مجله پژوهش نفت
پیاپی 78 (امرداد و شهریور 1393)

The high cost and risk of empirical tests on CNG cylinders make the use of numerical methods inevitable. In this paper، damage mechanics approach is used to investigate the effect of crash and damage caused by impact in CNG all-steel cylinders. The CSA standard in CNG cylinders is used as a damage detection criterion and cylinder ability to reuse. The simulation of cylinder failures caused by collision and drop is done by using Johnson-Cook damage model which is one of the efficient models in impact problems. Accomplished simulations are carried out in different impact directions، and the effects of cylinder internal pressure، collision velocity، and fall height are analyzed. Also، failures due to collision for various situations are discussed. These investigations for different cases، including crash and drop tests show that the maximum damage created in case of vertical impact and the resultant damage by changing direction from vertical to horizontal will be decreased. Furthermore، by eliminating failed elements and comparing damage depth caused by collision with CSA standard، it is observed that، in most cases of vertical accident and drop tests، the cylinders have been damaged and lost their ability to be used، while in horizontal impact cases the cylinders are intact or can be reused after repairing. The results show that، in collision process، the cylinder rear wall and the front hemisphere of the cylinder have further damaged and are the critical areas in the horizontal and vertical collisions respectively. For a specific impact direction in lower cylinder internal pressure، the damage caused by higher collision velocity and a higher altitude of falling will be more serious. The resulted diagrams indicate that the damaged area of the cylinders predominately are under compression and endure large plastic deformation. The low difference between the results by various meshes shows that this solution does not depend on the mesh size. Therefore، this damage model is insensitive to meshing in the various impact cases.

In this paper، two models، namely the Flory-Huggins (polymer) solutions theory and the model developed by Rassamdana and co-workers، which served as our basic model، were employed for estimating asphaltene precipitation. In the analyses، the asphaltene solubility parameter was initially considered as a function of pressure and was subsequently adjusted by varying the pressure with an aim of logical adjustment of the results with the asphaltene precipitation experimental data. The values established for the asphaltene solubility parameter in the first approach were somewhat underestimated compared to the reported values in the literature; however، the second approach gave more acceptable results. Finally، an empirical expression was proposed for asphaltene precipitation solubility estimation for the two oil samples with enhanced accuracy at different pressures.

An innovative inspection method to assess the condition of pipelines is proposed in this paper. The standard pipe inspection technique، based on closed-circuit television systems، has a relatively poor performance. A video camera is mounted on a robot and the video recording is provided off-line to an engineer who classifies any defects. Two of the main disadvantages of such camera-based inspection systems are 1) the poor quality of the acquired images due to difficult lighting conditions and 2) the susceptibility to error during the off-line video assessment conducted by human operators. The focus of this research is the automated identification and location of discontinuities in the internal surface of pipes. The sensor used is an assembly of a CCD camera and laser diode to generate a ring-shaped laser pattern. The automatic recognition and localization of pipe defects are carried out by means of the computation of a partial histogram based on image processing techniques. The proposed method has been conducted on a real gas pipe and the results are presented.

Wettability is an important parameter that influences the petrophysical properties of reservoir rocks. When drilling is doing، the penetration of mud filtration into formation causes considerable wettability alteration and affects the oil displacement by water. Hence the enhanced oil recovery methods will be affected because of formation damage. In this study، the effect of three samples (a bentonite commonly used in oil well drilling، a purified bentonite، and nanoclay) on wettability of sandstone and carbonate rocks has been studied using the contact angle method. The modification of surface properties of montmorillonite sheets by hydrophobic plug reformer changed the wettability of the clay particles from water-wet to oil-wet. This change resulted in the suitable dispersion of nanoclay (organic) into oil phase (as hydrophobic phase). The contact angle measurements of the prepared suspension from each of three samples showed that common and purified bentonites altered the wettability of the sandstone and limestone rocks to water wet، whereas the nanoclay changed contact angle to oil-wet behavior. Based on these observations، use of nanoclay، as an oil-based drilling mud additive، is useful due to its compatibility with oil zone wettability and suitable dispersion in oil-based drilling fluid.

