Kinetic modeling of the in-situ combustion process for Athabasca oil sands
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AbstractIn-situ combustion is an effective thermal recovery method and provides an important alternative to steam injection, but it is yet to be widely applied. A factor that has limited the application of ISC (in-situ combustion) is a lack of predictability at both the laboratory and field scales. The ISC process is very complex, and its modeling work requires an understanding of the behaviour of different physical phenomena including phase change, heat and mass transfer, and chemical reactions. A proper experimental kinetic analysis such as ramped temperature oxidation (RTO) provides critical parameters for modeling. In this study, the focus is to model appropriate kinetics and improve reaction models for this process. Different chemical reactions occur during ISC in different temperature ranges (Nader et al., 2007). For heavy oils and oil sands low temperature oxidation (LTO) dominates below 260°C, yielding partially oxygenated compounds and increasing the viscosity of oil, and as a result, limits the success of ISC. Negative temperature gradient (NTG) is observed from 280°C to 380°C, which is also named the middle temperature oxidation (MTO) or fuel deposition. This temperature range includes thermal decomposition and pyrolysis/cracking of hydrocarbons. Above 400°C, combustion reaction dominates, known as high temperature oxidation (HTO), producing carbon oxides and water. The objective of this study is to develop reaction kinetic models that can be used to describe the reactions of hydrocarbon fractions at various temperature conditions during the ISC of Athabasca bitumen. In this work, a set of improved kinetic models including LTO, MTO, and HTO reactions based on Saturates, Aromatics, Resins, and Asphaltenes (SARA) fractions in the crude oil are established. These kinetic models are used to reproduce the RTO experimental results through numerical simulation and to obtain successful history matched results. These models are developed using more data sets than what is currently available in the literature. An important feature of the improved models that differentiates the results of this study from those of previous studies is their ability to handle the whole combustion process starting from LTO to MTO to HTO for the Athabasca bitumen. This research will significantly increase the understanding of different chemical reactions occurring in heavy oil during the entire ISC process, and contribute to the development of reliable numerical models that can accurately predict ISC performance in different temperature scenarios.
Bibliography: p. 111-119