Laboratory tests have indicated that variations of pressure exerted on a petroleum fluid can cause the deposition of some of its heavy organic contents. A practical example is the heavy organics deposition during the flow of a crude oil in an oil well.
As the crude flows up in the well its pressure decreases which may cause the gas phase separation and, as a result, the heavy organics deposition. In this case if the depositions were merely due to the drop in pressure we would expect to observe heavy or ganic deposits at depths less than the bubble point depth. However, field data indicate that the deposition in the oil well could sometimes happen at depths less than the bubble point depth (see figure below taken from "Heavy Organic Deposition and Plug ging of Wells (Analysis of Mexico's Experience)" by J. Escobedo and G.A. Mansoori, Paper # 23696. Proc.II LAPEC, SPE, Caracas, Venezuela, March 8-11, 1992).
Variation of the heavy organic deposition depth with the bubble point depth in various wells in a Mexican Oil Field
This discrepancy is shown to be mostly due to the electrokinetic effect and partly due to the temperature drop in the upward flow of crude in an oil well. The fact that the deposition depths for most of the wells shown in the above figure are generally l ess than, but close to, the bubble point depth is indicative of the stronger role of pressure drop on the heavy organics deposition as it is also demonstrated in our simulation calculations.