Sharif Digital Repository

Asphaltene precipitation problems manifest themselves in different stages of oil reservoirs production. Experimental and modeling investigations are, therefore, employed as promising tools to assist in predictions of asphaltene precipitation problems and selection of proper production facilities. This study concerns experimental and modeling investigations of asphaltene precipitation during natural production and gas injection operations for a heavy Iranian crude oil at reservoir conditions. First, with design and performance of high pressure-high temperature experiments, asphaltene precipitation behavior is comprehensively investigated; the effects of pressure and temperature are fully... 

A precise semi-empirical correlation for the calculation of interfacial tension (IFT) between the carbon dioxide and paraffin group to be used in an enhanced oil recovery process and the chemical industry is introduced. Genetic programming and dimension analysis (GPDA) are combined to create a correlation for the calculation of the equilibrium interfacial tension of the carbon dioxide and paraffin group, based on the explicit functionality of the pressure and temperature. The parameters of the correlation consist of critical temperature, critical pressure, density of paraffin at normal temperature, and diffusion coefficients. The pool of experimental data for developing the correlation... 

Compressibility factor (z-factor) values of natural gasses are essential in most petroleum and chemical engineering calculations. The most common sources of z-factor values are laboratory experiments, empirical correlations and equations of state methods. Necessity arises when there is no available experimental data for the required composition, pressure and temperature conditions. Introduced here is a technique to predict z-factor values of natural gasses, sour reservoir gasses and pure substances. In this communication, a novel mathematical-based approach was proposed to develop reliable model for prediction of compressibility factor of sour and natural gas. A robust soft computing... 

A simple equation of state (EoS) has recently been introduced (J. Phys. Chem. B2009, 113, 11977-11987) as (Z - 1)v2 = e + f/ρ + gρ2, where Z ≡ pv/RT is the compressibility factor, v = 1/ρ is molar volume, and e, f, and g are temperature dependent parameters. This EoS has been found to be accurate for all types of nano and bulk solids and bulk fluids, in the entire temperature and pressure ranges for which experimental data are reported, except for the isotherms within 1 ≤ T r = T/Tc ≤ 1.1 for the spherical and near spherical species and for a wider temperature range for the cylindrical molecules. The aim of this work is to investigate the validity of a three-term expression similar to the... 

In the present study, we developed a multi-component one-dimensional mathematical model for simulation and optimisation of a commercial catalytic slurry reactor for the direct synthesis of dimethyl ether (DME) from syngas and CO2, operating in a churn-turbulent regime. DME productivity and CO conversion were optimised by tuning operating conditions, such as superficial gas velocity, catalyst concentration, catalyst mass over molar gas flow rate (W/F), syngas composition, pressure and temperature. Reactor modelling was accomplished utilising mass balance, global kinetic models and heterogeneous hydrodynamics. In the heterogeneous flow regime, gas was distributed into two bubble phases: small... 

Considering high temperature and pressure during single bubble sonoluminescence collapse, a hot plasma core is generated at the center of the bubble. In this paper a statistical mechanics approach is used to calculate the core pressure and temperature. A hydrochemical model alongside a plasma core is used to study the bubble dynamics in two host liquids of water and sulfuric acid 85 wt % containing Ar atoms. Calculation shows that the extreme pressure and temperature in the plasma core are mainly due to the interaction of the ionized Ar atoms and electrons, which is one step forward to sonofusion. The thermal bremsstrahlung mechanism of radiation is used to analyze the emitted optical energy... 

In this investigation, an accurate high pressure and temperature diffusion setup was applied to measure the diffusion coefficients of methane in Iranian heavy oils in presence and absence of porous media by using the pressure-decay method. The solvent diffusivity in heavy oil was determined by both graphical and numerical methods. In addition, the effects of the porous medium and the temperature on the molecular diffusion coefficient of the solvent gas in the liquid phase were discussed and finally, using experimental data, a functionality dependence of molecular diffusivity on temperature and porous medium characteristics was proposed  

In this paper, the extended finite element method is presented for thermo-hydro-mechanical (THM) modeling of impermeable discontinuities in saturated porous media. The X-FEM technique is applied to the THM governing equations for the spatial discretization, followed by a generalized Newmark scheme for the time domain discretization. The displacement field is enriched by the Heaviside and crack tip asymptotic functions, and the pressure and temperature fields are enriched by the Heaviside and appropriate asymptotic functions. The process is accomplished by partitioning the domain with triangular sub-elements. Numerical examples are presented to demonstrate the capability of proposed technique... 

Asphaltene precipitation during natural depletion and miscible gas injection is a common problem in oilfields throughout the world. In this work, static precipitation tests are conducted to investigate the effects of pressure, temperature and gas type and concentration on asphaltene instability. Three different oil samples have been studied under reservoir conditions with/without nitrogen and methane injection. Besides applying common thermodynamic models, a new scaling equation is presented to predict asphaltene precipitation under HPHT gas injection. Extensive published data from the literature are also used in model development. The scaling approach is attractive because it is simple and... 

