Sharif Digital Repository

We investigate the effect of wall roughness on water electrolyte transport characteristics at different temperatures through carbon nanotubes by using nonequilibrium molecular dynamics simulations. Our results reveal that shearing stress and the nominal viscosity increase with ion concentration in corrugated carbon nanotubes (CNTs), in contrast to cases in smooth CNTs. Also, the temperature increase leads to the reduction of shearing stress and the nominal viscosity at moderate degrees of wall roughness. At high degrees of wall roughness, the temperature increase will enhance radial movements and increases resistance against fluid motion. As the fluid velocity increases, the particles do not... 

Copper based hybrid composites containing nano-sized silicon carbide and carbon nanotubes reinforcements with minimal porosity were fabricated via mechanical milling followed by hot pressing technique. Microstructures of the powders and consolidated materials were studied using scanning electron microscope, X-ray diffraction, Raman spectroscopy, and scanning transmission electron microscope. Microstructural characterization of the materials revealed that the addition of nanosized silicon carbide reinforcement lowered the grain growth rate and enhanced the homogenization during mechanical milling. Microhardness measurements and compression test showed considerable improvements in mechanical... 

Carbon nanotubes (CNTs) were synthesized via arc discharge in aqueous solutions containing ferrous and ferric irons to reveal the effect of iron-charge mole ratio, R = [Fe2+]/[Fe3+], on the purity of CNTs and the process yield. Raman spectroscopy and transmission electron microscopy were used to analyze the cathodic deposits. It is shown that the nucleation of multi-walled CNTs is catalyzed by ferric irons while their growth is affected by ferrous ions. Well-graphitized CNTs with a high-yield are obtained at R = 1 and total iron concentration of 0.05 M. The effect of iron charge is described based on the two-stage formation mechanism  

Single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) were synthesized in aqueous solutions containing FeCl2, FeCl3, FeSO4 and Fe2(SO4)3. The effects of iron charge and the counter ions on the formation of carbon nanotubes (CNTs) were investigated. Thermogravimetric (TG) analysis indicated that carbon multilayer structures including CNTs and multishell graphite particles were formed in deionized (DI) water without the iron precursor. SWCNTs were also synthesized in the presence of the iron ions. It was also found that the mole ratio of [Fe2+]/[Fe3+] in the solution has a significant influence on the purity of CNTs and the process yield. The highest yield was... 

Horseradish peroxidase (HRP) was successfully immobilized on amine functionalized TiO2-coated multiwalled carbon nanotubes (NH2 – TiO2 – CNTs) by a convenient and efficient method. Electrochemical impedance spectroscopy, cyclic voltammetry and amperometry were applied to characterize the HRP/NH2 – TiO2 – CNT nano-composite. These techniques showed that the NH2 – TiO2 – CNTs greatly enhance the electron transfer between HRP and the modified electrode. Owing to the redox reaction of the electroactive centre of HRP, the HRP = NH2 – TiO2 – CNTs modified electrode exhibited a pair of quasi-reversible peaks with a peak-to-peak separation (ΔEp) of 70.6 mV and a formal potential (E 0′) of 367.65 mV... 

Nitrogen has emerged as a competitive gas injection alternative for gas-based enhanced oil recovery processes in the past two decades. The injection of nitrogen into the reservoirs has improved the oil recovery efficiency in various oil reservoirs from heavy to volatile oils. As it is known, interfacial tension (IFT) plays a key role in any enhanced oil recovery process, particularly gas injection processes; therefore, its accurate determination is crucial for the design of any gas injection process especially at reservoir condition. In this study, an axisymmetric drop shape analysis (ADSA) was utilized to measure the equilibrium IFTs between crude oil and N2 at different temperature levels... 

Interfacial tension (IFT) as one of the main properties for efficient CO2 flooding planning in oil reservoirs depends strongly on pressure, temperature, and composition of the reservoir fluids. Therefore, it is important to measure this property at real reservoir conditions for successful field development plan. In this study, an axisymmetric drop shape analysis (ADSA) has been utilized to measure the equilibrium IFTs between crude oil and CO2 at different temperatures and pressures. Moreover, minimum miscibility pressures (MMP) and first-contact miscibility pressures (P max) of crude oil/CO2 systems at different temperatures are determined by applying the vanishing interfacial tension (VIT)... 

