مجله پژوهش نفت
پیاپی 71 (مهر و آبان 1391)

Recovery of oil from fractured reservoirs is dependent on the water spontaneous imbibition in the matrix and depletion of oil contents into the fractures. However, this process is feasible only where the matrix blocks would be water-wet. The carbonate reservoirs are mostly oil-wet and thus applying spontaneous imbibition in the fractured carbonate reservoirs is dependent on the wettability alteration during the water flooding. In this work, imbibition experiments were performed using solutions incorporating various concentrations of potential determining ions present in the sea water (SO42-, Ca2+, and Mg2+) at four temperature levels (40, 60, 80, and 90 °C). The effects of ions, temperature, and salt concentration on the wettability alteration of carbonate reservoirs during spontaneous imbibition process were investigated. Calcite outcrops from a limestone mine in Limburg, the Netherland, and crude oil of Bangestan formation, Iran, with an API of 22.3, were applied. It is shown that the presence of SO42- ions The strongly affects the spontaneous imbibition to a maximum extent, in other words, the 75 percent removal of SO42- from imbibition solutions leads to 2% reduction in the oil recovery. Moreover, by increasing NaCl concentration the oil recovery decreases (2% at 90 °C), while by removal of NaCl from the solution the oil recovery increases (30% at 90 °C). No variation in the oil recovery is observed where variations in the concentration of Ca2+ and Mg2+ ions at 40, 60, and 80 °C are applied. However, at 90 °C, the recovery of oil is increased with increasing the concentration of potential determining ions.

Polystyrene latexes with dispersion of nanoclay layers were synthesized by using in situ miniemulsion reverse atom transfer radical polymerization at 90 °C. Final monomer conversion was determined by employing gravimetric method and droplet and particle size distributions were obtained by using dynamic light scattering (DLS) analysis. Also, the number- and weight- average molecular weight and polydispersity index of the nanocomposites were evaluated by using GPC. It was found out that the PDI value of the neat polystyrene is lower than that of the polystyrene chains extracted from the nanocomposites; PDI rose by increasing nanoclay content in the polymer matrix. The XRD results indicated that clay layers were dispersed in the polystyrene matrix and therefore exfoliated nanocomposites were formed. The successful formation of polystyrene chains and their living nature were demonstrated by FTIR spectra. The living nature of the polymerization was also confirmed by the HNMR results. The SEM micrograph presents the monodisperse distribution of spherical particles with sizes in the range of around 200 nm in the nanocomposite containing 1 wt% of nanoclay.

Miscible gas injection is one of the most effective enhanced oil recovery techniques and minimum miscibility pressure (MMP) is an important parameter in miscible gas injection processes. The accurate determination of this parameter is critical for an adequate design of injection equipment and thereby project investment prospects. The objective of the current paper is to develop a new universal artificial neural network model to predict the minimum miscibility pressure of CO2 and hydrocarbon gas flooding. Different MMP correlations and models are proposed regarding the type of injection gas and the mechanism of miscibility respectively based on mathematical and thermodynamic calculations. Almost all of the correlations proposed in the literature either represent condensing/vaporizing mechanisms or give reasonable results only for the limited range of data they are based on. Experimental data from different crude oil reservoirs obtained through slim tube tests are gathered in order to develop a new model in which the mechanisms are included. Mixing rules are used to decrease independent variables. The significance of this model is that MMP can be determined for any composition of oil and gas no matter which mechanism is dominant in achieving miscibility. The comparison of the model results with the reliable data published shows that the results obtained from the new MMP model is more accurate and universal than most of the published models. Finally, a computer program for determining minimum miscibility pressure is presented.

