Asphaltene Adsorption Research Articles

A novel test method for evaluate asphaltene inhibitor efficiency on reservoir rock

Asphaltene deposits can reduce the productivity of the reservoir as well as foul piping and surface equipment. Current chemical and mechanical methods for treating deposition are only partially effective partly because the deposition process is poorly understood. The most commonly way to asphaltene precipitation reduction is applying an asphaltene inhibitor. In order to investigate the extent of formation damage by asphaltenes in crude oil this work has used electro kinetic technique to study the adsorption of asphaltenes in rock pores. Most researchers investigate the kinetics of adsorption by monitoring changes in the concentration of asphaltene or polymer in a dispersion of adsorbent particles or capillaries. This study is a coherent approach to measure amount of asphaltene adsorption on rock surface and survey effect of asphaltene inhibitors on precipitation reduction in porous media.

Development of Nanofluids for Perdurability in Viscosity Reduction of Extra-Heavy Oils

The primary objective of this study is the development of nanofluids based on different diluent/dispersant ratios (DDR) for extra-heavy oil (EHO) viscosity reduction and its perdurability over time. Different diluents such as xylene, diesel, n-pentane, and n-heptane were evaluated for the formulation of the carrier fluid. Instability of asphaltenes was assessed for all diluents through colloidal instability index (CII) and Oliensis tests. Rheology measurements and hysteresis loop tests were performed using a rotational rheometer at 30 °C. The CII values for the alkanes type diluents were around 0.57, results that were corroborated with the Oliensis tests as asphaltenes precipitation was observed with the use of these diluents. This data was related to the viscosity reduction degree (VRD) reported for the different diluents. With the use of the alkanes, the VRD does not surpass the 60%, while with the use of xylene a VRD of approximately 85% was achieved. Dimethylformamide was used as a dispersant of the nanoparticles and had a similar VRD than that for xylene (87%). Subsequent experiments were performed varying the DDR (xylene/dimethylformamide) for different dosages up to 7 vol % determining that a DDR = 0.2 and a dosage of 5 vol % was appropriated for enhancing EHO VRD, obtaining a final value of 89%. Different SiO2 nanoparticles were evaluated in the viscosity reduction tests reporting the best results using 9 nm nanoparticles that were then included at 1000 mg·L−1 in the carrier fluid, increasing the VRD up to 4% and enhancing the perdurability based on the rheological hysteresis and the viscosity measurements for 30 days. Results showed a viscosity increase of 20 and 80% for the crude oil with the nanofluid and the carrier fluid after 30 days, respectively. The nanoparticles have a synergistic effect in the viscosity reduction and the inhibition of the viscoelastic network re-organization (perdurability) after treatment application which was also observed in the rheological modeling carried out with Cross and Carreau models as the reported characteristic relaxation time was increased almost a 20%. Moreover, the Vipulanandan rheological model denotes a higher maximum stress value reached by the EHO with the addition of nanofluids which is derived from the EHO internal structure rearrangement caused by the asphaltenes adsorption phenomenon.

A new insight into Fe3O4-based nanocomposites for adsorption of asphaltene at the oil/water interface: An experimental interfacial study

