Summary
Steam-assisted gravity drainage (SAGD) is a commercially viable recovery
method for oil sands of Athabasca used where other methods have been
unsuccessful. In one variation of SAGD, a small amount of a noncondensable gas
is added to the injected steam to maintain pressure in the chamber while using
the energy in place, reducing steam consumption and providing thermal
insulation from overburden heat losses. The role of gas during steam-gas
co-injection processes, in terms of its effects on chamber development, bitumen
flow rates, and heat losses, is not fully understood, and therefore is the main
focus of this work.
A new analytical model for gas injection in SAGD is derived, taking into
account the three-phase flow of gas, oil, and water in the reservoir. The
analytical theory is used to predict the fluid flow rates as well as phase
mobility, relative permeability, and saturation profiles in the mobile oil
region. The theoretical results are replicated by fine-grid numerical
simulations. Methane was used as the noncondensable gas for the purpose of this
study because it is the main solution gas in most reservoirs. It is, however,
believed that the findings of this study are equally applicable to other
noncondensable gases such as nitrogen, air, helium, and others. Fine-grid
numerical simulations were performed to gain a visual understanding of gas
distribution in a SAGD chamber and its effect on in-situ steam quality,
overburden heat losses, phase saturations, and fluid-flow rates. The simulation
results support the predictions of the mathematical theory.
The results of the analytical and numerical study reveal that methane
co-injection with steam is in general unfavorable in a SAGD operation. The
injected methane tends to accumulate at the steam condensation front, which
lowers the heat transfer rate of steam to the adjacent oil, resulting in lower
oil production rates and slower growth of the chamber.
© 2012. Society of Petroleum Engineers
View full textPDF
(
6,546 KB
)
History
- Original manuscript received:
18 August 2011
- Meeting paper published:
16 November 2011
- Revised manuscript received:
19 December 2011
- Manuscript approved:
3 February 2012
- Published online:
29 August 2012
- Version of record:
12 September 2012
View Cart
