Crude Oils Of Different Origins Research Articles

Quantitative Measurement of Multiple Elements in Micro‐Quantities of Crude Oil Using In Situ Analysis by Laser Ablation‐ICP‐MS

Multi‐element quantification in small amounts of material and in situ measurements at the micrometre scale are essential aspects of geological sample investigation. A direct and rapid simultaneous multi‐elemental determination of metals in crude oil samples was carried out by combining direct laser ablation of the oil inserted in silica capillaries with inductively coupled plasma‐mass spectrometry. The accuracy of LA‐ICP‐MS determination was demonstrated by analysing CONOSTAN reference material oils, certified for multiple elements, and by comparing LA‐ICP‐MS measurement results with those obtained by ICP‐OES using microwave‐assisted sample digestion. The results obtained by both methods were in agreement with certified values. The LA‐ICP‐MS method showed an adequate precision with a mean relative standard deviation of less than 10% for multi‐element determination, and was sufficiently sensitive to determine the majority of elements. LA‐ICP‐MS was also applied to the determination of elements in crude oils of different origins. LA‐ICP‐MS is a good alternative method allowing the determination of elements in organic fluids (oil and bitumen) in shorter times, involving less material consumption, smaller test portion size and with higher throughput compared with protocols using, for instance, sample digestion. It validates the possible application of metal analysis in hydrocarbon‐containing fluid inclusions for metallogenic purposes.

Machine learning approach for predicting crude oil stability based on NMR spectroscopy

Crude oils are extremely complex organic mixtures, composed of various constituents ranging in size, shape and polarity. Obtaining a detailed insight into the petroleum composition is of highest priority for quality evaluation of crude oils and crude oil product performances. The stability of crude oils and their components represents one of the major challenges in petroleum industry, since there is no existing single method to determine the stability of all fractions. In this study, statistical multi-way analysis (MWA) and machine learning (ML) methods were coupled with diffusion-ordered NMR spectroscopy (DOSY) and compared to different crude oil stability affecting parameters in order to explore possibilities to predict crude oil stability. The potential of this approach was explored to identify and classify the crude oils of different origin according to their composition, stability, density and diffusion properties. With the application of MWA using the TUCKER3 decomposition model for a set of DOSY NMR spectra, the principal components were determined for the model (5,5,5), which described 99.89 % of the total variance. The reduced space of the first 3 principal components was used for the sample classification. Similar samples were identified, and reduced space was further utilized for the regression of measured stabilities. Extensive ML multivariate linear regression was carried out for modeling crude oil stability in relation to DOSY NMR spectra and other measured properties, such as aromaticity, API gravity, percentage of aliphatic chains, asphaltene content and relative diffusivities. In both MWA and ML cases the best predictive models were determined. For such complex mixtures as crude oils are, exceptionally good correlations were obtained, proving that this new and robust model can accurately predict crude oil stability and other important parameters relevant for petroleum industry thus showing a great potential for practical applications.

Some Compositional Viscosity Correlations for Crude Oils from Russia and Norway

The current work is based on experimental viscosity and compositional data of about 200 crude oil samples from various parts of Russia and the Norwegian continental shelf. Data analyses were performed to estimate correlations between viscosity and density values as well as concentrations of main components from the crude oils of different origins. It appeared that, in some cases, it is possible to establish a general correlation of viscosity increase along with growing asphaltene, resin, and aromatics contents but also a decrease in viscosity with increasing saturates content. The spread of the data points can be rather wide for the oils of different origins. It was observed that asphaltenes from all of the crude oil samples acted as promoters of the viscosity growth at rather low concentrations, while resins and aromatics effectively increased viscosity in a higher concentration range. The effect of asphaltenes on the viscosity of real crude oils seems to be more important than when dissolved in a model ...

Estimation of the SARA Composition of Crude Oils from Bubblepoint Pressure Data

A statistical correlation to provide reasonable estimates of crude oiĺs SARA compositions (saturates, aromatics, resins, asphaltenes) from bubblepoint pressure and light-ends compositional data is presented. In developing the correlation, we collected experimental SARA compositions of 341 crude oils of different origin. The most-probable SARA compositions are then obtained by seeking the maximum probability according to its oil type, in line with the measured values of bubblepoint pressures. Results show that the proposed method is simple and provides reasonable values of SARA compositions of an oil in cases in which only the light-ends compositions and a few bubblepoint pressures are available.

