SAGD
Steam Assisted Gravity
Drainage (SAGD):
A New Oil Producton Technology
for Heavy Oil and Bitumens
T.N. Nasr, Alberta Research Council, Calgary, CanadaIntroduction
The capacity of world heavy oil and oil sands has been estimated
to be as much as that of the world’s total discovered light
and medium crude oils in place. Over 90% of the world’s heavy oil
and oil sands are deposited in Canada and Venezuela. Up to 90%
of Canada’s estimated reserves could be recovered by in-situ operations
and 10% by surface mining. As the resources available for
conventional crude in Canada continue to decline, further development
of heavy oil and oil sands recovery technologies is critical
in meeting Canada’s present and future energy requirements.
Most recently, advances made in directional drilling and measuring
while drilling (MWD) technologies have facilitated development
of new in-situ production technologies such as Steam Assisted
Gravity Drainage (SAGD) and combined SAGD-solvent processes.
These processes have significantly improved well-bore reservoir
contact and sweep efficiencies as well as reduced production costs.SAGD Oil Recovery Technology
Western Canada has large reserves of heavy crude oil and
bitumen. However, most of these reserves cannot be produced by
conventional recovery methods. Specialized techniques are therefore
required to produce these heavy oils. Recent thermal oil
recovery technology developments at the Alberta Research
Council (ARC) have focused on SAGD and SAGD-solvent r techno
processes.
The most promising thermal recovery technology is the SAGD
process. In this process, two horizontal wells separated by a
vertical distance are placed near the bottom of the formation. The
top horizontal well is used to inject steam, which rises forming a
large steam chamber above the well, and the bottom well is used
to collect the produced liquids (formation water, condensate, and
oil). The rising steam condenses on the boundary of the chamber,
heating and entraining the oil to the production well. The process
leads to a high recovery and high oil rate at economic oil-to-steam
ratios (OSR).
The Underground Test Facility (UTF-Phase A) at Fort
McMurray, Alberta, Canada was constructed in 1985 by the Alberta
Oil Sands Technology and Research Authority (AOSTRA) to test
the concept of SAGD. The process was tested from December 1987
to mid-1990. The UTF-Phase Aproject was the first successful field
demonstration of the SAGD process. In addition to proving the
concept of SAGD, it also provided operational know-how, which is
critical to its successful commercial application.
Following the success of the UTF Phase A project, 500 m long
horizontal wells have been used in subsequent phases to further
test the commercial viability of the SAGD process. In addition, a
number of field pilots are in progress in other heavy oil reservoirs
in western Canada (Alberta and Saskatchewan), and around the
world. These pilots tested the use of surface-accessed horizontal
wells and extended SAGD applications to problem reservoirs.
These reservoirs often have lower permeabilities, are deeper, have
bottom water transition zones, with initial gas-saturated “live” oil
and top water / gas caps. In Alberta, the success of these pilots has
led to a number of commercial SAGD projects currently underway.
Current developments of the SAGD process at ARC are aimed
at improving oil rates, OSR, reducing energy and minimizing
water disposal requirements. In addition to SAGD, progress has
been made in the development of combined steam-solvent injection
processes, a novel approach for combining the benefits of
steam and solvents in the recovery of heavy oil and bitumen has
been undertaken. A newly patented Expanding Solvent-SAGD
“ES-SAGD” process has been successfully field-tested and has
resulted in improved oil rates, OSR and lower energy and water
requirements as compared to conventional SAGD.