Onset Of Asphaltene Precipitation Research Articles

Investigating Asphaltene Precipitation and Deposition in Ultra-Low Permeability Reservoirs during CO2-Enhanced Oil Recovery

CO2 flooding is an economically feasible and preferred carbon capture, storage, and utilization technology. Asphaltene deposition is a common problem in the process of CO2 injection because it may cause reservoir damage. The mechanism of asphaltene precipitation damage to the formation remains elusive. Experiments were conducted to reveal the pore-scale formation damage mechanism in ultra-low permeability reservoirs caused by asphaltene precipitation during CO2 flooding. Initially, the precipitation onset point for asphaltene within the crude oil-CO2 system was determined using a high-pressure tank equipped with visual capabilities. Subsequently, CO2 flooding experiments were conducted on ultra-low permeability cores under miscible and immiscible conditions, with the support of nuclear magnetic resonance (NMR) to quantitatively evaluate the impact of asphaltene precipitation on ultra-low permeability reservoirs. The results indicate that within the pressure range from the asphaltene precipitation onset point to the minimum miscibility pressure (MMP). The level of asphaltene precipitation rises as CO2 injection pressure increases. In the miscible flooding stage, asphaltene precipitation can still occur, but to a lesser extent. Notably, asphaltene deposition predominantly occurs in larger pores; above the MMP, the permeability decreases significantly as asphalt particles agglomerate, resulting in notable pore-throat blockages. While asphaltene deposition has a minimal impact on porosity, the bridging effect of asphaltene particles reduces permeability.

Effect of simulated flue gas on pentane-induced asphaltene precipitation in bitumen froth

In paraffinic bitumen froth treatment, a paraffinic solvent such as n-pentane is mixed with bitumen froth at a high solvent/bitumen ratio of 1.5 to 2.0. The purpose of the high solvent/bitumen ratio is to induce asphaltene precipitation which helps clean the bitumen so that it can be processed directly by a high-conversion refinery without the need of an upgrader. However, the high solvent/bitumen ratio inevitably increases the complexity and costs of the paraffinic froth treatment process. In this study, we have attempted to reduce the solvent/bitumen ratio without affecting asphaltene precipitation by replacing part of the solvent with simulated flue gas (CO2/N2 mixture at 200 °C). The n-pentane/bitumen ratio was varied from 0.8 to 2.2, CO2 concentration in the gas mixtures from 0 to 100 vol%, gas pressure from 0.1 to 1.7 MPa, and temperature at 21 °C and 90℃. Asphaltene contents in the bitumen products were measured following ASTM D4055, and the contents of water, solids, C, H, N, S in the products were measured by Karl Fischer titration, ashing and hot filtration, and CHNS elemental analysis. It was found that at the asphaltene precipitation onset n-pentane/bitumen ratio of 1.4 at 90 °C, the amount of precipitated asphaltenes was linearly correlated to the partial pressure of CO2; at the CO2 pressure of 1.7 MPa, about 50 % of the asphaltenes were precipitated, corresponding to an n-pentane/bitumen ratio of 2.2 when no CO2 was used. A solvent saving of about 36 % could therefore be achieved under these conditions without changing the quantity of asphaltene precipitation. The bitumen product quality was not affected when CO2 was used. This work provided useful information on the function of CO2 gas in assisting asphaltene precipitation, so that a lower n-pentane/bitumen ratio could be used, reducing process complexity and cost without affecting performance.

EVALUACIÓN DE UNA UNIDAD HPHT ACOPLADA CON SONDA NIR PARA DETERMINAR EL INICIO DE LA PRECIPITACIÓN DE ASFALTENOS BAJO DIFERENTES PRESIONES

Asphaltenes are characterized as the crude oil fraction with the highest molar mass and polarity, presetting mainly (poly) aromatic groups. The flocculation and deposition of asphaltenes causes large losses to the oil industry. Understanding the phase behavior of asphaltenes under conditions closer to those found in reservoirs is important. Therefore, LMCP/UFRJ started operating a high-pressure high-temperature (HPHT) unit coupled to a near-infrared spectrometer probe that can use different flocculants. This work describes the development of a procedure as well as the validation of the results obtained from this unit. Due to the complex composition of crude oil, model systems (MS) were prepared with asphaltenes extracted with n-pentane (C5I) and n-heptane (C7I). The experiments were carried out at atmospheric pressure, titrated with n-heptane, and at 100 and 300 bar titrated with propane. As expected, C7I asphaltenes were more unstable, presenting lower precipitation onset than C5I asphaltenes under ambient conditions and higher pressures. However, for both MS, the stability increased with rising pressure when using propane as a solvent. The proposed method to evaluate asphaltenes precipitation onset was effective for MS in toluene and dead crude oil, and is a promising alternative for investigation of different types of crude oil.