NMR and Chemometric Characterization of Vacuum Residues and Vacuum Gas Oils from Crude Oils of Different Origin

NMR spectroscopy in combination with statistical methods was used to study vacuum residues and vacuum gas oils from 32 crude oils of different origin. Two chemometric metodes were applied. First- ly, principal component analysis on complete spectra was used to perform classification of samples and clear distinction between vacuum residues and vacuum light and heavy gas oils were obtained. To quanti- tatively predict the composition of asphaltenes, principal component regression models using areas of res- onance signals spaned by 11 frequency bins of the 1 H NMR spectra were build. The first 5 principal com- ponents accounted for more than 94 % of variations in the input data set and coefficient of determination for correlation between measured and predicted values was R 2 = 0.7421. Although this value is not signifi- cant, it shows the underlying linear dependence in the data. Pseudo two-dimensional DOSY NMR exper- iments were used to assess the composition and structural properties of asphaltenes in a selected crude oil and its vacuum residue on the basis of their different hydrodynamic behavior and translational diffusion coefficients. DOSY spectra showed the presence of several asphaltene aggregates differing in size and interactions they formed. The obtained results have shown that NMR techniques in combina- tion with chemometrics are very useful to analyze vacuum residues and vacuum gas oils. Furthermore, we expect that our ongoing investigation of asphaltenes from crude oils of different origin will elucidate in more details composition, structure and properties of these complex molecular systems.

Direct Insertion Probe–Mass Spectrometry (DIP–MS) Maps and Multivariate Analysis in the Characterization of Crude Oils

Crude oils are complex organic mixtures, with their composition changing not only with the geographical region but also with the oil field. Chemical fingerprinting of crude oils and the knowledge of dependence of their macrophysical properties from the major chemical characteristics are fundamental to both upstream and downstream operations. Direct insertion probe–mass spectrometry (DIP–MS), on the basis of the introduction of samples without previous manipulation directly into the ionization chamber, their vaporization, and eventual ionization by electronic impact, appears as a proper tool to map crude oil characteristics. The components of the oils are separated according to their boiling points up to masses of m/z 950. A set of crude oils of different origin and bulk physical properties were characterized by DIP–MS in a fast and easy way. The data represented in contour plots, with molecular weight and volatility (i.e., vaporization temperature) on the axes, gave immediately an idea of the nature of the oil in terms of its physical properties and allowed for its fingerprinting. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were applied to analyze contour plots, showing similarities and differences among the crude oils, confirmed by a comparison to bulk physical properties, such as American Petroleum Institute (API) gravity and viscosity.

Magneto-optical activity of crude oil and its heavy fractions

We have experimentally studied optical and magneto-optical spectra of solutions of crude oils of different origin and their heavy fractions in the visible spectral range. Magnetic circular dichroism of oil in the wavelength range ∼550 nm has been revealed. We show that the shape of the spectra of this dichroism depends on the origin of crude oil, with the magnetic dichroism magnitude being proportional to the concentration of the oil in the solution. A comparison of the data of magneto-optical spectroscopy with electron paramagnetic resonance spectra and chemical composition of samples has allowed us to conclude that the observed magneto-optical activity is determined by the occurrence of VO2+ complexes in the oil samples. The revealed magneto-optical activity of crude oil can form the basis of a unique method of analysis of the composition and properties of oils of different origin and heavy fractions thereof.

Application of TLC and LA ICP SF MS for speciation of S, Ni and V in petroleum samples

A coupling of thin layer chromatography with laser ablation ICP SF MS was developed for the fractionation of Ni, V, Fe and S in crude oil and its fractions (saturate, aromatic, resin and asphaltene). The detection limits were 18ngg−1 and 23ngg−1 for nickel and vanadium, respectively, and a sample could be characterized in terms of the metal distribution as a function of species polarity within 10min. The method was used to characterize the metal distribution in crude oils of different origins and their different fractions.

Thermo-oxidative reactions of crude oils

In this research, thermo-oxidative reactions of crude oils of different origin are determined in limestone matrix using simultaneous thermogravimetry and differential thermal analysis (TG–DTA) systems. Two different reaction regions were identified known as low temperature (LTO) and high temperature oxidation (HTO). Kinetic parameters of the samples were determined by four different methods and the results are discussed.

