Mohammed A. Fahim

Wax deposition from Middle East crudes

This paper reports measurements of wax content by acetone precipitation techniques as well as wax appearance temperature (WAT) by viscosity measurements and differential scanning calorimetry (DSC) of eight different stock-tank crude oils from the Middle East. Comparison of WAT measured by DSC and viscosity indicates that the viscosity method overestimates the WAT. Crude oil gravity measured, by digital density meter, and molecular weight, by vapor pressure osmometer, were used to characterize the plus fraction and predict WAT and amount of wax formed at a given condition by the thermodynamic model. Comparison between predicted and measured results shows that measured WAT by DSC compares very well with that predicted from the model for most crudes. Generally, wax contents measured by the modified UOP method 46-64 and that predicted by the thermodynamic model are in good agreement.

Retardation of asphaltene precipitation by addition of toluene, resins, deasphalted oil and surfactants

Abstract The aim of this work is to test the possibility of using deasphalted oil (DO) or resin (R) obtained from Kuwaiti crude to inhibit the asphaltene precipitation from such crude when n -heptane is added. The inhibition effect of toluene (T) and selected surfactants is also tested. Surfactants used are nonyl phenol (NP), dodecyl benzene sulfonic acid (DBSA), and dodecyl resorcinol (DR). The retardation of asphaltene precipitation with addition of inhibitor is found to be in the order: DR>DBSA>NP>R>T>DO. These results show that toluene and DO are not effective inhibitors. Their effect on the onset point becomes appreciable only when their mass fraction in the oil exceeds 60%. The resins have modest inhibition effect. The strong inhibition effect of the surfactants is due to the interaction between the acidic head of these molecules and the asphaltene. The mechanism of inhibition is explained in terms of the micellization model of Victorov and Firoozabadi. Onset point for asphaltene precipitation with n -heptane addition is calculated in the presence of different amounts of inhibitor. Calculated results agree well with experiment. It is possible by using the micellization model to predict the amount of inhibitor required for reaching a certain onset point.

MODELING THE HYDROCRACKING PROCESS USING ARTIFICIAL NEURAL NETWORKS

ABSTRACT Feed-forward neural networks that models the hydrocracking process of Arabian light vacuum gas oil are presented. The input-output data to the neural networks was obtained from actual local refineries. Several network architectures were tried and the networks that best simulate the hydrocracking process were retained. The networks are able to predict yields and properties of products of the hydrocracking unit (e.g. iC4, nC4, light and heavy naphtha, light and heavy ATK, Diesel, etc.). The predictions of yields and properties of various desired and undesired products at different conditions are required by refineries for process optimization, control, design, catalyst selection, and planning. The predictions of the prepared neural networks have been cross validated against data not originally used in the training process. The networks compared well against this new set of data with an average percent error always less than 8.71 for the different products of the hydrocracking unit.

Stability of Water-in-Crude Oil Emulsions: Effect of Oil Aromaticity, Resins to Asphaltene Ratio, and pH of Water

Abstract The formation of tight water-in-oil emulsions during production and transport of crude oils is a great problem challenging the petroleum industry. Tremendous research works are directed to understanding the mechanism of formation, stabilization, and controlling of oil field emulsions. This article presents experimental results of some of the factors controlling the formation and stabilization of water-in-crude oil emulsions. In this study, asphaltenes and resins separated from emulsion samples collected from Burgan oil field in Kuwait have been used to study emulsion stability. Model oils of resin to asphaltene ratio of 5:1 and toluene-heptane mixtures have been used to study the effect of oil aromaticity on emulsion stability. Results indicate that at low toluene content (below 20%) or high content (above 40%) less stable emulsions are formed. At a threshold value of 30% toluene, a very tight model oil emulsion is formed. The effect of resins to asphaltene (R/A) ratio on stability of model oil has also been investigated. Results reported in this paper show that as the R/A increases the emulsions become less stable. The effect of pH on stability of model oil emulsion made of 50/50 heptane-toluene mixture having R/A ratio of 5:1 have been studied. Experimental results revealed that as the pH of the aqueous phase of model oil increased from 2 to 10, the emulsion became less stable. At high pH, the asphaltene particles are subjected to complete ionization leading to destruction of the water-oil interface and eventually breakdown of the emulsion.

