مجله پژوهش نفت
پیاپی 76 (بهمن و اسفند 1392)

The influence of functionalizing carbon nanotube (CNT) of CNT-supported nanocatalyst in Fischer-Tropsch synthesis (FTS) has been investigated. The catalysts were synthesized by the wet impregnation of 10 wt. % of cobalt loading over CNT and functionalized CNT. The catalysts were characterized by using BET، XRD، H2 chemisorption، TPR، and TEM. According to the TEM analysis، smaller cobalt particles (3-8 nm) synthesized on functionalized CNT had very narrow particle size distributions and were mostly confined inside the CNT. The deposition of cobalt nanoparticles synthesized on functionalized CNT shifted the reduction peaks to a lower temperature، indicating higher reducibility of uniform cobalt particles. Using the proposed functionalized CNT-supported cobalt catalyst increased the FTS rate (g HC/gcat. /hr)، Co conversion (%)، and C5+ selectivity (%) from 0. 35 to 0. 43، 52. 8 to 62، and 85 to 90 respectively; however، CH4 selectivity (%) decreased from 11 to 5 compared to that of the catalyst prepared on conventional CNT. This new catalyst preparation method may offer an attractive alternative approach to nanoparticle synthesis with uniform and various size distributions.

The goal of investigating reservoir characteristics is to determine petrophysical properties such as porosity and permeability. The porosity and permeability relationships in the framework of flow units can be used to characterize heterogeneous reservoir rocks. A flow unit is defined as a volume of reservoir rock which is laterally and vertically correlatable and predictable. Moreover، the geological and petrophysical properties which affect the fluid flow within a reservoir are constant. Determining and investigating flow units in a reservoir are necessary in order to characterize the reservoir precisely and simulate it with simulation software packages. In this study، flow units were calculated with two methods، namely the statistical reservoir zonation technique and stratigraphic modified Lorenz plot (SMLP)، in Tabnak gas field. To determine these units، the combinations and comparison of petrophysical properties، such as porosity and permeability، of three wells were used. The comparison of results showed that flow units determined by these two approaches were nearly in agreement.

Using the sugars from lignocelluloses hydrolysate is a suitable strategy for biodiesel production by yeasts. In this work، Sudan black dye and Nile red florescent dye were used for staining and selecting the oleaginous yeast strains. Growth and single cell oil production in 11 selected native yeasts and 2 yeasts from microbial collection of DSMZ were investigated by using glucose، xylose، and a mixture of both as carbon sources. The results showed that native yeasts had a good sufficient potential for lipid production in the industrial field. According to the type of strain and carbon source، lipid production، dry cell weight، lipid content، and lipid production efficiency were achieved to be 0. 21-6. 95 g/l، 0. 73-10. 9 g/l، 26. 4-81. 4%، and 6. 41-21. 95% respectively. Among the investigated yeast strains، the highest lipid content (81. 4%) and lipid production efficiency (21. 95%) were related to strain UIMC65. The highest lipid production (6. 95 g/l) was acquired in strain UIMC35 (a mixture of glucose and xylose as the carbon source) and strain UIMC74 (glucose as the carbon source). TLC and FT-IR spectroscopy techniques were used for the quality analysis of produced single cell oil by yeast strains.

In this study، a set of smart coatings on the basis of micro/nano capsules، with the aim of corrosion reduction in oil and gas pipelines، has been investigated. The shell of capsules was made of urea-formaldehyde and their core was tong oil، which acts as a healing agent. In the present work، some parameters affecting the performance of the coating such as mechanical agitation rate in the encapsulation process، capsule size، and dispersed capsule concentration were varied and optimized. In addition، other coating properties such as adhesion and corrosion resistance of the coating were investigated by adhesion pull-off tests and electrochemical impedance spectroscopy respectively. The results indicated that using finer capsules، which were created at higher stirring rates، improved the corrosion resistance and adhesion to the substrate. Moreover، with the incorporation of capsules in the matrix، the protective ability was significantly increased; this could be realized from the results of water absorption and electrochemical tests. A capsule concentration of 15 wt. % was the optimum value which led to the highest corrosion resistance of the coating.

In response to the quality upgrading of producing sweet crude oil for export، four different types of chemical scavengers have been formulated and produced in laboratory and scaled up to bench scale. Cold stripping، affective technical reducing، and removal parameters of the process have been studied on four different sour crude oils by each formulated scavenger. Experimental design was performed to optimize effective parameters by using Minitab-14 software package. Main parameters such as concentration، temperature، and effective time were studied. Under optimal values of 1100 ppm scavenger concentration، 50 °C temperature، and 15 minutes contact time، the H2S content was significantly removed from 950 ppm to less than 15 ppm for an Iranian light sour crude oil.

