The influence of wettability and carbon dioxide injection on hydrocarbon recovery

This study can be divided into two sections. First, a detailed study of petrophysical properties and the impact of wettability is performed on cores from a producing heterogeneous carbonate reservoir from the Middle East. Second, a comparison between different injection schemes (waterflooding, gas injection, WAG and CO2 injection) for enhanced oil recovery is made for another giant carbonate reservoir in the Middle East. Knowledge of the wettability of a reservoir rock and its influence on petrophysical properties is a key factor for determining oil recovery mechanisms and making estimates of recovery efficiency. A full suite of experiments on well-characterised systems, including sandpacks, sandstones and carbonate cores, was performed to measure capillary pressure, relative permeability, NMR response and resistivity index. Cores aged in crude oil, with different wettability were studied. As a preliminary step to investigate the effect of wettability on heterogeneous carbonates from the Middle East, sandpack and sandstone samples were first tested because: 1) these samples are known to be quite homogeneous and of a wettability that can be controlled; 2) To test our experimental methods; and 3) to serve as a dataset for modelling studies. First, the static (porosity and permeability) and dynamic (initial water saturation and residual oil saturation) properties of Leavenseat (LV60) and Ottawa (F-42) sandpacks were measured. The formation factor and NMR response for these sandpacks were also determined. These experimental measurements have served as a benchmark for pore-modelling studies that have reproduced the experimental data. Fontainebleau sandstones have also been used as a benchmark in the industry because of its relatively simple pore structure. Mercury injection capillary pressure (MICP) measurements were performed on this sandstone. The MICP experimental measurements showed very low pore volume values, indicating very tight (consolidated) samples. These samples had a diameter of less than 0.02 m which made the experiments quite difficult. Once we had confidence in the experimental methodology, five carbonate samples from a typical Middle East reservoir were imaged and cleaned in order to render them more water wet. Conventional and special core analyses were performed on all the samples. The pore throat distribution from capillary pressure was successfully compared with the pore size distribution inferred from the NMR T2 relaxation curve. Formation resistivity factor and the formation resistivity index were also measured. Capillary pressure and relative permeability curves were measured using refined oil and synthetic formation brine. Then the samples were aged in crude oil from the same field at elevated temperature (120oC) and underwent the same experiments to evaluate the influence of wettability changes on these properties. The experimental data show that there is a significant difference in the relative permeability and capillary pressure of the cleaned and aged samples; the results are explained in terms of the pore-scale configurations of fluids. In contrast, electrical resistivity did not encounter significant changes for different wettability, suggesting that electrical properties in these carbonates are mainly affected by the porosity that remains water-wet, or is only neutrally-wet. This conclusion is supported by the significant displacement that is observed in the aged sample at capillary pressures close to zero. We show that wettability, imbibition capillary pressure and relative permeability have major impact on the waterflood sweep efficiency and hence on the distribution of remaining oil saturation. An incorrect understanding of the distribution of remaining oil saturation may lead to ineffective reservoir management and IOR/EOR decisions. The second part of this thesis is to assess the efficacy of CO2 injection into carbonate oil fields. The reservoir under study is a layered system. The reservoir consists of two main units, i.e. a lower zone of generally low permeability layers and an upper zone of high permeability layers inter-bedded with low permeability layers; the average permeability of the upper zone is some 10-100 times higher than that of the Lower zone. Under waterflooding, the injected water tends to flow through the upper zone along the high permeability layers and no or very slow cross flow of water into the lower zone occurs, resulting in very poor sweep of the lower zone. There is significant scope for improving oil recovery from such type of heterogeneous mixedwet carbonate reservoirs. The apparent impediment to water invading the bottom strata prompts suggests that a miscible fluid could be Injected into the lower zone. We conducted a series of core-flood experiments to compare the performance of different displacement process: waterflooding, hydrocarbon gas flooding and wateralternate gas (WAG) and compared them with CO2 injection. We show that the local displacement efficiency for CO2 flooding is approximately 97% - much higher than that obtained from waterflooding or hydrocarbon gas injection, due to the development of miscibility between CO2 and the oil. We use the results to discuss the potential of CO2 injection for storage and enhanced oil recovery in the Middle East carbonate reservoir discussed above, and proposes further research to develop a fuller understanding of the subsurface behavior of CO2

