With the ever increasing demand for energy to meet the needs of growth in population and improvement in the living standards in particular in developing countries, the abundant unconventional oil reserves (about 70% of total world oil), such as heavy oil, oil/tar sands and shale oil, are playing an increasingly important role in securing global energy supply. Compared with the conventional reserves unconventional oil reserves are characterized by extremely high viscosity and density, combined with complex chemistry. As a result, petroleum production from unconventional oil reserves is much more difficult and costly with more serious environmental impacts. As a key underpinning science, understanding the interfacial phenomena involved in unconventional petroleum production, such as oil liberation from host rocks, oil-water emulsions and demulsification, is critical for developing novel processes to improve oil production while reducing GHG emission and other environmental impacts at a lower operating cost. In the past decade, significant efforts and advances have been made in applying the principles of interfacial sciences to better understand complex unconventional oil-systems, while many environmental and production challenges remain. In this critical review, the recent research findings and progress in the interfacial sciences related to unconventional petroleum production are critically reviewed. In particular, the chemistry of unconventional oils, liberation mechanisms of oil from host rocks and mechanisms of emulsion stability and destabilization in unconventional oil production systems are discussed in detail. This review also seeks to summarize the current state-of-the-art characterization techniques and brings forward the challenges and opportunities for future research in this important field of physical chemistry and petroleum.

Investigations of nonaqueous extraction (NAE) of bitumen from minable oil sands have been extensively revisited in the past decade as an alternative to Clark hot water extraction (CHWE). Significant advances have been achieved in understanding NAE processes at bench and pilot scales, although many questions remain regarding the commercialization of NAE. This critical review summarizes recent research findings and progress on fundamental and practical aspects associated with novel extraction processes, focusing on the technological method, solvent selection, recovery of solvent, and removal of fines. The review also identifies opportunities and challenges for bitumen recovery from oil sands using nonaqueous processes.

A novel micropipet technique was developed to quantify the dewetting dynamics of individual microsphere particles by emulsified viscous crude oil drops in aqueous media. This technique allowed dynamic microscale receding contact angles of water to be measured in situ for solid−oil−water systems. System parameters, including modification of glass microspheres and characteristics of oil drops, were varied to study their effect on dewetting dynamics of the systems. Increasing solvent dosage in viscous oil was found to decrease static receding contact angle of water for clean and bitumen-treated glass surfaces, but showed a negligible effect on static receding contact angle for ethyl cellulose (EC)-treated glass surface. Interestingly, dynamic dewetting behavior exhibited a strong dependence on surface modification and the addition of solvent to viscous oil. No dewetting dynamics was observed for clean hydrophilic glass surface. For bitumen-or EC-treated glass surfaces, more rapid dewetting dynamics of water were determined with increasing addition of solvent to viscous oil. Both de Gennes viscous dissipation hydrodynamic and the Blake/Haynes molecular-kinetic models were developed for the current system to understand the observed dynamic dewetting characteristics.

Bitumen liberation is known to be an essential step for bitumen recovery from sand grains using the current warm/hot-water-based extraction process. This study aims at understanding the role of naphtha or toluene addition in enhancing bitumen liberation. Results from an in situ bitumen liberation visualization measurement indicate that soaking two oil sands ores by solvents at 10–30 wt % of the bitumen could significantly enhance not only the ultimate degree of bitumen liberation (UDBL) but also the rate of bitumen liberation (RBL) in the process water at ambient conditions. Although ore-type- and solvent-type-dependent, both the UDBL and RBL would increase sharply at 10–20 wt % solvent dosage. A further increase in solvent dosage showed a diminished increase in the UDBL. To understand the observed improvement, viscosities of bitumen directly extracted from the ores and its mixture with solvents were measured, as well as diluted bitumen–water interfacial tensions. Results showed that adding solvent into the bitumen reduced bitumen–water interfacial tension and more so for the reduction in bitumen viscosity. Interestingly, the viscosity and interfacial tension of diluted bitumen were found to be dependent upon the source of ores and type of solvents. The UDBL was found to be inversely correlated with the interfacial tension and bitumen viscosity, while the RBL correlated almost linearly with the interfacial tension/viscosity ratio, which acted as the balance of the interfacial tension driving force/adhesion drag force. These correlations were less dependent upon the types of ores and solvents.

