(55j) Solvents Effects on the Structure of Asphaltene Aggregates

Controlling asphaltene deposition is a critically important topic in petroleum production, but

asphaltene aggregate behavior remains poorly understood even with an abundance of hypotheses

and speculations concerning this topic. Current research suggests classifying asphaltenes into 2

types: soluble and insoluble based on their fractal dimension when precipitated in the presence of

heptane. Under these conditions two general fractal dimensions have been observed: ~2.1 for

insoluble asphaltenes (those that grow to the micrometer scale and precipitate), and ~1.7 for

soluble asphaltenes (those that remain on the nanometer scale and stay suspended in solution)1

.

Rheological measurements made in the lab also show that the intrinsic viscosity of asphaltene

aggregates changes as a function of heptane concentration. This observation is in agreement with

prior research that examined the molecular weights and intrinsic viscosities of asphaltene

aggregates in the presence of heptane2

. Indeed aggregate structure is a function of the solvent

environment, and this structure determines the phase behavior which is a precursor to deposition.

This talk will present research showing the changes in intrinsic viscosity and fractal dimension as

a function of flocculent concentration, and address the competing causes including aggregation

and solvation effects. A better understanding of aggregate behavior on the nanoscale is critical to

developing a more inclusive predicative model. Improving the understanding of asphaltene

behavior will ultimately benefit the petroleum industry by helping to avoid costly shutdowns due

to clogging and equipment failure.