World heavy oil and bitumen deposits contain more than twice the amount of crude compared to conventional reservoirs. Thermal production operations are used worldwide for heavy oil and bitumen production. Because of their nature, heavy oil and bitumen have a higher asphaltene content than conventional hydrocarbons. Asphaltene behaviour is affected by changes in pressure, introduction of gas to a reservoir, acidizing and other factors, including temperature. The effect of temperature on asphaltenes in heavy oil is still not well understood.

The paper presents new data on asphaltene behaviour in thermal heavy oil and bitumen production operations. Liquid crystals in asphaltenes are detected when heat is applied. Temperature when liquid crystals appear in asphaltenes of heavy oil and bitumen is significantly lower than that for conventional oil. An assumption is made that this phenomenon is caused by the structure of asphaltenes, namely an enhanced amount of "archipelago" type molecules in asphaltenes. In situ combustion causes an increase of condensed aromatic compounds in asphaltenes, asphaltene transformation up to coke and deposition in porous media. The process changes the individual characteristics of the oil system. The individual characteristics of heavy oil do not change when steam injection technology is applied. The paper also provides data on viscosity of heavy oil and bitumen versus temperature as a function of heavy oil composition and the effect of ultrasound on heavy oil viscosity.

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