Alkaline-Surfactant-Polymer flooding is one of the most novel chemical enhanced oil recovery methods in the petroleum industry. This method has attracted interest due to its remarkable advantages. In this work, a series of ASP floods are conducted on fractured/non-fractured carbonate rocks. The performance of the tests was investigated by various ASP floods consisting of five types of polymers, two surfactants and one common alkaline. ASP was flooded simultaneously and sequentially in four defined scenarios after water flooding. The results showed that although using hydrolysed polymers increases the recovery factor in the fractured medium, sulfonated polymers increase oil recovery even more... 

Thermodynamic modeling is known as a promising tool for phase behavior modeling of asphaltene precipitation under different conditions such as pressure depletion and CO2 injection. In this work, a thermodynamic approach is used for modeling the phase behavior of asphaltene precipitation. The precipitated asphaltene phase is represented by an improved solid model, while the oil and gas phases are modeled with an equation of state. The PR-EOS was used to perform flash calculations. Then, the onset point and the amount of precipitated asphaltene were predicted. A computer code based on an improved solid model has been developed and used for predicting asphaltene precipitation data for one of... 

Reservoir permeability is an important parameter that its reliable prediction is necessary for reservoir performance assessment and management. Although many empirical formulas are derived regarding permeability and porosity in sandstone reservoirs, these correlations cannot be accurately depicted in carbonate reservoir for the wells that are not cored and for which there are no welltest data. Therefore, having a framework for estimation of these parameters in reservoirs with neither coring samples nor welltest data is crucial. Rock properties are characterized by using different well logs. However, there is no specific petrophysical log for estimating rock permeability; thus, new methods... 

Three distinct methods, namely, the spectral density, the multifractal random walk approach, and the multifractal detrended fluctuation analysis are utilized to study the properties of four distinct types of well logs from three oil and gas fields, namely, the natural gamma ray emission, neutron porosity, bulk density, and the sonic transient time logs. Such well logs have never been analyzed by the methods that we utilize in the present study. The results indicate that the well logs exhibit multifractal characteristics, and the estimated Hurst exponents by the three methods are close to each other. Using multifractal detrended fluctuation analysis and the shuffled and surrogated data, we... 

Palladium catalysts supported on functionalized multi-wall carbon nanotubes were synthesized for hydro-purification of crude terephthalic acid containing 2100ppm 4-carboxybenzaldehyde (4-CBA) as impurity. PdCl2 and Pd(OAc)2 were used as precursors. Palladium loadings were 0.05 to 0.6wt.% with catalysts reduced at 200 to 400°C. Catalysts prepared from both precursors with least 0.3wt.% palladium resulted in 99%+ removal of 4-CBA. The most desired selectivity was obtained for the catalyst with PdCl2 as precursor, reduction temperature of 300°C, and palladium loading of 0.3wt.%. This catalyst had slightly better performance than the commercial catalyst (0.5wt.% of palladium on activated carbon)... 

A high silica CHA-type membrane was synthesized by the in-situ crystallization method on a disk like α-alumina porous support to separate both acid (H2S, CO2) gases from methane. The membrane showed a permeance of 3.39×10-8mol/m2sPa for pure CO2with CO2/CH4 ideal selectivity of 21.6 at 303K and 100kPa pressure difference across the membrane. The membrane was also tested with N2 and O2 pure gases indicating a small O2/N2 selectivity of 1.2-1.4, which shows that this type of membrane is not suitable for O2/N2 separation. The membrane performance was also analyzed by binary (CO2-CH4) and ternary (H2S-CO2-CH4) gas mixtures, with compositions near the real sour natural gas (CO2: 2.13mol%, H2S:... 

