Summary
This paper summarizes a set of SAGD experiments conducted live under an
X-ray scanner. These experiments were specifically designed for mapping
noncondensable gas distribution and their movement in an active steam chamber
during SAGD.
Many researches over the past 3 decades have shown that noncondensable gases
may have critical impacts on SAGD performance. Some may be positive and others
may be negative, depending on reservoir and operating conditions. To better use
the positives, avoid the negatives, and for better SAGD performance
predictions, it is crucial to understand how these gases behave in a steam
chamber. It is arguable that noncondensable gases tend to accumulate at the
steam front where steam condenses. However, this assertion has only been
supported by numerical simulations. Field observation data have been too
sparse. Meaningful tracking of gas production is not a normal practice in the
field.
The first experiment was conducted in an aluminum vessel packed with 4 darcy
sands at 1.0 MPa. The second experiment was conducted in a scalable system
consisting of a titanium pressure vessel and a PEEK cell, allowing the SAGD
experiment to run at 2.1 MPa. Both experiments used bitumen fully saturated
with methane at reservoir conditions and were run live under the X-ray scanner.
X-ray images were taken at given time intervals. Temperature profiles were
obtained directly from thermocouples. Density profiles were computed from the
X-ray images. Methane in the free gas phase were calculated and mapped. After
each experiment, samples from the opened cell were also tested for additional
observation and confirmation.
These experiments confirmed the assertion that noncondensable gas tends to
concentrate along the steam front. It was also demonstrated that the steam
temperature zone does not coincide with the oil-depleted zone, indicating that
in a SAGD reservoir with nontrivial presence of noncondensable gases,
temperature measurements at observation wells alone would not reflect the
boundary of the steam chamber. The more representative measure of a steam
chamber should be the mapping of the oil-depleted zone. A more comprehensive
monitoring of gas production plus 4D seismic would be needed to determine the
oil-depleted zone in the field operation.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
26 October 2010
- Meeting paper published:
19 October 2010
- Revised manuscript received:
5 January 2011
- Manuscript approved:
10 January 2011
- Version of record:
1 March 2011
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