Feasibility study on lengthening the high-voltage cable section and reducing the number of cable joints via alternative bonding methods

The mesosphere is perhaps the least explored region in the atmosphere with very few methods of observing. This thesis will primarily be exploring a new technique for measuring the distribution of kinetic energy in the mesosphere across a wide range of spatial and temporal scales. The method being used relies on correlation functions between pairs of meteor measurements. These measurements are made using a network of specular meteor radars located in Northern Norway. This network produced 32 million meteor measurements over a 2 year period. The correlation function estimation method has been previously used on a smaller data set, but has so far not been used for a longer data set and at high latitudes. The main advantage of the new technique is that by studying the second order statistics of the wind field, we can obtain significantly better temporal and spatial resolution than before. Such a large data set allows for great resolution for both spatial and temporal correlation functions. By using temporal correlation functions and the kinetic energy spectrum, different atmospheric wave phenomena can be studied. These include diurnal and semi diurnal tides. The horizontal and vertical correlation functions will be used to verify that the kinetic energy follows a power law, as theoretically expected by the Kolmogorov theory for turbulence. This was done by using a second order structure function applied to correlation functions. The temporal and horizontal correlation functions were used to study the summer-winter variation in kinetic energy, some variation in the temporal domain is the impact from large scale waves as well as in the power spectra were there is a steeper power law slope during the winter. As for the horizontal domain there are differences in kinetic energy in the zonal and meridional direction for both large and small scale waves. The dataset in this thesis a lot more can be found out about the mesosphere, in this thesis only a few of the possibilities are explored. The results are in agreement with earlier work, confirming the results obtained by the earlier study

A novel fault location method for a cross-bonded hv cable system based on sheath current monitoring

In order to improve the practice in the operation and maintenance of high voltage (HV) cables, this paper proposes a fault location method based on the monitoring of cable sheath currents for use in cross-bonded HV cable systems. This method first analyzes the power–frequency component of the sheath current, which can be acquired at cable terminals and cable link boxes, using a Fast Fourier Transform (FFT). The cable segment where a fault occurs can be localized by the phase difference between the sheath currents at the two ends of the cable segment, because current would flow in the opposite direction towards the two ends of the cable segment with fault. Conversely, in other healthy cable segments of the same circuit, sheath currents would flow in the same direction. The exact fault position can then be located via electromagnetic time reversal (EMTR) analysis of the fault transients of the sheath current. The sheath currents have been simulated and analyzed by assuming a single-phase short-circuit fault to occur in every cable segment of a selected cross-bonded high voltage cable circuit. The sheath current monitoring system has been implemented in a 110 kV cable circuit in China. Results indicate that the proposed method is feasible and effective in location of HV cable short circuit faults

Luminescent LaF₃:Ce-doped Organically Modified Nanoporous Silica Xerogels

Organically modified silica compounds (ORMOSILs) were synthesized by a sol-gel method from amine-functionalized 3-aminopropyl triethoxylsilane and tetramethylorthosilicate and were doped in situ with LaF3:Ce nanoparticles, which in turn were prepared either in water or in ethanol. Doped ORMOSILs display strong photoluminescence either by UV or X-ray excitation and maintain good transparency up to a loading level of 15.66% w/w. The TEM observations demonstrate that ORMOSILs remain nanoporous with pore diameters in the 5-10 nm range. LaF3:Ce nanoparticles doped into the ORMOSILs are rod-like, 5 nm in diameter and 10-15 nm in length. Compression testing indicates that the nanocomposites have very good strength, without significant lateral dilatation and buckling under quasi-static compression. LaF3:Ce nanoparticle-doped ORMOSILs have potential for applications in radiation detection and solid state lighting

