More recent developments in SAGD
Steam Assisted Gravity Drainage
by Franklin L. Foster, Ph.D.
[This article made possible thanks to
the co-operation and financial support of the
Petroleum Society of CIM, Lloydminster Heavy Oil Section]
In the second half of 2006, Husky Energy's Tucker
Thermal Project near Cold Lake began production. It is expected the
project will produce 30,000 barrels per day of bitumen and 90,000 barrels
per day of steam. Over the projected 30 year life of the plant, some
350 million barrels of bitumen will be produced.
Steam Assisted Gravity Drainage is at the heart of the
project, assisted by several recent developments. The producing
wells are 32 well pairs situated on only three well pads. This
greatly reduces the surface impact of the project on the environment.
From the well pads, the wells are directionally drilled to a depth of
about 450 meters and then the wellbores go horizontally through the oil
bearing sand for approximately 700 meters. The pay zone, in the
Clearwater Formation, consists of a layer of sand 30 to 50 meters thick
and so is ideally suited for SAGD.
A well pair, in the pay zone, consists of two well
bores, one above the other, running parallel with each other only three to
seven meters apart over the entire 700 meter horizon. Each of these
32 well pairs are approximately 100 meters apart in the pay zone.
Steam is continuously injected into the upper wellbore. A steam
chamber forms, heating the bitumen and enabling it to flow. Gravity
pulls the bitumen down into the lower horizontal well. Oil, water,
and particulate matter are produced through this wellbore to the surface.
Another recent advance is in electronic
instrumentation. Sensors are placed at both the well heel (where the
wellbore changes to horizontal) and the well toe (the far end of the
wellbore). The sensors must be able to perform at high accuracy
under high temperature conditions for a life span of 10 years. These
sensors allow for the monitoring of temperature, pressure and other
important information about conditions in the reservoir, especially
pressure, and this allows the oil to be produced without surface pumps but
instead relying on controlling the pressure below which is in the range of
3,300 kilopascals.
The demand for 90,000 bbl/day of steam introduces the
issue of water use. Earlier applications of SAGD, and other recovery
methods using steam, put a high demand on water. Use of surface
water became controversial as water table levels were lowered. Other
possible sources of water include fresh ground water (also controversial)
and saline ground water. A 6 month license has been granted to use
surface water during startup; however all produced water at the Tucker
Project will be processed to make steam. The Tucker Thermal Project
will use more than 7 million cubic meters of water per year. Of that
volume, 1.7 million cubic meters of brackish water will be sourced from
the McMurray Formation which underlies the Clearwater Formation which
contains the bitumen. The Tucker Plant will include equipment to
desalinize and soften the produced water for use in the five 280 million
BTU/hour steam generators on site. About 90% of the steam generated
will be reinjected into the reservoir or used on site for heating.
The produced fluids are initially processed in a free
water knockout vessel, followed by a treater where the remainder of the
water is removed from the oil, and then on to the usual settling and sales
tanks. From the sales tanks, the bitumen is blended with diluent for
transport by pipeline to the Husky Energy Upgrader in Lloydminster.
The Tucker Lake Project already promises to be a
success and Husky Energy will follow it with the Sunrise Thermal Project.
Such projects, with drilling budgets alone of more than $75 million and
overall project costs of over $500 million are an important reason why the
oil and gas industry accounts for more than 82% of the economic activity
in northeastern Alberta. In addition, the 30,000 barrels per day of
petroleum will make its contribution to meeting the energy needs of
today's world.
* * * * *
Information Sources:
Husky Energy
National Energy Board
Alberta Economic Commission
Pembina Institute
However, responsibility for the contents of the above article is
entirely that of the author.
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