Asphaltene Particle Size Distribution Research Articles

Numerical analysis of asphaltene particles evolution and flocs morphology using DEM-CFD approach

The agglomeration and fragmentation of asphaltenes which dictate particle size distribution (PSD) play an important role in deposition behavior of asphaltene. However, the physics underlying the agglomeration/fragmentation processes is grossly missing in the available literature. In this paper, Discrete Element Method (DEM) in combination with a coalescence model is coupled with Computational Fluid Dynamics (CFD) to simulate agglomeration/fragmentation considering asphaltene particles as real/irregular objects in the absence of deposition process. The evolution of asphaltene particles, asphaltene particle size distribution (PSD), and morphology of asphaltene flocs have been examined during the simulation. Also, the effect of fluid velocity (Vf), primary particle concentration (N0), inter-particle bond strength (Fb), and energy barrier (Ub) have been investigated. During asphaltene flocculation, mean floc size increases until a steady-state condition is attained where floc size and mass fractal dimension approximately remains unchanged. The size of asphaltene flocs increases up to 40 μm and fractal dimension values change in the range of 1.45–1.75. Higher Vf leads to the steady-state condition is attained more rapidly along with smaller floc sizes and higher fractal dimensions. Increasing N0 results in faster growth of asphaltene flocs, however, the stable mean asphaltene floc size is approximately insensitive to N0. The presence of larger flocs at higher N0 eventuates the smaller fractal dimensions. As Fb increases, the frequency of small particles decreases, and PSD shifts to larger sizes. Consequently, smaller fractal dimensions are obtained. The floc growth is insensitive to Ub at initial times, whereas the steady-state condition is reached more quickly with a smaller stable floc size for higher values of Ub. The fractal dimension shows a weak dependency on the energy barrier.

A Numerical Simulation Study on the Kinetics of Asphaltene Particle Flocculation in a Two-dimensional Shear Flow

In the current study, the kinetics of asphaltene particle flocculation is investigated under a shear flow through numerical simulation. The discrete element method (DEM) is coupled with computational fluid dynamics (CFD) to model the agglomeration and fragmentation processes. In addition, a coalescence model is proposed to consider the attachment of colliding particles. The changes in mean asphaltene floc size, the particle size distribution (PSD) of asphaltene flocs over simulation time, and the average fractal dimension are presented. Moreover, the effect of fluid velocity on the kinetics of asphaltene flocculation is examined. The mean asphaltene floc size increases exponentially at first, and then the growth slows; finally, it ceases due to the establishment of a dynamic equilibrium between the agglomeration and fragmentation processes. As expected, asphaltene PSD’s move from fine to coarse sizes during the simulation. Log-normal distribution matches the PSDs best, which is in agreement with the nature of asphaltene. As fluid velocity increases, the dynamic equilibrium is attained more rapidly at a smaller mean floc size and higher average fractal dimension; furthermore, PSDs shift to smaller asphaltene floc sizes. The obtained average fractal dimensions of the asphaltene flocs are in the range of 1.65 to 1.74, which is compatible with the values reported in the literature. Eventually, a semi-analytical model is utilized to fit the simulation results. It is found out that the semi-theoretical model is capable of predicting the evolution of asphaltene particle size appropriately.

Experimental evaluation of asphaltene dispersants performance using dynamic light scattering

In this study, the asphaltene particle aggregation process is studied and effects of asphaltene concentration, n-heptane to toluene volume ratio, type and concentration of asphaltene aggregation inhibitor are investigated on onset of precipitation and asphaltene particle size distribution (APSD). The measurement of APSD is performed through dynamic light scattering technique. The results show that the concentration of asphaltene doesn't have significant effect on the onset point; however, it leads to form bigger particles. An increase in n-heptane volume ratio leads to increases the asphaltene particles size where 5% of particles are bigger than 6 μm after 40 min. Dodecyl benzene sulfonic acid component displaces the onset point reasonably and causes 7% rise in the amount of required n-heptane. Dodecyl resorcinol has the best performance at concentration of 50 ppm as an asphaltene dispersant and causes required n-heptane volume increment of 2%. It reduces the asphaltene particles size significantly and delays the asphaltene particles agglomeration process of about 30 min.

