A. Ballard Andrews

Molecular Orientation of Asphaltenes and PAH Model Compounds in Langmuir−Blodgett Films Using Sum Frequency Generation Spectroscopy

Asphaltenes are an important class of compounds in crude oil whose surface activity is important for establishing reservoir rock wettability which impacts reservoir drainage. While many phenomenological interfacial studies with crude oils and asphaltenes have been reported, there is very little known about the molecular level interactions between asphaltenes and mineral surfaces. In this study, we analyze Langmuir-Blodgett films of asphaltenes and related model compounds with sum frequency generation (SFG) vibrational spectroscopy. In SFG, the polarization of the input (vis, IR) and output (SFG) beams can be varied, which allows the orientation of different functional groups at the interface to be determined. SFG clearly indicates that asphaltene polycyclic aromatic hydrocarbons (PAHs) are highly oriented in the plane of the interface and that the peripheral alkanes are transverse to the interface. In contrast, model compounds with oxygen functionality have PAHs oriented transverse to the interface. Computational quantum chemistry is used to support corresponding band assignments, enabling robust determination of functional group orientations.

Infrared contrast of crude-oil-covered water surfaces

Infrared oil spill detection utilizes either temperature or emissivity contrast of native and oil-covered water surfaces. In particular, the thickness dependent radiance contrast due to thin film interference has been studied. Together with detection boundaries derived from the radiative transfer equation, we can explain historically observed daytime contrast reversal and our observations during nighttime, better contrast from thin oil slicks than from thick films, which to our knowledge has not been mentioned in the literature. These findings have important implications to long-wavelength infrared (LWIR) instrument design and data interpretation for crude oil spill detection.

Molecular Size Determination of Coal-Derived Asphaltene by Fluorescence Correlation Spectroscopy

The molecular properties of asphaltenes have been the subject of uncertainty in the literature; in particular the molecular architecture is still a matter of debate. Some literature reports provide evidence that the contrast of petroleum asphaltenes versus coal-derived asphaltenes is useful for understanding the governing principles of asphaltene identity. Here, we employ fluorescence correlation spectroscopy to measure the diffusion constants of asphaltenes obtained from the distillation resid from coal liquefaction fluids. Concentrations employed herein are ∼10−8 molar, precluding asphaltene aggregation. These are compared with the same measurements on petroleum asphaltenes. These results confirm that the molecular sizes of these coal-derived asphaltenes are much smaller than virgin petroleum asphaltenes. Coal-derived asphaltenes are simpler than petroleum asphaltenes and provide correspondingly tighter constraints for understanding asphaltene molecular architecture. The small size, small alkane fraction, and large PAH of coal-derived asphaltenes are consistent with an “island” molecular architecture.

Fluorescence Methods for Downhole Fluid Analysis of Heavy Oil Emulsions

Acquisition of oil samples from the reservoir prior to oil production is essential in order to design production strategies and production facilities. In addition, reservoir compartmentalization and hydrocarbon compositional grading magnify the necessity to map fluid properties vertically and laterally in the reservoir prior to production. Downhole fluid analysis (DFA), performed in situ in the oil well, helps optimize this fluid mapping process. However, for heavy oil reservoirs drilled with water based muds, fluid mapping has been largely precluded due to the formation of stable water‐in‐oil (w/o) emulsions, which add significant complexity to sample acquisition and which can preclude standard DFA measurements. Here, fluorescence measurements are shown to be dependent on oil type but independent of the state of emulsion even at very high water fractions. Thus, downhole fluorescence measurements can be used to perform hydrocarbon fluid mapping in the reservoir. The sensitivities of fluorescence and optical absorption measurements are determined for different excitation wavelengths, oil type, and oil concentration.