Summary
In-situ extraction of ultraviscous deposits from the vast bitumen resources
in western Alberta, Canada, requires significant water and energy usage, which
consequently leads to greenhouse-gas emissions. Currently proven steam-based
recovery schemes include cyclic-steam-stimulation (CSS), steamflooding, and
steam-assisted gravity-drainage (SAGD) processes, which are accompanied by many
economic and environmental challenges. Coinjection of solvent with steam is a
technology that has the potential to improve the efficiency of steam processes
as well as reduce energy usage and carbon dioxide emissions.
In recent years, researchers and industry professionals have attempted to
develop the process further by conducting fundamental research as well as field
pilot trials, with varying degrees of success. However, the current level of
understanding of the process and the knowledge surrounding the fundamental
physics and mechanisms involved are not entirely satisfactory.
In this paper, a parametric simulation study was performed to address the
key aspects of the solvent-coinjection (SCI) process that contribute to further
understanding and development of the process. Simulation observations were
verified with experimental evidence where available to support the results and
conclusions. Effects of several operational and geological parameters were
evaluated on the performance of the SCI process, and the relative performance
benefits were assessed over normal SAGD operations. These parameters included
solvent type, solvent concentration, initial-solution gas/oil ratio (GOR),
relative permeability curves, and pay thickness.
The results revealed that the optimal solvent should not be chosen only on
the basis of mobility-improvement capability, but also under consideration of
other operational, phase- and flow-behavioral and/or geological conditions that
are set or present. Higher concentrations of solvents showed more energy-saving
upsides than rate-acceleration benefits. It was also observed that the
reservoir steam-intake rate is still likely to be the prime performance
indicator of the SCI process. In addition, SCI showed that the potential exists
for accessing more resources, particularly below the producer level.
Furthermore, steam trap control on the producer seems to be problematic when
used for SCI simulation. With the current well-control capacity of simulators,
a higher degree of subcool is likely to be needed to avoid live vapor-phase
production from the producer.
© 2012. Society of Petroleum Engineers
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History
- Original manuscript received:
27 August 2011
- Meeting paper published:
16 November 2011
- Revised manuscript received:
6 February 2012
- Manuscript approved:
1 March 2012
- Published online:
1 June 2012
- Version of record:
1 July 2012
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