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

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

Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies

Surface functionalized magnetic iron oxide nanoparticles (NPs) are a kind of novel functional materials, which have been widely used in the biotechnology and catalysis. This review focuses on the recent development and various strategies in preparation, structure, and magnetic properties of naked and surface functionalized iron oxide NPs and their corresponding application briefly. In order to implement the practical application, the particles must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of iron oxide NPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The problems and major challenges, along with the directions for the synthesis and surface functionalization of iron oxide NPs, are considered. Finally, some future trends and prospective in these research areas are also discussed

Biotechnological Perspective of Reactive Oxygen Species (ROS)-Mediated Stress Tolerance in Plants

All environmental cues lead to develop secondary stress conditions like osmotic and oxidative stress conditions that reduces average crop yields by more than 50% every year. The univalent reduction of molecular oxygen (O2) in metabolic reactions consequently produces superoxide anions (O2•−) and other reactive oxygen species (ROS) ubiquitously in all compartments of the cell that disturbs redox potential and causes threat to cellular organelles. The production of ROS further increases under stress conditions and especially in combination with high light intensity. Plants have evolved different strategies to minimize the accumulation of excess ROS like avoidance mechanisms such as physiological adaptation, efficient photosystems such as C4 or CAM metabolism and scavenging mechanisms through production of antioxidants and antioxidative enzymes. Ascorbate-glutathione pathway plays an important role in detoxifying excess ROS in plant cells, which includes superoxide dismutase (SOD) and ascorbate peroxidase (APX) in detoxifying O2•−radical and hydrogen peroxide (H2O2) respectively, monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) involved in recycling of reduced substrates such as ascorbate and glutathione. Efficient ROS management is one of the strategies used by tolerant plants to survive and perform cellular activities under stress conditions. The present chapter describes different sites of ROS generation and and their consequences under abiotic stress conditions and also described the approaches to overcome oxidative stress through genomics and genetic engineering

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.EThOS - Electronic Theses Online ServiceADNOC (Abu Dhabi National Oil Company)GBUnited Kingdo

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

725-731Molecular 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

Pore-scale simulation of NMR response

The random walk method is used to simulate magnetization decay in porous media. The simulations were performed on images of the pore space obtained using micro-CT scanning and in topologically equivalent networks extracted from these images using a maximal ball algorithm. The simulation results were validated through comparison with experimental measurements of T2 distribution, absolute permeability and resistivity in two sand packs and from comparing predictions on images and networks of Fontainebleau sandstone. In all cases, the comparisons were good, although the networks gave a slightly narrower T2 distribution, implying that some fine detail of the pore structure was lost. This work suggests that imaging, network extraction and pore-scale simulation can be used to predict single-phase transport properties successfully. It serves as a validation for pore-network models and the methods used to generate networks