the structural differences of asphaltenes in Colombian light crude oils from the same field, i.e., the Colorado oilfield, were presented. Colorado crude oil is a light crude with very low content of asphaltenes (<0.3%, w/w) and presents paraffin crystallization problems during its production. In the parafinic deposits, asphaltenes have also been found. In this work, a new methodology is proposed to determine the effects of chemical structure and concentration of asphaltenes on the wax crystallization of the crude oils from the Colorado oilfield. Six crude oils (from different sands) were fractionated in their respective asphaltenes and maltenes. The crystallization properties of crude oils and maltenes were obtained: wax appearance temperature (WAT), pour point, and crystallization enthalpy. Asphaltenes were characterized by nuclear magnetic resonance analysis, mass spectrometry, X-ray diffraction, and Raman spectroscopy, and their main average molecular parameters (AMPs) were calculated. Partial least-squares regression (PLS) analysis was used to understand the influence of asphaltenes chemical structure on the crystallization processes. The proposed characterization−statistical analysis methodology allowed for the understanding of the effect of the average molecular structure of asphaltenes on the crystallization properties of paraffins from the crude oils of the Colorado field. The effect of asphaltenes was analyzed through correlation between the differences in WAT, the differences in pour poin,t and the relative crystallization (C r ) with the AMPs of asphaltenes. The AMPs of the asphaltenes causing the greatest impact on the increase of the crystallization temperature are the pericondensed carbons (C aaa ), ratio of peripheral carbons/aromatic carbons (C p /C ar ), and aromaticity factor ( f a ), and decreases in these properties are attributed to the length of the aliphatic chains (n) and the naphthenic rings (C n ); the concentration of asphaltenes (C oasf ) has little effect. The degree of crystallization is increased by f a and decreased with C aaa , C p /C ar , paraffinic carbons (C s ), and C oasf . The pour point is only increased by f a and decreased withC aaa and C n , and C oasf is negligible.

A biomass adapted to degrade toluene and xylenes in mixture was grown in a batch reactor with substrates supplied by pulses. The inhibition of biomass growth in the course of substrate degradation was investigated. The maximal biomass concentration of 7 g l-1 was obtained using 150 microliters of toluene and 15 microliters of a mixture of xylenes in one litre of liquid medium, and the maximal biomass productivity and yield were 53 mg l-1 h-1 and 0.32 gDW gs-1, respectively. Higher quantities of substrate added by pulses, that is 200 microliters of toluene with 20 microliters of xylenes and 300 microliters of toluene with 30 microliters of xylenes, caused an accumulation of metabolites. These higher quantities of substrates caused inhibition of microbial growth. Among the metabolites produced, 4-methyl catechol was found in large quantities in the culture medium and in the cells.

Asphaltene accumulation in porous media is considered a formation damage issue, which may happen during miscible flooding processes, EOR or even primary production, and this may have deep effects on oil production. Although asphaltene precipitation is widely known in literature, the works related to asphaltene accumulation in porous media are rather limited. This work consists in an experimental quantification of asphaltene accumulation in porous media, and a numerical simulation of this process. An experimental methodology was developed in order to recreate asphaltene accumulation on laboratory, using synthetic cores and stock tank oil samples from two different Colombian fields. This methodology consists in determinate basic properties (API, BSW, % asphaltenes), precipitation onset (using n-heptane as a precipitating agent) and perform core floodings at constant rates, these displacement tests showed damage due to asphaltenes between 18% and 27%. The numerical model was developed using Simulink tool, from MATLAB. This model was validated with the experimental results, obtaining a satisfactory agreement, with relative errors between this data less than 5%. Different regimes of accumulation were observed, varying flooding rate. Besides modeling permeability reduction, the model was able to evaluate other variables in the accumulation process.

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