Water vaporization and its impact on the formation productivity and injectivity are important issues dealt with during gas injection into porous media. It is clear that there are many other issues associated with underground gas storage projects but water vaporization and its induced permeability impairment are particularly important issues during gas injection in the candidate reservoir in this work. This paper investigates water vaporization in a candidate reservoir for underground gas storage. It is important to encounter two parameters in this process، which are water saturation reduction and permeability reduction in reservoir rock sample to form salt precipitation. Water saturation reduction causes permeability improvement، but scale formation reduces permeability. According to the results، the medium with higher permeability experiences an improved injectivity during gas injection، while the medium with lower permeability experiences an impaired injectivity. It is worth mentioning that both media suffer from permeability impairment. Finally، injectivity and productivity changes caused by water vaporization differ from case to case depending on the porous medium characteristics and the properties of fluid within the porous medium. Therefore، independent experiments should be conducted for different systems، since there is no accurate formulation to predict the mentioned permeability impairments. Also، special experiments are necessary for different media which are related to pore structure.

Stable latexes of poly (styrene-co-methyl methacrylate) /clay nanocomposites were synthesized by in-situ reverse atom transfer radical polymerization at 90 °C and in miniemulsion system. Miniemulsion polymerization has been employed for its abundant advantages to encapsulate inorganic materials، simple nucleation step، and elimination of organic solvents. Final monomer conversion was determined by gravimetric method. Droplets and particles size distribution were obtained by using dynamic light scattering (DLS) analysis. Also، number and weight average molecular weight and polydispersity indexes of the samples were also evaluated by GPC method. In addition، the PDI value of the neat polymer was smaller than the extracted polymer from nanocomposites and in the case of nanocomposites it increased by increasing nanoclay content. Mole ration and fractional conversion of each monomer in copolymer chains were estimated by using 1H NMR spectroscopy. XRD patterns displayed no peak in in-situ synthesized nanocomposites which indicates an exfoliated structure of all the nanocomposites prepared by this method. FTIR spectra indicate successfully loading of nanoclay in the copolymer matrix. SEM micrographs presented a monodisperse distribution of spherical shape particles of poly (styrene-co-methyl methacrylate) /clay nanocomposite with a size in the range of around 200 nm.

The aim of this study is desalination and reuse of produced water by using basin solar still distillation to meet agricultural irrigation standards. The produced water is one of the main obstacles in oil and gas industries. The produced water contains high dissolved solid، oil and hydrocarbons، and other pollutants. Conventional treatment methods are not applicable and advanced technology and spending more money is needed for the treatment of the produced water. Availability of sufficient areas، high solar radiation، and a high number of sunny days in the south of Iran are suitable parameters for solar distillation by using basin solar stills. In the current work، to achieve the above aims، three basin solar stills with an area of about one square meter and different bottom surface covers were made and installed in Research Institute of Petroleum Industry. Water and the produced water entered the three basin solar stills with different water depth. Then، with running some tests، optimum water depth and bottom surface cover for the production of more treated water were determined. The results showed that the basin solar still with a 30-degree slope for glass surface، dark bottom cover، 2-centimeter depth of produced water، and positioned to the south geographical side can treat the produced water according to agriculture irrigation standards except for oil content. In the spring season، the amount of treated water was about 3 to 4 liters per square meter of basin solar still area.

The main objective of the present study was to conduct a comparative test program on unmodified bitumen and modified bitumen containing nanoclay and assess the effects of asphalt properties on pavement performance. To meet this objective، the main targets of this study are to find out if the nanoclays alter the critical properties of asphalt binder and influence the ageing and temperature sensitivity of the binder. Different tasks were performed to meet the objectives. The first task performed was studying the nanoclay modifiers at a nanoscopic level and the test performed in this area was the X ray analysis of the nanoclay modifiers. The second task was studying the influence of nanoclay modifiers on binder characteristics and the related tests performed were empirical studies of fresh (unaged) and aged bitumen types by empirical tests like penetration and softening points. Findings of the tests performed on binders proved that the cloisite-15A nanoclay modifications helped to increase the stiffness of the standard binder. This was especially true if the 4% cloisite modification was used. The nanofil-15 modification helps to improve the ageing resistance of the binder in short and long term applications. An overall conclusion from these findings is that the nanoclay modifications help to improve some characteristics of asphalt binders and asphalt mixtures، but at this level they are not at a stage to justify applications on large scales.

In this study، a three-dimensional model of a single fuel cell is considered. This modeling is done for a cathode half-fuel cell and consists of a parallel flow field، namely a cathode gas diffusion layer and a polymer membrane; it includes mass transfer at gas diffusion layer، electrochemical reaction at catalyst layer، and charge transfer in all the parts of fuel cell. Shoulder is considered in this model and thus concentration profile and charge distribution are more delicate. Governing equations are solved by FEMLAB software through the finite element method. This modeling could predict the behavior of fuel cell at different operation conditions by minimum cost. The performance of fuel cell is evaluated by different activation energies and، by comparing the results، the optimum operation condition is concluded.