Polycardanol's potential to deasphalt crude oil: Influence of polymer conversion degree, molar mass, and structure

AbstractCardanol is a natural material that acts to stabilize asphaltenes in crude oil. However, its derivative, polycardanol, obtained via cationic polymerization, has divergent behaviour, with reports of its acting both as asphaltenes stabilizer and flocculant. Recently, it was demonstrated that the reaction conditions influence the conversion rates, structures, and molar masses of the products from synthesizing polycardanol initiated with BF3 · O(C2H5)2. Seeking to elucidate the influence of these variables on the phase behaviour of asphaltenes, in this work six products, previously synthesized and characterized, had their performance evaluated by asphaltenes precipitation onset, using n‐heptane titration and monitoring by near‐infrared spectroscopy, using asphaltenes model systems (C5I and C7I) at 1.00 wt./vol.% in toluene. All the products had the ability to flocculate asphaltenes and have potential for deasphalting process. Flocculation efficiency increased with rising molar mass, higher reaction conversion degree, and presence of lateral hydrocarbon chains. The most efficient structures were not affected by the presence of unreacted cardanol. This indicated that the reaction does not require a purification step. Aged cardanol was also able to produce flocculant polymer, indicating that the distillation of cardanol is not required. The cost to obtain a product without needing reagent distillation becomes lower.

Effect of Solvents on the Stability of Water-in-Bitumen Emulsions

In this study, the role of the solvent in stabilizing water-in-oil emulsions was investigated below and above the onset of asphaltene precipitation. Two Western Canadian bitumens with significantly different emulsion-stabilizing capacities were evaluated. Water-in-asphaltene/solvent and water-in-diluted bitumen emulsions were prepared with extracted n-heptane-insoluble asphaltenes, toluene, and an alkane (n-pentane, n-heptane, n-decane, n-hexadecane, and cyclohexane). The organic phases were prepared with and without removing any precipitated asphaltenes. The stability of the settled emulsions was assessed in terms of the free water evolved after treatment with heating and centrifugation. Factors that could contribute to emulsion stability were measured including the drop size distribution, water volume fraction, and asphaltene mass surface coverage of the settled emulsions. Surface pressure isotherms of asphaltene films were measured to assess irreversible interfacial film formation in each solvent. In precipitate-free emulsions, emulsion stability was found to increase significantly at the onset of precipitation. The increase in stability was attributed to the increased irreversible adsorption of asphaltenes at the interface as their solubility in the oil phase decreased. Most of the emulsions became less stable at high n-alkane contents as more asphaltenes were precipitated out of solution and the supply of soluble emulsion stabilizers was depleted. The results demonstrate that oils at conditions near the onset of asphaltene precipitation are more likely to experience problematic emulsions. However, it was found that, with low-viscosity solvents, this effect may be mitigated by the presence of the precipitated particles in the emulsion.

The effect of asphaltene molecular characteristic on the instability of Kuwaiti crude oils

Asphaltene precipitation and subsequent deposition are challenging problems that hinder the continuous production of crude oil in many fields worldwide. In the present work, advanced technologies were implemented to effectively assess the effect of asphaltene characteristics on its stability in different Kuwaiti oils. Physical and chemical properties of stock tank oils (STO) have been measured. The extracted asphaltenes from the different STOs were characterized using X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) spectroscopy techniques. The results showed that asphaltene with the lowest H/C ratios, the greatest aromaticity, and the highest degree of condensation exhibited a higher tendency to precipitate due to extreme variations in thermodynamic factors. The onset of asphaltene precipitation for crude oil was determined by the indirect method using three different n-alkane solvents. The onset of asphaltene precipitation was found to be around 40, 50, and 60 vol% of n-pentane, n-heptane, and n-octane, correspondingly. Thus, indicating that low molecular weights alkanes have a higher tendency to precipitate a wider range of soluble asphaltene in the crude. Moreover, asphaltene that was characterized to be the least stable showed the lowest asphaltene onset point detected by the indirect method.

