The design is based on the transmission characteristics of ultrasonic compressional waves through cement slurries. In principle, an analyzer measures the transit time (reciprocal of velocity) of an ultrasonic wave pulse through a slurry sample, converts it to apparent compressive strength, and records the results continuously. One of the main advantages is that testing is nondestructive, and only one sample of slurry is required to determine both the compressive-strength development history and initial set of the cement slurry. Another important advantage of this device is that initial set of a cement slurry can be determined above 100 deg. C and at pressures far above atmospheric, the limiting factors in other methodsCompressive strengths, determined from ultrasonic transit time data, have shown deviations equal to or better than those obtained from mechanical tests. Since specimens are not removed and exposed to atmospheric pressure, the results should be more representative of actual downhole conditions. Also, the process promises to be well-suited to strength retrogression studies since there are no time gaps in the test results. Further experimental and analytical work is being carried out to evaluate the potential of this technique for measuring other slurry properties. Introduction The times required for and oil- or gaswell cementing slurry to reach an initial set and to develop useful compressive strength are important parameters in scheduling drilling or completion operations, such as temperature logs to locate top of cement fill, bond logs to evaluate cement jobs, continuation of drilling after setting intermediate casing or liners, perforating production zones, and cleanout and stimulation treatments. Without reliable set-time and compressive-strength data, temperature and cement bond logs can be run too soon or can be delayed unnecessarily. Further drilling also can be caned out either prematurely or later than needed, which translates into lost time and money. If cleanup and stimulation treatments are carried out too soon, inter-zone communication problems may develop. A complete knowledge of the history of compressive-strength development allows determination of the optimal time for perforation. This minimizes shattering and results in better zone isolation. Thus, a precise knowledge of initial set time and strength-development data is essential to perform these operations at the optimal time to avoid unnecessary delays. In the past, the usual method of determining the time required to reach initial set or a specific compressive strength was to cure a number of cube specimens in different HP/HT autoclaves and schedule test times that bracketed the strength value specified. Such procedures often wasted time and equipment. Problems were compounded in situations where slurries had to be specially tailored for a specific job. This is especially true for deep wells, where basic variations in the cement itself often necessitated extensive testing. JPT P. 2611^