New insights into the oxidation behaviours of crude oils
MetadataShow full item record
AbstractSustainable economic development of many of the world's oil reservoirs requires application of novel technologies. High pressure air injection (HPAI) into light oil reservoir has been proven as a new alternative improved oil recovery (IOR) method for both secondary and tertiary recovery processes. The normal aim of a high-pressure air injection process is for the oxygen from the injected air to react with a small fraction of the reservoir oil at an elevated temperature to produce a mixture of carbon dioxide and nitrogen, which mobilizes the oil downstream and sweeps oil towards the production wells. However, what is actually taking place upon air injection into oil reservoir has not been fully understood. Some misconceptions of concerning high pressure air injection process still exist because of the complexity of oxidation reactions for crude oils. The goal of this investigation is to fingerprint the oxidation behaviour of hydrocarbons and to determine which physical and chemical processes can significantly affect the interpretation the oxidation performance for crude oils using two thermal analysis techniques, thermogravimetry and pressurized differential scanning calorimetry (PDSC), accelerating rate calorimetry (ARC). Systematic studies are performed to investigate oxidation behaviours of several pure paraffin and aromatic hydrocarbon compounds using the thermal analysis techniques. Then; the oxidation behaviours of saturates, aromatics, resins and asphaltenes (SARA) fractions of three different types of crude oils (the light oil, medium oil and Athabasca bitumen) are determined. Systematic experiments are also conducted on four crude oils with different compositions (the two light oils, one medium oil and Athabasca bitumen). This study looks at the effect of pressure on the energy generation associated with the oxidation reactions in the different temperature ranges. In the end, a simplified mathematical model is developed as an aid to better understand the thermal behaviour of hydrocarbons. In this study, the preliminary tests are performed to investigate the feasibility of improving ignition characteristics by adding certain chemicals into the selected light oil sample using thermal analysis techniques. This study addresses the important aspects of the oxidation behaviours of light oil and Athabasca bitumen. It is concluded that the behaviour of light crude oil is substantially different from that of heavy oils. For the light oils tested, in the low temperature range (<350°C), vaporization is a dominant physical process. Under certain conditions, such as high pressure and a suitable concentration of evaporated hydrocarbon fraction or/and decomposed fraction in the vapour phase, bond scission reactions in the vapour phase may be dominant. Therefore, the oxygen addition or low temperature oxidation reactions in the liquid phase and bond scission reactions in the vapour phase may overlap. The largest amount and the highest rate of energy generation occur in the low temperature range. The combustion or high temperature oxidation reactions in the high temperature range are weak for the light oils and the medium oil tested, due to insufficient fuel availability for those reactions. In contrast, for Athabasca bitumen in the low temperature range, oxygen addition reactions are dominant but the energy generation is at a low level. In the temperatures above 400°C, bond scission or high temperature oxidation (combustion) reactions are intensive, with the higher amount and the faster rate of energy generation. The experimental data further addresses the effect of composition of crude oils on their oxidation behaviours, which can be an aid to understanding the difference in oxidation behaviours between the light oils and Athabasca bitumen. These data provides a better understanding of the oxidation reaction mechanism for crude oils. This information is vital for interpreting and optimizing field performance during air injection process into light oil reservoirs.
Bibliography: p. 239-254