Coalescence inhibition and agglomeration initiation near the critical dilution of asphaltene precipitation

In bitumen recovery from oil sands, solvent addition is used to destabilize the water-in-diluted bitumen emulsions and separate the valuable oil product from water and solids. For each solvent, a critical solvent-to-bitumen ratio or critical dilution can be determined that coincides with the onset of bulk asphaltene precipitation, at which the system properties change abruptly. Above the critical dilution, solvent addition promotes bulk asphaltene precipitation and separation by the agglomeration of water droplets, solids and precipitated asphaltenes. Below the critical dilution, separation occurs by the coalescence of water droplets. The properties of the water-diluted bitumen interface could be key to improving the mechanistic understanding of water-in-diluted bitumen emulsions and bitumen recovery. In this work, we explore the behavior of water-in-diluted bitumen emulsions at macro- and microscopic scales, and provide novel insights at conditions below critical dilution. Bench scale bitumen froth treatment settling experiments highlight the possibility to attain effective water and solids separation based on agglomeration, without any noticeable bulk asphaltene precipitation. Light microscopy images reveal the inhibition of water droplet coalescence and the initiation of agglomeration due to the transformation of the oil continuous phase into a gel-like structure in the contact zone between water droplets. Thin liquid film observations show drastic changes in the continuous oil phase properties in the contact zone between water droplets at similar conditions that are attributed to the formation of both asphaltene aggregates at the interface and an oil gel-like structure that expands around them. These findings lead to the proposal that agglomeration can occur below critical dilution by surface asphaltene precipitation at the water-oil interface, without bulk asphaltene precipitation. The multiscale insights highlight opportunities to improve further not only bitumen froth treatment but also other oil-water-solids separation processes.

Asphaltene precipitation modeling in dead crude oils using scaling equations and non-scaling models: comparative study

This research study aims to conduct a comparative performance analysis of different scaling equations and non-scaling models used for modeling asphaltene precipitation. The experimental data used to carry out this study are taken from the published literature. Five scaling equations which include Rassamadana et al., Rassamdana and Sahimi, Hu and Gou, Ashoori et al., and log–log scaling equations were used and applied in two ways, i.e., on full dataset and partial datasets. Partial datasets are developed by splitting the full dataset in terms of Dilution ratio (R) between oil and precipitant. It was found that all scaling equations predict asphaltene weight percentage with reasonable accuracy (except Ashoori et al. scaling equation for full dataset) and their performance is further enhanced when applied on partial datasets. For the prediction of Critical dilution ratio (Rc) for different precipitants to detect asphaltene precipitation onset point, all scaling equations (except Ashoori et scaling equation when applied on partial datasets) are either unable to predict or produce results with significant error. Finally, results of scaling equations are compared with non-scaling model predictions which include PC-Saft, Flory–Huggins, and solid models. It was found that all scaling equations (except Ashoori et al. scaling equation for full dataset) either yield almost the same or improved results for asphaltene weight percentage when compared to best case (PC-Saft). However, for the prediction of Rc, Ashoori et al. scaling equation predicts more accurate results as compared to other non-scaling models.

On the applicability of regular solution and Flory‐Huggins theories to asphaltene liquid mixtures

AbstractWe critically review two classic, molecular‐based solution theories, the regular solution theory and the Flory‐Huggins theory, in the context of revealing their limited applicability to liquid mixtures containing asphaltenes, a significant fraction of crude oil. Asphaltene molecular structures, either as depicted by the Archipelago model or the island model, are non‐linear (not chain‐like) and rigid, making the application of the aforementioned theories to describe their phase behaviour problematic. In addition, since asphaltenes contain chemical moieties that are able to interact through directional dependent specific intermolecular interactions (e.g., hydrogen bonds), this renders the incorporation of Hildebrand solubility parameters into the theories inappropriate. As a result, the two theories do not always predict the onset and amount of asphaltene precipitation correctly for crude oil under different conditions (e.g., temperature, pressure, chemical composition of crude oil, solvent concentration). It is the hope of this author that researchers in the field channel their efforts into developing a brand‐new solution theory for asphaltene liquid mixtures by taking the key molecular attributes of asphaltenes into account.

