Hossein Rassamdana

Asphalt flocculation and deposition. III. The molecular weight distribution

Extensive new experimental data are presented for the molecular weight (MW) distributions of the asphalt and asphaltene aggregates formed when a solvent is injected into a crude oil. The effects of various factors such as the nature of the solvent, the solvent-to-oil volumetric ratio and ageing of the solution are all investigated. It is shown that if the asphalt- or asphaltene-containing solution has not been aged for long enough, a bimodal MW distribution is always obtained, which is due to the existence of two different types of aggregates with distinct structures and mechanisms of formation. However, after long enough the MW distribution is unimodal. Based on models proposed for the formation of the structure of the asphalt and asphaltene aggregates, which are based on the analysis of small-angle X-ray and neutron scattering and precipitation data, analytical equations are proposed for the MW distribution of the aggregates which provide accurate predictions of the data.

Asphalt flocculation and deposition IV. Dynamic evolution of the heavy organic compounds

The dynamics of formation of asphalt and asphaltene aggregates are studied. Three different characteristics of the aggregates and their time evolution are compared, namely their precipitation, small-angle scattering, and molecular weight distributions. Thin-layer chromatography is used for the precipitation measurements, and its performance is compared with that of the standard IP-143 method. The effects of the precipitating agent on the structure and the precipitation properties are also investigated, as is the time-dependence of the amount of the resin in the solution. It is shown that the short- and long-time properties of the asphalt and asphaltene aggregates are very different, and the experimental data that are collected shortly after the aggregates are formed can be misleading. Moreover, the time dependence of the amounts of precipitated asphalt and asphaltene aggregates are also very different. A novel scaling approach is proposed for predicting the time-dependence of the amount of precipitation, whose predictions are in excellent agreement with the data.

Asphalt Formation and Precipitation: Experimental Studies and Theoretical Modelling

We present extensive new experimental data for the amount of precipitated asphalt and asphaltene aggregates formed with crude oil and various solvents, and their molecular weight (MW) distributions. A new scaling equation is proposed for predicting the onset and amount of the precipitates, somewhat similar to those encountered in aggregation and gelation phenomena. The scaling function takes on a very simple form, and its predictions are in very good agreement with the available data. We also present an analysis of small-angle X-ray and neutron scattering data to delineate the structure of the asphalt and asphaltene aggregates. Our analysis suggests that the asphalt and asphaltene aggregates are fractal structures with well-defined fractal properties. We identify the mechanisms that give rise to such fractal aggregates, based on which we propose a new analytical form for the MW distribution of the asphalt and asphaltene aggregates which provides accurate predictions for our data.

ON POSITION-SPACE RENORMALIZATION GROUP APPROACH TO PERCOLATION

In a position-space renormalization group (PSRG) approach to percolation one calculates the probabilityR(p,b) that a finite lattice of linear sizeb percolates, wherep is the occupation probability of a site or bond. A sequence of percolation thresholdspc(b) is then estimated fromR(pc,b)=pc(b) and extrapolated to the limitb→∞ to obtainpc=pc(∞). Recently, it was shown that for a certain spanning rule and boundary condition,R(pc,∞)=Rc is universal, and sincepc is not universal, the validity of PSRG approaches was questioned. We suggest that the equationR(pc,b)=α, where α isany number in (0,1), provides a sequence ofpc(b)s thatalways converges topc asb→∞. Thus, there is anenvelope from any point inside of which one can converge topc. However, the convergence is optimal if α=Rc. By calculating the fractal dimension of the sample-spanning cluster atpc, we show that the same is true aboutany critical exponent of percolation that is calculated by a PSRG method. Thus PSRG methods are still a useful tool for investigating percolation properties of disordered systems.

FORMATION, GROWTH AND PRECIPITATION OF FRACTAL MOLECULAR AGGREGATES IN POROUS MEDIA

Analysis of small-angle scattering data, as well as novel precipitation measurements, are used to delineate the structure of the molecular aggregates that are formed when a fluid is injected into a porous medium to displace the in-place fluid. Our analysis suggests conclusively that these aggregates are fractal formed by diffusion-limited processes. The implications for the molecular weight distribution of the aggregates and modelling their flow and precipitation in a porous medium are discussed.