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Asphaltene aggregation is a two-step process concerning phase separation and asphaltene particle growth which provoke crude oil destabilization and significant problems during the production, transport, and refining of heavy and extra heavy crude oils. A recent and innovative approach to overcome this problem is the use of ionic liquids (ILs) as inhibitors or stabilizers of asphaltene aggregation. Since the information concerning the properties of the studied ILs is scarce, we characterized some of their electronic properties and critical aggregation concentration (CAC) by quantum chemistry and spectrofluorometry, respectively. We found that the presence of a complex anion such as [AlCl 4 ] -, [BF 4 ] -, and [PF 6 ]incremented the HOMO-LUMO gap (Δ H-L ), electronegativity (χ), absolute hardness (η), and dipole moment (μ) when compared to [Br] --containing ILs. Moreover, the ILs' CAC values showed a linear correlation with the dipole moment. Afterward, we studied the effect of various commercial ILs on the aggregation point (AP) of a heavy crude oil (HCO) due to the increment of (a) its concentration in toluene solutions or (b) the n-heptane volume by means of fluorescence spectroscopy. We have found that the aggregation of HCO occurs at larger crude oil concentration or n-heptane volume in the presence of some ILs. Here, ILs set a polar microenvironment around HCO asphaltenes, which stabilized them against further aggregation and precipitation. The better performance of ILs as inhibitors or stabilizers of asphaltene aggregation was found with those comporting a complex anion, a pyridinium ring, or a shorter alkyl substitution on the cation. Such ILs present the higher values of the calculated electronic properties.

Dynamic displacement experiments, simulating temperature and pressure conditions of an oil-bearing formation during primary production stage, were carried out to investigate the processes of asphaltene-induced precipitation and deposition during pressure depletion on a core sample and their effects on the absolute permeability. A representative monophasic-bottom-hole fluid sample and one core of consolidated Bedford limestone were used in coreflood tests. To identify the pressure and temperature conditions at which the asphaltene will begin to precipitate, as well as the bubble-point pressures of the reservoir fluid sample, the light-scattering technique solid detection system (SDS) using a variable volume, visual P V T cell was used. The coreflood test results indicated that the in situ asphaltene precipitation and deposition on porous medium damage absolute permeability and reduce effective porosity as reservoir fluid pressure is reduced until a point near bubble-point pressure. Core impairment, resulting from asphaltene deposition, was found to cause a 24% and 20% loss of initial oil permeability and effective porosity, respectively. A mathematical model, based on the transport of stable particulate suspensions in porous media, for asphaltene deposition was developed and validated directly with experimental results obtained in this investigation, as well as those found in the literature. On the basis of the developed mathematical model, two distinct mechanisms were identified as a consequence of the deposition process, namely, asphaltene adsorption and trapping. The porous medium was represented as a network of sites and bonds, with pore bodies identified as sites and pore throats as bonds. A satisfactory qualitative agreement was observed with the experimental results.

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Vapor-liquid equilibrium data are presented for the binary system carbon dioxide-N,N-dimethylformamide at 293.95, 313.05, and 338.05 K and pressures up to 12 MPa. The data are correlated using the Peng-Robinson equation of state with Wong-Sandler mixing rules. Agreement between the calculated and the measured equilibrium data has been found within 0.03% for vapor mole fractions and within 0.6% for pressures.