Performance Of steam stimulation or steam flooding processes can be improved by the use of an appropriate gaseous additive such as carbon dioxide or methane. Several beneficial effects are postulated such as improving steam injectivity, increasing the size of the heated areas and providing additional drive energy which is likely to increase production rate. The over-all effect of these mechanisms on performance is difficult to predict. A laboratory program for the Lindbergh Field (Cummings Formation) was conducted to investigate the effect of carbon dioxide and methane on the performance of steam processes and investigate the differences in performance between simultaneous injection of steam and a gaseous additive and injection of a gas slug prior to steam injection. A total of eight coreflood tests were carried out, employing core and fluids from the Cummings zone of the Lindbergh Field. In addition, a validated numerical model was used to evaluate the impact of adding non-condensible gases to steam under various conditions. Results indicate that the presence of a non-condensible gas improved steam injectivity. Injectivity improvement was most pronounced when a gas slug was injected prior to steam injection, but the presence of a non-condensible gas with steam did not improve recovery and resulted in much higher residual oil saturation compared to steam injection alone. Results from numerical simulation work supported these observations. Introduction PanCanadian Petroleum Limited has a significant land position in the Lindbergh Field located near the town of Elk Point in northeastern Alberta. Formations of the Upper Mannville Group in this field are generally unconsolidated sands and contain heavy oil of 12 to 14 °C API. The Cummings formation, at a depth of about 600 m. contains the majority of the Upper Mannville oil in place and is considered to have good potential under primary and thermal recovery. Its thickness varies up to 20 m. The main purpose of the work reported in this paper was to evaluate the effect of gaseous additives on the performance of steam stimulation and steamflooding processes for the Cummings Formation. It should be noted that the over-all effect of gaseous additives on these processes is difficult to predict. Several potentially beneficial mechanisms could be assumed such as improving injectivity, increasing the heated volume, reducing interfacial tension between oil and water, providing additional reservoir energy by solution gas mechanisms, etc. But, gaseous additives could also have detrimental effects due to the presence of a free gas saturation and the associated effect of reducing relative permeability to oil. Limited field tests have been reported to date on the effect of gaseous additives on steam processes. Moreover, the published laboratory and simulation studies have led to some conflicting results. Additional investigation was necessary for the Cummings formation. Literature Review Meldau(1) reported the results of air-steam stimulation field tests in Paris Valley, California. The addition of air to steam nearly doubled oil production. He attributed this to several mechanisms including displacement of residual oil by trapped gas, gas drive and increased reservoir pressure.
Field results from many heavy oil reservoirs in the Lindbergh and Frog Lake fields in northeastern Alberta suggest that primary recovery is mainly governed by the processes of sand production and foamy oil behaviour. Sand production leads to the creation of high porosity zones with increased permeability, while foamy oil generation provides the necessary support mechanism to sustain higher production rates. PanCanadian Petroleum Limited and Centre for Frontier Engineering Research (C-FER) conducted experimental and numerical studies to understand the various reservoir mechanisms contributing to the high primary production recovery observed in the Lindbergh and Frog Lake fields. Laboratory tests were conducted to study the foamy oil behaviour and evaluate its contribution to the enhanced primary production observed in the field. The numerical modelling included a series of idealized models developed and analyzed to determine the most probable shape of the sand-producing zones. The evaluation focussed on matching not only the observed oil production but also the observed sand volumes removed from the reservoir. The analysis from vertical well simulation was also extended to horizontal wells. The evaluation of heavy oil reservoir mechanisms for Lindbergh and Frog Lake fields is reported in two parts. Part I includes field testing and preliminary reservoir simulation based on the production data. Part II includes analytical and numerical studies for coupling the effects of sand and oil production, and laboratory testing of unconsolidated sand under foamy oil conditions. Introduction The observed primary oil production of many heavy oil reservoirs in the Lindbergh and Frog Lake fields in northeastern Alberta has been significantly higher than predicted by classical darcy flow models. PanCanadian Petroleum Limited (PanCanadian) and Centre for Frontier Engineering Research (C-FER) conducted experimental and numerical studies to understand the various reservoir mechanisms contributing to the observed high primary production recovery. This evaluation was conducted in two parts. Part I of the evaluation of heavy oil reservoir mechanisms for the Lindbergh and Frog Lake Fields was previously reported by the authors in Ref. (1). Part I included geological description of the Lindbergh and Frog Lake reservoirs, a summary of various field tests conducted in the area to evaluate recovery mechanisms and the results of reservoir simulation. P. 87
cheese ripening affected the toxin content. At 6°C the toxin concentration was hardly affected, but at 20°C the concentration was reduced by 16% The occurrence, distribution, and stability of stengmatocystin (STG) in after 90 days. In Ras cheese contaminated with spores of Aspergillus versi-Ras cheese were investigated. An incidence value for STG in market sam-color, toxin production started after 45 days of the ripening, reached a maxples of Ras cheese was 35% with a mean value of 22.2 pg/kg. In experi-imum after 90 days, and declined thereafter. Cow's milk favoured toxin formental Ras cheese from milk contaminated with STG, 80% of the toxin was mation in comparison with buffaloe's milk. Aged cheese (more than retained in the curd while 20% was found in the whey. The temperature for 6 months) inhibited toxin production.
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