Browsing by Author "Wanambwa, Silagi"

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    Effects of Tropospheric Height and Wind Speed on Solar Power Generation: Energy Exploration Above Ground Level
    (SSRN, 2022) Nnamchi, Stephen Ndubuisi; Natukunda, Faith; Wanambwa, Silagi; Musiime, Enos Bahati; Tukamuhebwa, Richard; Wanazusi, Titus; Ogwal, Emmanuel
    Terrestrial and extraterrestrial factors hinder the exploitation of solar power using a ground platform. This paper is concerned with the generation of solar power above ground level. This paper employs modeling and simulations coupled with experimentation to establish a functional relationship between the percentage of solar power gain, tropospheric height and wind speed. The natural wind flow equation established a linear relationship between tropospheric height and wind speed, between tropospheric height and the percentage of solar power gain. It is evident that an insignificant percentage of solar power gain (≈2%) corresponded to 1000 m above ground level; the tropospheric height of 8100 m recorded 20% of solar power gain. Furthermore, wind speeds of 0 to 33 ms-1/distance (1000 m) correspond to ground level and tropospheric height of about 8100 m. However, there is a prospect of achieving more percentage of solar power gain by applying high-altitude platforms. The results obtained apply to other study areas having elevations below or equal to 1100 m, it serves as a guide in the estimation of the percentage of solar power gain by the virtue of tropospheric height and wind speed.
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    Experimental Study on the Enhanced Oil Recovery by in Situ Foam Formulation
    (Energy Science & Engineering, 2020) Hailong, Chen; Li, Zhaomin; Wang, Fei; Wanambwa, Silagi; Lu, Teng
    In situ CO2 foams (ISCF) are studied systematically by combining in situ CO2 gas reactants (carbonate anhydrous, hydrochloric acid) and bio-based surfactant. Sandpack flooding experiments at 60°C along with PVT experiments were carried out to analyze the oil displacement mechanisms. The results showed that ISCF could increase oil recovery from heterogeneous multilayer formation of permeability ratio over 6, and displacement efficiency increased with the injection volume increased before the injection of 1 PV. The incremental oil recovery by ISCF was much greater than that of conventional foam or in situ CO2 (ISC) without foam under the same injection conditions. The generated CO2 foam could reduce the interfacial tension between displacement phase and displaced phase effectively which contributed to the great increase in capillary number. The CO2 dissolution greatly reduced the viscosity of crude oil, and the highest viscosity reduction rate at 60°C could be as high as 98%. The Ca2+ concentration of produced liquids analysis revealed the ISCF could distribute intelligently the acid in heterogeneous formations.
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    Fractal Characterization of Dynamic Structure of Foam Transport in Porous Media
    (Journal of Molecular Liquids, 2017) Wang, Fei; Li, Zhaomin; Chen, Hailong; Wanambwa, Silagi; Chen, Zhuo
    The evaluation and simulation of foam fluid are still matters of significant debate despite the large number of available studies due to the excellent properties of foam and its successful applications, especially in oil and gas field development. The properties of foam fluid are substantially determined by its dynamic structure in porous media; however only a few studies that investigate and perform measurements related to such structure have been reported. In this research, a new method based on fractal theory is proposed for evaluation of aqueous foam in porous media. As a first step, the fractal characteristics of foam in porous media are confirmed by image processing and calculations. Accordingly, the foam dynamic structure is quantitatively studied by defining and calculating the foam fractal dimension. Secondly, a concise relation is established which reveals that the foam fractal dimension is nearly time-independent. Finally, a sensitivity analysis is carried out by discussing three major factors affecting foam structure in porous media. These results are expected to be helpful for further understanding the dynamic characteristics of foam fluids and their advanced applications.
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    Properties of Carbon Dioxide Foam Stabilized by Hydrophilic Nanoparticles and Hexadecyl Trimethyl Ammonium Bromide
    (Energy & Fuels, 2017) Li, Songyan; Qiao, Chenyu; Wanambwa, Silagi
    Nanoparticles can improve the stability of CO2 foam and increase oil recovery during CO2 flooding in reservoirs. The synergistic effect of hydrophilic SiO2 nanoparticles and hexadecyltrimethylammonium bromide (CTAB) on CO2 foam stability was examined in this study. Experimental results show that the synergistic effect requires a CTAB/SiO2 concentration ratio of 0.02–0.07, with 0.033 representing the best concentration ratio. With the increase in the concentration ratio, the synergistic stabilization effect of CTAB/SiO2 dispersion first increases and then decreases. In the monolayer adsorption stage (concentration ratio from 0.02 to 0.033), when the hydrophobicity of SiO2 nanoparticles increases with the concentration ratio, the nanoparticles tend to adsorb on the gas–liquid interface and the stability of CO2 foam increases. In the double-layer adsorption stage (concentration from 0.033 to 0.07), when the hydrophobicity of SiO2 nanoparticles decreases with an increase in the concentration ratio, the nanoparticles tend to exist in the bulk phase and the stability of CO2 foam decreases. The CTAB/SiO2 dispersion stabilizes CO2 foam via three mechanisms: decreasing the coarsening of CO2 bubbles, improving interfacial properties, and reducing liquid discharge. CTAB/SiO2 foam can greatly improve oil recovery efficiency compared to water flooding. Experimental results provide theoretical support for improving CO2 foam flooding under reservoir conditions.