Revisiting asphaltenes instability predictions by probing destabiliztion using a fully immersed quartz crystal resonator

Abstract

The method of Asphaltene Instability Trend (ASIST) was derived from London dispersions first principles and Flory-Huggins theory to model the microscopical appearance of unstable flocs using limited number of refractive index (nD) measures on stock-tank oils (STO), series of liquid precipitants (n-alkanes) and routine PVT data (Buckley et al., 2007).In order to eliminate the tuning of the aging time of solutions in the method, the experimental protocol was modified by monitoring the signal of a fully immersed Quartz Crystal Resonator (QCR) to detect the instantaneous destabilization of asphaltenes in the surrounding media. Isothermal titrations were performed under atmospheric pressure while mixing. The test matrix was designed to vary the chain length of the n-alkanes titrant and the temperature. Subsequent refractive indices at detected conditions were used to calculate solubility parameters (δ) and to predict the instantaneous detection of unstable asphaltenes during the expansion of gas dissolved systems using the exact same immersed apparatus. Predictions were then challenged against experimental observations of artificial live oil systems created by recombining dead oils with gas mixtures at pressures up to 1000 bar. Isothermal Constant Mass Expansion (CME) experiments provided measured volumes as a function of pressure which served for modeling, along with the QCR sensor signal to probe the first agregation and deposition of unstable asphaltenes for each system at various conditions. Prediction results were compared to experimental detections for 2 different crude oils, temperatures ranging from 45°C to 120°C and gas dissolved concentrations ranging from 0 to 60 %mol.