Single Photon Ionization Orthogonal Acceleration Time-of-Flight Mass Spectrometry and Resonance Enhanced Multiphoton Ionization Time-of-Flight Mass Spectrometry for Evolved Gas Analysis in Thermogravimetry: Comparative Analysis of Crude Oils

Coupling thermal analysis (TA) with a subsequent analytical method in order to investigate evolved gaseous products from the thermal analysis is a well established method. A popular practice to analyze the gaseous products evolving from thermal analysis is mass spectrometry using electron impact ionization (EI).(1-4) As the kinetic energy of the electrons thereby is typically far beyond the ionization energies of the assayed samples, the electron impact effects fragmentation particularly of organic compounds, hampering the correlation of the ion signals to the gaseous compounds. This applies for complex mixtures in particular. Fragmentation can be reduced using so-called soft ionization techniques. In the course of the presented setup, single photon ionization (SPI) using electron beam pumped excimer lamps (EBEL) emitting vacuum ultraviolet (VUV) light (λ = 126 nm) is employed. For the instrumentation, a TA system has been coupled to an EBEL-SPI-oaTOFMS (oaTOFMS: orthogonal acceleration time-of-flight mass spectrometry) system using a heated transfer capillary in order to detect semivolatile organic substances from the gas flow of a thermobalance with high temporal resolution. Presented measurements focus on crude oils of different origins. In-depth analysis demonstrates that it is possible to tell apart different crude oil samples on the basis of temperature resolved mass spectra gained from the described setup. TA allows for the assay of crude oils without sample preparation via a distillation process which precedes the thermal decomposition of nonvolatile oil components, i.e., resins and asphaltenes. The gases that evolve during thermal analysis are a complex mixture of organic compounds. These can be analyzed without losing molecular information using mass spectrometry with a soft ionization technique, such as SPI.

EPR and Fluorescence Spectroscopy in the Photodegradation Study of Arabian and Colombian Crude Oils

EPR and fluorescence spectroscopy were used to evaluate the degradation of crude oils of different origins that were submitted to photochemical weathering under tropical conditions. The EPR spectra obtained showed signals of the paramagnetic species: the vanadylVO2+ion and organic free radicals. A decrease in linewidth of free radical signals was observed for both oils irradiated for 100 hours with sunlight of 350 W/m2. The reduction in the linewidth of the free radical of 9.8% in Arabian oil and 18.5% in Colombian oil, as well as the decrease in radical numbers, indicated photochemical degradation, especially in Colombian oil. The linewidth narrowing corresponding to free radicals in the irradiated oils occurred due to the rearrangement among radicals and aromatic carbon consumption. The irradiated oils showed a reduction in the relative intensity of fluorescence of the aromatics with high molecular mass, polar aromatics, and asphaltene. The fluorescent fraction was reduced by 61% in Arabian oil and 72% in Colombian oil, corresponding to photochemical degradation of crude oil aromatic compounds.

Emulsions of Heavy Crude Oils. I: Influence of Viscosity, Temperature, and Dilution

Twenty‐seven crude oils of different origin have been systematically analyzed with regard to viscosity, density, molecular weight, and SARA (saturates, aromatics, resins, asphaltenes) fractionation. Emulsion stability of water‐in‐oil emulsions of the different crude oil samples have been measured by the critical electric field technique (E‐critical). In addition, droplet size distributions for some of the water‐in‐oil emulsions have been determined by NMR self‐diffusion. Rheology measurements show that some of the crude oils have Bingham plastic type flow behavior at temperatures below 20°C, indicating content of waxes. Analysis of the critical electric field measurements shows that the E‐critical value depends on the applied electric field gradient. At low applied electric field gradients, the droplets are given more time to organize into water‐continuous bridges, resulting in a lower E‐critical value than when the applied electric field gradient is higher. The value of E‐critical also increases as the volume of the water phase decreases, due to the increased distances the droplets must move to form linear chains between the two electrodes. E‐critical measurements of emulsions of diluted crude oils show that, in general, the emulsion stability decreases with increased dilution of the oil phase. However, some systems show regions where the emulsion stability is independent of the dilution ratio or viscosity of the crude oil. Here the coalescence rate controls the level of emulsion stability. Viscosity and emulsion stability for water‐in‐oil emulsions were measured for the complete crude oil matrix (27 crude oils), and in general there is an increase of the emulsion stability as the viscosity increases. However, viscosity also correlates well with the SARA data of the crude oils. E‐critical shows a temperature dependence according to the Arrhenius law.

Generalized relation between surface tension and viscosity: a study on pure and mixed n-alkanes

A generalized relation is presented to correlate liquid–vapor surface tension with viscosity, both for pure compounds and mixtures. Plots of different data sets verify that the natural logarithm of the surface tension is linear with the reciprocal viscosity, with slope-dependent on the molecular weight and constant intercept for n-alkanes with chain length greater than n-C 10H 22. For these, the value of the intercept can be related to the surface tension at the temperature of homogeneous nucleation, where the reciprocal viscosity tends to zero. The relations found for the slope and intercept of pure components are also shown to be valid for mixtures, so that only a viscosity (or surface tension) value is required to calculate a surface tension (or viscosity). Some distillation cuts from crude oils of different origins were also presented. Although the linear relation is still valid, the proposed correlations for the slope and intercept of n-alkanes cannot be used, confirming that mixing rules and family specific correlations are required for fluids containing components of different families. The results presented on this work show how bulk transport and equilibrium surface properties can be interrelated.