Bubble and slurry bubble column reactors usually work under pressures beyond the atmosphere in the industries. Although many studies have been done about bubble and slurry bubble column reactors, experimental studies under elevated pressure are very limited. In this study, the effects of pressure and slurry concentration on the gas holdup have been investigated by using pressure difference tests. The experiments of this study are made under pressures up to 18 bar and paraffin and silica are used as the liquid and solid contents. Increasing the operation pressure leads to an increase in gas holdup. It is also found out that the effect of pressure is vanished by increasing the slurry concentration. The experiments are performed in a column with a diameter of 16 cm and a height of 2.8 m. The gases used are nitrogen and air. Finally, a new experimental correlation is developed as a function of gas density (ρg), superficial velocity of gas (Ug), slurry density (ρSL), slurry viscosity (μSL), and liquid surface tension (σL); the correlation is obtained by using the data extracted from this investigation and is in good agreement with the experimental data.

The relation between compressional wave velocity and porosity depends on porosity, porosity type, mineralogy, saturation, and pressure in carbonate rock. Therefore, data points are scattered in a velocity-porosity cross plot. In this study, two methods of rock typing in carbonate rocks are analyzed to investigate the relation between compressional wave velocity and porosity. For this purpose, flow zone indicators and velocity deviation values are used. Flow zone indicators are determined from differences between sonic velocity and the velocity obtained from Wyllie time average equation using neutron porosity. The results show four hydraulic flow units with flow zone indicators from 2.23 to 19.95 and four rock types based on velocity deviation values from 139 to 1135 (m/s). Moreover, the results show that the rock typing based on velocity deviation values is more accurate than that obtained by flow zone indicators. The average value of correlation coefficient is 95% for grouping based on velocity deviation values, whereas this value is 67% for grouping based on flow zone indicators.

Catalytic gas-solid reactions are used widely using conventional packed bed reactors. Conventional packed bed reactors have some difficulties and disadvantages such as pressure drop, intra particle diffusion limitation, flow channeling and so on. Recently, to overcome these difficulties, research has led to the use of structured catalysts such as monolithic reactor instead of a random packed bed. Herein, using an iron based Fischer-Tropsch synthesis catalyst, a novel bulk monolithic catalyst is manufactured by extrusion and molding methods. The effect of various parameters on monolith quality and strength are experimentally evaluated. The molding method showed good results and the best conditions are found at 5% moisture; 20-25% binder, and 3500-5800 kg/cm2 pressure. Also, the performance of the catalyst in Fischer Tropsch synthesis is tested experimentally. The results show that this novel concept leads to superior advantages such as lower intra particle mass transfer limitation and pressure drop and more catalyst usage.

Although CO2 injection is one of the most common methods in enhanced oil recovery, it could alter the fluid properties of oil and cause some problems such as asphaltene precipitation, reduced permeability of formation, production reduction, etc. Asphaltene onset pressure is especially important for the optimization of the miscible CO2 injection. The purpose of this research is to predict the onset pressure of asphaltene precipitation during pressure reduction process in the presence of carbon dioxide by using theories of artificial intelligence. The developed models include a software simulator called “Intelligent Proxy Simulator (IPS)” which is based on structure artificial neural networks. To evaluate the prediction of artificial intelligence networks at the onset pressure of asphaltene precipitation, a thermodynamic solid model using Winprop (CMG) software was employed. The results obtained by using artificial intelligence models in the prediction of the onset pressure of asphaltene precipitation during pressure reduction process in the presence of carbon dioxide are more accurate than that of the thermodynamic solid model.

In this work, the effect of flow rate change, temperature, and fluid type are considered on meter factor in turbine meter with the aid of Computational Fluid Dynamics (CFD) simulation. Continuity and momentum equations along with the proper boundary conditions are numerically solved in a steady finite volume frame. SIMPLE algorithm is used for coupling the velocity and pressure field. For the simulation of turbulent flow, the RNG k-ε, and for discretizing the advection scheme the second order upwind are used. The drag and lift force on turbine impellers, and the meter factor utilizing angular momentum balances are gained. The results show that the accuracy increases with temperature enhancement and is almost constant with augmenting flow rate. Moreover, the shift from heavy oil to light oil causes the measurement accuracy to increase.

