To assess the relationship of wax chemical structure and viscoelastic properties of waxy gels, model oils composed of single and blended waxes were prepared at a fixed concentration of 7.5 wt % and then gelled. The investigation encompassed four different well-characterized commercial paraffin waxes, solubilized in a mineral oil matrix. Previous rheological measurements pointed out that these systems reproduce essential features of crude oil gels (e.g., gel-like mechanical response) when gelled. Among the employed waxes, two are predominantly linear, whereas the others are nonlinear branched molecules. The waxes were molecularly characterized to aid in the investigation by means of GC-FID, 13 C NMR, DSC, FT-IR, and XRD. Rheological properties were measured via a controlled-stress rheometer by oscillatory shear experiments. Polarized light microscopy was adopted for morphological characterization of precipitated crystals. It was found that yield stress and elastic modulus at linear viscoelastic region are highly correlated (R 2 = 0.94). For single wax systems, the increase in chain length resulted in a yield stress increase, although there is a competitive effect among chain length (positive effect) and branching content (negative effect). The results indicated that for blended systems the small-chain linear wax was able to interact favorably with the long-chain nonlinear wax, possibly due to its ability to accommodate within the later molecule, ensuring the highest yield stress value (630.2 Pa). The wax structural arrangement of 37 carbon atoms on average, including approximately three tertiary carbons, was effective for lowering the yield stress of particular blended systems. The lowest viscoelastic properties were measured for a blended system composed of nonlinear waxes, which was also characterized by the smallest and rounded crystals visible by optical microscopy.

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The observation of lamellar liquid crystals (LCs) is reported in fractions of Brazilian crude oil emulsions. Through polarized light microscopy, several structures exhibiting Maltese cross-optical pattern were observed, mostly in aqueous-rich fractions (bottom fractions). Microscopy observations were carried out immediately after emulsion preparation and after a destabilization protocol by centrifugation. Four oils were used: two waxy crude oils and two non-paraffinic oils. The experimental variables investigated were oil composition, aqueous content, and saline solution concentration. The liquid crystalline structures had a similar pattern for all samples observed with a thickness of 1.77 ± 0.14 μm surrounding droplets of 4.57 ± 0.47 μm diameter. Neither the presence of wax nor NaCl (up to 35 g/L) exhibited any correlation with liquid crystal (LC) appearance. However, the increase of the aqueous phase added to the systems favoring LC formation.

RESUMO -A maior parte da produção de petróleo brasileiro é proveniente de campos offshore, inclusive de poços localizados em águas profundas da camada pré-sal. Esta produção, entretanto tem enfrentado problemas com relação à deposição de parafinas nos dutos de transporte. Os óleos localizados em águas profundas passam por um processo de resfriamento natural devido às baixas temperaturas do mar, cerca de 4ºC. A combinação de baixas temperaturas e óleos parafínicos ocasiona a precipitação e deposição nos dutos de escoamento promovendo obstruções totais e/ou parciais. Pouco se sabe sobre as relações entre as taxas de resfriamento, comportamento reológico e morfologia de parafinas, bem como as interações das cadeias parafínicas com água ou outros componentes do petróleo. Assim, este trabalho tem como objetivo caracterizar a estrutura das parafinas presentes no petróleo, bem como parafinas isoladas solubilizadas em uma matriz inerte, por meio de microscopia de luz transmitida. A morfologia observada das parafinas do petróleo cru e do sistema modelo solubilizada na matriz inerte apresenta estruturas relativamente semelhantes nas mesmas condições experimentais. INTRODUÇÃOSegundo dados do Anuário Estatístico Brasileiro do Petróleo, Gás Natural e Biocombustíveis do ano de 2013, o Brasil produziu 754,4 milhões de barris de petróleo no ano de 2012, sendo 66,04 milhões de barris oriundos de campos onshore e 688,4 milhões provenientes de campos offshore. A produção offshore, entretanto tem enfrentado problemas com relação à deposição de parafinas em dutos de transporte.Os petróleos da camada pré-sal são parafínicos e passam por um processo de resfriamento natural devido às baixas temperaturas marinhas (cerca de 4ºC). Estas condições favorecem a precipitação e deposição das moléculas de parafina nos dutos de escoamento promovendo obstruções totais e/ou parciais. Estas deposições ocorrem quando a temperatura da linha encontra-se abaixo da temperatura inicial de aparecimento dos cristais (TIAC) e, se tornam mais críticas conforme ocorre a diminuição gradual da temperatura.Segundo Hammami e Raines (1999), as parafinas são cadeias longas de hidrocarbonetos,