Characterization of crude oils by inverse gas chromatography

It was shown that the flocculation onset of asphaltenes in crude oils could be predicted on the basis of the inverse gas chromatography characterization of the crude oil properties. Hildebrand’s solubility parameters of four crude oils were calculated from inverse chromatography data and compared with values obtained from the onset of asphaltene flocculation measurements. A good agreement was observed with three crude oils of different origin. A relation between Hildebrand’s solubility parameter and linear solvation energy relationship descriptors was established and it was demonstrated that the solubility parameter of a crude oil is determined mainly with dispersion interactions and the hydrogen bond basicity. A large basicity lowers the oil solubility parameter, and increases its stability in respect to flocculation.

Simulation of Interactions in Asphaltene Aggregates

Molecular mechanics and dynamics calculations were carried out for asphaltenes and resins from crude oils of different origins. Average structural models were used in order to study the forces that determine the association process of asphaltenes and resins in crude oils. The stabilization energies obtained for asphaltene and resin associates were due mainly to the van der Waals forces between the molecules. Comparatively, the contribution of the hydrogen bonding to the stabilization energy was low. It was also found that few structural changes occur in the molecules due to aggregation. Therefore, the contribution of the conformation changes to the stabilization energy was also very low. According to the results obtained, the stabilization energy of the associates depends on the structural characteristics of the molecules. In particular, the stabilization energy is more favorable for those molecules with lower hydrogen-to-carbon ratio, higher aromaticity, and higher aromatic condensation degree. When different solvents were used to break the associates, this tendency was confirmed. The breaking of the associates occurred for those molecules with higher hydrogen-to-carbon ratio and lower aromaticity. These results can be linked to the experimental finding of a greater tendency to precipitate for those asphaltenes with low hydrogen-to-carbon ratio and high aromaticity.

Selectivity of desulfurization activity of Desulfovibrio desulfuricans M6 on different petroleum products

A strain of sulfate-reducing bacterium Desulfovibrio desulfuricans M6 was used to examine the degradation of model sulfur compounds found in fossil fuels, and to remove sulfur from crude oils of different origins and their products. The bacterium showed different abilities to degrade model compounds, ranging from 96% for benzothiophene to less than 10% for thiols. Degradation of some model compounds were inhibited in the presence of n-dodecane. Differences were also observed in the desulfurizations of crude oils from different origins. More sulfur was removed from the heavier fractions of petroleum than the crudes and the lighter fractions. Petroleum samples treated by the bacterium were analyzed by gas chromatography using a sulfur specific flame photometric detector. Some sulfur compounds were found to be removed completely, while others were unaffected. From these results, it was concluded that sulfur-carbon bonds in aromatic sulfur compounds are more susceptible to the reductive degradation by the bacterium than those in the aliphatic sulfur compounds, and that the low degrees of desulfurization on some petroleum samples are due to the nature of the sulfur present in the samples. it is suggested that the bacterium could be used to develop a process to desulfurize heavy fractions of petroleum.

Correlations between carboxylic acids and hydrocarbons in several crude oils. Alteration by biodegradation

The acids and the hydrocarbons of five crude oils of different origins and degrees of biodegradation have been studied by mass spectrometry, gas chromatography and computerized GC-MS. The biodegraded oils show a strong increase of the amounts of acidic components and a preferential removal of the linear acids. The non-biodegraded oils contain pentacyclic hopanoids and tricyclic terpenoids in both fractions. A comparison of their distributionssuggests a possible neoformation of part of the alkanes by decarboxylation of the acids during maturation. Pentacyclic acids and hydrocarbons undergo similar biodegradation pathways with a notable preferential attack of the higher homologs bearing a linear side chain, but the alkanes appear to be more resistant. Moreover, the hopanoic acids could be used as sensitive biodegradation indicators. The tricyclic terpenoids are the least affected by the biodegradation process and are therefore concentrated in biodegraded oils.

Determination of major and trace elements in crude oils by neutron activation and reflection methods

The concentrations of O, Na, Cl, V, Mn and Ni in crude oils of different origins were determined, using sampling (SNAA) and on-stream (ONAA) activation analyses. Samples were irradiated with thermal and fast neutrons produced by a 0.3 mg252Cf source and a 14 MeV generator. The H-content and the C/H atomic ratio have been determined by thermal neutron reflection method using an 18 GBq Pu−Be source.