مجله پژوهش نفت
پیاپی 104 (فروردین و اردیبهشت 1398)

In this study, the effect of hydrogen on the mechanical properties of pipeline steel weld metal was investigated. In pipelines, weld metal is a significant part, and this part especially has been evaluated because of the presence of sour gas containing hydrogen atoms and other hazardous solutes which can harm base metal and weld metal. In this research, hydrogen charging was carried out due to the diffusion of hydrogen atoms into the sample through electrochemical pre-charging and immersion in the solution method. According to the results obtained in this study, in the presence of hydrogen, the yield stress of weld metal in Shielded Metal Arc Welding (SMAW) increased by 16%, and hardness in both direct and indirect charging method increased by an average of 10%. In the presence of hydrogen, elongation was reduced by 28%, and the percentage of ductile fracture decreased by 60% which indicate the brittle fracture. The content of diffused hydrogen was 1.5E-06 mol/cm3 using the Electrochemical Oxidation of hydrogen method. This amount was higher than that of other microstructures. According to microstructures observation (which provided from Optical Microscope (OM), Scanning Electron Microscope (SEM) photos), previous information, and recent reports in this field, it can be inferred that hydrogen diffuses into weld metal microstructure, which most of this is acicular ferrite by residing in dislocation tangles, grain boundaries, precipitations, and inclusions, causes hardening and decreases properties of weld metal. Overlay, the results of this study indicate that hydrogen degrades mechanical properties of weld metals and causes hydrogen defects. Also, weld metal microstructure has a significant effect on materials degradation in the presence of hydrogen.

Molecular diffusion is the controlling mechanism for oil recovery from fractured reservoirs with low permeable and low height matrixes during gas injection process. However, the application of conventional models for simulation of molecular diffusion process faces with some limitations. The main purpose of this study is to investigate the performance of different diffusion molecular models for oil recovery from fractured reservoirs during gas injection process and compare the results with a commercial simulator. Therefore, the models are introduced and implemented as a simulator, then the prepared simulator is validated by experimental data. Lastly, the developed simulator is applied for evaluation of CO2 and methane injection in one matrix block. The difference among the results of different models is based on using irreversible thermodynamic for calculating component concentration in gas-oil interface, using matrix form of molecular diffusion coefficients and using chemical potential gradient as the driving force in generalized Fick and Maxwell-Stefan verse classical Fick. In addition, the results of commercial simulator are near classical Fick model results because of same formulation. Also, mole fraction of methane and CO2 and oil viscosity verse time are compared for gas injection. Finally, the result of this work demonstrates that using classical Fick’s law or the commercial simulator for forecasting oil recovery from fractured reservoirs when the molecular diffusion is the main mechanism is not accurate, so generalized Fick and Maxwell-Stefan are more efficient models.

In this research, two silver salts, AgNO3 and AgBF4 with similar molar concentrations were incorporated into the active layer structure of PES/PVP composite membranes separately. Their different effects on the morphology and performance of ethylene-ethane separation process were investigated through FTIR-ATR, SEM, and gas permeation analysis. FTIR-ATR analysis was performed to survey the variant carbonyl group-silver cations’ complexes. Also, C=O bonds with various weakness and strength cause to create different complexes between carrier cations and non-saturated gas molecules such as ethylene. Therefore, ethylene/ethane separation quality can be affected by carbonyl bond energy. Structure of PVP active layer beside PES support section were observed through scanning electron microscopy. Pure and mixed gas permeation tests were carried out to verification of FTIR analysis and evaluation of separation quality. FTIR experiment demonstrated that Ag+ cations from AgBF4 salt make stronger complexes among polymer chains than cations of other salt and react with higher numbers of PVP active sites, which means AgBF4 salt distribute more effectively in the active layer structure. Permeation test revealed that AgBF4 salt attract ethylene molecules more effectively than AgNO3 salt, which leads to obtain higher ethylene/ethane selectivity. Finally, the maximum ethylene permeation and selectivity was occurred at maximum molar concentration of AgBF4 (50%) and at maximum operational pressure, which were 9.5 GPU and 43 respectively at mixed gas case. These parameters changed to 15 GPU and 64 at pure gas separation test.

In this paper, the oxidative desulfurization process has been studied using MoO3/g-C3N4 mechanically synthesized catalyst. At first, Dibenzothiophene (DBT) was selected as the target compound for synthesis of the model oil, and this model was used to optimize operating conditions. Also, H2O2 and acetonitrile were used as oxidant and extract solvents respectively. The effect of molybdenum loading on g-C3N4 and the operating conditions related to the ODS process including temperature, amount of catalyst, H2O2/DBT molar ratio, and time of reaction was investigated using the Box-Behnken (BB) method in experimental design. The maximum efficiency of DBT removal was obtained about 97.7%, at optimum conditions of 70 °C, catalyst content of 0.04 g, H2O2/DBT=8.44, and within 55 min reaction time. Also, the regeneration of the catalyst was evaluated four times, showing yield decreasing 6% for 10% MoO3/g-C3N4. Finally, at optimum conditions, performance of the catalysts in the removal of sulfur compounds of gasoline and gas oil from Oil Refining & and Distribution Company was investigated, and the obtained efficiencies of sulfur removal were 58.35% and 41% respectively. The MoO3/g-C3N4 catalyst was characterized by XRD, FTIR, EDX, FE-SEM, and BET analyses.

