مجله پژوهش نفت
پیاپی 81 (خرداد و تیر 1394)

The incorporation of anticorrosion pigments into the coating formulation is one of the most effective approaches to enhance the resistance against cathodic disbonding. Accordingly، new generations of phosphate-based anticorrosion pigments could be used to improve inhibition efficiency of zinc phosphate pigment as a conventional alternative to toxic chromates. In addition to studying the role of zinc aluminum phosphate، which represents the second generation of phosphate-based anticorrosion pigments in the protective performance of an epoxy-polyamide coating through electrochemical noise method، this paper intends to investigate the effect of the modification of zinc phosphate pigment on the resistance to cathodic disbonding. In the presence of the modified pigment، the improved adhesion strength and decreased disbonding rate were connected to local pH control in the disbonding front and the precipitation of a protective layer، confirmed by electrochemical impedance spectroscopy parameters. Although elevated temperature and more cathodic potential accelerated coating disbondment، zinc aluminum phosphate still revealed superior performance in strengthening the adhesion between the anticorrosive coating and steel substrate and enhancing the resistance against cathodic disbonding.

Electrofacies study is one of the useful methods in the petrophysical analysis of wells without real geological data that can be used in the study of reservoir properties. In this research, on the basis of thin section studies from the Bangestan reservoir in one of the wells within the Mansouri oil field, four sedimentary facies were identified. Based on electrical logs analysis and using clustering method of MRGC, electrical models with 14 electrofacies were identified. The combination of electrofacies, based on average values of their CGR, led to an optimized model which was composed of three facies. Because of a good correlation between the optimized model and real geological data in one of the studied wells, this model can be used for the evaluation of other wells in this field. We hope this model can be used in the future studies of this field in the evaluation of reservoir properties and modeling.

In this work, the changes of drilling mud viscosity have been studied and Cross and Bingham plastic model parameters were determined based on some reported experimental data. For the non-Newtonian behavior of drilling mud, Cross model has a better prediction than the other models. Moreover, an analytical solution was derived for fluid with Cross model and a 2D numerical code was developed to solve momentum and continuity equations with a finite volume method. For the validation of the code, the velocity profiles and friction coefficient of Newtonian and non-Newtonian fluids in pipes and annulus were calculated and compared with the results of theoretical relations and analytical solutions. The results show good agreement and the friction factor error for Cross model is 5%, while, for Bingham model, it is 12%. Additionally, the flow field for Cross non-Newtonian fluid through the annulus was simulated and the results were presented in dimensionless terms. The friction factor in fully developed region and the entrance length was calculated and for the prediction of these two quantities, two new correlations were presented as a function of Reynolds number.

Hydraulic fracturing is a reservoir stimulation technique which is used to increase the flow from low permeability formations. In this paper, the mechanism of hydraulic fracturing with a focus on factors affecting hydraulic fracturing pressure has been investigated. The effects of axial and confining stresses are examined via a triaxial cell that has been designed and made in Sahand University of Technology. To this end, thirty one rock samples including reservoir samples (Aghagari sandstone, Asmari limestone and Sarvak limestone) and non-reservoir samples (Varzaghan field sandstone) are used. Water-based mud is used to study the effect of fluid type and viscosity. Xanthan gum, Guar gum, and polymer are added to increase the viscosity of the water. Axial stress applied to the top of cylindrical sample and the confining stress applied radially. The direction of failure by stresses (axial and confining stress) is determined. The results show that the fracture pressure increases by increasing the confining stress; also, fracture pressure goes through a maximum of 10 MPa by raising the axial stress but decrease from 10 Mpa. The initiation and extension of cracks in hydraulic fracturing are influenced by the rock permeability and the fracturing fluid viscosity. The fracture pressure for low viscosity fluid (water) is less than that of high viscosity fluid (xanthan gum).