A Review of Wettability Alteration using Surfactants in Carbonate Reservoirs

The wettability of carbonate rocks is often oil-wet or mixed wet. A large fraction of oil is still remained in carbonate reservoirs, it is therefore of particular significance to implement effective methods to improve oil recovery from carbonate reservoirs. Altering wettability from oil-wet to more favorable water-wet has been proven successful to achieve this goal. Surfactants are widely investigated and served as wettability modifiers in this process. Yet a comprehensive review of altering wettability of carbonate reservoirs with surfactants is ignored in literature. This study begins with illustration of wettability evolution process in carbonate reservoirs. Techniques to evaluate wettability alteration extent or to reveal behind mechanisms are also presented. Several surfactant systems are analyzed in terms of their wettability alteration mechanisms, influential factors of performance, applicable conditions, and limitations. Mixture of different types of surfactants could obtain synergic effects, where applicable conditions are extended, and final performance is improved. Gemini surfactants have many desirable properties, which warrants further investigation for understanding their wettability alteration mechanisms and performance. At the end, this review discusses strategies related with surfactant cost, surfactant adsorption, and challenges at high temperature, high salinity reservoirs conditions. Also, some unclear issues are discussed

Descriptive Statistical Analysis of Experimental Data for Wettability Alteration with Surfactants in Carbonate Reservoirs

Surfactants have been the widely used agents to alter the wettability of carbonate rocks to more water-wet and enhanced oil recovery (EOR). As one of major EOR methods, an effective surfactant huff-puff application design requires comprehensive guidelines about where, how, and when this method could be applied. In order to construct such guidelines, a dataset including 338 effective surfactant imbibition tests is established by collecting information from nearly 50 publications. Based on this dataset, descriptive statistical analysis methods are used to conduct data analysis, including three main parts. The first part establishes the application guidelines for surfactant huff-puff treatments which displays suitable application ranges of critical parameters regarding rock, oil, and water. Results show that surfactants can be effectively applied in wide ranges: porosity from 3.1 to 51.7%, permeability from 0.04 to 1458 mD, starting oil saturation from 37.7 to 100%, temperature from 20 to 100 °C, average contact angle from 55 to 180°, oil gravity from 22 to 75.2 °API, oil viscosity from 0.3 to 23 cp, acid number from 0 to 4.5 mg KOH/g oil, base number from 0 to 1.83 mg KOH/g oil, asphaltene concentration from 0 to 10.7 wt%, salinity of connate water and imbibition water from 0 to 263.7 g/l, divalent cations concentration of connate water and imbibition water from 0 to 24.6 g/l. The second part discusses several aspects about design of surfactant huff-puff treatments. Results show that anionic, cationic, and nonionic surfactants have been applied in 83% of tests. Among them is cationic surfactants which have the most frequency. Surfactant concentration is suggested to be remained close or above a critical concentration to obtain the best performance. It is shown that 97% of tests are conducted with surfactant concentration less than 2.0 wt%. In addition, blends of different surfactants and usage of additives could enhance the effectiveness of surfactants. The last part evaluates the performance of surfactant imbibition tests. Results show that surfactants are capable to improve oil recovery either from secondary phase or tertiary phase. In general, the range of oil recovery from secondary phase and tertiary phase are similar, which covers from 1.0 to 93%. However, the average oil recovery from secondary phase is 39.1% which is higher than 32.2% from tertiary phase. Based on this, it is recommended that the treatment timing should be considered in the design of treatments

Luminescence enhancement of CdTe nanostructures in LaF\u3csub\u3e3\u3c/sub\u3e:Ce/CdTe nanocomposites

Radiation detection demands new scintillators with high quantum efficiency, high energy resolution, and short luminescence lifetimes. Nanocomposites consisting of quantum dots and Ce3+ doped nanophosphors may be able to meet these requirements. Here, we report the luminescence enhancement of LaF3:Ce/CdTe nanocomposites which were synthesized by a wet chemistry method. CdTe quantum dots in LaF3:Ce/CdTe nanocomposites are converted into nanowires, while in LaF3 /CdTe nanocomposites no such conversion is observed. As a result, the CdTe luminescence in LaF3:Ce/CdTe nanocomposites is enhanced about five times, while in LaF3 /CdTe nanocomposites no enhancement was observed. Energy transfer, light reabsorption, and defect passivation are the likely reasons for the luminescence enhancement