Inhibition of asphaltene precipitation using hydrophobic deep eutectic solvents and ionic liquid

Precipitation and subsequent deposition of asphaltene in oil reservoirs may cause severe flow assurance problems due to clogging/blocking of pore spaces and wettability alteration of reservoir rocks towards oil-wetness. The present study focuses, for the first time, on the potential application of three hydrophobic deep eutectic solvents (HDESs) prepared by mixing methyltrioctylammonium chloride (N81Cl) as their hydrogen bond acceptor (HBA) with alcoholic hydrogen bond donors (HBDs), namely 1-propanol, 1,3-propanediol, and glycerol. The performance of HDESs was compared with a phosphonium-based hydrophobic ionic liquid (IL), Trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate (TTPBP), as well as dodecylbenzene sulfonic acid (DBSA), a conventional asphaltene precipitation inhibitor. Initially, the kinetic and onset of asphaltene precipitation were evaluated using an ultraviolet-visible (UV-Vis) spectrophotometer to determine the chemicals' inhibition propensity. Next, Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric (TGA), and elemental analyses were used for the recovered asphaltenes from HDESs and TTPBP solutions to examine their structures. Spectrophotometry results revealed that glycerol-based HDES (HDES 3) and TTPBP could effectively inhibit the asphaltene precipitation, where their performances were comparable to that of DBSA. Besides, aromaticity index, thermal degradation, and H:C and oxygen contents provided evidence that HDES 3 and TTPBP could disrupt the asphaltenes structure, thus stabilizing them in the oleic environment.

Regular solution theory applied to asphaltene related phase behaviour

AbstractAsphaltenes are the least soluble fraction of crude oil and they can phase separate from the oil upon a change in temperature, pressure, or composition. This phase separation, often described as precipitation, may be beneficial (eg, in a partial deasphalting process) or detrimental (eg, in pipeline and surface equipment fouling). A phase behaviour model that can predict the onset and amount of asphaltene precipitation and is compatible with process simulators is desirable for the design and operation of these processes. This brief review focuses on the regular solution modelling approach. The regular solution model is based on activity coefficients and therefore is well suited for liquid‐liquid phase separations such as asphaltene precipitation. The model and its internal correlations are presented and its performance on asphaltene phase separation from mixtures of heavy oils and solvent is demonstrated. Recent updates to this approach are presented and potential future applications are discussed. The strengths and limitations of this approach for oilfield applications are highlighted.

Application of surfactants on asphaltene stability in heavy oil by interfacial tension approach

ABSTRACT The objective of this work is to understand the effect of asphaltene on surface properties including interfacial tension (IFT) and reach a specific surfactant in order to inhibit asphaltene precipitation in heavy oils. IFT experiments are implemented by Pendant Drop method and effective mechanisms causing IFT fluctuations are interpreted. The uniform trend of IFT for water/synthetic oil diminished at 25 volume percent of n-heptane which is attributed to asphaltene precipitation onset. Repetition of the experiment with 31 volume percent of n-heptane and real oil sample of field “S” resulted in asphaltene precipitation onset point. This change is justified by different density of synthetic and real oil samples. In addition, three surfactants of L-DBSA (linear dodecyl-benzene-sulfonic acid), B-DBSA (branched dodecyl-benzene-sulfonic acid), and DR (dodecyl resorcinol) are used to retard the asphaltene precipitation onset. Due to special chemical structure and polar group of DR, it is a weaker surfactant than DBSA in terms of inhibition of asphaltene precipitation. Furthermore, chemical structure and spatial avoidance of branches in B-DBSA causes little adsorption to asphaltene molecules and insignificant stability that eventually postpones the onset of asphaltene precipitation at lower degree compared to L-DBSA. When surfactants are introduced, the thin film of asphaltene formed on water-oil interface exhibits enhanced stability with the order of L-DBSA>B-DBSA>DR. Results show 0.25 wt% of L-DBSA can considerably delay the onset point that remedies the problem of asphaltene precipitation in heavy oil fields to great extent.

