Revisiting Asphaltene Deposition Tool (ADEPT): Field Application

Asphaltenes tend to deposit in reservoir, well tubing, flow lines, separators, etc., causing significant production losses. Asphaltenes are originally stable in crude oil at reservoir conditions. However, changes in temperature, pressure, and/or composition may cause asphaltenes to precipitate and potentially deposit onto the surfaces of a flowing conduit. There are several publications in the literature that discuss modeling of asphaltene phase behavior in oil as well as development of deposition models to simulate asphaltene deposition profiles along a flow path. In this paper, a previously reported asphaltene deposition tool (ADEPT) is used to study the deposition in a subsea pipeline in the Gulf of Mexico. This is the first demonstration of an asphaltene deposition simulator that has been used in a fully predictive manner. All of the required kinetic parameters used for deposition predictions were experimentally measured. A new methodology to scale up the deposition constant measured from a small-scale capillary deposition experiment to a large-scale subsea flow line is also reported in this paper. The predictions that made use of such an appropriately scaled deposition constant were in good agreement with field observations. The simulator was also able to predict the effects of a decreasing deposit thickness with increasing flow rates as observed in the Hassi Messaoud field. The paper further discusses a modified pseudo-transient simulator that is capable of incorporating the effect of deposit buildup on flow velocities and frictional pressure drop, which, in turn, affects the phase behavior of asphaltene. The differences between ADEPT and the pseudo-transient simulator is discussed. Simulation results show that incorporating the effect of deposit buildup causes a decrease in deposition rates with time, as reported from field observations.