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         SEMINAR OF THE LABORATORY FOR COMPUTER DESIGN OF MATERIALS
           Institute for Computational Sciences and Informatics
		CSI 929  (http://science.gmu.edu/physics/)
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	Volumetric and Thermal Properties of Asphaltenes from
                   Molecular Dynamics Simulations

			      Mamadou S. Diallo
	   Materials and Process Simulation Center, Beckman Institute
	    California Institute of Technology, Pasadena, CA, 91125

   Asphaltenes are complex geomacromolecules operationally defined as the non
volatile and polar fractions of crude oil insoluble in aliphatic solvents such
as n-heptane. A commonly accepted view in the petroleum chemistry literature is
that crude oil asphaltenes form micelles which are stabilized by adsorbed
resins kept in solution by aromatics. Two key parametes that control the
stability of asphaltene micelles in a crude oil are the ratio of aromatics to
saturates and that of resins to asphaltenes. When these ratios decrease,
asphaltene micelles will coalesce and form larger aggregates. The precipatation
of asphaltene aggreagtes can cause several problems such as reservoir plugging
and wettability reversal. The adsorption of asphaltene aggregates at oil-water
interfaces has also been shown to cause the steric stabilzation of (W/O)
petroleum emulsions. Consequently, the oil industry is in critical need of
quantitative tools and thermodynamic data to predict asphaltene aggregation and
precipitation as a function of crude oil composition and reservoir temperature
and pressure.

   This presentation will describe a new method of estimation of the
thermodynamic properties of asphaltenes. This method combines computer assisted
structure elucidation (CASE) with molecular dynamics (MD) simulations. We use
quantitative and qualitative structural data as input to a CASE program
(SIGNATURE) to generate a sample of ten molecular models of asphaltenes from a
Saudi crude oil (Arab Berri).We then use NPT molecular dynamics simulations and
molecular mechanics to estimate the molar volume, density, cohesive energy,
solubility parameter, enthalpy, thermal expansion coefficient and specific heat
at constant pressure of the model asphaltenes structures. We find that the
estimated values are in good agreement with the available experimental data.

	               Monday , November 4 1996
                               5:00 pm
                       Room 206, Science & Tech. I
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