The use of hydrocarbon solvents in the recovery of heavy oil has been increased because of the advantages they have over the thermal methods under some reservoir conditions. The injection of a miscible solvent in the reservoir implies a mass transfer process which is governed by a diffusion coefficient. Consequently the measurement of the diffusion coefficient is extremely important. This, however, presents a significant amount of challenges in the laboratory and in the data analysis, mainly because of the viscous and opaque nature of the heavy oil and the dependence on concentration of the diffusion coefficient. The MatanoBoltzmann method has been used in the past to obtain the concentration dependency of the diffusion coefficient of solvents in heavy oil. Although the method successfully shows that such dependency exists, the results exhibit abnormal trends.In this work the concentration profiles of three n-alkanes in heavy oil were obtained in the laboratory using Computed Assisted Tomography (CAT), and the "Slopes and Intercepts" analytical technique was used to calculate the concentrationdependent diffusion coefficients. The results are in good agreement with the theory of diffusion in binary mixtures. In addition a comparison is presented with the Matano-Boltzmann method. Finally the Vignes model was successfully used to also perform predictions on the studied systems.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractMass transfer of solvents in bulk heavy oil and bitumen was monitored successfully using X-ray Computer Assisted Tomography (CAT). Concentration gradients were obtained from analysis of bulk density maps as a function of location and time. Analysis of the data using Fick's Law provided apparent diffusion coefficients, which were consistent with previously published data using different solvents and different oils.A second series of experiments was then performed whereby the heavy oil was mixed with sand at a level that is similar to what expected in heavy oil reservoirs. There was no connate water in the system. Different solvents were then placed on top of the oil/sand mixtures and the diffusion of the solvent into the sand pack was observed. X-ray CAT was used to monitor density and concentration profiles.Oil concentration profiles in solvent were clearly observed but the solvent concentration in the sand pack proved to be more challenging. The same Fickian approach that was used in bulk oil systems was applied to predict apparent diffusion coefficients for the liquid volume portion of the experiment. Preliminary results showed that the apparent diffusion coefficients are of the same order of magnitude as in the bulk oil systems.
Mass transfer of solvents in bulk heavy oil and bitumen was monitored successfully using X-ray Computer Assisted Tomography (CAT). Concentration gradients were obtained from analysis of bulk density maps as a function of location and time. Analysis of the data using Fick's Law provided apparent diffusion coefficients, which were consistent with previously published data using different solvents and different oils. A second series of experiments was then performed whereby the heavy oil was mixed with sand at a level that is similar to what expected in heavy oil reservoirs. There was no connate water in the system. Different solvents were then placed on top of the oil/sand mixtures and the diffusion of the solvent into the sand pack was observed.X-ray CAT was used to monitor density and concentration profiles. Oil concentration profiles in solvent were clearly observed but the solvent concentration in the sand pack proved to be more challenging. The same Fickian approach that was used in bulk oil systems was applied to predict apparent diffusion coefficients for the liquid volume portion of the experiment. Preliminary results showed that the apparent diffusion coefficients are of the same order of magnitude as in the bulk oil systems. Introduction The increased interest in secondary production (or post-cold production) of heavy oil has renewed interest in solvent-based methods for heavy oil recovery such as Vapor Extraction (VAPEX). Butler and Mokrys (1), as an alternative to Steam Assisted Gravity Drainage (SAGD), proposed the VAPEX process for reservoirs where heat loss in the formation would make SAGD uneconomical. In VAPEX, vapor solvent instead of steam is injected, and the solvent mixes with the heavy oil to reduce its viscosity. The diluted oil then drains by gravity to the production well. Several experiments have been published using Hele-Shaw cells (2, 3), pore network glass micromodels (4), magnetic resonance imaging (MRI) (5) and pressure-volume-temperature (PVT) experiments (6). The mechanisms for solvent-based processes involve diffusion and dispersion of the solvent into the oil sands. Dispersion coefficients are related to the diffusion coefficients, making it important to evaluate the diffusion coefficients in both cases. X-ray CAT has potential as an attractive tool for measuring the properties of reservoir fluids in a non-intrusive way. CAT can non-destructively image a host of physical and chemical properties of porous rocks and multi phase fluids contained within their pores. The images are taken within seconds to minutes, at reservoir temperature and pressure (7). Employing x-ray CAT techniques to generate solvent and bitumen concentration profiles, allows for the calculation and comparison of the diffusion coefficients of hydrocarbon solvents in bulk heavy oil and oil sands to be calculated and compared. In solvent-based EOR techniques, mass transfer, viscous forces and gravity drainage affect the rate of oil recovery, given that accessibility is provided. The solvent diffuses and/or disperses into the heavy oil reducing its viscosity, therefore the solvent-oil mixture then drains and is recovered from the production well. Background If two miscible fluids are in contact, with an initially sharp interface, they will slowly diffuse into one another. As time passes, the sharp interface between the two fluids will become a diffused mixed zone grading from one pure fluid to the other. This diffusion arises because of the random motion of the molecules (8). Therefore diffusion flux can be defined as a flow due to the concentration difference between two fluids. Even if the two fluids are stable, there will be mixing due to the difference in concentration.
fax 01-972-952-9435. AbstractThe increased interest in secondary production (or post-cold production) of heavy oil and the current rise of oil prices has renewed interest in solvent-based methods for heavy oil recovery. Although the Vapor Extraction (VAPEX) process is the most heavily favored process for potential field application, other methods are also worth investigating. Moreover, the relative merit of mass transfer and viscous mechanisms in the overall recovery efficiency remains a topic of debate in the literature. This paper is a small part of a greater effort to study mass transfer phenomena in heavy oil/bitumen solvent systems. A series of core flooding experiments were performed whereby liquid solvents (octane, pentane) displaced heavy oil (12Pa.s). Different configurations and displacement rates were employed and heavy oil recovery factors were determined. Solvent concentrations in the effluent oil-solvent mixtures were accurately evaluated using the non-intrusive Nuclear Magnetic Resonance (NMR) technique and conventional density measurements.Mass transfer analysis was performed in an effort to determine dispersion coefficients.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.