Oxidation of ethane to ethylene and acetic acid by MoVNbO catalysts

The influence of niobium on the physicochemical properties of the Mo-V-O system and on its catalytic properties in the oxidation of ethane to ethylene and acetic acid is examined. Solids based on MoV0.4Ox and MoV0.4Nb0.12Oy composition and calcined at 350 or 400°C were studied by X-ray diffraction, and by laser Raman and X-ray photoelectron spectroscopies. Their reactivity during reduction and reoxidation was examined by in situ XRD and by XPS after pre-treatment. Their stability in air was evaluated by means of Raman spectroscopy during laser heating of particles. Niobium is responsible for both stabilization and nanosize of MoO3 and (VNbMo)5O14 crystals. The high global selectivity to ethylene and acetic acid (90-96 mol%) is related to the presence of both phases while higher activity is owed to nanoparticles. The model already proposed by Merzouki et al. (Stud. Surf. Sci. Catal., 72 (1992) 81) suggesting that MoVNbO catalysts could be made up from (VNbMo)5O14-type microdomains embedded in MoO3 matrix seems still topica

MoVO-based catalysts for the oxidation of ethane to ethylene and acetic acid. Influence of niobium and/or palladium on physicochemical and catalytic properties.

The influence of niobium and/or palladium in MoV0.4Ox on both solid state chemistry and catalytic properties in the oxidation of ethane to acetic acid and ethylene is examined. Catalysts without molybdenum (VNb031Pd3e-4Ox) are also studied for comparison. The structural properties of the precursors and of the catalysts obtained by calcination of precursors at 350 and 400°C are studied by X-ray diffraction, and by laser Raman and X-ray photoelectron spectroscopies. These properties depend on the presence or absence of niobium, and to a lesser extent, of palladium. Nb-free precursors and catalysts are heterogeneous mixtures of crystalline oxides, among which hexagonal and orthorhombic MoO3. The presence of Pd favors the instability of both precursors and catalysts. The catalysts are poorly active (conversion < 4%), but they are mainly selective to acetic acid (SAA max = 61-73 mol%) and to COx (SCOx max = 30-72 mol%). The Nb-containing precursors without or with Pd are more stable, and the catalysts are made up of nanocrystalline particles of V,Nb-doped Mo5O14 and of VxMo1 xO3 x/2. They are active (conversion < 15%) and very selective to ethylene and acetic acid (Stot = 90-96 mol%). The surface being enriched with vanadium in most cases, the discussion deals with the relative role of Nb and Pd and their possible location in the identified oxides. Because no M1 and/or M2 oxides could be identified, synergistic effects between nanocrystals of (VMoNb)5O14 and VxMo1-xO3-0.5x are proposed to account for the high catalytic performance of the multicomponent MoVNb(Pd)oxides

Ultradispersed Electro-explosive Iron Powders as Catalysts for Synthesis of Liquid Hydrocarbons of CO and H[2]

Catalytic activity of ultradispersed iron powders (UDIP) obtained by electric explosion of the conductor in media of nitrogen, carbon monoxide, and carbon dioxide in synthesis of liquid hydrocarbons by Fischer-Tropsch method was studied. It was shown that iron powder obtained in media of CO[2] has the highest specific surface area. A sample of powder was pelletized at pressure of 21 MPa during 30 seconds with use of 10 mass% polyvinyl alcohol as adhesive for experimentation in catalytic system. Catalyst fraction of 1-2 mm was selected for study. The experiments were carried out under conditions of 1 MPa, 300 mln/min of total reactants consumption, and varied values of temperature and reactants ratio. The maximal conversion level of CO was reached at 290°С and reactants ratio of H[2]:CO=2 in the initial mixture. It was shown that UDIP has high activity at lowered concentration of hydrogen in the initial mixture. The obtained mixture of liquid hydrocarbons is applicable for further refining for upgrading and improving of operating features

Spectroscopic ellipsometry study of barrier width effect in self-organized InGaAs/GaAs QDs laser diodes

Molecular beam epitaxy (MBE) is used to grow InGaAs/GaAs quantum dots (QDs) laser diodes (LDs) with different barrier widths (5, 10 and 15 nm) at 580 ºC on GaAs substrates. Optical properties of the InGaAs/GaAs QDs LDs have been investigated by using the spectroscopic ellipsometry (SE) technique. A general oscillator optical model has been utilized to fit the experimental data in order to obtain the LD layer thicknesses, refractive index and absorption coefficient. The dielectric function, the energy band gap and the surface and volume energy loss functions are computed in the energy range 1-6 eV. The optical properties of the deposited InGaAs/GaAs QDs LDs are found to be affected by the barrier width, which give more insight into carriers dynamics and optical parameters in these devices. The refractive indices, the extinction coefficients and the dielectric constants of the LDs with barrier widths 15 and 10 nm are relatively larger than those of the LD with barrier width 5 nm. These indicate that optical properties of LDs with larger barrier widths (15 and 10 nm) will be improved. The interband transition energies in the three devices have calculated and identified. Two energy gaps at 1.04 and ~1.37 eV are obtained for all the heterostructures which indicates that fabricated LDs may be operating for a wavelength of 1.23 m at room temperature

Synthesis of active supported gold catalysts for CO oxidation and light alkane activation.