The composition and distribution of saturates, aromatics, resins, and asphaltenes (SARA) fractions in the bituminous layer on the surface of Athabasca oil sands were identified using elemental analysis (EA), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (SEM) with an energy-dispersive spectrometer (EDS), and Fourier transform infrared spectrometry (FTIR). The contents of elements sulfur (S) and nitrogen (N) and the ratios of carbon/ sulfur (C/S) and carbon/nitrogen (C/N) were characterized as potential indicators for evaluating the distribution of SARA fractions in the bituminous layer. Results indicated that saturates and aromatics tend to deposit at the outer bituminous layer, while asphaltenes and resins were inclined to distribute at the inner layer. Results also suggested that the distribution of SARA fractions was thermodynamically dependent and susceptible to thermal treatment. On the basis of the experimental results, a conceptual distribution model was proposed, which is supposed to serve as a basis for future studies on the liberation of bitumen from oil sands and the operation conditions for oil sands processing.

A major drawback associated with current hot or warm water-based bitumen extraction processes is the high consumption of energy. To address this issue, an aqueous–nonaqueous hybrid bitumen extraction process (HBEP), in which a portion of the diluent (solvent) was added upfront to soak mined oil sands prior to its water-based extraction, was proposed and demonstrated to be feasible to process mineable oil sands at ambient temperatures. This study investigates the effect of adding ethyl cellulose (EC) as a promising demulsifier to the solvent on bitumen recovery and froth quality in the ambient HBEP. The laboratory flotation results clearly showed a significant improvement in froth quality with a negligible setback on bitumen recovery by 100–200 ppm EC addition to the HBEP. Determined by an online visualization method, the addition of EC in solvent to the HBEP was found to further enhance separation kinetics of bitumen from sand grains of real oil sands ores. The addition of EC in solvent also increased the probability of bitumen droplet coalescence determined with a micropipette technique, but hindered the attachment of air bubbles to solvent-soaked bitumen, in particular at high EC dosages as evaluated by increased induction time of air bubble-bitumen attachment.

Dynamic evolution of liquid/liquid/solid contact line at micrometer length scale, corresponding to the Bond number Bo∼0, was investigated in a system with tuneable interfacial properties. Viscous oil was spontaneously displaced by water on a micro-sized and spherical glass surface. By controlling wettability of substrate and chemistry of surrounding aqueous solution, the displacement dynamics of three phase contact lines over a wide range of capillary numbers was studied. The rates of spontaneous oil displacement showed strong dependence on fluid viscosity and interfacial properties of the system. The observed wetting dynamics were modeled using hydrodynamic and molecular-kinetic theory. Energy dissipation in the immediate neighborhood of the contact line was shown to determine the wetting dynamics of our micro-scale experiments, even when capillary numbers were well above 10 -4 in which hydrodynamic flow regime could be usually expected for conventional macroscopic systems. † B. K. Primkulov and F. Lin contributed equally to this work.

An essential requirement for efficient heavy oil production is liberation of heavy oil from host rocks, which is determined by the wettability of the rocks, and the interfacial tension and viscosity of heavy oil. Recent progress on the design of an online visualization flow cell allows capture of dynamic heavy oil liberation processes from the surfaces of sand grains in real time under a water flooding environment. However, the accurate assessment of heavy oil liberation remains a challenge, due to uncertainties in defining oil-free areas of heavy oil contaminated rock surfaces. In this study, three new image-processing algorithms of modified empirical, Gridding, and Edge-covering methods were applied to image transformation for heavy oil liberation analysis. These methods were found to be more accurate and robust in determining the threshold value distinguishing liberated from unliberated sand surfaces. The use of wavelet transform theory in the Gridding and Edge-covering methods led to faster calculations with a typical error of less than 2 % in the quantitative analysis on the threshold value determination and the degree of heavy oil liberation. Among these three methods, the Gridding method with a sound theoretical foundation was shown to be the most reliable. The results showed that the threshold value determined was highly dependent on the types of ores and the image capture settings such as lighting conditions, exposure time, and microscope magnification.