This study presents the phenomena occuring in small scale single-pellet for the oxidative coupling of methane (OCM) where heat transfer plays an important role. Computational fluid dynamics (CFD) is used as a tool for obtaining detailed rate and temperature profiles through the porous catalytic pellets where reaction and diffusion are competing. Inter particle temperature and concentration gradients are taken into account by solving heat transfer coupled with continuity equations in the catalyst pellet. In the heat transfer equation, a source term of energy due to high exothermic reactions is considered. Subsequent to achieving this goal, two external programs are successfully implemented to the CFD code as kinetic and heat of reaction terms. The influence of reaction temperature on catalytic performance is studied. This study is based on the experimental design which is conducted in a differential reactor using an Sn/BaTiO3 catalyst (mesh 7-8) at atmospheric pressure and different temperatures of 1023, 1048 and 1073 K with a GHSV value of 12000 h-1 and a methane to oxygen ratio of 2. Based on the results for titanate perovskite catalyst, the highest C2 yield in OCM process is obtained at a temperature of 1048 K. The results of CFD simulation indicate that temperature variation within the catalyst pellet is less than 2 K due to the completion of exothermic oxidation reactions. Also, the results show that exothermic oxidation reactions occur before endothermic coupling reaction in the pellet length. The modeling results such as selectivity and conversion at the pellet exit are in good agreement with the experimental data.

In this study, a comprehensive mathematical model is developed to study the water evaporation process and brine concentration in a solar pond to recover the valuable salts in Bandar Imam Petrochemical Company. In this model, the energy source is just solar irradiation. The solar irradiation depends on the geographic characteristics of the location. The present model accounts for heat losses from (the surface of) the pond such as convection, conduction, radiation, and evaporation losses. Also, the wind effect and the variation of the brine physical properties with salinity are considered in the model. The mathematical results are also compared with experimental data. The results show that there are good agreement between the mathematical predictions and experimental data and the developed model can predict the variation of concentration and salt recovery accurately. Finally, by considering all important parameters, the developed model was applied to determine the optimum size of solar evaporation pond based on the concentration and initial volume of brine.

The efficiency of enhanced oil recovery projects, most notably water injection, is influenced by some factors such as the composition of water and oil, porosity, permeability, and the mineralogy of rock. Pore size, pore size distribution, and the water saturation are the other factors at play; but, the most important one is the composition of oil and water and the physical and chemical interaction between them during the production process. The study of this factor is of much importance. This research aims for conducting a review on the oil production of three carbonates of Asmari and Bangestan formations located in the south of Iran under the reservoir simulated conditions. The results show that the oil production depends on the composition of oil and water and their interaction. Apart from the value of asphaltene in oil, carboxylic organic acids in crude oil influence the production as well. The amount of injected water for the maximum oil production is also influenced by forces between water and oil surfaces, which are attractive and repulsive forces. The study and evaluation proves that oil important parameters, acid number and its four SARA fractions alongside interfacial tension between oil and brine are imperative to study the procedure of production. The results of most important carbonate wells as well as a review on the above mentioned factors can lead to a better prediction of production level in Iranian south oil fields. This prediction is based on water injection in enhanced oil production projects and the analysis of its results.

Hydrogen sulfide is one of the most important impurities in crude oil and natural gas, which is required to be separated before crude refining or gas transport. From the viewpoint of environmental and quality control aspects, many problems rise due to organosulfur compounds available in crude oils especially in oil refining and oil product consumption. In spite of a variety of methods such as stripping and extraction requiring long term programs and high cost processes, chemical scavengers are recently introduced as short-time solutions with a suitable economic potential—especially in sweetening processes of gas and oil industry. One of the methods used for removing hydrogen sulfide is using chemical scavengers. Nowadays, the present technology is ideally used for upgrading gas and crude oil for export purposes. Unfortunately, no standard method has been established for evaluating H2S scavengers yet. Herein, conventional methods for evaluating H2S scavengers are initially studied due to lack of standard methods. Owing to the disadvantages of the conventional methods, a novel method (named RIPI Method) is described to evaluate the performance of synthetic and commercial H2S scavengers in crude oil matrices. The method is basically so dynamic and rapid that at least 20 real samples can daily be analyzed with a relative error of 2.4%.