(194c) An Industrial Vision of Asphaltene Risk during Oil Production

Efficient development strategies from reservoir to topside process chain require a perfect knowledge of the phase behavior of the produced fluids. Among these fluids, the ones containing asphaltene have a very singular position.

Asphaltenes have been studied for decade, as their very peculiar properties open a quasi infinite number of interesting studies to be performed, either from an academic perspective or from a more practical and operational point of view.

The most conventional way to describe the behavior of asphaltenes consider that, at reservoir conditions at high pressure, asphaltenes are stabilized in solution through the high density of the oil. As the pressure decreases during production, the density can decrease ultimatly to the point where the solvency power of the fluid phase is not good enough, so that asphaltenes start to flocculate. It is usually considered that this flocculation onset pressure has to be at least above the saturation pressure, as below that pressure the gas / liquid phase separation will cause the density of the liquid phase to increase again. It is particularly true if the nature of the gas does not influence the stability of asphaltenes by other mechanisms than its role of the density of the oil. Asphaltene risk is thus a complex interplay between the solvency power of the oil and the nature of the asphaltenes, and between thermodynamic and kinetics effects.

 

Ideally, the perfect workflow for flow assurance studies linked to asphaltene deposition would require 3 steps :

1/ to be able to predict the risk from a thermodynamic standpoint,

2/ to be able to quantify this risk through the integration of the kinetics effects, and

3/ to determine how to efficiently mitigate this risk, in particular through the use of chemical additives.

 

Recent developments or projects tend to raise the difficulty of achieving efficient predictions, by complexifing the systems, through higher temperature, pressure and nature of the gases, and commingling of different fluids.

 

By comparing our internal industrial practices to what can be found in the open academic literature, we will share our view of what is well understood, and the points that are still to be improved.