a b s t r a c tAsphaltene precipitation and subsequent deposition is a potential flow assurance problem for the oil industry nowadays. Moreover, because oil production is moving to more difficult production environments -e.g. deeper waters -or is focusing on extracting residual oil using enhanced oil recovery techniques, the significant changes of pressure, temperature and/or composition can aggravate the asphaltene deposition problems. One of the most common strategies to prevent or at least reduce asphaltene deposition is the utilization of chemical additives. However, there are still several unresolved challenges associated to the utilization of these chemicals: First, the experimental conditions and results obtained in the lab are not always consistent with the field observations. Also, in some cases these chemical additives seem to worsen the deposition problem in the field. Therefore, there is a clear need to revisit the commercial techniques that are used to test the performance of asphaltene inhibitors and to provide a better interpretation of the results obtained. In this work, a technique based on NIR spectroscopy is presented to evaluate the performance of three commercial asphaltene dispersants. The method presented in this work is faster and more reproducible compared to the available methods such as the Asphaltene Dispersion Test (ADT) and the Solid Detection System (SDS). Also, unlike the ADT test, our proposed method can evaluate the performance of the dispersants in a wide range of temperatures and compositions. The experimental evidence shows that the asphaltene dispersants neither shift the actual onset of asphaltene precipitation nor reduce the amount of asphaltene precipitated. We believe that some results that have been reported that suggest that asphaltene dispersants can actually shift the onset of asphaltene precipitation are an unfortunate combination of insufficient sensitivity of the commercial instruments used and the slowing down of the asphaltene aggregation process by the effect of the added dispersants. The chemical additive dosage, aging time and temperature effect on the asphaltene aggregation process are also discussed in this manuscript.With this work we aim to contribute to a better understanding of the variables that affect the performance of asphaltene dispersants, and the effect that these chemicals have on the complex multi-step mechanism of asphaltene precipitation and aggregation.

Asphaltene deposition is one of the major flow assurance problems that can potentially deteriorate due to the current tendencies to produce from the deep-water environment or as a result of enhanced oil recovery operations based on miscible gas injection. The deposited asphaltenes in the wellbores and on the surface of the oilfield pipelines can impede the productivity of the wells significantly. The comprehensive understanding of the mechanisms and the techniques to control asphaltene deposition at high temperature and under dynamic conditions can help resolve this critical issue. Thus, it is imperative to develop reliable, straightforward, and inexpensive tools to investigate the asphaltene deposition tendency and the performance of asphaltene inhibitors in the laboratory. In this work, a new stainless steel packed bed column deposition system that was inspired by the work of Vilas Bôas Fávero et al. was successfully developed. The packed bed design allows the feasibility of investigating a variety of factors affecting the deposition process under a wide range of temperature (20–300 °C) and gauge pressure (0–3000 psi). The impacts of operating temperature, type of precipitant, degree of asphaltene stability, and chemical additives on the deposition tendency of asphaltenes were investigated. It was found that the solubility of asphaltenes, the diffusion of precipitated asphaltenes, and the formation of aged asphaltene aggregates were competing factors controlling the deposition of asphaltenes under different operating temperatures. Additionally, asphaltenes precipitated by n-pentane induced more deposition than those destabilized by n-heptane. The liquid-like deposits collected from the experiment with n-butanol provided evidence that stronger ability to retain the softness reduced their tendency to build up aged asphaltene deposition on the metallic surface. Variation of the precipitant-to-oil ratio showed that the rate of asphaltene deposition increased linearly with the driving force toward asphaltene precipitation. Furthermore, a comparison between the capillary flow loop and the packed bed column on the assessment of asphaltene inhibitors was conducted. It was found that higher dosage of the asphaltene inhibitor seemed to delay the onset of deposition but did not further reduce the amount of deposition. With this packed bed column operating at high-pressure and high-temperature conditions, advanced simulation tools to predict asphaltene deposition under more realistic production conditions can be developed. Also, it can be used to assess asphaltene deposition inhibitors and solvents to prevent and remediate the asphaltene deposition problems.

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We have investigated the model light harvesting systems (LHSs) A and B typifying energy transfer (ET) between a naphthalene, Np (donor, D), and an azobenzene, Az (acceptor, A), shown schematically in Scheme 2 . These models were actualized as the naphthyl azo molecules 1 and 4 containing a methylene tether (Scheme 1). The methoxy azo molecules 2 and 5, respectively, served as benchmarks for the assessment of ET. Photophysical data, including initial rate constants for photoisomerization (trans to cis, t-1 --> c-1, and cis to trans, c-1 --> t-1), the relevant c-1 --> t-1 quantum yields, and fluorescence quenching with free naphthalene, 3, as D were measured. Therefore, (1) irradiation of 3 at (270 nm) to give 3* generates fluorescence at 340 nm that is 65% quenched by the trans isomer of 2 (t-2) and 15% quenched by c-2. Comparable naphthalenic fluorescence of c-1 (LH model A) is quenched beyond detectability. (2) Rates of photoisomerization were determined spectrophotometrically for c-1 --> t-1 starting from the c-1 photostationary state as compared with the c-2 --> t-2 benchmark. (3) Progressing toward more complex LH systems, the initial rate constants, k(i), for c-4 --> t-4 (LH model B), were measured as compared with the c-5 --> t-5 benchmark. (4) A new criterion for ET (D --> A) efficiency emerges that combines k(i) (c --> t) ratios and light absorption on irradiation (at 270 nm) ratios. On the basis of this new criterion, both 1 and 4 exhibit virtually quantitative ET efficiency. (5) Quenching data of 1 (almost complete) and 4 (95%) and ET are discussed by comparison with the relevant model azoarenes, 2 and 5, respectively, and in terms of geometrical considerations. Implications for the extension of the results, notably the new criterion for ET efficiency, in these LH models A and B to the polymer and block copolymer D-(CRR')(n)-A and D-(CRR')(n)-A-(CR''R''')(m)-D targets are considered.