Analysis of the asphaltene properties of heavy crude oil under ultrasonic and microwave irradiation

Using new technologies are quite significant in the production and development of heavy oil reservoirs. In this study, the effects of microwave (MW) and ultrasonic (US) waves on the properties of Ellam heavy crude oil of the southwest oil reservoirs of Iran have been investigated. Experimental results show that different processes occur in samples under MW radiation for 5, 10, 15 and 20min. Under MW for 5 and 10min we have viscosity reductions from 15.836 mPa.s to 12.234 mPa.s and 11.122 mPa.s, respectively. This is due to volume expansion with decreasing viscosifying component and high absorption capacity of heavy molecules of oil toward MW that charges the cracking process. US waves increase the viscosity of oil for all time durations because the power from US waves causes the evaporation of light compounds. Next, the effect of MW and US radiation on the asphaltene clusters using microscopic images was investigated. Results of asphaltene particle size distribution show that increasing duration of wave radiation makes the particles smaller, and the size range of asphaltene particles in the samples under MW radiation is much smaller than for the samples under US wave radiation. Moreover, in samples under MW radiation, the large particles cannot be seen. Consequently, the average particle size of asphaltene is smaller in samples under US wave radiation. But the particle size range is high, and large-sized particles in different time intervals of US radiation are observed. The results of scanning electron microscopy show that microwaves make the asphaltene conglomerate forming particles smaller and more regular in shape than the primary state, whereas ultrasonic waves completely alter the structure of the asphaltene particles, creating asphaltene clusters with a different structure. Based on the Fourier transform infrared spectra, ultrasonic exposure increases the cracking rate of the weaker bands and the condensation of aliphatic bands more than does exposure to microwaves, due to an increase in the intensity of the spectra.

Application of population balance equation in modeling of asphaltene particle size distribution and characterization of aggregation mechanisms under miscible gas Injection

Abstract Particle size distribution (PSD) is an important factor that determines how asphaltene instability can damage porous media during natural depletion and enhanced oil recovery processes. In this work, aggregate size distribution under natural depletion and miscible nitrogen injection processes are determined via image analysis techniques and the results are modelled by population balance equation. Unimodal distribution curves in natural depletion show the dominance of particle-particle aggregation mechanism and the clustering is detected only around crude oil bubble point pressure. It is also observed that miscible nitrogen injection considerably increases the number and size of asphaltene flocs and directs the agglomeration process towards cluster-cluster aggregation (i.e. bimodal distribution curves) which can severely damage porous media. Results of population balance modeling characterize dominant aggregation mechanisms providing one optimum collision factor for unimodal curves and two optimum collision factors for bimodal distributions which confirms the alteration of aggregation mechanism due to miscible gas injection.

The evolution of heavy crude oil's asphaltene particle size distribution by elevating temperature

Temperature variation during crude production, transportation, and processing gives heavy organic deposition problems. Asphaltene particle size evolution from two Iranian heavy crudes (I and II) in thermal de-asphaltene in the absence of n-alkane by temperature variations from 60°C to 160°C was investigated by dynamic light scattering. Onset and optimum asphaltene dissociation temperatures were specified as characteristic parameters for thermal de-asphaltene. Onset temperatures for crudes and are 100°C and 80°C, respectively. Maximum asphaltene particle size and best filtration rate occurred at 150°C and 120°C for crudes I and II, respectively, suggesting asphaltene optimum isolation temperature. Particle aggregation size decreased from 60°C to onset temperature, increased from onset to optimum temperature and decreased by passing optimum temperature. Size decrease over optimum temperature confirmed partial reversibility of asphaltene dissociation mechanism. Results suggest operating temperature in thermal de-asphaltene approaches between onset and optimum temperatures with maximum yield at optimum temperature, which is crude dependent. [Received: August, 3, 2015; Accepted: November 25, 2015]

The evolution of heavy crude oil's asphaltene particle size distribution by elevating temperature

The evolution of heavy crude oil's asphaltene particle size distribution by elevating temperature

Effect of dispersants on the kinetics of asphaltene settling using turbidity measurement method

ABSTRACTOrganic deposition especially asphaltenes in reservoirs, wells, and equipment has a detrimental effect on petroleum economy. Generally, for chemically control of asphaltene precipitation using dispersants and inhibitors of precipitation or solvents of asphaltene is very common. Although asphaltene in crude oil is stable under specific conditions, but there is no assurance that the system will be stable and asphaltenes could be remaining in suspension state. In this study, the kinetic effects of three dispersants on stabilization of asphaltene aggregates were investigated by turbidity measurement method. Turbidity measurement showed as the dispersant strength rises, the turbidity of unstable sample containing dispersant less declines versus time. In order to carry out further studies on dispersants, the effect of dispersant on asphaltene particle size distribution was investigated. The results of asphaltene particle size distribution measurements showed that adding dispersant cause to decrease the volume percent of particles with medium diameter.

