The Effects of Steam on the Combustion of Oil on Sand
- David L. Urban (U. of California) | Kent S. Udell (U. of California)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- May 1990
- Document Type
- Journal Paper
- 170 - 176
- 1990. Society of Petroleum Engineers
- 5.2 Reservoir Fluid Dynamics, 4.1.2 Separation and Treating, 5.4.6 Thermal Methods, 4.1.5 Processing Equipment, 5.1 Reservoir Characterisation, 2.4.3 Sand/Solids Control, 5.8.5 Oil Sand, Oil Shale, Bitumen, 4.2 Pipelines, Flowlines and Risers
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A simultaneous differential thermal analysis (DTA)/evolved gas analysis (EGA) system was developed to study in-situ oil-oxidation reactions. The oxidation of crude oil deposited on sand was studied, including catalysis by dissolved ionic compounds and reservoir sand materials and changes in the reaction mechanism caused by the presence of steam. The influence of steam was the most significant of these factors. In the presence of steam, the low-temperature-oxidation (LTO) exothermicity is similar to the dry case, but the oxygen consumption is dramatically reduced and, unlike the dry case, all consumed oxygen appears in the effluent carbon oxides. Participation of water and its radicals in the reaction mechanism is probably responsible for this change. These reactions should have a major influence on wet in-situ combustion.
In-situ combustion holds promise as an effective thermal technique for enhanced oil production because of its intrinsic advantages of exceptional resource use and applicability to deep reservoirs. This technology has been slow to develop, however, presumably because of the inherent complexity of the coupled thermal, chemical, and hydrodynamic interactions, particularly during field operations. Nevertheless, more effective variations of this technology, such as super-wet combustion, are possible, enabling broader application under more controllable conditions. This work addresses the issue of oil oxidation at low temperatures under conditions representative of wet combustion.
Three general classes of reactions are considered to occur during in-situ combustion: pyrolysis, LTO, and char oxidation. These reactions have different roles in in-situ combustion. Pyrolysis reactions are responsible for the deposition of residual carbonaceous material and consequently are also called fuel-deposition reactions. Pyrolysis can occur as a result of either thermal (free-radical) or Pyrolysis can occur as a result of either thermal (free-radical) or catalytic cracking. Given the large range of potential catalysts in oil sand, catalytic cracking is likely to dominate the process. LTO, defined as oxidation that occurs near 300 degrees C [570 degrees F] . is poorly understood. A number of reactions have been proposed; however, poorly understood. A number of reactions have been proposed; however, only some of these have been shown to be significant under reservoir conditions. Nevertheless, LTO is believed to be very important because it increases oil viscosity and is exothermic. The char oxidation reactions that oxidize the residual carbonaceous material produced by the pyrolysis reactions are important because they are believed to provide the major fraction of the thermal energy released during in-situ combustion and to consume the oxygen necessary for front propagation.
The majority of kinetic studies of in-situ combustion reactions fall into two categories depending on what parameters are measured. The first category includes such techniques as DTA and differential scanning calorimetry (DSC) that measure the energy consumed or produced by the oil as its temperature is increased in the presence of oxygen. The second category, EGA, involves measurement of the gaseous species produced by the reactants as they are heated. A small but significant group of experiments use stirred batch reactors and measure the change in the chemical composition of the reactor contents as a function of time and temperature.
In the first extensive use of DTA to study in-situ combustion reactions, Bae reported two distinct exothermic intervals. The first interval occurred below about 300 degrees C [570 degrees F], and the second occurred between 300 and 600 degrees C [570 and 1,100 degrees F]. The first interval was called LTO. The higher-temperature interval was believed to involve oxidation of the residual carbonaceous material that remains after all lighter materials have evaporated, Further DTA and DSC work has been done by a number of authors. Among the salient results was Drici and Vossoughi's finding that a critical sand surface area existed below which oils did not oxidize in the manner seen by Bae and others, but instead exhibited a large number of smaller exothermic peaks.
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