Application of the Modified Regular Solution Model to Crude Oils Characterized from a Distillation Assay

The modified regular solution model was developed to predict onset and amount (yield) of asphaltene precipitation from mixtures of crude oil and solvents. The most recent version of the model inclu...

Experimental study on the change of the onset of asphaltene precipitation during oil production

During oil production from stratum to wellbore, to prevent the asphaltene precipitation, the rules of the changes of the onset of asphaltene precipitation under different temperature and pressure are systematically studied by laboratory experiment. The results show that the AOPP of the oil samples at 30 °C, 50 °C, and 70 °C are 20 MPa, 17.7 MPa, and 15.5 MPa, respectively. Combined with the temperature and pressure curve of the sampling wellbore, it is predicted that the depth of asphaltene precipitation in the wellbore is 1200–1400 m, which is extremely important for the prevention of asphaltene precipitation during oilfield exploitation.

Laboratory evaluation of a novel multifunctional chemical solution for asphaltene precipitation and aggregation problem: Comparison with an industrial chemical solution

Asphaltene deposition in the near-wellbore area and within the pipelines reduces productivity and is costly. There are usually 2 methods to remedy this hardship that are using dispersants or inhibitors to preventing asphaltene deposition or using solvents when asphaltene deposits on inner surface of pipes or in the porous media. In this study, additive called AUT Force 110 has been developed and its properties have been inspected. This solvent has multifunctional efficiencies (MS) such that can be used as asphaltene inhibition and dispersion and dissolve asphaltene deposits. Furthermore, its performance is compared to an industrial solvent called PL5001 (CS). Analyzing the fourier-transform infrared spectroscopy (FTIR) of the two additives were found to have polar functional groups of hydroxyl, thiol, carbonyl and carboxylic acid in their molecule. The existence of various functional groups gives the MS molecule the ability to interact with adjacent molecules through hydrogen bonding. In addition, aliphatic compounds were observed in the MS molecule with a low carbon number, which leads to its compatibility with crude oil. In contrast, the CS consists mainly of aromatic rings. Two carbonyl and ether functional groups were also observed in its molecular structure, which are very low in concentration compared to polar compounds of MS. Then, the confocal microscopy imaging was used to observe asphaltene aggregates with precipitant. The crude oil and n-heptane were combined in a ratio of 1–30 volumes. The addition of 100 ppm MS reduced about 87% of the mean diameter of asphaltene aggregates; while this reduction was less than 70% by adding CS. Also, adding MS narrowed the dispersion range of the asphaltene particles diameter to 2–16 μm. The carboxylic acid and thiol functional groups play important roles in asphaltene dispersion in MS system. Both MS and CS delayed the onset of asphaltene precipitation, however MS has greater asphaltene inhibition power as well as improving the rheological properties of crude oil and n-heptane solution due to the reduction in the size of asphaltene aggregates, the interaction of MS with asphaltene, and the reduction of the interaction between the asphaltene-asphaltene molecule besides the polar nature of MS. Turbiscan test was also used to measure the solvation power of two additives. The solubility number of MS was lower than that of CS and was reported to be a good solvent, indicating that it has better solvation power than CS. Because MS has the ability to hydrogen bond with asphaltene molecules as both donor and acceptor. Secondly, its aliphatic chains cause steric hindrance, which contributes to the stability of asphaltenes within MS.

Hydroconversion of asphaltene in a hydrogen donor solvent: Stability analysis of the asphaltene-solvent colloidal system

Asphaltene aggregation and precipitation out of the reaction mixture limits the extent of its hydroconversion. In this work, the colloidal stability of asphaltenes undergoing hydroconversion in tetralin solvent was monitored with time. The separability number was measured and the Gibbs energy of mixing together with the onset of asphaltene precipitation were calculated. The results show that the hydrogen transfer from tetralin to asphaltene radicals effectively quench the radicals. The colloidal stability of the system, nevertheless, decreased with reaction time and vanished for reaction times >3 h. In line with this observation, the onset of asphaltene precipitation decreased and, while the Gibbs energy of mixing was negative, it increased with time. The colloidal stability of the reaction system was chiefly influenced by the increased aromaticity of the asphaltene, which in turn decreased its solubility parameter. Within the stable colloidal domain, approximately 44% of the asphaltenes were converted with <1 wt% coke generation. This work is the first attempt in the literature to analytically and mathematically characterize the colloidal stability of asphaltenes undergoing reactions in a hydrogen donor solvent.

