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Analysis of non-equilibrium foamy oil behavior in pressure depletion processes
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- Author / Creator
- Chen,Tong
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Cold Heavy Oil Production with Sand (CHOPS) is considered to be a promising non-thermal primary-recovery technique, in western Canada and Venezuela. However, it offers low oil recovery factor (only 5 to 15%) and creates high porosity and high permeability channels known as wormholes. Further approaches are entailed (post-CHOPS) to increase oil recovery. Thermal methods and waterflooding are not efficient and economical due to heterogeneity and reservoir instability. Cyclic Solvent Injection (CSI) is the most commonly used method for post-CHOPS process. Non-equilibrium foamy oil behavior (i.e., solvent dissolution/exsolution) and solvent transport are two dominant recovery mechanisms for CSI processes in post-CHOPS reservoirs. The trapped gas bubbles generated during the pressure depletion stage are the typical characteristics of foamy oil flow. Although a number of models were developed in the past to describe the dissolution of solvent and bubble formation, calibration of these models against actual observations remain challenging. Many existing solvent technologies suffer from low production rates due to limited solvent /heavy oil interaction. Improving our understanding of solvent dissolution/exsolution under different pressure conditions would aid in the design of operating strategies (e.g., pressure depletion and solvent injection schemes) for enhanced solvent/oil mixing and transport.
A detailed mechanistic simulation model is constructed and calibrated against a set of experimental measurements. The fluid model is defined based on equilibrium saturation pressures and gas-oil ratios corresponding to different combinations of solvent and dead oil. The viscosity model is formulated using measurements at different temperatures and solvent-oil mixtures. Reaction kinetics is implemented to represent the non-equilibrium exsolution of gas from solution gas to bubble gas and free gas in foamy oil flow. The simulation model predicts a delay in free gas formation in the sand pack, as observed in the experimental program. Propane-based and carbon dioxide-based solvent mixtures exhibit significant foamy oil characteristics, enabling the oil viscosity to remain close to its live oil value. The rates of gas exsolution and oil production are strongly dependent on the pressure depletion schedule, as well as the solvent compositions and properties.
Next, a field scale post-CHOPS model is constructed and upscaled from the core model to analyze the impacts of simulation scales, heterogeneous wormholes, and the operating schedules on foamy oil behavior of different solvent systems. A fractal wormhole network is modeled. To analyze the impacts of pressure depletion strategies, single stage pressure depletion involving three live oil-solvent systems, as well as two cycles of CSI production processes, are examined. Detailed sensitivity analyses involving different solvent compositions are discussed. Similar as the observations from core model: the results illustrate that both C3H8-based and CO2-based solvents performe significant non-equilibrium foamy oil behaviors; the amount of foamy oil flow is strongly dependent on the pressure depletion rate. On the contrary to the core models, where CO2 outperforms C3H8 (as no C3H8 bubbles could be observed), the field-scale simulations show comparable recovery performance for both C3H8-based and CO2-based solvents. The developed simulation is useful for providing important insights regarding the interplay between wormhole heterogeneity, time scale and non-equilibrium solvent dis(ex)solution on the characteristics of foamy oil flow and oil recovery at the field level. -
- Graduation date
- Spring 2020
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.