Prediction of Asphaltene Precipitation from Empirical Models

Abstract Asphaltene precipitation in the reservoir has proved to be a difficult problem to define and study. Field conditions conducive to precipitation include normal depletion, acid stimulation, gas-lift operations, and miscible flooding. Asphaltene precipitation is generally believed to be an irreversible process, which is the main reason it can have a profound impact on production operations. Investigations into asphaltene precipitation have been impeded by a shortage of experimental data and information on precipitation mechanisms. The aim of this work is to generate empirical models with other thermodynamic models to describe and predict precipitate formation models with a variety of reservoir fluids. Experimental asphaltene precipitation data on several live-oil at reservoir conditions were measured to study the effects of temperature, pressure, and composition on precipitate formation and the relationships between critical properties. Data generated by the model can be used to identify operating amount of asphaltene deposited under different conditions.

Empirical Equations for Estimating ADE of Crude Oils

Abstract There has been an increasing interest in the construction of asphaltene deposition envelope (ADE) to determine a safe zone of operation during oil production. Equations of state are usually used for calculations of ADE; however, the method requires tuning some experimental Pressure Volume Temperature (PVT) data of the reservoir fluid. The objective of this study is to develop a simple, accurate, and reliable empirical equation for estimating the ADE by determining the upper and lower onset pressures as well as the saturation pressures. Three simple empirical equations are developed to calculate these onset pressures of several crude oils. Experimentally measured compositions, saturation, and onset pressures of 33 crude oil samples, primarily from the Middle East, at different temperatures were used to develop the equations. Another set of compositions and upper saturation and lower onset pressures of different crude oil samples from the literature were used to test the accuracy of the empirical equations. The results were also compared with equations of state predictions. The results indicate that the method is accurate, valid, reliable, and eliminates the splitting and characterizing of the heavy fraction, which is necessary for the equations of state predictions. The method is useful for estimating the ADE of crude oils where experimental data is not available.

Six-Lump Hydrocracking Model for Maximizing Aviation Turbine Kerosene

In this study, the six-lump model was sufficient to describe the kinetics of vacuum gas oil (VGO) hydrocracking to produce aviation turbine kerosene (ATK). The model aim was to test various operating parameters on maximizing the ATK yields. These parameters were temperature, pressure, catalyst deactivation, residence time, and reaction rate order. Temperature and pressure increase were in favor of increase ATK yields. Residence time had an optimum value that was around 0.5 h after which no increase of ATK yield was observed. Increasing reaction rate order of VGO increased ATK yields.

Further Investigation into the Stability of Water-in-Crude Oil Emulsions Formed in Burgan Oilfield: Effect of Toluene, Resins to Asphaltenes Ratio, and Surfactant

Factors controlling the formation and stabilization of water-in-crude oil (w/o) emulsions in oil fields are of great concern to the petroleum industry for the economic development of underground oil reservoirs. Controlling and minimizing the formation of w/o emulsions and demulsification of water from emulsions are also important for environmental development. Because of its importance, the mechanisms, formation, and stability of w/o emulsions have received considerable attention. This article deals with some of the factors responsible for the formation and stabilization of w/o emulsions formed in Burgan oil field in Kuwait. Some of the factors investigated in this study are the naturally occurred surface active components of crude oils such as asphaltenes and resins. Stability of emulsion samples with resins to asphaltenes ratio (R/A) contents of 3, 5, 9, 12, and 20 has been studied. It was found that Emulsion tightness is correlated with resins to asphaltene content of the sample. As the R/content increases the emulsion becomes unstable. The effect of additives such as toluene and dodecyle benzene sulfonic acid (DBSA) on the stability of various emulsion samples collected from oil field are also reported. A 2 wt% of DBSA was found to resolve all the water from emulsion samples collected from Burgan oilfield.

Maximizing Diesel Production From Vacuum Gas Oil Using a Two Stage Hydrocracker

In this study, a six-lump model was sufficient to describe the kinetics of vacuum gas oil (VGO) hydrocracking in order to maximize the production of middle distillate diesel. The kinetic lump model target was to obtain the reaction rate constants that represent all the hydrocracking reactions in the process. The operating conditions such as temperature, pressure, and hydrogen severity were tested to find the optimum parameters that maximize diesel yields. Mild hydrocracking operating conditions of temperature and pressure were used in a commercial hydrocracker with hydrogen severity similar to hydrotreating processes. The main reaction was the VGO conversion to diesel based on its high reaction rate constant compared with other reactions. In addition, the main reaction had the highest effect on catalyst deactivation based on the resulted deactivation factor. A multi-linear regression correlation was obtained for maximizing diesel production as a function of operating pressure, temperature, and hydrogen amount, keeping the diesel specifications within the market demand.