The present study is concerned about monitoring 4D seismic of Azadegan oil field; Sarvak formation is a major reservoir and supposed to be the prospect formation At first، 31 plug samples taken from cores and all of the Sarvak formation limestone were sent to the Japan National Oil Corporation’s Technology and Research Center (TRC) for laboratory measurements of P and S wave velocities in the reservoir conditions and at different amounts of fluid saturation، pressures، and temperatures. Moreover، the porosity of core samples and petrophysical data were studied and measured at RIPI. Afterwards، seismic responses of Sarvak formation were analyzed from two points of view، namely velocity and amplitude، and their changes in relation to reservoir conditions were modeled and analyzed. Then، to examine the validation of Gassmann’s equation، laboratory core samples were used. The results reveal that the Gassman’s model with a relative error of less than 4% provides acceptable data for the studied reservoir. The results of this study show that changes in the effective pressure will lead to 12% changes in compressional wave velocity and 21% variation in shear wave velocity. Such a change in reflection coefficient of compressional wave velocity is equal to 6%. However، changes induced by manipulating saturation were less than 2% which had low validity in seismic monitoring. Therefore، the probability of imaging the changes due to fluid displacement is insignificant and it is not successful for monitoring the studies of reservoir internal changes. However، simultaneous changes of pressure and fluid displacement on compressional seismic data (present seismic data) are estimated about 13%، which means that it is possible to interpret such changes. Thus it is suggested conducting 4D seismic monitoring during the Azadegan development program for the Sarvak reservoir fluid and studying pressure changes.

Secondary and tertiary recovery processes can lead to severe and permanent reductions in permeability due to the interactions between injected fluids and the reservoir rock; this is especially true in high clay content، low permeability، and poorly consolidated reservoirs. The formation damage could be both temporarily، by exceeding the turbulent limit of fluids in porous media، and permanently، by fine and sand production or fissure and fracture activation; because of this overall pressure drop will be noticeable in near wellbore. Since the carbonate formations are stronger than sandstone formations، the results of velocity formation damage are different and comparable with results of sandstone formations. In this study، a series of core flooding experiments have been carried out to determine the critical injecting flow velocity in porous media of the carbonate formation by the use of a new and practical method. The formation damage limits in linear system were determined by both qualitative and quantitative methods for different plugs. The proposed method incorporates two different methods، one of which uses base line permeability and returning the injection rate to base rate after each incremental stage and the other determines formation damage degree. The results show that the induced damage mechanism is in the form of fine migration or activation of natural fractures and، to prevent formation damage، the injecting flow velocity must be kept less than its critical value. Otherwise، the induced damage will be permanent and irreversible.

In this paper، the numerical analysis of erosion/corrosion in gas pipelines and gas stations were investigated using computational fluid dynamics. The effects of various parameters such as velocity، temperature، turbulence، tiny particles floating in gas، and multi-phases were analyzed. For this purpose، comprehensive information on gas stations was first collected. Then، equipment of gas stations and pipelines was modeled and created using Catia and Solidwork commercial software packages. Finally، the numerical results were obtained using the method of computational fluid dynamics by employing Gambit 2. 2. 30 and Fluent 6. 0 commercial tools. Several items of equipment such as pipe، valve، reducer، bend، etc. were considered in this analysis. The results proved that erosion/corrosion was increased by increasing velocity، temperature، turbulence، tiny particles floating in a gas، and multi-phases.

Secondary and tertiary recovery processes can lead to severe and permanent reductions in permeability due to the interactions between injected fluids and the reservoir rock; this is especially true in high clay content، low permeability، and poorly consolidated reservoirs. The formation damage could be both temporarily، by exceeding the turbulent limit of fluids in porous media، and permanently، by fine and sand production or fissure and fracture activation; because of this overall pressure drop will be noticeable in near wellbore. Since the carbonate formations are stronger than sandstone formations، the results of velocity formation damage are different and comparable with results of sandstone formations. In this study، a series of core flooding experiments have been carried out to determine the critical injecting flow velocity in porous media of the carbonate formation by the use of a new and practical method. The formation damage limits in linear system were determined by both qualitative and quantitative methods for different plugs. The proposed method incorporates two different methods، one of which uses base line permeability and returning the injection rate to base rate after each incremental stage and the other determines formation damage degree. The results show that the induced damage mechanism is in the form of fine migration or activation of natural fractures and، to prevent formation damage، the injecting flow velocity must be kept less than its critical value. Otherwise، the induced damage will be permanent and irreversible.