Investigating time-dependent asphaltene precipitation behavior

Abstract

Asphaltenes precipitation is strongly a time-dependent phenomena and it can take up to several months for destabilized asphaltenes to grow to their final state after precipitant addition. The main focus of this work is to investigate differences in properties and aggregation behavior of asphaltenes precipitated at different times. Asphaltenes are fractionated from crude oil by adding a precipitant (e.g. heptane) at a fixed concentration, and destabilized asphaltenes are collected at different times until equilibrium is reached. Small-Angle X-ray Scattering (SAXS), Nuclear Magnetic Resonance (NMR). Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Elemental Analysis (EA) were used to characterize fractionated asphaltenes samples. Preliminary results showed that the differences in the properties of asphaltenes fractionated at different precipitant concentrations and timesareslightly different for SAXS. ICP-MS and EA techniques. However. there was no significant trend observed from NMR results. We also investigated the aggregation behavior of time-based fractionated asphaltenes by dissolving them in a solvent and monitoring their aggregation behavior after precipitant addition by microscopy experiments. The microscopy results showed that the aggregation behaviour of the time based fractions are different. The fraction that precipitate earlier has significantly higher aggregation rate than the fraction that precipitate later. This indicated that the first fraction to precipitate is the more unstable fraction and has higher aggregation tendency.