The surfactants produced by bacteria are known as biosurfactants. Low toxicity and high biodegradability are among the main characteristics of these surface active materials. These features make biosurfactants potential alternatives for chemically synthesized surfactants in a variety of applications such as microbial enhanced oil recovery. One of the best known biosurfactants, i.e. surfactin, is a cyclic lipopeptide produced by various strains of Bacillus subtilis. In this work, the production of surfactin by Bacillus subtilis NLIM 0110 isolated from an Iranian agricultural area was studied. The produced surfactin showed a good surface activity and was able to reduce the surface tension of water from 69 mN/m to 26 mN/m and the interfacial tension from 38 mN/m to 2 mN/m at 50 mg/l (CMC concentration). The oil spreading technique showed that the diameter of appeared clear zone on the oil layer increased immediately as the produced biosurfactant was added at CMC concentration. Also, in visual experiments, the effect of produced surfactin on enhanced oil recovery was studied using a micromodel. Oil displacement experiments in the micromodel with crude oil showed a recovery of residual oil around 10.1% after water flooding when the biosurfactant of Bacillus subtilis NLIM 0110 was added. Moreover, 4.9% of the original oil in place was recovered using this biosurfactant after water flooding in the core. These results suggest that the produced biosurfactant is an appropriate candidate for enhanced oil recovery.

A hybrid nanocatalyst based on multiwall carbon nanotube was synthesized and added to diesel fuel to improve NOx, CO, uncombustioned hydrocarbons (HC), and soot emissions as well as diesel engine performance including power, torque, and fuel consumption. The applied nanostructure includes the hybrid of cerium oxide and carbon nanotubes of 7-10 nm size, functionalized by an amide group to homogenize the catalyst and fuel mixture. The nanocatalyst was added to the diesel fuel at concentrations of 30, 60, and 90 ppm respectively, and the performance and emissions tests were carried out using OM355 EU2 diesel engine (Idem Co. Iran, under the license of German Mercedes Benz Co.). The nanosized catalyst, and hence the high contact area of the catalyst-fuel, the proper distribution of the catalyst in the fuel, and the occurrence of catalyst oxidation reaction will result in the enhancement of combustion reaction and decreasing the amount of emitted component including NOx (max 17.84%), CO (max 12.7), HC (max 30.77%), and soot (max 20.63%); also, the performance, including a maximum increase of 3.77% and 1.44% respectively in the produced power and torque and a maximum decrease of 4.74% in bsfc, was improved.

Drilling low-pressure reservoirs is associated with economic and technical issues; thus the development of these fields has been non-profitable. One of the major drilling problems of these wells is the uncontrollable loss of mud in fractures. Nowadays, new drilling technologies use sustainable micro bubbles with diameters between 10 and 100 micrometers and polymer to solve this problem. Unique characteristics of micro bubbles in water-based mud forms an inner elastic, firm, and solid connection in pores and fractures, which minimizes the penetration of tiny air bubbles deep into the network. This is simply a micro blockage which is washed and goes away with a reverse flow when the production starts and this reduces the cost of the stimulation processes of the well. These are non-Newtonian fluids and their apparent viscosity is higher in comparison with the water-based mud. Their behavior is similar to pseudoplastic drilling fluids and they can be modeled with a power law model. This study investigated the rheological properties of micro bubbles drilling fluids with different concentrations of polymer and surfactants; it was shown that increasing the surfactant concentration increased the viscosity of micro bubbles and the size of bubbles at a fixed polymer concentration; also, the size of the bubbles was reduced by increasing polymer concentration at a fixed amount of surfactant

Isomerization process is the most interesting method insofar as it converts straight chain paraffinic hydrocarbons with a low octane number to branched chains hydrocarbons with a higher octane number. In this process, light naphtha can be converted to gasoline. In this work, the importance of hydrocracking reactions has been investigated that occur along with other reactions such as isomerization, ring opening of naphthenic hydrocarbons, and saturation reactions. A reaction network has been developed which includes 15 lumps and 16 reactions. In the present study, a kinetic model was developed using a reaction network and the model was tested by the experimental data from a pilot plant using various operational conditions and industrial feeds with different qualities. There is good agreement between the product composition obtained by the kinetic model and the experimental data. The results of modeling indicated that the optimum reactor temperature could be affected by hydrocracking reactions. This temperature occurs before the acceleration of the hydrocracking reactions and the maximum octane number of the liquid product can be obtained at this optimum temperature. The results of the kinetic modeling demonstrated that the optimum temperature could be changed by the variation of hydrogen to feed ratio and liquid hourly space velocity.