Among the various types of Poly (ether block amides), Pebax1657 shows excellent separation properties for polar or condensable gases such as carbon dioxide in comparison with other light gases. In this research, Pebax1657 as an organic phase and silver nanoparticles as an inorganic phase were considered for preparation of mixed matrix membranes. Moreover, in one side, silver nanoparticles as fillers could enter the polymer chains and enhance the gas permeability by increasing the fractional free volume of membranes. On the other side, partially positively polarized silver nanoparticles beside electron rich parts of PEO segment of the copolymer could increase the CO2 affinity of membranes, which results in increasing the permselectivity of the MMMs for CO2 over CH4 and N2. Also, permeability and selectivity of membranes were studied at different operating temperature and pressures. Moreover, (fabricated) membranes were characterized by FTIR, SEM, and XRD analyses. Obtained results revealed that Ag nanoparticles have decreased the membrane crystallinity and interacted with soft segment of the copolymer, which could enhance transport properties of the polar gases. In addition, the results of gas permeation have shown excellent improvement in permeability and selectivity at temperature of 35 °C and pressure of 10 bar. For the optimum membrane in comparison with the neat one, CO2/CH4 and CO2/N2 selectivities have increased about 112 about 76 % respectively. On the other hand, an increase in the fractional free volume of the neat polymeric matrix has caused to enhance the CO2 permeability up to 141 %.

Petrophysical rock type is a part of the reservoir that has the same properties such as geological and petrophysical characteristics. Therefore, the relationship between geological and petrophysical units can be useful for understanding the heterogeneity of the reservoir, especially in carbonates, which are highly variable from the pore type and pore throat size radius viewpoints due to the effect of diagenetic processes. The pore type and pore throat size radius as parameters which are relevant to the product of the geologic process (depositional and diagenesis) control the petrophysical properties of the reservoir. Accordingly, these two parameters are the best tools for communicating the geological and petrophysical characteristics of each petrophysical rock unit. In this paper, three methods including flow zone indicator, Winland R35, and discrete rock types (DRT) were used to determine the petrophysical rock type. The results show that the flow zone index outperforms the other methods, although the other two methods can have useful applications. To determine pore type and pore throat size radius in five flow units, which were identified by the flow zone indicator method, the velocity deviation log was used. Moreover, to determine the continuous distribution pore type the velocity deviation log was used. In addition, mercury injection data were employed to measure pore throat size radius. According to the results obtained from this study, the best flow units are in accordance with positive and zero velocity deviations, which have interconnected vuggy and intergranular which are the product of the dissolution (diagenesis) and depositional process. Finally, the results indicate that the reservoir quality of the Fahliyan Formation is affected by the two factors of diagenesis and sedimentation, but in general, diagenesis has the most contribution to determine the all reservoir quality of the formation.

Considering the working conditions of down hole mud motors, enhancing the mechanical and thermal strengths of their elastomeric parts is crucial. Some attempts have been done to increase the motor performance through geometrical changes, but lack of material improvement is significant in previous studies. In this study, NBR/nanoclay composite was prepared through melt intercalation in an internal mixer. In order to evaluate the mud motor performance with regard to down hole working conditions, different mechanical and thermal tests were done. Moreover, tensile test results showed that the stiffness and toughness of prepared composites are increased simultaneously. While, tensile fatigue test results revealed the enhanced fatigue life of NBR/nanoclay composite samples in comparison with neat NBR sample. Dynamic mechanical analysis also showed a decrease in the damping factor, tan δ of composite samples compared to neat elastomer, indicating the less dissipation heat production in each cycle and hence increasing fatigue life of the samples. Based on the results of this study, it is confirmed that the incorporation of right selected nanoclay into NBR matrix offers increased mechanical and thermal strengths and barrier properties over conventional virgin elastomer. Therefore increasing the working life and performance of the motor is achievable through replacing its elastomeric stator lining with the NBR/nanoclay composite.

Particulate matter such as black carbon and soot produced due to incomplete combustion of hydrocarbons is one of the most critical and hazardous sources of air pollution, which can cause fatal diseases. Pars Special Economic Energy Zone is located in southern Iran, close to Naiband National Marine Park in Bushehr Province. Twelve natural gas processing plants and 16 huge petrochemical complexes have been developed in this area. They produce more than 70% of Iranian domestic natural gas and 45% of the petrochemical products. Due to the complexity of the process and possibly the lack of access to the best available technologies, daily more than 11,100 tons of gas are combusted at 60 active flares, which could be one of the main reasons for the release of black carbon and soot.. Due to the importance of the flow and composition of flared gas in estimating particulate matter, in the present study, based on actual process data and field measurements, flow rate and composition were determined and verified. To achieve this purpose, first, all of the control valves on the flare network were recognized and then, the flow rate and composition of the flared gas was calculated based on the equations and correlations of the valves. Finally, the particulate matter emission from the flares was calculated based upon the flared gas flow, composition and existing emission factors. The accuracy of the predicted flow rate was validated using a flowmeter. The actual cumulative measured flaring rates were compared with cumulative model flaring rates. By comparing the calculated cumulative flaring rate against measured values as determined by flow meters, the square of the Pearson correlation coefficient (SPCC) was found to be 0.986, showing high correspondence between measured and predicted values. The accuracy of the predicted composition by the model using gas chromatography indicates a deviation of less than 13% between predicted values and actual values. This point shows the acceptable accuracy of the method on an industrial scale for estimating the total particulate matter emitted from flaring.

