Journal of Canadian Petroleum Technology
A smooth start-up is crucial to the successful operation of a SAGD process. A
simulation study was conducted to analyze the start-up or circulation period of
SAGD well pairs. A coupled reservoir/wellbore model was developed and used to
history match field data obtained from wells with extensive instrumentation at
Petro-Canada's MacKay River development. The history matched model was then
used to conduct a sensitivity study on some of the parameters that affect the
circulation of a well pair.
First, the steam-to-toe time was examined for the two typical wellbore
completions that Petro-Canada employs at MacKay River. Various flow rates were
tested for the two completions to see how the steam injection rate affected the
Next, the circulation pressure along with the injector/producer pressure
gradient was investigated. Various pressure gradients were applied between the
injector and producer to examine the effects on the circulation duration and
the formation of steam coning.
Finally, the distance between the injector and producer was studied. The
purpose was to explore the effect of the vertical separation between the
injector and producer wells on conversion time.
The Steam-Assisted Gravity Drainage (SAGD) process has become the leading in
situ bitumen recovery technique in the Athabasca oil sands deposit. In the SAGD
process, two horizontal wellbores are drilled approximately 5 m apart
vertically. The upper well is used as an injector. High quality steam is
injected into the reservoir, heating the bitumen and reducing its viscosity.
The bitumen then flows, by gravity, to the lower producer well, and is then
produced to the surface.
Before the SAGD process can be initiated, the horizontal well pair must be
heated by circulating steam in both the injector and producer. The purpose of
the circulation process is to heat the near wellbore region and to establish
flow communication between the two wells. Two common completions of SAGD
horizontal wellbores are shown in Figures 1 and 2. In the injector completion,
there is a single long tubing string landed at the toe. The long tubing string
is placed within the casing of the well. During circulation, steam is injected
down the long tubing string and exits into the annulus at the toe of the well.
The steam then travels back to the surface through the annulus of the well. In
the producer completion, there are two tubing strings; a long tubing string
landed at the toe and a short tubing string landed at the heel. Steam is again
circulated down the long tubing string. It then exits into the annulus at the
toe and travels to the heel. At the heel, the steam travels back to surface via
the short tubing string, versus the annulus in the injector completion.
Petro-Canada is operating the MacKay River SAGD commercial project and is
preparing for a project expansion. At MacKay River, the initialization of SAGD
included three stages(1). The first stage involved getting steam to
the toe. To do this, steam is circulated into the long tubing of both the
injector and producer at equal pressure.
© 2009. Petroleum Society of Canada (now Society of Petroleum Engineers)
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- Original manuscript received:
15 February 2007
- Meeting paper published:
12 June 2007
- Revised manuscript received:
26 June 2008
- Manuscript approved:
1 December 2008