Naphthenic acids are believed to be responsible for a number of unwanted phenomena occurring during the processing and transport of crude oil, such as pipeline corrosion and precipitation of calcium salts. In this paper, Fourier transform ion cyclotron resonance mass spectrometry is used to analyze a mixture of naphthenic acids. Naphthenic acids have been shown to form multimers, and the study of multimer association could lead to a better understanding of naphthenic acid phase behavior in crude oil production systems. The dependence of the signal intensity of such aggregates on the accumulation time within the ion source hexapole has been studied, and it has been highlighted that such a dependence suggests a noncovalent interaction as the primary cause for aggregation. This would account for the decrease in signal intensity with accumulation time as a result of the increasing chance of undergoing collisional dissociation. The nature, role and behaviour of naphthenic acid dimers may be better understood by the application of mass spectrometry and this has potential to be applied to samples of importance to the oil industry.

In this work, a sensitivity study was conducted on naphthenic acid derivatization agents. Four silylation chemistries and one methylation chemical were initially evaluated on 10 model naphthenic acids using gas chromatography. An experimental design procedure was setup to look at a number of effects, including contact time, catalyst presence, and reagent concentration. Overall, the silylation agents resulted in higher derivatization yields compared to the methylation agent. Moreover, the silylation agents did not show major evidence of selective derivatization as a function of the naphthenic acid structure. A silylation agent [(N,O-bis-(trimethylsilyl)trifluoroacetamide (BSTFA)] was then used to test commercial naphthenic acid mixtures with two-dimensional gas chromatography coupled to time-of-flight mass spectrometry using the electron-impact source (GC×GC−TOFMS). The results enabled identification of many different naphthenic acid species. To test the derivatization agents on realistic samples, naphthenic acid extracts obtained from two crude oils of flow assurance significance were separated with a liquid-phase extraction procedure. The naphthenic acids were then treated with a silylation agent (BSTFA) and a methylation agent (BF3/methanol). The derivatized naphthenic acids together with the non-derivatized naphthenic acids from both crude oils were further examined using medium-resolution time-of-flight mass spectrometry with an electrospray source (TOFMS). Differences were observed in the TOFMS spectra for the naphthenic acid extracts. Extracts that did not contain ARN naphthenic acid species did not show major differences between non-derivatized and derivatized spectra in the negative mode. Extracts that contained ARN did show differences between derivatized and non-derivatized samples in the negative mode. Use of BSTFA resulted in enhanced signals for ARN, particularly the second ionization. Use of BF3/methanol resulted in a poor ARN response compared to the non-derivatized spectra. ARN species were also observed in the positive mode after treatment with both BSTFA and BF3/methanol, but signals were very poor. Moreover, use of BF3/methanol resulted in poor solubility of the naphthenic acid extracts from the crude oil containing ARN species. No solubility issues were observed with the use of BSTFA. Overall, the results point to the shortcomings of the application of methylation chemicals as derivatization agents, particularly for naphthenic acids extracted from crude oil samples containing high-molecular-weight acids of flow assurance significance (e.g., ARN species).

The prediction and prevention of both sodium and calcium naphthenate "scales" is an important issue in oil production. A broad description of how these scales form has been available for some time, although most experimental findings are still of a qualitative nature. In this paper, an equilibrium thermodynamic model is presented for predicting naphthenate partitioning and precipitation in an oil/brine immiscible system from some chosen initial conditions (i.e., naphthenate initial concentration in oil, brine pH, [Ca 2+ ], etc.). This model has, with some assumptions, been applied to both model and real naphthenate system. This model describes two types of naphthenate experiment: 1) full naphthenate precipitation, and 2) simpler "pH change" experiments in which no precipitation occurs. To predict naphthenate precipitation, the theory suggests knowing: 1) the partition coefficient of the naphthenic acid, HA, between the oil and the water phases, K ow ; 2) the pK a of the naphthenic acid in water; and 3) the solubility product, K CaA2 (or other similar solubility parameter), of the naphthenate deposit. In the simpler pH change experiments, only the first two of these parameters (i.e., K ow and pK a ) are required. Using the naphthenate model without precipitation, the effect of varying parameters on the degree of pH change predicted at equilibrium in the oil/naphthenic acid/brine system was studied. Also, the model was used to examine the sensitivities of the various parameters on the final pH was also applied. The comparison between the model predictions and experiment at a higher brine pH value is overall satisfactory.

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Nonaqueous capillary electrophoresis was used for the separation and characterization of asphaltene samples from different sources. For the separation medium (background electrolyte), mixtures of tetrahydrofuran and a high-permittivity organic solvent could be used. The best results were obtained with an 80:20 mixture of tetrahydrofuran and acetonitrile, containing 1−10 mM of lithium perchlorate. In this separation medium, asphaltene samples were found to be composed of two fractions that could be clearly separated: one fraction of neutral species and a fraction that carries a positive charge in the solvent mixture employed. Between samples of different origin, differences were found in the relative amounts of the neutral and the charged fractions and in the average electrophoretic mobility of the charged components. Taylor dispersion analysis was applied to estimate the average diffusion coefficient of the asphaltene species in the solvent mixture used. From the results, it is concluded that the asphaltenes are present as nanoaggregate clusters of 3000−4000 Da and that the charged aggregates carry a net charge of approximately +1. The possible correlation between the electrophoretic properties of asphaltenes in crudes of different origin and their field behavior is discussed.