One of the major problems in the oil industry is asphaltene adsorption on various surfaces, including the surface of the reservoir rock. The adsorption of asphaltene on the surface of the reservoir›s rock causes wettability change, blockage of cavities and, consequently, reduction of crude oil production. In this study, the addition of inhibitor as an agent to reduce the adsorption of asphaltene has been used. To observe this effect, two inhibitors of coconut diethanol amide and dodecyl benzene sulfonic acid have been used. For statistical analysis and optimization of experiments, Design Expert software and D-Optimal surface design were used. The model results have high creditworthiness. The test design factors included the initial asphaltene formation in the range of 3000-1000 mg.L1-, the weight ratio of asphaltene to the inhibitor 1: 1, 1: 2, 1: 3 and 1: 0 (without inhibitors) and two types inhibitor include Coconut diethanol amide and dodecyl benzyl benzene sulfonic acid. According to the results of the software output, has a 1:2 ratio of the least amount of asphaltene adsorption. Coconut diethanol amide inhibitor also has the greatest effect on reducing asphaltene adsorption. The adsorption range of asphaltene in the absence of an inhibitor is within the range of the initial concentration of asphaltenes between 63/13 and 83/5 mg.g1-, and the addition of inhibitor in the best case can reduce up to 35% adsorption of asphaltenes.

In this paper, an examination of gas-phase photocatalytic oxidation of n-Hexane into CO2 and H2O using nitrogen modified TiO2 under visible-light is reported. The morphology of photocatalyst samples was characterized through XRD, SEM, XRF, and FTIR analyses, also photooxidized products were identified by GC and FTIR in the gas medium. The SEM analysis resulted that the surface of catalysts did not change significantly by modification. Moreover, results from photocatalytic activity showed that the N-doped TiO2 was able to transform different concentrations of feed into CO2 and H2O under visible-light. A comparison between photocatalytic performances of N-doped TiO2/Visible-light and TiO2/UV showed that the former was more efficient for n-Hexane conversion (93% photocatalytic conversion). Based on the results from FTIR analysis that have proved the formation of some intermediates such as alcohols, aldehydes, ketones, and carboxylic acids, a mechanism study has been done.

In this paper, the possibility of use of p-Xylylenediamine (PXDA) as a new amine in CO2 absorption process is inspected. Also, data regarding CO2 solubility in PXDA at pressures of 8-500 kPa, concentrations of 2 to 5 mol/L and temperatures of 313 to 353 K were obtained by experiment. The response surface methodology (RSM) was used to model CO2 solubility in amine solution. Moreover, the results illustrated the good accuracy of the mode (R2=0.9708). The 3D charts obtained from the model have shown that CO2 loading has an inverse relation with temperature and concentration and a direct relation with pressure. The simultaneous effect of temperature and pressure on CO2 loading indicates that, at low pressures, an increase in temperature has limited impact on CO2 loading, but at higher pressures, this effect is more pronounced. For ability test of PXDA in absorption of CO2, this solution compares with MEA. Finally, the results indicate that PXDA in both concentrations have more 45% CO2 loading, 44% absorption rate, 50% net cyclic capacity, and about 35% further resistance again oxygen.

In recent years, one of the important advances in the transportation of oil compounds and bitumen application is the use of emulsions. Selection of emulsifier plays a decisive role in the formation of emulsion and its stability. Bioemulsifiers are alternative or complementary to emulsifiers and, in addition to better biodegradability, have less environmental pollution. In this paper, a domestic strain of Bacillus licheniformis was cultured in optimal conditions and the extra-cellular bioemulsifier was separated by a multi-stage process. By preparing mixture adding different values of the bioemulsifier and Stabiram 4582 emulsifier, the exact emulsification process was devised resulting in various emulsion with different values of heavy hydrocarbon and emulsification agent in water by using rotor-stator. According to the Taguchi experimental design method, reduction of viscosity and stability tests have been performed and demonstrated that this bioemulsifier has the ability to produce a stable hydrocarbon in water emulsion. Subsequently, the conditions of emulsion production have been optimized. In optimal conditions (60 % heavy hydrocarbon, 1.32 % emulsifier (90 % bioemulsifier and 10 % chemical emulsifier), and 45 °C temperature), the viscosity of the heavy hydrocarbon decreases significantly (about 98 %), and then remains stable for 96 hours. Finally, the use of this emulsion can reduce the consumption of energy in the preparation of bitumen emulsions and also in the transport pipelines of heavy crude oil and products such as mazut or fuel oil significantly.