(650f) Characterization of Asphaltenes In Stock-Tank Oil and Prediction of Its Phase Behavior At Reservoir Conditions

Asphaltene deposition is one of the most widely found flow assurance problems in upstream and downstream operations. It is well known that asphaltene precipitation is a necessary but not a sufficient condition for deposition. Although substantial amount of work has been done on this area, the mechanisms by which asphaltene precipitate and deposit are still being actively investigated.

Current methods used to determine the stability of asphaltenes in crude oil systems are based on near-infrared spectrometry and high pressure microscopy. Although these methods are widely used and accepted in the industry, they require time and can be expensive. This is the case particularly when a comprehensive study requiring different gas injections and temperatures needs to be performed.

In this work we propose as an alternative method the determination of the asphaltene behavior in stock-tank oil at room conditions by determining the onset of precipitation upon addition of different n-alkanes, which are known to be asphaltene precipitants. Determination of onset of asphaltene precipitation is done by using NIR spectrometry at room conditions.  These data can then be used to tune asphaltene parameters of a model. This model will then be used to extrapolate the behavior at reservoir conditions including the associated gas. Comparison with data at high pressure and temperature is also presented and discussed.

Because the precipitation and flocculation of asphaltenes is a process greatly affected by kinetic factors, systematic experimentation was done to determine the effect of time on determining the asphaltene precipitation onset. Including this information, a detailed experimentation procedure was developed that matches the experiments done at high pressure and temperature. Different crude oils were studied to validate the proposed methodology.

Finally, the spectrometric methodology was also applied to the study of the effect of asphaltene inhibitors. Advantages of the proposed methodology over current experimental methods will be highlighted in this presentation. Also, important insight into the mechanism of action of asphaltene inhibitors will be presented and discussed.