Abstract Concerning the potential positive role of water in oil emulsification in enhancing oil recovery, the current research builds on finding reasons responsible for the considerable water in oil emulsification observed in the produced fluid during carbonate sand pack floodings in the previous works. Allowing a systematic comparison, the results on floodings of three Fe3O4-based nanocomposites were selected from previous studies. The XRD and FESEM of nanocomposites, zeta potentials, stability of synthetic emulsions, IFT, bulk and interfacial oil/water viscosities, and asphaltene adsorption in the presence of nanocomposites were analyzed. The XRD and FESEM results showed a successful synthesis for all nanocomposites. Zeta potential measurements showed values far above −40 mV, which confirm a good stability for all nanocomposites in the base fluid. In terms of emulsion stability, microscopic images showed that all synthesized nanocomposites had better performance in stabilizing synthetic emulsion droplets as compared to Fe3O4 NPs. IFT measurements indicated an 18–21 mN/m decrease with the addition of nanocomposites to the seawater. The bulk viscosity measurements indicated that Fe3O4/Chitosan nanocomposites present in the aqueous phase increase the water/oil (30/70 vol%) emulsion viscosity up to 334 cp. The interfacial viscosity measurements also showed a reduced oil/water interfacial viscosity by the addition of nanocomposites to the aqueous phase, which is probably due to the increased presence of asphaltene molecules at the interface. In the end, the absorbed asphaltene particles by nanocomposites were measured using batch adsorption experiments and fitted to the BET adsorption isotherm. The results showed that by deploying at the interface, Fe3O4-based nanocomposites are highly capable of asphaltene adsorption, which can stabilize the water in oil emulsions.

In Situ Monitoring of the Inhibition of Asphaltene Adsorption by a Surfactant on Carbon Steel Surface

Simple surfactants have proven to be some of the most effective agents to mitigate the deposition of asphaltenes on pipeline walls; however, the best practices for their application are often empir...

Experimental investigation of dynamic asphaltene adsorption on calcite packs: The impact of single and mixed‐salt brine films

AbstractIn this study, the dynamic adsorption of asphaltene on a calcite surface is investigated. This study investigates the effect of mixed‐salt brines on asphaltene adsorption. The results of this work can facilitate the understanding of the complex wettability behaviour of carbonate reservoirs. All experiments were performed in porous media, which were sand‐packs filled with calcite powder, to study the influence of the type and concentration of salt on adsorption. The experiments were conducted with asphaltene concentration of 500 mg/L for brines of NaCl, Na2SO4, and a mixture of the two at various ionic strengths. In addition, two tests were performed with an asphaltene concentration of 2000 mg/L to observe the effect of increasing the asphaltene concentration on the adsorption. Moreover, the impact of brine film on asphaltene adsorption was investigated by conducting an additional experiment without brine saturation. The results show that by increasing the ionic strength, asphaltene adsorption increased at first owing to the reduction of electrostatic forces, then it reached its maximum, and it finally decreased as a result of the rise in the hydration force. The results show that in the presence of Na2SO4 brine, the asphaltene adsorption is more than that of the NaCl brine. For the mixed‐salt brine, as the ionic strength was increased, the asphaltene adsorption decreased at first and then it became constant. Furthermore, quadrupling the initial asphaltene concentration increased the adsorption up to 3.4 times. Additionally, the presence of brine film reduced the asphaltene adsorption by ∼80 %.

Experimental and mathematical model evaluation of asphaltene fractionation based on adsorption in porous media: Part 1. calcite reservoir rock

This study investigates the properties of asphaltene fractions in porous media and their role in reducing permeability and porosity. Based on the classification of a whole asphaltene deposited in porous media, the fractions can be defined as bulk, hard (h)-adsorbed, normal (n)-adsorbed, and irreversible (i)-adsorbed, which effects on porosity and permeability reduction in the reservoir rock. According to laboratory results for five types of calcite cores with porosity and permeability close to each other, the highest reduction in porosity (55%) and permeability (76%) is related to bulk asphaltene fractions. The n-adsorbed and h-adsorbed asphaltenes have approximately equal influence in reducing the porosity and permeability values in the reservoir rock. The i-adsorbed asphaltene, which has the highest adsorption on the rock surface, has the lowest porosity and permeability decrease due to lower amounts of asphaltene deposits in porous media. The amounts of hydrogen (H), nitrogen (N), sulfur (S), and oxygen (O) are higher in adsorbed fractions of asphaltene. In the case of h-adsorbed asphaltene, H has the highest value in the asphaltene fractions (7.13 wt%). Compared with adsorbed asphaltene fractions, N values are higher in n-adsorbed (1.89 wt%) than h-adsorbed (1.41 wt%) fractions. This suggests that the S element plays a more significant role in the adsorption of asphaltene to the calcite surface. Based on the results, asphaltene compounds that adhere to the rock surface contain lighter carbon compounds than whole asphaltene. This means that the peak of the carbon compounds of h-adsorbed asphaltene in each rock sample is C17. Fourier-transform infrared spectroscopy (FTIR) results show that the highest concentrations of carbonyl, carboxylic acid or derivative groups are found in h-adsorbed and n-adsorbed asphaltenes, respectively. A new experimental model of asphaltene deposition has been presented based on the deposition analysis of each asphaltene fraction in a porous medium under dynamic conditions, which results in a high correlation coefficient for each of the asphaltene classifications in the porosity and permeability reduction model. The reason for the high accuracy and uniqueness of the model is the use of parameters such as the velocity of fluid flow in the pores and the amount of volume injected in the reservoir rock sample, as well as the asphaltene fractions and their polarization ratio.

