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Abstract The literature of the past thirty years shows that the low- temperature oxidation (LTO) of hydrocarbon liquids generally results in a more viscous end product. The In Situ Combustion Research Group at The University of Calgary has found, however, that upgrading can occur during LTO in the presence of caustic additives. Because it was believed that caustic inhibits oxidation reactions as evidenced by a reduction in or absence of coke formation, and allows the oil to upgrade by thermal cracking via a free radical mechanism, a systematic study was undertaken to investigate the effect of caustic on the LTO of heavy oil. To date, nearly 200 LTO tests have been performed on Athabasca bitumen. These experiments were carried out by varying caustic concentrations, temperatures, oxygen partial pressures, total cell pressures, and run times. All effluent gases were analyzed using gas chromatography, the pH of free water was measured, and hydrocarbon products underwent determination of coke and asphaltene contents, viscosity, and density. CHN and S analyses were carried out on the whole oil, and coke and asphaltene fractions. Several instances of upgrading were observed. Optimum conditions occurred at lower caustic concentrations, lower temperatures, lower oxygen partial pressures, and longer run times. The amount of oxygen reacted appears to be the most critical parameter affecting the system. The presence of caustic apparently did not inhibit the oxidation reactions from taking place, but, rather, modified the process by impeding the asphaltene fraction from converting to coke. Introduction The amount of information available on the LTO of crude oils is relatively limited. Several published studies investigate the chemical and physical changes accompanying LTO of many different grades of oil. Studies on the LTO of Athabasca bitumen described by Babu and Cormack show a decline in the aromatic content, an increase in asphaltenes content, and a stable saturates content. The same authors report a steady increase in coke production with the extent of oxidation. The overall trend is for a conversion from aromatics to resins, from resins to asphaltenes, and from asphaltenes to coke. This transformation to a heavier, more polar oil results in increased viscosities and densities. Millour et al. describe and relate the oxygen uptake to coke deposition, and Severin et al. provide a relationship between viscosity and the percent increase in oxygen concentration in the oxidizing gas. It has been accepted, therefore, that LTO causes undesirable changes in the chemical and physical properties of oil. It may, however, be beneficial to subject an oil to LTO. Unpublished experimental work performed by co-workers at The University of Calgary showed that a pre-oxidized oil underwent accelerated thermal cracking compared to an unoxidized sample of the same oil when subjected to the same reaction conditions. It was thought that pre-oxidation of the oil incorporated oxygen into the structure, thereby providing labile bonds which more readily generated free-radicals. Introduction of oxygen into the molecular structure of the oil can have two consequences; either a downgraded or an upgraded product. P. 529
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.87)
Abstract A new in-situ combustion strategy, the top down process, is currently under detailed laboratory study. The process, aimed at overcoming some of the problems that have restricted the successful application of in-situ combustion in oil sand and heavy oil formations, involves the stable propagation of a combustion front from the top to the bottom of a reservoir, exploiting gravity drainage of the mobilized oil to a lower horizontal well. Operational parameters that have been investigated and presented here include: air injection flux, degree of pre-heating, internal steam flood pre-heating and injection of normal air versus injection of oxygen enriched air. To compliment the experimental investigation, the thermal numerical simulator STARS has been applied to the in-situ combustion process by incorporating reaction kinetics for Athabasca oil sand. A successful history match of an experimental test is presented accompanied by a discussion of application of the model to field scale. Introduction In-situ combustion has long been recognized as having the potential for being an economical thermal oil recovery process in heavy oil and oil sand deposits. The energy required to supply heat to the reservoir compares quite favourably with steam. The estimated cost1 to place 1 GJ of energy in a 7 MPa reservoir is $2.6-$4.4 using steam and $ 1.0 for in-situ combustion using air (assuming $2/GJ fuel cost, capital cost not included). In-situ combustion is not compromised by large heat losses to overburden and underburden in thin formations or by high heat losses from the well bore to the overburden in deep formations as is the case with steam injection. Also in-situ combustion theoretically has important applications in reservoirs containing bottom water and as a follow up process to waterflooded and steamflooded formations. Previous in-situ combustion field projects, however, have been less successful than steam, primarily because of the difficulty in controlling the combustion front advancement. The customary in-situ combustion operation of the past involved the injection of an oxygen containing gas into a central vertical injection well surrounded by a number of vertical production wells (typically as part of a larger pattern of injection and production wells). Combustion was initiated near the injection well and horizontally propagated radially outwards, aiming to drive the mobilized oil towards the production wells. The problem frequently encountered was that the combustion fronts tended to advance erratically with the vertical sweep constrained by gravity override of the displacing gas and the areal sweep reduced by preferential flow to one well of the pattern. Injected oxygen, overriding the combustion zone, created problems at the production end and the overriding hot steam and combustion gases did little to heat the formation ahead of the burn zone. The displacement geometry of the process requires that the mobilized oil be displaced ahead of the combustion front into the colder immobile oil, increasing oil saturation and further reducing mobility, with the limited producibility of the vertical production wells unable to alleviate the situation. P. 487
- North America > United States (1.00)
- North America > Canada > Alberta > Athabasca Oil Sands (0.25)