Quantification of Asphaltene and Wax Sludge Build-up in Crude Oil Storage Facilities

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAt some thermodynamic conditions, asphaltenes flocculate into larger, almost spherical particles that have a specific gravity of 1.05 to 1.10. Work is cited here that indicates that asphaltene stable colloids exist in oil as very minute particles and that their pre-flocculation sizes are in the range of about 10 to 15 Å. This corresponds to 334 and 1,128 molecular weight respectively, assuming asphaltene spherical colloids and an experimentally determined asphaltene density of 1.06 g/cm 3 . The reason for this high specific gravity of asphaltene particles compared to the rest of the molecules of oils is that they consist mostly of asphaltenes and resins, the heaviest constituents of oils. Roughly, resins have specific gravities of 0.95 to 1.0 and asphaltenes 1.1 to 1.2. Because of their high specific gravity asphaltene particles settle by the force of gravity in storage systems where the convection currents and shear forces are minimal. Some of these particles are large enough to overcome the convection currents and shear forces and settle in large separators and occasionally in large pipes due to Stoke's law effects, especially at elbows changing the direction of flow where the particles impinge against the pipe wall and are temporarily halted. This paper presents a modeling methodology for the simulation of sedimentation of asphaltene and wax particles in both onshore and offshore storage systems. The asphaltene and wax particle size distribution is usually available from microscopic observations, filtration, and thermodynamic models. The sedimentation calculation is done by assuming that the particles have settled and are at gravimetric equilibrium. Two examples are presented: one 1,000,000barrel FPSO case and one 250,000-barrel oil storage tank case. Both the FPSO and the tank had lost a substantial fraction of their capacity due to accumulation of asphaltene and wax sludge.

Asphaltene-Induced Precipitation and Deposition During Pressure Depletion on a Porous Medium: An Experimental Investigation and Modeling Approach

“…It must be pointed out that, in these two models, we assumed that asphaltene particles have the same average size. This hypothesis could be an unrealistic condition; however, Leontaritis demonstrated that asphaltene particles distribution (at least in tank oil conditions) is close to a gamma distribution, and for all practical purposes it can be considered unimodal.…”

Asphaltene Formation Damage Stimulation by Ultrasound: An Analytical Approach Using Bundle of Tubes Modeling

“…Also, there are computational models which can estimate the APSD such as the thermodynamic colloidal model which is a phase behavior model capable of simulating the APSD as a function of the thermodynamics of the system [26][27][28]. Although many distribution functions can be fitted on asphaltene particle size data, we have chosen Gamma distribution because it is common in the literature [29,30]. This is partly due to the fact that the gamma distribution provides high flexibility in representing such data [29].…”

“…Although many distribution functions can be fitted on asphaltene particle size data, we have chosen Gamma distribution because it is common in the literature [29,30]. This is partly due to the fact that the gamma distribution provides high flexibility in representing such data [29]. The gamma distribution function is given as…”