The effect of asphaltene particle size and distribution on the temporal advancement of the asphaltene deposition profile in the well column

Asphaltene deposition in oil wells is an inconvenient production problem. Generating a precise deposition model for the well column is essential for optimal well design and prevention/reduction of deposition-associated difficulties. The goal of this study is to determine the effects of various parameters on the deposition process. These parameters include oil viscosity, temperature, flow velocity, well diameter and asphaltene particle size and particle size distribution. The first five parameters are analyzed using Escobedo and Mansoori (2010), Cleaver and Yates (1975) and Friedlander and Johnstone (1957) asphaltene deposition models. The last parameter (asphaltene particle size distribution) is not directly included in the asphaltene deposition models. Therefore, a dynamic well column model is generated by combining transport phenomena (mass, heat and momentum transfer) equations with thermodynamic models. The model is fine-tuned and verified based on field data from an Iranian producing oil well with frequent asphaltene deposition problem and subsequently used for predicting the time-dependent development of the asphaltene deposition profile in the well column for a series of asphaltene particle size distributions. The results show the effect of the said parameters depends on how the buffer layer and Brownian motion are defined. The Escobedo and Mansoori (2010) model is found to make better predictions of deposited asphaltene in the studied well.

Asphaltene Formation Damage Stimulation by Ultrasound: An Analytical Approach Using Bundle of Tubes Modeling

This study presents a novel approach for bundle of tubes modeling of permeability impairment due to asphaltene-induced formation damage attenuated by ultrasound which has been rarely attended in the available literature. Model uses the changes of asphaltene particle size distribution (APSD) as a function of time due to ultrasound radiation, while considering surface deposition and pore throat plugging mechanisms. The proposed model predicts the experimental data of permeability reduction during coinjection of solvent and asphaltenic oil into core with reasonable agreement. Viscosity variation due to sonication of crude oil is used to determine the fluid mobility applied in the model. The results of modeling indicate that the fluid samples exposed to ultrasound may cause much less asphaltene-induced damage inside the porous medium. Sensitivity analysis of the model parameters showed that there is an optimum time period during which the best stimulation efficiency is observed. The results of this work can be helpful to better understand the role of ultrasound prohibition in dynamic behavior of asphaltene deposition in porous media. Furthermore, the present model could be potentially utilized for modeling of other time-dependent particle induced damages.