The preparation of gold catalysts supported on different metal oxides such as ZnO and Fe2O3, using two coprecipitation methods is investigated to determine important factors, such as selection of support material and preparation method, and preparation parameters, such as preparation temperature, pH, and ageing process. These factors control the synthesis of high activity catalysts for the oxidation of carbon monoxide at ambient temperature. The two preparation methods differ in the manner in which the pH is controlled during coprecipitation, either constant pH throughout or variable pH in which the pH is raised from an initial low value to a defined end point. Non- calcined Au/ZnO catalysts prepared using both methods are very sensitive to pH and ageing time. Catalysts prepared at higher pH give lower activity. However, all catalysts require a short indication period during which the oxidation activity increases. In contrast, the calcined catalysts are not sensitive to preparation conditions. Non-calcined Au/Fe203 catalysts exhibit high activity when prepared at pH > 5. Active calcined Au/Fe2O3 catalysts can be prepared when the pH is controlled at pH 6-7, 8, whereas calcined catalysts prepared using the variable pH method are inactive. The study demonstrates the immense sensitivity of catalyst preparation methods on the performance. Catalysts exhibited excellent catalytic activity and stability compared with the pure supports, ZnO and Fe2O3, and the best preparation temperature was 80 C. Use of temperatures > 80 C led to inactive catalysts. The deposition-precipitation (DP) method was also employed using four different supports in this study (ZnO, Fe2O3, MgO, and MnO2). A comparison between these catalysts was taken rather than an investigation of the effect of the preparation parameters on catalysts prepared by DP method because they have been well studied previously. Several characterization techniques including AAS, BET surface area, XRD, TPR, and XPS, were utilised to investigate the physical and chemical properties of the prepared supported gold catalysts. Characterization results were combined with catalytic results for the low temperature CO oxidation reaction of catalysts in order to study the aforementioned factors that can affect either the properties of catalysts or their activities. Subsequently, several experiments at high GHSV were conducted to study the catalytic activities of these catalysts in-depth and to correlate data with alkane activation reactions. CH4 activation reaction using supported gold catalysts at light temperatures and the effect of the preparation parameters, types of supports on catalysts activities were investigated. The Au/Fe2O3 catalyst prepared by coprecipitation method B at pH 8 showed the highest catalytic activity for CO oxidation and CH4 activation reactions. The most active catalysts were also evaluated for C2H6 and C3H8 activation at low temperature. After this, a comparison between CO oxidation and alkane activation over supported gold catalysts was undertaken to investigate the relationship between the behaviour of supported gold catalysts for these two types of reactions. Activation energies and pre-exponential factors of many catalysts were calculated based on the Arrhenius equation either for CO oxidation or for alkane activation. The preparation of gold catalysts supported on different metal oxides such as ZnO and Fe2O3, using two coprecipitation methods is investigated to determine the important factors that control the synthesis of high activity catalysts for the oxidation of carbon monoxide at ambient temperature. (Abstract shortened by UMI.

Navigating new territory: discourses of assessment moderation in UAE higher education

IntroductionThis study investigates faculty perceptions of discourses associated with assessment moderation at a higher education institution in the UAE.MethodologyThis study employed a survey incorporating closed- and open-ended components. Adie and her associates' (2013) framework of assessment moderation discourses was used as an analytical framework for qualitative data with the purpose of identifying the discourses faculty associate with the purposes of assessment moderation practice at the target institution.ResultsThe findings revealed community building as the most dominant discourse among faculty responses. Significantly, the study identified a fifth discourse category extending beyond the existing four-category framework: faculty resistance characterized by minimal or negligible valuation of assessment moderation practices. Approximately 25% of respondents questioned the fundamental pedagogical or institutional value of assessment moderation, suggesting theoretical gaps in current frameworks that assume universal acceptance of moderation principles.DiscussionThese findings advance assessment moderation theory by identifying a distinct faculty discourse characterized by the perception of minimal or negligible value in the moderation process. The study demonstrates that theoretical frameworks developed in Western educational contexts require substantial adaptation for diverse cultural and institutional settings. The research has significant implications for policy development and implementation of assessment moderation practices in higher education environments, highlighting the need for culturally responsive approaches to quality assurance in global academic settings

A Complicated Case of Thrombotic Thrombocytopenic Purpura in Pregnancy with Superimposed Preeclampsia

A 32-year-old woman at 26 weeks gestation presented with severe unexplained thrombocytopenia with signs and symptoms of severe pregnancy-induced hypertension and what appeared to be hemolysis, elevated liver enzymes, and low platelet count syndrome, leading to a severe diagnostic challenge. The multidisciplinary team identified her condition as thrombotic thrombocytopenic purpura. Timely management decisions and multidisciplinary care ensured a safe delivery