Application of low-field nuclear magnetic resonance to assess the onset of asphaltene precipitation in petroleum

Knowledge of the onset of the asphaltene precipitation point is important in preventing pipe clogging and the reduction of productivity. In this study, we propose a new and simple strategy to determine the onset point of asphaltene precipitation by a low-field nuclear magnetic resonance (NMR) technique based on transverse relaxation time (T2) measurements. Six Brazilian crude oil (light, medium, and heavy) samples, with asphaltene contents ranging from 0.10 to 7.10 wt%, were assessed using n-heptane as the precipitant, according to the ASTM D6560 method. The good correlation between T2 and the n-heptane/oil ratio indicated the onset precipitation values between 0.931 and 2.759 mL g−1. NMR results shows agreement with optical microscopy and literature results. We also propose a correlation between asphaltene content and onset of the asphaltene precipitation. This new idea expand the applicability of low-field NMR in crude oil studies, providing an alternative method for asphaltene precipitation under laboratory conditions and opens the possibility to quantifying the asphaltene content in crude oil without the laborious standard ASTM method.

Extending the Modified Regular Solution Model To Predict Component Partitioning to the Asphaltene-Rich Phase

The modified regular solution (MRS) model is an activity coefficient approach previously developed to predict the onset and amount of asphaltene precipitation from n-paraffin-diluted crude oils. Th...

A comparative study of CPA and PC-SAFT equations of state to calculate the asphaltene onset pressure and phase envelope

The Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equation of state (EoS) and the Cubic-Plus-Association (CPA) EoS have been widely applied to describe the asphaltene precipitation onset in crude oils because the association term of these models can appropriately account for the polar-polar interactions between asphaltene and resin molecules. In this study we have compared the PC-SAFT and CPA EoS capabilities in the calculation of the Asphaltene Precipitation Envelope (APE) of eight oils from the literature and discuss the physical meaning of the cross-association energy parameter between asphaltene and resin. For all oils the PC-SAFT EoS predicts an increase in the stability of the oil at higher temperatures with the consequent closure of the APE while the CPA model predicts a decrease in the stability at higher temperatures. For both models the fitted values of the cross-association energy parameter between asphaltene and resin show a dependency on temperature, but for PC-SAFT model this parameter has a clearer physical meaning. Results indicate that the PC-SAFT EoS is more accurate for APE calculations outside the experimental temperature range.

Understanding the stabilization mechanism of bitumen-coated fine solids in organic media from non-aqueous extraction of oil sands

Considerable amounts of fine solids retained in the bitumen product have been a challenging issue impeding the industrial application of the non-aqueous extraction (NAE) of oil sands ore. The undesired stable suspension of bitumen-coated fine solids in the bitumen-solvent mixture is generally considered as the origin of solid migration to the NAE bitumen. In this work, two advanced nanomechanical techniques, i.e., colloidal probe atomic force microscope (AFM) and quartz crystal microbalance with dissipation (QCM-D), were utilized to unravel the stabilization mechanism of fine silica solids in organic solvents, including cyclohexane, heptane and the mixed solvents. The adsorbed bitumen layer on the silica surfaces exhibited a swelling behavior in cyclohexane-rich solvent, giving rise to strong repulsion between the fine silica solids. Addition of heptane to the organic media could notably weaken the inter-particle repulsion by causing the shrink and collapse of bitumen layer. The degree of adsorption of bitumen layer on the silica surfaces could be significantly enhanced by slightly decreasing volume fraction of cyclohexane (φc) in the mixed solvents but could be inversely inhibited as φc was smaller than the asphaltene precipitation onset. The stability of bitumen-coated silica solids in organic solvent was also examined via sedimentation tests. It was found that the settling efficiency could be markedly enhanced by decreasing φc in surrounding solvent. Our results provide useful insights into the stabilization mechanism of fine solids in NAE bitumen, with important implications for developing effective and economical strategies of removing fine solids from the NAE bitumen product.