The best reservoir intervals, i.e. pay zone in a well interval, include some sections of a reservoir formation with the highest hydrocarbon volume and the lowest water volume. In the present study, in the interval of a carbonate gas reservoir, pay zones were determined using two completely different methods. In the first method of pay zone determination, i.e. cut-off method, intervals were specified by determining cut off for two petro-physical parameters of porosity (PHIE) and effective water saturation (SWE). In the second method, namely clustering method, the zones were determined by combining clustering log data and new method of multi-reference graph cut (MRGC). Based on National Iranian Oil Company (NIOC) standards, in the first method, cut offs were considered 3 and 55 for PHIE and SWE of a gas reservoir respectively. In the clustering method, two models were applied; in one model, raw data were considered, while in the other one the evaluated logs were taken into account. With respect to the accumulation of hydrocarbon in the isolated facies in the two models, the model with evaluated logs showed higher accuracy. Finally, the accuracy of determining pay zones in the two models was investigated and compared. Given that the two methods were completely different, the accuracy of both methods to determine pay zones was observed at a very high level; the two methods were also highly consistent. As a result, in addition to cut-off method, clustering method can also be used to determine pay zones.

Hydraulic fracturing is the most common stimulation method for wells the production rate of which is uneconomical due to reservoir low permeability or near wellbore damage. Since many Iranian oil and gas producer wells have low productivity and many Iranian hydrocarbon fields have also entered the second half of their life, hydraulic stimulation is inevitable for recovery enhancement and thereby safeguarding these blessing resources. This study presents an integrated scheme to estimate recovery enhancement and to forecast the performance of hydraulic fracture treatment in oil wells. This model integrates a fracture geometry model, a production model, and an economic model. These models determine fracture geometry, the production of hydraulically fractured reservoirs, and the net present value resulted from hydraulic fracture treatment. The results of applying this model to a producer well in one of the Iranian western oilfields are presented. These results can be used in the preliminary design stage of hydraulic fracture treatment.

The asphaltene is the heaviest and the most polar parts of crude oil. The change in pressure, temperature, and/or composition can induce the instability of the asphaltene in petroleum system and finally lead to asphaltene precipitation and deposition. In this work, a pseudo–dynamic approach is used for the prediction of the complex dynamic behavior of the asphaltene in the well column path of three Iranian oil wells. The main aim of this work is getting some reference diagrams which will be independent of multiphase flow in a well. By predicting saturation pressure profile in the well flow path from wellbore to surface or separator temperatures, one can access temperature and pressure for the calculation of the maximum asphaltene precipitation in well. In other words, having the saturation pressure profile, asphaltene precipitation profile in well can be obtained. Comparing the flow pressure and saturation pressure profiles, the high-risk locations in well can be determined. The MMFH model is used for asphaltene and saturation pressure predictions.

Regarding the presence of appropriate conditions for the growth of Legionella pneumophila in cooling tower water, the population of this bacterium can rapidly increase in contaminated systems. When these waters are aerosolized, small respirable-sized droplets containing Legionella can reach the respiratory system of the susceptible person and cause Legionnaires’ disease. Legionnaires’ disease is a severe form of pneumonia that can be lethal if not detected in the early stage of contamination. In this research, the contamination of five Iranian oil refinery cooling towers with L. pneumophila was investigated by culture-dependent methods. The results showed that cooling towers in three refineries were contaminated by L. pneumophila. Seasonal investigation showed that in these cases bacterial count almost were more than 100 CFU/ml. In the two cases, in some seasons, bacterial counts were 1000 CFU/ml and in one another case it was 800 CFU/ml, which all were in the risk limit. The results showed that cooling tower water treatment and their management in some refineries were not sufficient and must be modified as soon as possible. Using suitable biocide and system cleaning along with extra attention on anti-microbial treatment should be applied.

