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Heavy Oil Properites & Processing Research Program
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Click on a research theme to see the expanded description: Projects in the HOPP program address the following topics:
Current projects address the following topics: Oil characterization involves dividing the oil into components and pseudo-components and assigning properties such as molecular weight, density, and critical properties to each component. With conventional oils, the characterizations are often constructed based on GC analysis and/or distillation data. However, this data only represents about half of a heavy oil. We are developing new characterization methods for the non-distillable fraction of heavy oils including a deep vacuum fractionation method and a supercritical fractionation method. We are also examining the extrapolation of existing property correlations and the interplay between extrapolations and equation-of-state based phase behavior calculations. Heavy Oil and Solvent Phase Behavior Phase behavior is critical for solvent based recovery and surface processes. For example, solubility of a gaseous solvent in the oil is maximized near the dew point but the formation of a second liquid phase is undesirable for recovery processes. We are measuring phase diagrams for heavy oil and solvents such as methane, ethane, propane, and butane. Phase boundaries are being determined for liquid-liquid, vapour-liquid, vapour-liquid-liquid, and asphaltene precipitation regions. Phase volumes and compositions are also being measured. We are developing equation-of-state based approaches to model the observed phase behavior with a single oil characterization methodology. Schematic of PVT Cell:
Heavy Oil and Solvent Physical Properties Density, viscosity, and diffusivity play an important role in heavy oil recovery and processing. For example, in solvent assisted heavy oil recovery methods, the solvent must diffuse into the oil where it reduces the density and viscosity so that gravity drainage can occur. We are measuring these properties for mixtures of heavy oil and solvents such as methane, ethane, propane, and butane. We have developed a correlation for the viscosity of heavy oils and liquid solvents and are extending the correlation to mixtures with light solvents. Current projects are to: develop a correlation for diffusivity of solvents into heavy oils; develop a method to predict the density of solvent diluted heavy oils. Viscosity of a heavy oil diluted with a condensate:
Asphaltene Self-Association and Precipitation Asphaltene precipitation is a common problem in oil recovery and processing and yet there has been limited success in quantitatively predicting asphaltene solubility. Part of the challenge is that asphaltenes self-associate and solubility may be determined in part by the degree of association. Furthermore, the degree of self-association must be predicted as a function of temperature, pressure and composition. We measured self-association in terms of average molar mass over a range of conditions using vapor pressure osmometry. We developed a new view of asphaltene association analogous to polymerization and successfully fit the measured molar mass data with this model. We also showed that asphaltenes and resins can be considered as a continuum of self-associating species. We are also adapting regular solution theory and equation of state (EOS) approaches to predict asphaltene precipitation in pure solvents and from heavy crude oils given an asphaltene molar mass distribution. We separated crude oil into solubility fractions and developed correlations for the properties of each fraction. The correlations required only the molar mass of the fraction. We then predicted molar volumes and solubility parameters using the parameters as input to a regular solution model. We successfully fitted and predicted onsets and amounts of precipitation from a variety of heavy oils at ambient conditions. We have extended the model to a range of temperatures and pressures based on data collected in a PVT cell that was adapted to measure asphaltene yields. Current projects are focused on: measuring and modeling the solvent content in asphaltene-rich phases; measuring and modeling precipitation from bitumens diluted with light solvents such as propane. Asphaltene precipitate as particles with diameters in the order of 1 μm. These particles tend to flocculate into aggregate with diameters up to several hundred micrometers. The extent of the flocculation depends on the amount of precipitate, the solvent, shear rate and temperature. Flocculation data and predictions are likely required to understand and predict asphaltene deposition. We measured the size distribution of flocculated asphaltenes in mixtures of toluene and heptane at different shear rates and developed a kinetic flocculation model which was capable of fitting the data. We also measured and modeled the size distribution of flocs of asphaltenes precipitated from n-alkane diluted bitumens. Micrograph of asphaltenes precipitated from a solution of asphaltenes in toluene and n-heptane (adapted from Rastegari, M.Sc. thesis, 2003):
Rheological and Interfacial Properties of Water-in-Bitumen Emulsions Emulsion treatment is often required in crude oil production, transportation, processing and in bitumen froth treatment. Many bitumen and crude oil emulsions are stabilized by components found in the oil itself, such as asphaltenes and native solids. Effective emulsion treatments are dependent on the fundamental study of interfacial properties, such as interfacial tensions and elasticity. Our research has shown that asphaltenes initially adsorb at the interface as a monolayer of self-associated molecular aggregates. This film gradually reorganizes into a rigid network with the effect of increasing the overall emulsion stability. These films may be so cross-linked with asphaltenes as to form a skin that resists contraction. Fine clays 100-500 nm in diameter, inherent in bitumen and crude oil have also been shown to stabilize emulsions beyond that conferred by asphaltenes or solids alone. We have also shown that coarse clays (1-10 μm diameter) destabilize emulsions at low concentrations when they displace asphaltenes from the interface. However, coarse clays stabilize emulsions at very high concentrations where they form a barrier between droplets. Other oil constituents such as resins and naphthenic acids, as well as chemical additives, may also contribute to emulsion stability and are currently under investigation. Some water-oil separations such as oil sands froth treatments involve diluted heavy oils and bitumen; hence, a range of concentrations under a variety of conditions must be investigated.
Bitumen Extraction from Oil Sands & Froth Treatment This project focused on the relationship between oil sand type, extraction conditions and froth treatment effectiveness. Athabasca oil sand is mined in a variety of qualities, from lean ores containing as little as 6% bitumen, and possibly with high fines content, to rich ores with greater than 14% bitumen. The traditional hot water flotation method yields a multi-component froth comprised of bitumen, water, and fine solids. As extraction conditions or oil sand type vary, the oil recovery needs to be maximized to ensure success. The water extraction process is dependent upon external factors, such as temperature, conditioning aids (usually NaOH), shear, aeration, diluents, and possibly other additives. Bitumen liberation from the sand matrix is made possible by exploiting the differences in system physical properties. Our work with Dr. Schramm (now at SRC) identified key mechanisms where, at optimum processibility conditions during extraction, interfacial tensions between the bitumen froth phase and its corresponding aqueous tailings are at a minimum and surface charges on bitumen droplets are at a maximum negative value. Froth produced by BEU: Testing froth treatment:
Froth treatment is a process where a bitumen froth is diluted with a solvent and heated to reduce bitumen viscosity and create a density difference between bitumen and water. Specifically two froth treatment methods are in use: the paraffinic solvent (or gravity settling) and aromatic solvent (centrifuging) methods. A successful froth treatment yields a oil-rich product with no water or solids. We performed a parametric study on extraction and froth treatment operating conditions and found that there is a strong link between froth treatment performance and extraction conditions, most notably with the use of NaOH as a conditioning aid. Current research is focused on rag layer accumulation in oil sand froth treatment processes. |
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Heavy Oil Characterization