Characterization of Nanosilica and Comparing Its Effect on Crude Oils and Diesel Fuel

Heavy oils generally exhibit high viscosity, which is detrimental to their production, transport, and refining. The Oil & Gas industry has thoroughly investigated the use of chemical agents to improve the mobility of this type of low-quality crude oils at the surface as well as reservoir conditions for many years. In this sense the main objective of this work is to investigate the viscosity reduction of heavy oil resulting from the presence of silica nanoparticles by asphaltene adsorption process. Silica nanoparticles was produced successfully in this work from sand of Mount Sannam in Basra city (south of Iraq) by chemical and physical methods (SiO 2ch and SiO 2ph respectively). The XRD results indicated a high purity SiO 2ch NPs was produced with purity of 96.8%, while, the purity of SiO 2ph NPs was about 87.2%. The main particle size analyzer (PSA) were measured to be 35 nm and 22 nm for SiO 2ch and SiO 2ph respectively. On the other hand, the BET total surface area of SiO 2ch and SiO 2ph NPs were 520 m 2 /g and 705 m 2 /g respectively. Also, the SEM results showed a uniform distribution of nanoparticles for both prepared silica nanoparticles. The FTIR results indicated a high intensity bonds were formed due to present of functional groups of Si-O-Si, O-Si-O and Si-O. Two Iraqi crude oil samples was selected to be as base fluid with APIs (17.4 and 29.1). Also, diesel fuel with API= 40.91 was tested. For each hydrocarbon a nanofluid was prepared by adding silica nanoparticles to parent fluid. Four concentration of silica nanoparticles were added to the parent fluid (250, 500, 1000 and 1250 mg/L). And also, used a bath ultrasonic method for dispersing NPs inside the parent oils. Keywords: Petroleum Pipelines; natural nanoparticles; viscosity reduction; silica preparation; silica characterization; asphaltene adsorption; crude oil DOI : 10.7176/JNSR/9-4-08

Experimental investigation of stability of water in oil emulsions at reservoir conditions: Effect of ion type, ion concentration, and system pressure