The unwanted discharge of oil from different types of reservoirs into sea water has brought many environmental and economic difficulties in the world. In the past، attempts have been made to remove the floating oil from water surface in the oceans using synthetic and natural adsorbents such as polypropylene، cotton، and wool fibers. In the present work، nonwoven fabrics made from the blend of solid and hollow polyester (PET) fibers (0، 25، 50، 75، and 100% hollow fibers) were examined for oil retention and pickup capacities. Four types of oils were used in the experiments. The sorption capacity and oil retention capability of 100%-hollow fiber was found to be superior among the samples tested. The results showed that the replacement of solid fibers with the hollow fibers increased oil pickup capacity and prevent fibers from sinking into deep water. These advantages of hollow fibers are attributed to the higher specific surface area and larger apparent volume of this type of fibers.

The weld residual stresses decrease the design stress in high-pressure large-diameter gas transportation pipelines. In this paper، two API X70 steel pipes (with spiral seam weld) with an outside diameter of 56 inch and a wall thickness of 0. 780 inch were first girth welded (according to NIGC code). Next، hole drilling tests were conducted for strain measurement on the surfaces of the pipes. The values of residual stresses on the internal and external surfaces of the pipe were then determined from the measured strain data. To ensure the integrity of the seam weld، different experiments، including chemical analysis، metallographic observation، tensile، and impact tests were performed. The experimental data showed that the maximum tensile residual stress (of the order of 318 MPa) was located on the centre line of the seam weld on the pipe outer surface alongside with the pipe hoop direction. This was more than 60 percent of the yield strength of the seam weld. In the welded zone، micro-alloys content reduced around 75% and un-tempered martensite was observed on the outer weld pass. The carbon content increase resulted in an increase in martensite volume fraction، and thus reduced the residual stress in this region. On the other hand، this effect reduced the material strength. The reduction in material yield strength in the weld caused the increase in residual stress with respect to static yield strength of the pipe. In addition، the minimum Charpy fracture energy (of the order of 45J) was observed in the pipe hoop orientation in the weld center line. Therefore، the external surface of the pipe (weld center line) in its hoop direction with the maximum residual stress، maximum martensite content، minimum micro-alloyed contents، minimum yield strength، minimum elongation and minimum Charpy energy is the critical point in the structure.

In this paper، the corrosion behavior of stainless steel 316L was evaluated in used catalyst solution in Sulfiran plant in temperature range of 35-45 °C. The electrochemical techniques consisted of polarization curves and electrochemical impedance spectroscopy (EIS) were used in laboratory tests. It was found that the corrosion rate of stainless steel 316L alloy was less than 1 mpy in this process. In the meantime، there was low possibility of pitting corrosion on stainless steel 316L. The weight loss technique was used for the determination of corrosion rate in pilot tests. In addition، surface analysis techniques such as XRD، XRF، and SEM were applied in this research. The evaluations of microstructure of stainless steel 316L were also carried out. The results of pilot tests confirmed the findings of laboratory tests. While inclusions were present in alloy stainless steel 316L microstructure، the investigation of metallurgical aspect of the mentioned alloy showed negligible uniform corrosion damage.

Shell and tube heat exchangers are widely used in industries. These heat exchangers have their own limitations and special working conditions. They have always been designer’s first choice because of their advantages such as available design standards and ability to handle a wide range of heat duties. Design engineers have made a lot of effort to increase the performance of shell and tube heat exchangers. The installation of static mixers is one of the most effective ways to enhance heat transfer in the tube side of heat exchangers. In this study، by the evaluation and modification of performance correlations given for static mixers، the more reliable ones have been identified. In addition، using CFD، velocity، temperature، and pressure profiles for both laminar and turbulent regimes have been studied. For a typical case study، the heat transfer and flow pattern of water flow inside a tube equipped with six helical Kenics inserts have finally been analyzed.