Special Issue

Formation damage refers to the impairment of petroleum-bearing formations by various adverse phenomena occurring in a manner to reduce the recovery of oil and gas from petroleum reservoirs. Evaluation and mitigation of formation damage in petroleum reservoirs are among the issues of primary interest for the operators in order to accomplish the economically effective production strategies during the productive life of petroleum reservoirs and to maximize the ultimate oil and gas recovery. However, circumventing the formation damage problems is a highly challenging undertaking because the formation damage phenomena involve many inherently complex interaction processes between the operation conditions and configuration of wells, the reservoir and externally-introduced fluids and particulate matter, and the constituents and conditions of the petroleum-bearing formations. This special issue presents ten papers providing information on the recent advancements made in the experimental, theoretical, and field understanding of the practical formation damage issues and the optimal measures and strategies considered for controlling and minimizing the reservoir formation damage.J. M. Schembre and A. R. Kovscek carry out laboratory core tests, apply the theory of colloidal stability, and demonstrate that high temperature, alkaline, and pH, and low salinity conditions induce fines mobilization and permeability reduction in Berea sandstones.A. Hayatdavoudi explains that the water hammer phenomenon created during the various injection and production operations may cause the sand liquefaction and production. The pressure wave-induced acceleration of the sand particles is shown to be highly sensitive to the water level variation and/or water encroachment in unconsolidated sand formations.K. J. Leontaritis presents a model for the near-well formation damage caused as a result of pore throat plugging by asphaltene particles during oil production. This model incorporates the thermodynamic-colloidal model of asphaltene in oil and an asphaltene phase behavior model for prediction of the asphaltene particle size distribution and its affect under the prevailing fluid conditions.E. J. Mackay and M. M. Jordan describe the scaling potential and formation damage due to precipitation of inorganic scales during conventional waterflooding in deepwater regions associated with the offshore production environments. The various risk management strategies for effective scale control are reviewed by means of reservoir simulation.H. A. Nasr-El-Din discusses the measures required to minimize and control the various formation damage problems caused by the common chemical treatment techniques originally designed to remove the particular formation damage problems.C. Li, T. Xie, M. Pournik, D. Zhu, and A. D. Hill apply a fine-scale model for the sandstone core acid flooding process by numerically solving the acid and mineral balance equations for a three-dimensional flow field. The reservoir heterogeneities are shown to cause the acid to penetrate much farther from the injection face into the formation than for a homogeneous case.G. Penny, J. T. Pursley, and D. Holcomb demonstrate by laboratory core tests and field examples that a new microemulsion additive helps for effective cleanup of injected fluids in tight gas formations. The applications involving the remediation and fracture treating of coals, shales, and sandstone reservoirs result in lower formation damage and higher production rates.D. B. Bennion and F. B. Thomas review the formation damage mechanisms associated with very low in-situ permeability gas reservoir formations, emphasizing on the relative permeability and capillary pressure effects leading to phase trapping. The challenges encountered during the drilling and completion practices in order to minimize the impact of formation damage on the well productivity are described.H. Jahediesfanjani and F. Civan investigate the damage tolerance of the conventional well-completion and stimulation techniques in reducing the formation damage effects and increasing the productivity of the coalbed methane reservoirs. The efficiency and performance of the openhole cavity completions, hydraulic fracturing, frack and packs, and horizontal wells are compared with a nondamaged vertical well in terms of the normalized productivity index.Y. Ding and G. Renard present an integrated approach for evaluation of the performance of oil and gas wells after drilling induced formation damage by means of a near-wellbore modeling using the input data obtained by laboratory tests.

Asphaltene Near-well-bore Formation Damage Modeling

When during oil production the thermodynamic conditions within the near-well-bore formation lie inside the asphaltene deposition envelope of the reservoir fluid, the flocculated asphaltenes cause formation damage. Mathematically, formation damage is a reduction in the hydrocarbon effective mobility, λ, λ=ko∕μo=kkro∕μo. Three possible mechanisms of asphaltene-induced formation damage have been discussed in the literature. Asphaltenes can reduce the hydrocarbon effective mobility by a) blocking pore throats thus reducing the rock permeability, k, b) adsorbing onto the rock and altering the formation wettability from water-wet to oil-wet thus diminishing the effective permeability to oil, ko, and c) increasing the reservoir fluid viscosity, μo, by nucleating water-in-oil emulsions. In the most frequently encountered case of asphaltene-induced formation damage where under-saturated oil is being produced without water, the most dominant damage mechanism is blockage of pore throats by asphaltene particles causing a reduction in rock permeability k. This paper presents a rather simple, yet realistic way of modeling asphaltene-induced near-well formation damage caused by blockage of pore throats by asphaltene particles. The model utilizes both macroscopic and microscopic concepts to represent the pore throat blockages. It also utilizes the Thermodynamic-Colloidal Model of Asphaltene, TCModelSM, an existing AsphWax asphaltene phase behavior model capable of simulating the asphaltene particle size distribution as a function of the thermodynamics of the system. The new asphaltene near-well formation damage model is applied in one case where it is used to track the degree of formation damage as a function of time and the effect it has on near-well-bore and well-bore hydraulics. Similarly the model can be used to study a priori the economics of developing a reservoir known to contain under-saturated asphaltenic oil.

Thermodynamic Model of Petroleum Fluids Containing Polydisperse Asphaltene Aggregates

New version of thermodynamic aggregation model of asphaltene-containing crude is formulated and analyzed with regard to characteristics of resin molecule shape and deformation of the resin shell of the asphaltene aggregates. The relation between the shape factors and elastic constants is discussed, and their effect on the size distribution of asphaltenic aggregates is considered. The model is applied to describe asphaltene precipitation from petroleum fluid upon its dilution with a liquid alkane. The effect of dilution on the asphaltene particle size distribution is studied. The model calculation has shown that the behavior of asphaltenic crude varies dramatically with the change of molecular characteristics of resins.