Different ions present in formation water (FW) and aqueous phases injected into the oil reservoirs can affect the formation and stability of water-in-oil (W/O) emulsions. Previous studies regarding this issue devoted attention to the chemical compounds of the oil and water with a partial focus on different parameters at ambient pressure and temperature. However, pressure can multilaterally control the formation of emulsification phenomena. One important factor of emulsion stability is the asphaltene that is present in the crude oil. These particles are subjected to instability when they encounter a change in chemical composition and pressure, which affects the formation and stability of the emulsion. In this study, emulsification at various pressures and salinity were analyzed to determine the role of affecting factors, including asphaltene and various ions in the aqueous phase. The apparatus used for monitoring the emulsification was a HP-HT Emulsion Analyzer, designed and constructed by our research group. According to the results, the type and concentration of cations present in the aqueous phase govern the stability of the emulsion. At low salinities (i.e. up to 10,000 ppm), the emulsion stability increases and then decreases with increasing salt concentration in the water phase. At high pressures (i.e. from 4000 to 6000 psi), divalent cations form a more stable emulsion in comparison with monovalent ones. In addition, among divalent cations, Mg2+ introduces a more stable emulsion than that of Ca2+. Based on the results, the thermodynamic conditions affect the precipitation and deposition of asphaltene. Since dead oil was used in this research, the emulsion stability decreases with a decreasing asphaltene content at the interface at high pressures (i.e. 4000–6000 psi). This is due to the considerable reduction in the number of emulsifiers at the interface. Therefore, at high pressures, pressure increase reduces the emulsion stability. However, at low pressures (i.e. from 14.7 to 4000 psi), the increase in shear energy and asphaltene adsorption at the interface by ions overcomes the decrease in asphaltene due to its increased solubility. Therefore, at low pressures, pressure increase raises the emulsion stability.

Application of Novel Fe3O4–Polyaniline Nanocomposites in Asphaltene Adsorptive Removal: Equilibrium, Kinetic Study and DFT Calculations

Recent investigations have shown that surface modification can improve the colloidal stability and chemical properties of the metallic nanoparticles. In this study, poly aniline (PANI) coated Fe3O4 nanoparticles were synthesized and used for asphaltene adsorption. The prepared nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, Fourier-transform infrared spectroscopy and vibrating-sample magnetometer techniques. The effects of adsorbent amount, initial asphaltene concentration and heptane to toluene volume ratio on the sorbents adsorptive capability were studied. The experimental sorption isotherm data was fitted to the Langmuir isotherm model for coated and uncoated adsorbents. The kinetic data was consistent with Pseudo second order kinetic model. Asphaltene adsorption on Fe3O4/PANI composite was much higher than pure Fe3O4 due to the significant π–π interactions between asphaltene and adsorbent and stability effect of PANI. The results indicated that PANI coated Fe3O4 is an appropriate candidate for crude oil upgrading. Moreover, density functional theory calculations confirm that the adsorption energy of asphaltene over the Fe3O4/PANI composite is larger than that over the bare Fe3O4. This can be mainly attributed to the more favorable orbital interactions as well as charge-transfer effects between asphaltene and PANI in the former system.

A Complete experimental study of oil/water interfacial properties in the presence of TiO2 nanoparticles and different ions

Previous studies on Nanoparticles (NPs) application for Enhanced Oil Recovery (EOR) methods have revealed their effective role in the rock wettability alteration, relative Interfacial Tension (IFT) and oil viscosity reduction, formation and stabilization of the emulsions, and reduced asphaltene precipitation, which are all in direct relationship with oil/water interfacial properties. This study focuses on the interfacial properties of oil/water in the presence of Titania NPs and different ions at different pressures and temperatures. For this, different concentrations of TiO2 NPs in the Formation Water (FW) were prepared to monitor the effects of NPs on the oil/water IFT, carbonate rock wettability, zeta potential, and asphaltene adsorption. The results on IFT values indicated that NPs behavior at high pressures and temperatures is completely different, as compared to the ambient conditions, and 1000 ppm NPs introduced the lowest IFT at 600 psi and 60 °C. This reduction is potentially attributed to the asphaltene adsorption at the oil/water interface by TiO2 NPs, which hinders the asphaltene deposition at the interface and in turn IFT increasing. Contact angle results revealed two distinctive behaviors for NPs at high and low concentrations. In other words, with the first interval (below the optimum concentration), an increase in NPs concentration led to a quick wettability alteration toward the water-wet condition, and with the second one (above the optimum concentration), there was an increase in contact angle with an increase in NPs concentration, which is due to the NPs stacking near the rock surface. These results were in good accordance with zeta potential measurements, in which 1000 ppm nanofluid presented the highest stability (zeta potential value of −46.9 mV). Batch adsorption experiments resulted that catalytic TiO2 NPs are capable of adsorbing asphaltene at the oil/water interface. In addition, the results on fitting experimental data to the Langmuir and Freundlich Isotherms showed that the adsorption best fitted Langmuir Isotherm and hence the adsorption type is a monolayer.