Water gas shift is an exothermic reaction used to enhance hydrogen content and reduce CO concentration in synthesis gas. In this study, the effect of nickel catalysts supported on CeO2, Al2O3, TiO2, ZrO2, and SiO2 on carbon monoxide conversion and producing carbon dioxide was investigated. Nickel was loaded taking the advantage of wet impregnation. In order to investigate the structure and morphology of the as prepared catalysts, BET, XRD, SEM, and TEM tests were employed. The test reactor was a tabular reactor made of quarts. Total flow rate was considered 300 ml/min and 150 mg mass of catalyst was loaded in the reactor. The performance of catalysts was investigated in the temperature range of 300-500 °C and at steam to carbon monoxide ratio of 1, 2, and 4. In addition, catalyst stability test was performed for 570 minutes. The results indicated that both catalysts had the maximum activity at 450 °C. The most conversion of CO and CO2 selectivity was observed for Ni/CeO2 due to high oxygen capacity of cerium oxide. The optimized loading of nickel was 13% of catalyst weight. Increasing steam to carbon monoxide ratio leaded to enhance activity.

Electrokinetic (EK) technology is advanced methods for the degradation and extraction of heavy metals and organic contaminants from saturated and unsaturated soil and groundwater. In this method, with the application of an electric field, pollutants will be migrated towards anode or cathode by electrolysis, electro-osmosis, electromigration, and electrophoresis. In this study, the behavior of perchloroethylene contaminated soils in an electrokinetic (EK) system enhanced by Triton X-100 on laboratory scale for 10 days was investigated. Electrical current and cumulative electro-osmosis and pH in anode and cathode reservoirs were measured every 24 hours during the run and perchloroethylene content was measured at the end of the experiments. According to the results, perchloroethylene is not influenced by electro-osmosis and ion migration due to low solubility, non-polar, and high adsorption to soil. However, by using the TX-100 in EK process, pollutant removal efficiency is significantly increased and perchloroethylene content of the soil is decreased by 51%.

Sieve tray CFD modeling with the assessment of k-ε Turbulence method and VOF framework has been considered in the current research work. Gas superficial factor has been varied from 0.462 to 1.464 ((kg/m)0.5.s-1), while, the liquid flow rate changed from 17.8×10-3 (m3/s) to 6.94×10-3 (m3/s). Comparison between VOF and Eulerian methods proved that simulation error decreased from 16%to the only 2%for clear liquid height in different gas superficial factors. Moreover, this error was only 7% in comparison with 35%with the variation of liquid flow rates. These error values are obtainable when they are compared with the experimental data of Solari & Bell. Consequently, froth height has the good agreement with the mostly well known Colwell correlation. Interfacial area as the most important characteristic of the VOF has been investigated in this work and showed an increase from 0.18 m2 to 1 m2 with the increase of gas superficial factor to 1.464. The pressure profiles have also been investigated.

Anisotropy is defined as the variation of the properties of a medium in different directions. The accurate determination of anisotropy is very important in exploration geophysics studies, reservoir geophysics, the detection of appropriate drilling direction and the prevention of sand problems. The DSI tools measure shear waves slowness in two directions perpendicular to each other and parallel to the well axis. Anisotropic zones and the maximum in situ stress can be determined by using DSI log and mathematical method of Alford Rotation. The large difference between the maximum and minimum values, especially when the minimum energy is low, shows zones with significant anisotropy. In this study, the anisotropy of a carbonate reservoir was studied and the maximum in situ stress was determined. In the interval discussed, isotropic and anisotropic zones were separated. The maximum in situ stress from DSI has been determined to N30E direction, which is in agreement with the direction resulted from FMI (N19E) and the maximum stress in Zagros.