Advances In Smart Water Flooding: A Comprehensive Study On The Interplay Of Ions, Salinity In Carbonate Reservoirs

The utilization of smart water flooding to enhance oil recovery (EOR) has gained great interest in carbonate reservoirs. This research analyzed previous studies on how smart water injection affects the wettability and dissolution of various carbonate rocks. A table was presented summarizing the multiple authors\u27 agreement on primary mechanisms. A critical analysis was then performed, focusing explicitly on the agreement and disagreement among authors regarding various factors related to calcium carbonate, limestone, and dolomite rock. For the first time, salinity vs contact angle change plots have been created based on rock\u27s initial condition. The data collected included contact angle, salinity, ion concentration before and after flooding, temperature, and crude oil properties. The modification of wettability is primarily ascribed to the electrical double layer and multi-ion exchange processes, while rock dissolution plays a secondary role in this regard. The use of low salinity smart water led to a change in wettability from being oil-wet to becoming water-wet when initial conditions strong oil wet, oil wet or intermediate wet. The sulfate ion played an important role in dolomite, calcium ion concentration in limestone, and a combination of calcium-sulfate and magnesium-sulfate ions in calcium carbonate rock. The research has established that high salinity triggers the formation of more oil-wet conditions in calcium carbonate rock, and individual ions have been identified as playing a crucial role in enhancing oil recovery. Dissolution of the rock is not a continuous process and is dependent on equilibrium. This process occurs mainly during the early stages of brine injection. The dissolution rate is affected by the injection pressure and contact time, and it is unlikely to contribute significantly to improving oil recovery by altering permeability. The study has shown that increasing temperature can enhance the rock surface\u27s ability to adsorb ions. These findings are crucial for developing and enhancing smart water flooding techniques aimed at increasing oil recovery from carbonate reservoirs

Insights to Surfactant Huff-Puff Design in Carbonate Reservoirs based on Machine Learning Modeling

Surfactants could react with adsorbates on carbonate rock surface to alter wettability from oil-wetness to water-wetness, which is effective to enhance oil recovery. Surfactant huff-puff treatment is mostly applied for this purpose and the resulting surfactant performance is the outcome of complex interfacial processes. Currently, the effect of important parameters on surfactant performance is not completely reported and the contribution of each parameter to surfactant performance is hard to be quantified. Traditional methods to optimize surfactant performance are time-consuming and show strong dependency on extensive experiments. In this paper, we address these problems from machine learning (ML) perspectives. Several ML models are established to predict surfactant performance and Random Forest (RF) model presents better accuracy. Based on RF model, we apply Shapley additive explanations (SHAP) approach to interpret modeling results to obtain new insights and provide solutions to unsolved problems. Results show that when interfacial tension is lower than a critical value or oil API gravity is higher than a critical value, surfactant performance shows obvious improvements. In general, porosity, permeability, and surfactant concentration are positively associated with surfactant performance. The trend becomes less obvious when parameter value exceeds a certain level. In addition, SHAP value could effectively decompose surfactant performance into individual effect of each parameter. This analysis is valuable to indicate certain parameters to be optimized. It is shown that surfactant concentration in a proportion of samples is kept in a low level and complete wettability alteration is not achieved. To optimize surfactant concentration, an innovative procedure integrating RF prediction model with Powell\u27s method is proposed. This procedure is effective to avoid deficient and superabundant surfactant concentration. With optimization, the average surfactant concentration is increased from 0.37 wt% to 0.93 wt%. The average probability of high-oil-recovery class is improved from 0.38 to 0.50. The incremental oil recovery is improved from low-oil-recovery class to high-oil-recovery class. Our work promotes the understanding of wettability alteration by surfactants and provides a fast framework to predict, analyze, and optimize surfactant performance. This framework could greatly save experiment time and cost