Asphaltene Aggregation from Crude Oils and Model Systems Studied by High-Pressure NIR Spectroscopy

Abstract

The aggregation of asphaltenes by pressure depletion both in a live crude oil and model systems of asphaltenes in toluene/pentane solvents is studied. Near-infrared spectroscopy utilizing a high-pressure NIR cell with a maximum operating pressure of 325 bar is used to study the onset of asphaltene aggregation. The NIR spectra are subject to a principal component analysis (PCA) in order to detect the asphaltene aggregation onset pressure. The effect of fluid compressibility on the NIR spectra is also demonstrated. The aggregation behavior of asphaltenes in model systems is shown to resemble the aggregation behavior for the crude oil. However, while the asphaltene aggregation in the crude oil is more or less completely reversible with repressurization, indications of only a partial redissolution are seen in the model systems. The kinetics of the redissolution is quite slow. A time of 72 h to equilibrate at the original pressure of 300 bar was required to redissolve the asphaltene aggregates formed within the crude oil by depressurization of the sample. Near-infrared spectroscopy in combination with principal component analysis is shown to be an efficient tool in detecting both bubble points and asphaltene aggregation onset pressures in high-pressure systems.

Asphaltene aggregation in organic solvents

“…Optical densities at a wavelength of 1600 nm are shown. The single wavelength analyses at 1600 nm have been reported previously [26][27][28][29][30][31]. The optical density values were relatively higher as the asphaltene concentrations increased.…”

The bitumen microstructure: a fluorescent approach

“…The asphaltene agglomeration theory is mainly based on the observation of asphaltene precipitation in various solvents and also crude oil [3]. The capability for self-assembly of polyaromatic structures is an often observed phenomenon.…”

Pore Wetting and Its Effect on Breakthrough Pressure in Water-Wet and Oil-Wet Pores

“…Some of reservoirs are water-wet and altered to be oil-wet during oil production [19]. This wetting inconsistency could severely affect the rheological properties of reservoir fluids in porous reservoir rocks and influence the multiphase flow displacement efficiency during the oil exaction in surfactant flooding process [20]- [22]. So, it would be necessary to investigate the wetting and displacement of liquids in both water-wet pore and oil-wet pore.…”