Influence of silica nanoparticles on heavy oil microrheology via time-domain NMR T2 and diffusion probes

The objective of the present work is to determine the effect of silica nanoparticles on the microrheological properties of heavy and extra-heavy crude oils using time-domain nuclear magnetic resonance (TD-NMR) methods. Three heavy crude oils with different asphaltene contents were studied. The oils steady-state rheograms were collected as a function temperature and nanoparticles concentration. Transverse relaxation time (T2) and diffusion coefficient measurements were used as probes of the crude oils microrheological responses. A clear inverse correlation between either the log-mean T2 (T2,LM) or the diffusion coefficient and the rheometric oil viscosity in the presence of nanoparticles was found. Results further show the likely existence of an optimal concentration of nanoparticles in the vicinity of 1000 mg/L. The maximum viscosity reduction of roughly 35–45% was observed for the three heavy crude oils. The heavy oil refractive index decreases after the oil was placed in contact with nanoparticles, confirming adsorption of polar material on nanoparticles. T2 and the diffusion coefficient increase in the apparent region of optimal concentration of nanoparticles and decrease at higher concentration. The improved NMR responses, which reflect the enhanced translational and rotational motion of restricted hydrogen-bearing oil molecules/aggregates proves that microrheological changes occur as oil polar molecules aggregates break down due to the adsorption of asphaltenes. Finally, a multivariate statistical analysis evidences which parameter has the greatest influence on the system response. It is the first time, to the best of our knowledge, that these characterization tools have been used in heavy crude oils in the presence of nanoparticles.

Optimization of Fe3O4/Chitosan nanocomposite concentration on the formation and stability of W/O emulsion

Asphaltene plays a major role in the emulsion stability as an emulsifier. The Fe3O4/Chitosan nanocomposite is one of the nanocomposites that are newly studied for asphaltene adsorption. Thus, the presence of the referred nanocomposite in the aqueous phase and adsorption of asphaltene can affect the formation and stability of the water in oil emulsion. In this study, we examined the synthesis of Fe3O4/Chitosan and compared two iron oxide and chitosan nanoparticles in terms of the formation and stability of the emulsion. We studied the role of asphaltene in the formation and stability of the emulsion in the presence of nanocomposite by measuring the interfacial viscosity and the elasticity modulus. Also, we quantified the emulsion stability by measuring the average area of water droplets in oil, the bulk viscosity, and the interfacial tension. According to the results of this study, the synthesized nanocomposite was able to further stabilize the emulsion than its constituent compounds. Based on the results from measuring the interfacial viscosity, elasticity modulus, and electrical conductivity, the nanocomposite forms a stable emulsion through the adsorption of asphaltene and placement at the interface of water and oil. By increasing the concentration of nanocomposites up to 0.05% by weight, the size of water droplets in oil decreased, the interfacial tension decreased, and consequently the stability of the emulsion increased.

Asphaltene Adsorption from Toluene onto Silica through Thin Water Layers.

Asphaltenes in crude oil play a pivotal role in reservoir oil production because they control rock-surface wettability. Upon crude oil invasion into a brine-filled reservoir trap, rock adherence of sticky asphaltene agglomerates formed at the crude oil/brine interface can change the initially water-wet porous medium into mixed-oil wetting. If thick, stable water films coat the rock surfaces, however, asphaltenic-oil adhesion is thought to be prevented. We investigate whether water films influence the uptake of asphaltenes in crude oil onto silica surfaces. Water films of known thickness are formed at a silica surface in a quartz crystal microbalance with dissipation and contacted by toluene-solubilized asphaltene. We confirm that thick water films prevent asphaltene molecular contact with the silica surface blocking asphaltene adhesion. The thicker the water film, the smaller is the amount of asphaltene deposited. Film thickness necessary for complete blockage onto silica is greater than about 500 nm, well beyond the range of molecular-chain contact. Water films of thickness less than 500 nm, sandwiched between toluene and solid silica, apparently rupture into thick water pockets and interposed molecularly thin water layers that permit asphaltene adherence.

