Oxidation of heavy crude oil in different type of formation

Thermal energy is used to extract heavy crude oil from their formations. This thermal energy can be introduced from the surface (hot injection) or it can be generated in-situ by burning a part of oil. Generation of thermal energy by burning part of oil in-situ, is known as in-situ combustion. Partial burning of oil during in-situ combustion involves various competing reactions occurring over different temperature ranges. These reactions are Low Temperature Oxidation (LTO), Medium Temperature Oxidation (MTO) and High Temperature Oxidation (HTO). Low Temperature oxidation take places when none or little carbon oxides are produced in effluent gas despite the rate of oxygen consumption being at its highest level. The result shows that the LTO reactions did not appear in consolidated formation, whereas in unconsolidated formation the LTO reactions occurred. The occurrence of LTO reaction in unconsolidated formation is attributed to increased bed thickness and better accessibility to the oil. Better accessibility and increased bed thickness favoured the LTO reactions. The presence of LTO reactions in in-situ combustion process has effected the pre-exponential constant and activation energy of the HTO reactions. With the occurrence of LTO reactions the amount and Hydrogen to carbon ratio of fuel also changed. Fassahi and direct Arrhenius methods were used to evaluate the kinetic parameters by assuming first order reaction rate with respect to carbon and oxygen concentrations. (author)