Summary
The commercial viability of the steam-assisted gravity-drainage (SAGD)
process is affected negatively by several undesirable reservoir features, such
as pronounced heterogeneity, low vertical permeability, thick and areally
extensive shale barriers, and steam thief zones. The efficiency of SAGD
projects is also affected by the presence of higher water saturation in the
target zone. Although the presence of small mobile-water saturation is not
considered harmful, reservoirs with high water saturation may be poorly suited
for the SAGD process. Nonetheless, SAGD remains the only practical technology
for in-situ extraction of oil from oil-sand reservoirs, even when mobile water
is present. This raises the question of how much mobile water is
prohibitive.
To investigate the effect of water saturation on SAGD performance,
high-pressure physical-model experiments were carried out. Different levels of
water saturations were established in the model by modifying the packing and
saturating techniques. SAGD experiments were carried out by injecting
superheated steam at controlled rates and producing the oil from the production
well at constant pressure. The injection rate was selected to keep the pressure
difference between the injector and the producer at a low level.
The oil-production behavior was analyzed to evaluate the effect of water
saturation on the thermal efficiency of the process. On the basis of the
results of low- (immobile) and high- (mobile) water-saturation experiments, it
was observed that the oil-recovery factor dropped by 6.6% when the initial
water saturation was increased from 14.7% to 31.8%.
© 2012. Society of Petroleum Engineers
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History
- Original manuscript received:
17 September 2010
- Meeting paper published:
2 December 2010
- Revised manuscript received:
11 February 2012
- Manuscript approved:
16 February 2012
- Published online:
16 August 2012
- Version of record:
5 September 2012
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