An experimental and modeling study of asphaltene adsorption by carbon nanotubes from model oil solution

The adsorption of asphaltene on the surface of nanoparticles in the crude oil industry is a significant issue. In this regard, carbon nanostructures can be applied as an adsorbent for the removal of asphaltene from crude oil. In this paper, carbon nanotubes (CNTs) were used for the adsorption of three different asphaltenes from toluene solutions. The CNTs were synthesized by Chemical Vapor Deposition (CVD) method. The synthesized CNTs were characterized by Brunauer–Emmett–Teller (BET), Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM). The asphaltenes were analyzed by X-ray Diffraction (XRD) and elemental analysis techniques. In addition, asphaltene adsorption isotherms and kinetics were offered. The adsorption of asphaltene was fast since equilibrium was reached in 1 h. The kinetic data were fitted well to the pseudo-second-order kinetic model. The equilibrium data of asphaltene A and B was fitted well to the Freundlich model. However, for asphaltene C, Temkin model was consistent with the experimental data due to the strong interactions between asphaltene C and surface arising from pyridinic, pyrrolic, sulfide and disulfide functional groups which existed on the surface of asphaltene C. The results indicated that the capacity and affinity depend on the molecular structure of the asphaltenes. The high adsorption capacity of asphaltene A was attributed to its high aromaticity. An increase in the aromatic nature of asphaltenes increases the self-association of asphaltenes and π−π interactions between asphaltenes and CNTs, which increases the asphaltene adsorption. The thermodynamic parameters indicated that the adsorption of asphaltenes on CNTs is exothermic and spontaneous. According to the results, CNTs showed high adsorption capacity and can be considered as an appropriate choice for asphaltene removal from crude oil.

Effects of the N, O, and S heteroatoms on the adsorption and desorption of asphaltenes on silica surface: A molecular dynamics simulation

The adsorption and desorption of asphaltene on silica surface is highly dependent on the heteroatoms present in its structure. Herein, some model asphaltene molecules with different heteroatoms (i.e., N, O, S) at different positions (in the aromatic cores, in the middle and termination of alkane side chains) are selected as the adsorbates to investigate their adsorption and desorption behaviors on silica surface through molecular dynamics (MD) simulation. Results reveal that the characteristic adsorption configuration of asphaltenes is ascribed to the competition between the asphaltene-silica interaction and π–π stacking interaction among the asphaltene polyaromatic rings. The presence of heteroatoms is found to be able to strengthen the interactions between asphaltenes and silica, depending on their type and location. For example, the terminal polar groups, especially the carboxyl (COOH), exhibit the greatest contribution to the electrostatic interaction (increasing from −81 to −727 kJ/mol). The S atoms are also found to increase the van der Waals interaction energies by 25%. According to the equilibrium desorption conformation and density profile, the presence of heteroatoms is found to significantly hinder the desorption of asphaltenes from silica due to the enhanced polar interactions. The impeded desorption is also confirmed by the slower detachment of asphaltenes based on the time-dependent interaction energies and center of mass (COM) distances analysis. Additionally, the terminal polar groups lead to extraordinary desorption properties of asphaltenes. It is observed that the strong asphaltene-silica and asphaltene-water interactions coexist in these systems due to the high polarity and hydrophilicity of the terminal polar groups.

