Richard McFarlane

Molecular structure of reactive coals during oxidation, carbonization and hydrogenation—an infrared photoacoustic spectroscopic and optical microscopic study

Abstract Coals from western Canada were examined for structural changes occurring during oxidation, carbonization and hydrogenation by means of FT-IR spectroscopy, optical microscopy and chemical analysis. The coals are of Cretaceous to Eocene age, ranging in rank from subbituminous C to medium-volatile bituminous (0.42–1.47% R o ). Results indicate that the reactivity of the coals during the above mentioned processes depends on rank and petrological composition. Infrared spectroscopy is shown to be sensitive to the molecular structural changes occurring during these processes and provides a chemical basis for interpreting data from chemical analysis and optical microscopy.

Evaluation of Steam Circulation Strategies for SAGD Start-Up

The impact of steam quality, circulation rate and pressure difference between the well pair during SAGD initialization using steam circulation was explored through the use of numerical simulations employing a discretized wellbore model. These operating parameters appear to affect uniformity of reservoir heating, occurrence of steam breakthrough and time required to establish communication between the well pair. The simulation results indicate that, for the given tubing and liner sizes and reservoir properties, relatively lower circulation rates at high steam quality are more favourable for faster initialization and development of uniform temperature between the horizontal well pair. At lower steam qualities, however, higher circulation rates appear more favourable. The use of high steam quality in combination with high circulation rates leads to slower rates of initialization, less uniform heating along the length of the wells, and possibility of premature steam breakthrough at the heel. It was also found that having a higher steam quality in the lower well than in the upper well could lead to faster initialization and more uniform heating between the well pair. A small pressure difference, offsetting the natural hydraulic pressure (50kPa), appears to be more favourable for faster and more uniform initialization.

Chemistry of fresh and weathered resinites. An infrared photoacoustic spectroscopic study

Abstract Photoacoustic infrared spectroscopy has been used to examine the chemical structures of resinites collected from coals of western Canada, Arctic Canada and Australia. Variations in the chemical structure of the resinites were examined from the point of view of location of the resinite within the coal-bearing strata and coal-bearing section and the effect of rank and age. The effects of weathering were analyzed in terms of the structures determined by infrared spectroscopy of the more weathered exterior surface as compared to the less weathered, unexposed interior surface. The molecular structure of the less weathered interior surfaces was found to be rather similar for resinites of similar rank. The exterior weathered surfaces were usually quite different and these differences were related to rank and the degree of weathering influenced by the depositional environment.

Evolution of the chemical structure of Hat Creek resinite during oxidation: a combined FT-IR photoacoustic, NMR and optical microscopic study

Abstract Resinite, hand picked from a subbituminous coal in the Hat Creek No. 1 deposit in south central British Columbia, Canada, was subjected to oxidation in air at temperatures between 50°C and 400°C. The initial and oxidized resinite samples were analyzed for variations in molecular structure by the use of Fourier transform infrared (FT-IR) photoacoustic spectroscopy and 1H and 13C nuclear magnetic resonance spectroscopy. The changes in molecular structure determined were correlated with differences observed in optical reflectance and fluorescence properties. The resinite in its initial state was predominantly aliphatic in nature and could be characterized as a diterpenoid, with alkene and carboxylic functionalities exocyclic to the six-membered rings composing the diterpenoid skeleton. Oxidation between 50°C and 100°C resulted in only minor structural changes. During oxidation between 100°C and 250°C there were very significant changes, involving the diminution in the number of aliphatic CH structures, the complete loss of the exocyclic alkene function, the appearance of aromatic structures and the conversion of carboxylic acids to acid anhydrides. Above 250°C, aliphatic groups continued to decline in number, aromatic character continued to increase and spectroscopic features, attributable to acid anhydrides, achieved maximum intensity. The optical reflectance of resinite increased with increasing oxidation temperature and the trends in reflectance and fluorescence properties (colour, wavelength of maximum intensity and red/green quotient) could be ascribed, as reported in earlier studies, to: (1) chemisorption, which occurs between 25° and 100°C, and decomposition of chemisorbed components at 100–150°C; (2) oxycoal formation (150–300°C), in which oxygen complexes and oxidation rims develop; and (3) combustion (>350°C). The variations n mass, infrared peak ratio (CH/C=O), fraction of aromatic carbon (fa) and fraction of hydrogen attached to aromatic carbon (Har), with the variation in the temperature of oxidation mirrored the changes observed by optical microscopy. The results show that the physical changes observed by optical microscopy have a direct correlation with the molecular structural changes determined by FT-IR and NMR spectroscopy. Additionally, it has been observed that resinites underwent thermal aromatization, a phenomenon not well studied for these materials. The changes observed in oxidation structures can be related to reactions involving thermal dehydrogenation of the diterpenoid ring structures and those involving oxygen addition. Oxygen inclusion occurs at all temperatures above 100°C, whereas thermal aromatization occurs mainly above 250°C.