New Insights Into Oxidation Behaviours of Crude Oils

Abstract

Abstract Systematic studies are performed to investigate oxidation behaviour of three different types of crude oils (light oil, medium oil and Athabasca bitumen) by using two thermal analysis techniques: Thermogravimetry and Pressurized Differential Scanning Calorimetry. This study is also to look at the effect of pressure on energy generation associated with oxidation reactions in different temperature ranges. It is observed that oxidation behaviours for light and medium oils are substantially different from those of Athabasca bitumen. The difference is seen in the temperature ranges where significant oxidation reactions occur. The experimental data in this work provide further evidence and addresses the difference in the oxidation behaviour of light oil and heavy oil. Introduction It is important to distinguish air injection applied to a light oil reservoir from the same process for heavy oil. Generally, the former is called air injection for light oil and the latter is termed in situ combustion. In both processes, various oxidation reactions take place(1). However, the main objective of air injection for light oil is to produce flue gas though oxidation reactions and to sweep the oil with the flue gas given that light oil is mobile under reservoir conditions(2), whereas in the heavy oil case, a thermal effect is desired for reducing the viscosity of heavy oil and to mobilize it. Moore et al. (2) reported that for both light oil and heavy oil, effective displacement requires the oxidation kinetics to be in the bond scission or combustion mode, i.e., effective displacement for both light and heavy oil needs a vigorous high temperature oxidation front to be maintained. There is some controversy about the application process for light oils. Some researchers state that light oil can be displaced without the need to generate higher temperatures. Ren et al.(3) point out that air injection in a light oil reservoir could be viewed as a conventional gasflooding process, as long as the oxygen in the injected air is removed in the oil bearing zones. Kisler and Shallcross(4), Moore et al.(2) and Ferguson(5) have addressed the different oxidation behaviours between light and heavy oils that might occur in the different temperature intervals. Because of the lack of a full understanding of light oil oxidation at reservoir conditions, people simply apply the concept of oxidation behaviour from heavy oil onto the case of light oil, which creates misleading information regarding the oxidation behaviour of light oils. Therefore, the principle objective of this study is to provide experimental information about the effect of pressure on the oxidation behaviour of crude oils and the difference between the oxidation behaviours of light oils and heavy oils. Instruments and Test Conditions Two different thermoanalyzers are used to conduct this study: Pressurized Differential Scanning Calorimeter (Q10P TA Instrument, US) and Thermogravimetry Differential Scanning Calorimeter (TG/DSC 111 Setaram, France). Pressurized Differential Scanning Calorimeter (PDSC) Experiment The test pressure is up to 7 MPa (1,000 psig) and the temperature range is from 20 to 650 °C.