The use of adjusted/optimized saline water categorized into two different classes namely smart water (SW) and low salinity (LoSal) water injection has been proposed for more oil recovery from specific types of oil reservoirs. There are possible mechanisms concerning SW flooding that have been proposed in the literature, some of them are still subject to more examination. In this study, an experimental investigation is performed to determine the influence of type and amount of salt to the surface properties including interfacial tension (IFT) and contact angle (CA) of aqueous solution + acidic and asphaltenic crude oil + carbonate rock systems. For this purpose, the concentration of different... 

The purpose of this study is to investigate separation performance of poly(ether-b-amide6) (Pebax1657)/glycerol triacetate (GTA) gel membranes for CO2 removal from H2, N2 and CH4. GTA as a low molecular weight and highly CO2-phill compound was added to membrane structure at various weight fractions, 20%, 40%, 60% and 80% of Pebax, to fabricate a new high solubility selective membrane with improved performance. Permeation of pure gases was studied at different temperatures from 25 to 65°C and pressures from 4 to 24bar and ideal selectivities were calculated. Results indicated enhancement in permeation for all tested gases. For example, at a pressure of 4bar and a temperature of 25°C, membrane... 

In this paper, the Heidaryan and Jarrahian equation of state (Heidaryan and Jarrahian, 2013) has been adapted as a first worldwide cubic EOS to calculate the density of dry natural gases, wet natural gases, and single-phase gas condensates "sweet and sour mixtures" (up to 73.85, 97.63 and 38.37 mol percent of H2S, CO2, and N2 respectively) even when the gas composition is unknown, through new gas specific gravity correlation equations. Correction terms of water content as high as 10 mol percent of H2O and hythane (natural gas + hydrogen) as high as 74.9 mol percent of H2 were obtained. The equation of state was validated with 8985 experimental compressibility factor data points from 308... 

In this work, asphaltene adsorption in a sandstone core sample under dynamic conditions and during miscible CO2 injection was studied using live oil sample which is close to real conditions in petroleum reservoirs. In order to investigate of damage in sandstone core sample by the deposited material such as asphaltene, the morphology analysis of sandstone core sample using scanning electron microscopic method was studied. Also analyses of the adsorbed material in sandstone core sample by Soxhlet extraction using an azeotrope mixture and with SARA method were performed. The experimental results show that by increasing the flow rate of injected CO2, the amount of asphaltene in retained material... 

The authors present the results of numerical tests and simulations to investigate and analyze the likelihood of asphaltene precipitation and deposition during CO2 flooding in a reservoir. The effects of asphaltene precipitation on oil properties such as oil viscosity and density during miscible CO2 flooding process were elaborated by using Winprop software of Computer Modeling Group. Also oil properties change during CO 2 miscible flooding by numerical slim tube were investigated by a compositional simulator (GEM). A fluid sample of Saskatchewan Reservoir that had been flooded miscibly with CO2 was chosen for performing the sensitivity analyses. The results showed that asphaltene... 

The aim of the present study was to experimentally investigate the interaction between a low replacement ratio of different nano-particles (SiO2, Al2O3, clay, and CaCO3) and aminosilane in the matrices of cement paste and mortar. Results showed that the optimum content of aminosilane for improving the 28-day compressive strength of cement mortar was 0.75% (by weight of the total binder). The utilization of nano-SiO2 and nano-clay particles improved the strengths of the cement mortar containing hybrid systems of nano-particles/aminosilane at early (7 days) and middle curing ages (28 and 91 days). The 28-day compressive strength enhancement of cement mortar with hybrid systems of nano-SiO... 

In this paper, we describe a carbon dioxide mineralization process and its associated solid products. These solid products include amorphous silica, iron hydroxides and magnesium carbonates. These products were subjected to various characterization tests, and the results are published here. It was found that the iron hydroxides from this process can have different crystalline properties, and their formation depended very much on the pH of the reaction conditions. Different forms of magnesium carbonate were also obtained, and the type of carbonate precipitated was found to be dependent on the carbonation temperature. Hydromagnesite was obtained mainly at low temperatures, while dypingite was...