The luminescence parameters of laser-induced bubble in the presence of an acoustic field in water are studied. A comparison is made between parameters such as bubble radius, interior temperature, and pressure of the bubble induced by laser and an acoustic field influenced by different driving pressure amplitudes. It is found that the bubble volume induced by laser at the collapse instant is more than 106 times larger than the one induced by an acoustic field. It is also noticed, by increasing the driving pressure amplitude, the bubble radius decreases in both cases, however, the bubble interior pressure and temperature increase  

Optical propulsion via laser source is a relatively new and non-contact tool for manipulation of microscopic objects. The method is based on the radiation pressure of light photons on the micron sized particles. Applications of the technique mainly cover microscopic separation, purification and cellular studies. Due to high power intensity of laser beams, absorption of light may result in heating and damage of objects to be manipulated. In addition, the difference between heated and cold zones can lead to a naturally driven flow around the objects. So precisely controlled conditions should be set up to avoid thermal effects. In this work, a theoretical study is conducted to investigate the... 

Asphaltene precipitation during natural depletion and miscible gas injection is a common problem in oilfields throughout the world. In this work, static precipitation tests are conducted to investigate effect of pressure, temperature and gas type and concentration on asphaltene instability. Three different oil samples are studied under reservoir conditions with/without nitrogen and methane injection. Besides applying common thermodynamic models, a new scaling equation is presented to predict asphaltene precipitation under HPHT gas injection. Published data from literature are also used in model development. The scaling approach is attractive because it is simple and complex asphaltene... 

Many oil reservoirs encounter asphaltene precipitation as a major problem during natural production. In spite of numerous experimental studies, the effect of temperature on asphaltene precipitation during pressure depletion at reservoir conditions is still obscure in the literature. To study their asphaltene precipitation behavior at different temperatures, two Iranian light and heavy live oil samples were selected. First, different screening criteria were applied to evaluate asphaltene instability of the selected reservoirs using pressure, volume, and temperature data. Then, a high pressure, high temperature filtration (HPHT) setup was designed to investigate the asphaltene precipitation... 

A new-generation equation of state, perturbed-chain statistical association fluid theory (PC-SAFT), has attracted much attention to modeling the phase behavior of fluids using molecular-based equations of state. A set of three pure component parameters is needed for non-associative compounds, conventionally determined by fitting vapor pressure and liquid density data simultaneously. Unfortunately, experimental data are scarce, and the number of pure substances is too large. Thus, it is indispensable for developing predictive methods to determine the pure component parameters. In the present paper, a new model has been developed to estimate PC-SAFT parameters for different pure components,... 

In this research, direct conversion of wet algal biomass into biodiesel using supercritical methanol was studied. In this process, microalgal lipids simultaneously was extracted and converted to biodiesel under high pressure and temperature conditions without using any catalyst. Several experiments have been performed to optimize the methanol amount and it has been revealed that the best performance was achieved by using methanol/wet biomass ratio of 8:1. The effect of using various co-solvents in increasing the efficiency of the supercritical process was investigated. It has been shown that hexane was the most effective co-solvent and its optimal ratio respect to wet biomass was 6:1. The... 

Despite the numerous experimental studies concerning asphaltene, the extent of reversibility of asphaltene aggregation at reservoir conditions remains still an elusive and controversial issue in the available literature. In this work, a series of depressurization and repressurization experiments were performed on three different live oils for qualitative and quantitative evaluation of the reversibility of asphaltene aggregation under typical pressure and temperature conditions of oil fields. The obtained results reveal that the kinetics and the extent of reversibility of asphaltene aggregation at elevated pressure and temperature are majorly controlled by the characteristics of the reservoir... 

The main objectives of this study are to determine the influence of crude oil type, salinity, temperature and pressure on the dynamic interfacial tension (DIFT) of crude oil based on the experiments and modeling approaches. DIFT is also modeled using dynamic adsorption models, mono-exponential decay model as well as empirical equations. The results showed that when temperature increases, unlike deionized water which inversion phase temperature was observed, the equilibrium IFT of crude oils/sea water increases due to reduction of surface excess concentration of natural surfactants at the fluid/fluid interface as a dominant mechanism  

The thorough knowledge of the asphaltene aggregation phenomena and pressure/temperature related kinetics is helpful for accurate prediction/control of the asphaltene issues in all facets of petroleum production/processing. However, characterizing the asphaltene aggregation phenomena in live oils at high pressure-high temperature conditions is not well discussed in the available literature. In this work, the asphaltene aggregation phenomena as well as the kinetics of aggregation at different levels of pressure and temperature are investigated in light and heavy live oils using high pressure microscope. The results are presented and discussed in terms of asphaltene onset pressure, aggregates... 

In spite of the development of different experimental methods and theoretical models devoted to understand and predict the asphaltene behavior in dead/model oils, the asphaltene aggregation phenomena in live oil systems at high pressure-high temperature conditions has been grossly missing in the available literature. In this study, a population balance model with geometric scaling approach is proposed to simulate the asphaltene aggregates growth in time for live oil systems. Appropriate collision kernels are incorporated to describe the aggregation mechanisms taking into account the effect of pressure, temperature and oil characteristics. In modeling of the asphaltene aggregation phenomena... 

In this work, high-pressure microscopy technique was used to measure the size and fractal dimension of asphaltene aggregates formed in different live oil samples at elevated pressures and temperatures. It was found that the asphaltene aggregates in live oil samples are irregular fractal-like structures with pressure−temperature-dependent fractal dimensions. By monitoring the variation of the fractal dimension and size of the asphaltene aggregates with pressure and temperature, the mechanisms responsible for asphaltene aggregation process at elevated pressures and temperatures can be well predicted. The range of fractal dimension of asphaltene aggregates in live oils is similar to that...