A reproducible and linear method for separating asphaltenes from crude oil

Petroleum asphaltenes exhibit strong structural similarities to their parent kerogen. Thus, they can be used to help determine the source rock characteristics of active kitchen areas and to reconstruct the filling histories of reservoirs. The analysis of asphaltenes from compartmentalised reservoirs with complex charging and alteration histories presents a particularly difficult challenge because the in situ compositional variations are sometimes subtle. It is, therefore, of paramount importance that asphaltene separation methods be utilised which are highly reproducible and linear, thereby minimising experimental uncertainty and providing high resolution interpretative capability. The asphaltene separation method described here is built on many that have been proposed before. Different parameters for asphaltene separation were investigated, which influence the asphaltene amount and properties, with the main focus on reproducibility and linearity. Gravimetric and thermal analysis techniques were used to evaluate yield and quality. The developed asphaltene separation method described in detail has four sequential steps: (1) dissolution of the oil in dichloromethane/1 vol% methanol, (2) addition of an excess of n-hexane, (3) settling time and (4) filtration, purging and weighing; this sequence of steps is repeated three times. Results concerning the reproducibility depending on solvent type, solvent amount and aging time, as well as the linearity depending on sample amount, are presented.