Abstract
Pressure drop along the horizontal wells and between the injector and producer
could have a significant impact on SAGD process performance. However, this
issue is poorly understood due to difficulties in simulating pressure drop.
This paper presents the results of a numerical study on the topic.
When pressure drop between the injector and producer exists, the downhole
vapour production rate must be increased significantly. Without adequate vapour
production, the oil production rate is lower and SOR is higher. Increasing the
vapour production rate may affect pad facility design as more vapour handling
capacity is required under these conditions.
On the other hand, pressure drop inside the injection well may also alter steam
distribution. However, the impact on oil production is limited as steam can
move relatively easily inside the steam chamber. In the present case, oil
production is reduced by approximately 5% when a pressure gradient along the
injection well is considered.
Introduction
Steam-Assisted Gravity Drainage (SAGD), a thermal process that involves the
application of steam and the use of horizontal wells, is a bitumen recovery
method used in the Athabasca Oil Sands. The most common implementation involves
the use of two horizontal wells drilled parallel to one another with a vertical
separation distance of about 5 m. The upper well is known as the injector and
the lower well is known as the producer.
Through the operation of commercial projects, it has been observed that once
steam is injected into the reservoir, a pressure gradient is observed along and
between the wells. There have been a number of publications addressing this
issue(1, 2).
As the SAGD process has been applied to more locations in recent years,
considerable interest has been generated around the topic of pressure drop and
its effect on SAGD process performance. It is generally understood that a
pressure drop across or along the wellbore could result in wells with a
non-uniform steam chamber, a reduced effective wellbore length, liquid build-up
above the production well or reduced oil production rate.*
When a new reservoir is developed, a great effort is required to understand the
reservoir characteristics and how to incorporate them into production
forecasting models. Petro-Canada is currently expanding their MacKay River
project and, in order to develop a better understanding between pressure drop
and oil productivity, the field data from their existing project was analyzed
so that recommendations could be made to increase the project's
productivity.
One factor that needs to be addressed for drilling and completion planning is
the wellbore size. Larger wellbore size results in more uniform steam
distribution in the injection well and increased productivity from the
production well. However, a larger wellbore size incurs a higher cost.
In some existing wells, it was found that liquid build-up was occurring due to
limited lifting capacity. In addition, a larger pressure drop between the
injector and the producer has been observed.
© 2009. Petroleum Society of Canada (now Society of Petroleum Engineers)
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History
- Original manuscript received:
27 March 2008
- Meeting paper published:
17 June 2008
- Revised manuscript received:
1 June 2009
- Manuscript approved:
31 July 2009
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