Shape evolution of a water drop in asphaltene solution under weak DC electric fields

The microscopic shape change of a pendent water drop, surrounded by an organic solution containing asphaltenes extracted from heavy crude oil, under electric field is investigated. Weak constant DC electric fields were applied in the direction perpendicular to gravity. The asphaltenes extracted from a heavy crude oil from Norwegian continental shelf were mixed in xylene at low concentrations. The simultaneous action of electric field and the asphaltene adsorption at the drop interface determines the shape of drop. Upon application of the electric field the drop exhibits instantaneous deformation in the direction of the field. Interestingly, the subsequent shape change occurs perpendicular to the field direction. The drop shape is observed to be asymmetric about both axes and the asymmetry intensifies with magnitude of the applied field and the concentration of asphaltenes in the surrounding medium. We thoroughly analyzed the temporal changes in shape features of the drop, which was held in the asphaltene solution for an hour. The influence of a range of concentrations and electric field strengths is investigated. The counter-intuitive shape development and the asymmetry are attributed to the electric field-reinforced asphaltene mass transport at the drop interface and the resultant interfacial properties.

The role of calcite and silica interfaces on the aggregation and transport of asphaltenes in confinement

The structure and transport of the heavy asphaltene molecules in unconfined bulk fluids and fluids confined in a 4 nm slit-shaped nanopores of calcite and silica were studied using classical molecular dynamics simulations. The pores were filled with 7 wt% of asphaltene dissolved in an equimolar solvent of heptane and toluene. The mixture was considered since asphaltenes are insoluble and soluble in heptane and toluene, respectively. Our studies showed that asphaltene molecules tended to aggregate in unconfined bulk fluids to form a large cluster composed of all the asphaltene molecules. However, the size of nanoaggregates is smaller in the confined fluidic environments due to the adsorption of asphaltenes on silica or calcite surfaces. The aggregation and adsorption of asphaltenes initially located in the bulk fluid occurred at the pore entrances of calcite and silica. However, the asphaltene molecules located within the pore were adsorbed onto the pore surface. Further, confinement influenced the structure of the solvent. Toluene showed preferential adsorption for the calcite and silica surfaces over heptane due to differences in the polarities of these molecules. The adsorption behavior of the asphaltenes and solvents prove that the chemistry of the surfaces and edges have a crucial role in determining the structures of confined hydrocarbons. Further, confined fluids had a significant influence on the diffusivities of the asphaltenes and the solvents. Asphaltene and toluene diffusivities in confined fluids are lower compared to in bulk fluids. Further, the diffusivities of asphaltene with a higher molecular weight in confined and bulk fluids were lower compared to asphaltenes with lower molecular weights. The aggregation of asphaltenes proceeded via π-π stacking arising from the van der Waals affinity between the polyaromatics cores. These findings have important implications for predicting the influence of earth-abundant solid interfaces on the aggregation and transport behavior of complex heavy hydrocarbon molecules such as asphaltenes which are known to cause challenges in flow assurance for the recovery of hydrocarbons at the field-scale.

Application of low-field, 1H/13C high-field solution and solid state NMR for characterisation of oil fractions responsible for wettability change in sandstones

Asphaltene adsorption on solid surfaces is a standing problem in petroleum industry. It has an adverse effect on reservoir production and development by changing rock wettability, plugging pore throats, and affects oil transport through pipelines. Asphaltene chemistry constitutes important part of the ageing process as part of petrophysical studies and core analysis. The mechanisms and contribution of various oil components to adsorption processes is not fully understood. To investigate the kinetics of the ageing process and address the relative contribution of different oil components, we prepared three sets of sandstone core plugs aged in different oil mixtures over various time intervals. Cores were then re-saturated with decane to evaluate their wetting state using low-field NMR relaxometry by monitoring a change of surface relaxivity. Adsorbed deposits were then extracted from cores for solution-state NMR analysis. Their 1H and 1H-13C correlation spectra obtained using heteronuclear single quantum coherence (HSQC) technique were matched to spectra of four SARA (saturates, aromatics, resins and asphaltenes) components of oil mixtures to deduce components of deposits and inter-component interactions. We notice that wettability reversal of rock is inversely proportional to initial asphaltene concentration. Analysis of deposits reveals an increase in their aliphatic content over ageing time, which is accompanied by a change of the morphology of the pore space due to cluster aggregates forming a network. Results suggest that the ageing process in respect to the wetting state of rock samples consists of three distinctive stages: (i) an early-time period, when the fraction of most polar asphaltenes creates a discontinuous layer corresponding to mixed-wet state; (ii) an intermediate-time interval, at which the full grain coverage may be achieved (at favourable chemical environment) corresponding to strong oil-wetting; (iii) a late-time stage, where intense macro-aggregates accumulation occurs, changing the pore space integrity. It is likely asphaltene-aliphatic interactions leading to growth of sub-micron size macro-aggregates.