Process design and simulation of different natural gas dehydration processes including membrane systems، absorption، and adsorption were investigated in the current study and the results of the economic assessments of these processes were compared with each other. The absorption process was simulated by means of Aspen-Hysys and the modeling and simulation of membrane system were implemented by MATLAB. All of the processes were designed to reduce the water content of natural gas to less than 7 lb/MMSCF. According to the results، under assumed operating conditions، the total separation cost of membrane separation system was lower than that of other dehydration processes at low feed flow rates. The difference decreased with increasing feed flow rates followed by a decrease in the total separation costs of absorption and adsorption processes. In addition، under the operating conditions assumed in this study، the membrane systems showed lower total separation costs than the adsorption processes. According to the economic evaluation and optimization of membrane-absorption and membrane-adsorption hybrid processes، the use of membrane system on the upstream of other dehydration processes would result in a significant decrease in total separation costs depending on the operating conditions in each dehydration unit.

Amplitude Variation with Offset (AVO) is one of the effective methods for identifying the fluid type in subsurface exploration. In this paper، we investigate the existing of light hydrocarbon in Gorgan Plain with Direct modeling and Inverse modeling as an AVO analysis. Direct Modeling can indicate the identity of attributes (litho logy or fluid dependent attributes). The analysis has been done using both P-P and P-Sv attributes. Inverse modeling deals with real data and is fed from the results of direct modeling for detection of the light hydrocarbon zones. Using this methodology in Gorgan Plain showed that attributes which are related to converted attributes such as S-wave Impedance Reflectivity and S-wave Velocity Reflectivity have higher ability in identifying fluid from litho logy with respect to non-converted attributes for example P-wave Impedance Reflectivity and P-wave Velocity Reflectivity. Making the inverse sections of fluid-dependent attributes indicated two light hydrocarbon zones under the Cretaceous-Tertiary unconformity. It expects that there have been wet zones under them. By investigation on three inverse sections of density contrast، P-Wave velocity contrast and S-Wave velocity contrast with considering Ramos & Castagna graph، It is concluded that the amount of Sw is about 90% and the amount of Sg will be approximately 10%.

3D reservoir property modeling is one of the most important steps in fluid flow simulation. A more accurate model would provide a more realistic reservoir simulation. In this study، four different geostatistical approaches، including Kriging، collocated cokriging، sequential Gaussian simulation (SGS)، and Cosimulation were applied to well data for 3D porosity model building. Initially، Kriging method was based only on well data and utilized for porosity estimation. Then، seismic acoustic impedance data as a secondary seismic attribute was used in collocated cokriging algorithm for 3D porosity modeling. Kriging and collocated cokriging-based SGS approach were also used for 3D model building. The cross validation of all the four approaches revealed that the best model obtained using co-simulation with secondary data.

In this paper، static adsorption tests were performed using asphaltene extracted from a sample of crude oil from Iranian southern oil fields and different reservoir rock minerals. The amount of adsorbed asphaltene was calculated after determining the equilibrium concentration by UV/VIS method (328 nm). The adsorption isotherms of asphaltene on Kaolin، Calcite، Dolomite، and Quartz were analyzed and compared. Among the different minerals، the maximum adsorption was found for Kaolin. Modified Langmuir isotherm was used for comparing between the model and experimental data. Modified Langmuir coefficients were obtained from four linearized modified Langmuir equations by linear regression method. Kaolin، Calcite، and Quartz followed the Langmuir isotherm، indicating that there was the monolayer formation of adsorbed asphaltenes onto the surface; however، the adsorption behavior of Dolomite was different from the others and does not follow the Langmuir isotherm. It indicated the multilayers formation of asphaltenes onto the surface. Multilayer adsorption was justified using the modified Langmuir isotherm. There was good agreement between the model and the experimental data. The values of R2 at their optimum X for Kaolin، Calcite، Dolomite، and Quartz were 0. 991، 0. 994، 0. 95، and 0. 991 respectively.

There is no history of cement slurry design incorporating nanotechnology. However، in developed countries، lightweight slurries have been designed using foam، microspheres، and Lite Crete technology. These slurries differ significantly from RIPI’s slurry containing nanoparticles in properties. Generally، lightweight cement slurry presents some disadvantages such as undesirable rheological properties، low compressive strength، and high porosity and permeability. In this study، by using HSL nanoparticles، microspheres، and cement class G and employing particle size distribution، 62-pcf slurries were obtained according to downhole conditions. In this method، with choosing the optimum range of particle size، the problems of lightweight slurries were solved. In addition، the waiting time of cement (WOC) to reach a minimum compressive strength of 500 psi was decreased to 8 hours. The 24-hour compressive strength was 2000 psi at 190 °F; moreover، the porosity and permeability of the cement were about 36% and 0. 01 md respectively for a slurry formulation with 8. 34 ppg. Furthermore، the special properties of anti-gas migration additives such as low shrinkage and fast compressive strength were inherently developed in the slurries.