Browsing by Subject "Carbon Dioxide"
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Item A Comparison of Fault Detection Methods For a Transcritical Refrigeration System(2012-10-19) Janecke, Alex KarlWhen released into the atmosphere, traditional refrigerants contribute to climate change several orders of magnitude more than a corresponding amount of carbon dioxide. For that reason, an increasing amount of interest has been paid to transcritical vapor compression systems in recent years, which use carbon dioxide as a refrigerant. Vapor compression systems also impact the environment through their consumption of energy. This can be greatly increased by faulty operation. Automated techniques for detecting and diagnosing faults have been widely tested for subcritical systems, but have not been applied to transcritical systems. These methods can involve either dynamic analysis of the vapor compression cycle or a variety of algorithms based on steady state behavior. In this thesis, the viability of dynamic fault detection is tested in relation to that of static fault detection for a transcritical refrigeration system. Step tests are used to determine that transient behavior does not give additional useful information. The same tests are performed on a subcritical air-conditioner showing little value in dynamic fault detection. A static component based method of fault detection which has been applied to subcritical systems is also tested for all pairings of four faults: over/undercharge, evaporator fouling, gas cooler fouling, and compressor valve leakage. This technique allows for low cost measurement and independent detection of individual faults even when multiple faults are present. Results of this method are promising and allow distinction between faulty and fault-free behavior.Item Experimental Investigation on the Use of Water Soluble Polyacrylamides as Thickeners During CO_(2) WAG EOR(2014-07-24) Tovar, FranciscoCO_(2) flooding often results in poor sweep efficiency due to the high mobility ratio caused by its low viscosity. To mitigate this problem, alternate injection of water and CO_(2) slugs (WAG) is widely applied. Recently, numerical simulation and core flood experiments in heavy oil indicate that the use of chemicals in the water slug may improve mobility control during WAG. Therefore, stability studies of common polymers used for EOR applications in CO_(2) saturated environments becomes necessary. Also, the possibility to extrapolate the benefits observed in heavy oil to light and medium oil reservoirs needs to be assessed as they gather the majority of the existing CO_(2) applications. This thesis presents an evaluation of the use of polymers as water thickeners during CO_(2). The work has been divided into three stages: An investigation on the stability of acrylamide based polymers exposed to CO_(2) for 328 days at 122 ?F. The determination of the MMP for the system crude oil ? CO_(2) using the slim tubing technique in a fast approach that employs a short column of 20 ft in length. And the execution of 12 core flooding experiments under miscible and immiscible conditions, in homogeneous and heterogeneous rock. We conclude that polyacrylamide based polymers can resist the presence of CO_(2). HPAM was able to retain 54% of its original viscosity after 215 days at 122 ?F. PAM - ATBS increased its viscosity to 104% of its original viscosity after 328 days. A MMP of 1563 psia was calculated, which has a good correlation to previous laboratory measurements and EOS predictions for live oil. The core flooding experiments gave insights regarding the role of miscibility, frontal advance rate, heterogeneity and water viscosity on the viscous fingering of CO_(2) into the oil and suggested that thickening the water during WAG could be beneficial in highly heterogeneous formations. The limitations to scale reservoir heterogeneity prevented us to reach a fully understanding of the process. An approach combining numerical simulation with experimental work is recommended.