Potential effects of metal oxide/SiO2 nanocomposites in EOR processes at different pressures

This study intends to take a new look at the application of NPs as a nanocomposite form for the first time to gain the most from the effects of them for EOR purposes. For this, TiO2/SiO2 and Fe3O4/SiO2 nanocomposites were first synthesized and investigated for EOR purposes by different experiments, including contact angle, interfacial tension (IFT), injected fluid viscosity, NPs retention in porous medium and carbonate sand pack floodings. The results showed that each NP and nanocomposite presents a distinctive behavior depending on the pressure of the porous medium, with all bringing higher oil production compared to that of seawater (SW) injection. At the ambient pressure, the dominant mechanism during TiO2 and TiO2/SiO2 nanofluid injection was found to be the IFT reduction along with wettability alteration. Whereas, at the intermediate pressure (1500 psi), the wettability alteration by TiO2 NPs and TiO2/SiO2 nanofluids was regarded to be the dominant EOR mechanism and recorded a recovery factor of 60 and 72%, respectively. At the high pressure (3500 psi), the dominant mechanism was observed to be asphaltene adsorption by Fe3O4 NPs and Fe3O4/SiO2 nanocomposites leading to the ultimate recovery factor of 56 and 69%, respectively. The highest incremental recovery for NPs was observed for tertiary injection of SiO2 nanofluid at 1500 psi, which increased the oil recovery by 14%. Whereas, Fe3O4/SiO2 and TiO2/SiO2 nanofluids increased the oil recovery by 24 and 23% at the pressures of 3500 and 1500 psi, respectively. This confirms the efficient role of the synthesized nanocomposites for improved oil recovery. Finally, the results of absorbance measurements of the inlet and outlet of the sand pack during Fe3O4/SiO2 nanofluid injection indicated a 32.4% NPs retention in the porous medium.

Adsorption of asphaltenes on mixed oxide synthesized by auto-combustion method

The oil classified as heavy is the one with the largest number of deposits at present. However, these deposits are usually difficult to exploit since they contain a high concentration of asphaltenes which cause problems in the refineries at the time of extraction. Different strategies were used to decrease the effects of asphaltenes, being the most effective the use of adsorbents based on metal oxides. This is because metal oxides prevent the re-precipitation of asphaltenes under oil extraction; these methods can be easy implemented in modern refineries.In this work, we propose the synthesis of mixed oxide (Ni(3/2)xFe2-xO4) by self-combustion technique, being then used as an effective asphaltene adsorbent. Its asphaltene adsorption capacity was compared with nickel oxide and hematite, which were synthesized by controlled precipitation. The oxides were characterized by the techniques of X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR); their morphological characterization was carried out by scanning electron microscopy (SEM). The capacity of adsorption of asphaltenes was determined with the technique of UV-Vis spectroscopy. The results show that the Ni(3/2)xFe2-xO4 is a good adsorbent being compared with hematite and nickel oxide, both for asphaltenes with ether and amino groups. The mixed oxide shows a mayor affinity to asphaltenes containing amino groups, being compared with the hematite and nickel oxide; in addition, the mixed oxide has a low affinity to petroleum, which makes it selective to asphaltenes.