Residual Organic Matter Associated with Toluene-Extracted Oil Sands Solids and Its Potential Role in Bitumen Recovery via Adsorption onto Clay Minerals

Adsorption of hydrocarbon components, particularly by clay minerals, has an important influence on the recovery of conventional oil from reservoir rocks. In the same vein, biwetted clay particles have been associated with bitumen losses during processing of surface-mined oil sands. In this work, we examined four oil sands with very different batch-extraction unit (BEU) bitumen recovery profiles. Bitumen-free solids from these ores were subjected to supercritical fluid extraction with methanol to separate quantitatively any toluene-insoluble, residual organic matter. The yield of extract correlated well with the amounts of solids in the fine (<44 mu m) and clay ( < 3 mu m) size fractions as well as with the concentrations of kaolinite and illite present in the oil sands ores. It is generally assumed that organic matter adsorbed by reservoir solids is asphaltic in origin; however, in the results discussed here, the compositional and structural analysis of the methanol extracts showed more similarities to the resin component of bitumen. Also, in comparison to other bitumen saturates, aromatics, resins, and asphaltenes (SARA) fractions, the extracts from each oil sands were somewhat enriched with pyridines, sulphoxides, and sulphones. We argue that the physicochemical properties of the residual organic matter separated by supercritical extraction strongly influence the wettability of solids in the ores through adsorption onto clay minerals. We suggest that this mechanism is a prerequisite for the formation of biwetted clay particles capable of stabilizing emulsified bitumen-in-water droplets that are too small to be successfully recovered by flotation.