An Expanded Compositional Model For Lowtemperature Oxidation Of Athabasca Bitumen

More than ninety low-temperature oxidation tests were performed on Athabasca bitumen in the presence of rock matrix and water. These tests were run to evaluate the role of low-temperature oxidation with regard to oil composition and to develop kinetics parameters for application in numerical combustion simulators. This program was initiated as experience with laboratory combustion tube tests indicates that both low-temperature oxidation and thermal cracking reaction kinetics are required to predict the oxygen requirements and oil production performance. In addition to the Whole bitumen runs, tests were also conducted using maltenes, asphaltenes and the heavy oil fraction of the bitumen as the starting material. All work was performed in plug flow reactors at a total pressure of 4190 kPa (600 psig). Feed gas oxygen concentrations were 5, 10 and 50 mole per cent. The temperature varied from 22 °C to 275 °C and the time, from 4 to 72 hours. The gas phase was analyzed during the tests to follow the oxygen uptake history. After unpacking, the residual and produced hydrocarbons were analyzed in terms of mass per cent coke, asphaltenes and maltenes. It was found that the oxygen uptake rate did not follow typical Arrhensus behaviour over the temperature range investigated. The effect of the oxygen partial pressure was very important at low temperature but the reaction order, with respect to oxygen partial pressure, approached zero at temperatures in the range of 175 °C. Three definable low-temperature oxidation reaction regimes were identified. Transitions between the regions were characterized by the rapid formation of coke and the virtual disappearance of the asphaltenes fraction. Times corresponding to the transitions were found to depend on both temperature and oxygen partial pressure. Modelling of the region prior to coke formation was found to be described by a slightly modified version of the previously developed model of Adegbesan (1982). Simple relationships have been developed to describe the experimental coke, asphaltenes and maltenes (by difference) yields as a function of time, for the other two regions. Introduction Oxygen consumption and oil production are the important considerations in the design and operation of an in-situ process. Under high temperature (above 300 °C and ideal sweep conditions such as those normally associated with dry laboratory combustion tube tests, both the oxygen requirements and oil production are closely related to the fuel availability. Fuel for high-temperature combustion is that portion of the original oil which is consumed to form carbon oxides and water. Oil production is dictated by fuel consumption since no appreciable hydrocarbon remains behind the burning zone and all oil other than that burned is recovered. Oxygen requirements are related to the fuel availability through the oxygen / fuel ratio which is generally in the order of 2.3 m3(ST)/kg, hence a knowledge of the fuel requirements for a given reservoir allows for estimation of the operating and economic parameters. It is for this reason that traditional in-situ combustion literature concentrates on fuel availability [Showalter (1962) and Alexander et al. (1957)].